# Up Front Bass - A New Way?



## Patrick Bateman (Sep 11, 2006)

I am *incredibly* picky about subwoofers. So picky that I literally have over twenty dub drivers in my garage, and a pile of finished subs.

*But no subwoofer in either of my cars.*

I just can't seem to find a sub that I can live with.

Yesterday I was working on yet another design, when I stumbled across something which *might* enable us to get the 'bass up front' illusion, but in a new and novel way.

Hang on kids, this is about to get technical...


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## Bayboy (Dec 29, 2010)

Subscribed and pulling out the V. Dickason audio Bible.


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## Patrick Bateman (Sep 11, 2006)

Before I get into the technical details of my idea, I wanted to get into some things that *have* worked for making good musical bass, and what *hasn't* worked. (For me at least.)

First, things that *haven't* worked:

1) On paper, bandpass subs should reduce harmonic distortion and increase efficiency. But every bandpass sub I've ever built, even the very well engineered ones, weren't 'musical' to me. YES there were some that were close, but something was always 'off.'
2) I've built surprisingly few vented boxes. It's probably been five years since I built a vented box.
3) Front loaded horns like the 'autotuba' sounded great, and absorbed a lot of power. But due to the fact that they're basically a sealed box below 60hz, they didn't have the 'weight' of a big twelve in a sealed box.

And things that *have* worked:









1) For the life of me I can't figure out why my TH-Mini clone sounds so good, but it's really hard to beat. It basically has the extension and 'weight' of a sealed box, but the efficiency and 'punch' of a vented box. Year after year I keep trying to make something that exceeds the TH-Mini, but I haven't been able to do it. It's been my reference sub for something like three years now, and I've built easily four or five other subs in a (failed) effort to one-up it.
2) At home, I've been doing multi-subs, as popularized by Geddes (Multiple Small Subs - Geddes Approach - diyAudio)
The Multisub approach is about as good as it gets; it solves a lot of those integration issues which plagues subwoofers. The only thing that's a drag is that it really needs a LOT of subs. At one point I had something like ten, and that was noticeably more transparent than just three, and a quantum leap beyond a single sub. So, clearly not the most practical arrangement for car audio.








3) At CES I heard Whitledge's Magic Bus, and it's by far the best bass I've ever heard in a car. I've run my TH-Mini in my car, and the Magic Bus was deeper and more authoritative, without any kind of 'ringing' or overhang. More importantly, *the magic bus didn't sound like the sealed or bandpass subs that I've heard.*


In summary:

I can't figure out how to make a bandpass sound good.
TH-Mini sounds better than any sub I've ever built, even better than sealed subs. Whitledge's sub is even better.


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## thehatedguy (May 4, 2007)

Is he still doing isobaric subs? At one point he had 3 pairs of iso 12s.


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## Patrick Bateman (Sep 11, 2006)

Here's my hypothesis:

*The reason that all three of my favorite sub setups sound good is that they actively absorb reflected bass.*

In this post, I will try to make a case for why this is a good idea.

Before we get into the WHY, let's talk about how bass propogates.









The measurement above shows the impulse response of a well engineered sealed box loudspeaker. (The Dunlavy SC-IVA)

Theoretically, a sealed box has the best impulse response, and the best phase response.

Unfortunately, the superiority of the sealed solution hasn't correlated with my own listening experiences. It's not that sealed boxes are BAD; it's just that the tapped horns sound a little better.

This has really baffled me for years, and I've pondered at least a dozen reasons that the TH sounds better... But was never able to put my finger on it.

Some ideas I had:
1) Perhaps the high efficiency and low distortion plays a part? I dismissed this possibility, as the TH-Mini sounds better at *all* volumes. Even at 90dB my tapped horn sounds better than my vented sub.
2) One of the crazier ideas I had was that the symmetry of the excursion had something to do with it. IE, a sealed box experience more pressure on the inward stroke than the outward stroke. I dismissed this, as it would also be level dependent.
3) Perhaps it's the phase response and group delay? *This was the idea that I'd held on to for at least a year, and I've written about this extensively at my forum.* (forum.audiopsychosis.com)
But this idea was ALSO shaky, as sealed boxes have better phase response and group delay than tapped horns. And front loaded horns are superior too. So if sealed and FLH have better group delay, than *why do tapped horns sound so good?*


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## thehatedguy (May 4, 2007)

I would say the high efficiency/low distortion since you are coupling the driver better to the air/environment.

John's van is unlike our cars in which he would have the physical diminsions to have bass (to a degree) wave propagation...which is why I would suspect he spent a lot of time with the modal issues in the bass/


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## Patrick Bateman (Sep 11, 2006)

Continuing my last post, I'm attempting to argue the following:

*Subwoofer designs that cancel reflected bass energy produce the most natural sounding bass.*

My argument is based on listening to my own tapped horns, my own multisub installs, and Whitledges Magic Bus (which is the only vehicle I'm aware of that's designed to nullify bass reflections.)









Here's an impulse response of a good sealed box. *See how it decays to nothing in about a quarter of a millisecond?*

















Now HERE is a sealed box in a real room. OH MAH GAWD

In a real room, we see reflections in the time domain for TWO HUNDRED AND FIFTY MILLISECONDS. A full quarter of a second.

Just imagine how that effects the music you're listening to? For instance, if you're listening to a 120bpm bassline, you're hearing a new beat every 500ms. That means that half of the 'gap' between notes is filled with 'mud' by the reflected energy from the room.

Does that make sense? Ideally you want a perfect black between beats, but the reflected energy from your speakers may be taking as long as a quarter of a second to 'fade to black.'

There are a few ways to fix this:

1) Room shape and size will play a big role. For instance, concrete walls will make the decay take longer because concrete walls do not 'give'
2) Room treatment might seem like an option. *Unfortunately, it's not.* 40hz is TWENTY EIGHT feet long. These wavelengths are so long, the only real way to 'treat' the room would be to literally move the walls around. (IE, there's going to be certain combinations of ceiling height, room width, and room depth which work better. But egg crate foam won't do a damn thing because it's nowhere near the same size as the wavelengths we're dealing with.)

There's a couple of other ways to deal with the bass reflections; Whitledge uses one and tapped horns use the other. I'll go into that in my next post.


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## Navy Chief (Jun 14, 2010)

Patrick Bateman said:


> 3) At CES I heard Whitledge's Magic Bus, and it's by far the best bass I've ever heard in a car. I've run my TH-Mini in my car, and the Magic Bus was deeper and more authoritative, without any kind of 'ringing' or overhang. More importantly, the magic bus didn't sound like the sealed or bandpass subs that I've heard.


if I remember from the build log isn't the Magic Bus enclosure just an extremely well built sealed enclosure. I know that it started with 3 sets of isobaric pairs and that know it contains 3 drivers conventionally mounted. Other than rigidity and dampening materials used inside, what makes the Magic Bus enclosure well "magical"? Does running drivers in odd numbers have a benefit in some way.

By the way I love reading threads started by you Patrick, however I do get a headache sometimes trying to understand the concepts.


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## thehatedguy (May 4, 2007)

Nothing magical about the enclosure...heavy as all hell sealed enclosure in a well treated room.


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## RNBRAD (Oct 30, 2012)

I think Jon's subs sounds so good is partly due to the transfer function of the large interior. Not to mention the decrease in panel vibration and subsequent drop in distortion levels as compared to packing woofers in a trunk. My guess he positioned the subs very carefully to get the low end transfer effect such like a corner in a listening room of your home. Combine this with proper crossover slopes and damping and you would probably experience a nice and smooth, yet efficient and full sounding sub bass coming from the front. I'm not so sure these positive attributes can be easily if possibly duplicated in a smaller car like interior.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Nothing magical about the enclosure...heavy as all hell sealed enclosure in a well treated room.


Au Contraire 

There *is* something different about the bass in the Magic Bus. (And also the bass from tapped horns.)

*The reflected energy is cancelled out.*

First, let's talk about how this works:









In the Magic Bus, there are helmholtz resonators next to the subs. The Helmholtz work the same way as they do in a vented box, but have the OPPOSITE effect. Instead of ADDING bass at a particular frequency, they SUBTRACT it.

(Yes, they're huge. See those big boxes next to the subs? Those ain't subs  They're helmholtz resonators.)

If you can, try and visualize a 40hz bass note coming out of those subs. At zero milliseconds, the bass note is produced. Nine milliseconds later, that bass note reaches the front of the car. *Then it's reflected back.* At the eighteen millisecond mark, that bass note has made it's way to the rear of the vehicle, *where a signficant percentage of the bass energy is absorbed by the Helmholtz resonator.*



^^^ That's the important part right there. I hope the motion of the sound wave makes sense. Back to front to back to front, over and over and over again. But in the Magic Bus, that wave is sloooowly absorbed by the Helmholtz Resonator.

THAT is why the pitch is so perfect. No overhang, tight as a drum.


Now... Who can think of another way to absorb reflected bass? (Hint: foam won't do the job.)










The answer is simple:

Another woofer, but in reverse phase.

For instance, let's say you had a sealed box in the trunk of your car. Your sealed box played a 40hz note. About eleven milliseconds later, that note has hit your front windshield, and is now right back where it started, at the rear of the car. *What if you could play that note *again*, but 180 degrees out of phase?* It would cancel out the first wave.

Voila! Tight bass. No reflected energy.


^^^ if that last paragraph made your head explode, please ask questions, because my head hurts thinking about that. And I'm the one that wrote it 











If you see where I'm going with this, you'll see why the tapped horns sound good. Although they look like a box, they're really a 6'-12' tube that's been folded. So we're 'injecting' a signal 180 degrees out of phase, about every eight milliseconds.

If you're REALLY clever, you could probably size the pathlength to null the reflection off of the windshield. Basically juggle the distance to windshield and distance down the horn so that the woofer cone is 180 degrees out of phase when the energy reflected from the windshield hits it.

My TH-Mini wasn't designed to do this; it's mostly a happy accident that it gets close.


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## Patrick Bateman (Sep 11, 2006)

Here's some data to back up my argument, which is that a subwoofer that actively cancels reflected energy sounds 'tight.'

















The measurements above show the measured response of the same sub in the time domain. The first sub is sealed. The second sub is dipole. In the dipole config, we see the following:

1) It's decay is faster than the sealed sub
2) The 'shape' of the decay is arguably more natural; ideally we'd want a nice symmetrical curve as the pulse 'fades to black'


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## thehatedguy (May 4, 2007)

That's where the well treated room comment came from...

It's not magic, it's just something car audio guys don't do or can't do. I like how Geddes and Toole remedy the problem with multiple subs...but that doesn't do much for us car guys.


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## Patrick Bateman (Sep 11, 2006)

There's one more advantage to the dipole. This advantage may be a bit difficult to visualize, as you have to consider the motion of the loudspeaker cone:

I would argue that *both methods of cancelling reflections would likely improve the 'pitch' of bass notes. But the first method will hurt dynamic range more than the second.*

Here's why:

In the Helmholtz resonator configuration, ALL bass notes of a particular frequency will be absorbed by the resonator. For instance, if the resonator is tuned to 40hz, then all 40hz notes will be affected. (If you've listened to systems that use DSP to 'clean up' bass, the loss of dynamic impact is immediately noticeable.)

When using a second loudspeaker cone to cancel out reflections, only HALF of the notes will be affected. This is because the cone is moving; so half of the time the reflected energy will be out-of-phase, and will nullify. The other half of the time, the reflected energy will be IN-phase, and the energy will sum.

Now that statement might lead one to believe that the out-of-phase driver will create more problems than it solves. IE, who cares if some of the bass is absorbed, when some of the bass is also augmented?

The reason that isn't a big concern is that the maximum gain from reflections is six dB; while the maximum loss is infinite. When two sounds are 180 degrees out of phase, they null each other to zero. When they're in phase the maximum 'boost' is 6dB. *So overall, I'd argue that the net affect is positive.* But don't take my word for it; the measurements of in-room impulse response are consistent with my statement.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> That's where the well treated room comment came from...
> 
> It's not magic, it's just something car audio guys don't do or can't do. I like how Geddes and Toole remedy the problem with multiple subs...but that doesn't do much for us car guys.


Jason has a point here; any type of bass cancellation will be ineffective below a certain frequency, simply because the wavelengths are so long. We can calculate this:

1) Given a car cabin that's about 96" long
2) and given that we only want to address frequencies which are one quarter wavelength or shorter;
3) Then we should only concern ourselves with frequencies above 35 hz. (speed of sound / 96" / 4)

But this is pretty consistent with what I heard with the tapped horns and with the magic bus. It's not like 20hz suddenly had pitch definition; the area that was cleaned up was certainly in the two octaves between 40 and 160hz.

If I did this in MY car, I'd probably do something like this:

1) Big ol' sealed sub covering 20-40hz
2) Dipole, front loaded horn, or tapped horn covering 40hz to 160hz
3) Conventional drivers above 160hz


Another way to implement it is like this:

1) Sealed or vented sub from 20-80hz
2) Sealed or vented midbass from 40hz and up
The above config would take some tweaking, but basically you would 'overlap' the midbasses in front with the sub in back, and tweak things so that the sound from the back arrives at the front of the vehicle in-phase. Overlapping would be tricky, but it could definitely work. For instance, if the door midbasses were delayed by about seven milliseconds they'd be in-phase with the sub. All of this would require some serious tweaking though; you'd need to do impulse measurements and there's a ton of variables to do it with three drivers in multiple locations. (It CAN be done however.)

I like the dipole solution because it's not as tweakable, but it sure seems to work


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## Nismo (Jan 10, 2010)

Pat, its funny you mention doing the midbasses really low with the sub. I had that thought the other day. My Koda 8 has a 32 Hz fs, and the Brahma 12 is 28 Hz. That lends itself to what you're talking about quite well. I would just need something to delay the front speakers.

Eric


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## asawendo (Nov 22, 2009)

Gee Patrick, this is really interesting

Since last December I have two subwoofers in the back seat of my car playing different frequencies.

The first one is Phase Aliante Evolution 12" covering 20-32Hz 24db and the second one is 12" Orion XTR3 playing 33-80Hz 36db also in 1 cu ft sealed enclosure. FYI my Midbass is Accuton C173-6-191 covering 80-800Hz 12db. 

I'm heavily sandwiched all my panels with different sound deadener in order to have minimum rattles and resonant frequencies I do not delay the subwoofers at all but have been delayed my midbass exactly 7.32ms related to the subs.











For the result I'm really impressed with the upfront bass illusion as if there is no subwoofers on the back of my car. It's like coming from the center of the dash.

I must admit it is far from bass perfection but PB ideas always inspired me to enhanced my experiment furthermore. Thank you so much PB!


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## asawendo (Nov 22, 2009)

cajunner said:


> ....with the van, having the sub in the center of the vehicle means it's equidistant from all sound containment structures, so the helmholtz resonators have to deal only with the small band of frequencies native to the distances between the subs and the dimensional differences between, you can tune the resonator to absorb the same frequency component that is dominant as the primary resonant mode, or modes. Distance to back door, distance to ceiling, distance to front glass, distance to floor and distance to sidewalls. The closer you can get all of these dimensions, the easier to tune a helmholtz.
> 
> in a car, you'd have to have the subs in a rear seat elevated console, much too close to the driver to accommodate the same blanking scheme.


Cajunner I really thinking for doing this....Thank you friend


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## quietfly (Mar 23, 2011)

sub--- cribing....


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## pionkej (Feb 29, 2008)

Question: Why not just run multiple subs "Geddes style"?


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## Patrick Bateman (Sep 11, 2006)

pionkej said:


> Question: Why not just run multiple subs "Geddes style"?


That'll work too, or at least it will work above 35hz. (What Jason noted about it not working below 35hz is true.)

The 'nice' thing about dipoles is that they basically behave like two drivers, not one. So dual dipoles are similar to having four sealed boxes, albeit four sealed boxes where two of them are out-of-phase. And in this scheme, you *want* some of that energy to be out-of-phase, as it appears to be reducing the amount of time that signals 'fade to black.'

I stole my data from John Kreskovsky; and his graphs show that the decay ranks like this:

1) dipole
2) cardioid
3) multiple sealed drivers
4) single sealed driver

Basically the most common configuration in a car - a single sealed box - performed the worst.

Here's the measurements, in the same order as listed above:





































On 2nd thought, it's hard to say if single driver sealed or dual driver sealed was worse. They're both bad, but bad in a different way.


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## audiguy (Jul 30, 2007)

What about IB? That is what I run in my house. 4-18's IB with 2500 watts.


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## Patrick Bateman (Sep 11, 2006)

audiguy said:


> What about IB? That is what I run in my house. 4-18's IB with 2500 watts.


A 'true' infinite baffle will behave like a big ol' sealed box.

One thing I'm curious about tho, is if a 'infinite baffle' in a car acts like a dipole. For instance, when you put a couple 12s across the rear deck of a sedan, a certain percentage of the rear wave will make it into the cabin. I wonder if one of the reasons that "IB" works so well in-car is because of this phenomenon. Perhaps we're cleaning up the impulse response a bit, the same way that a dipole would.

The effect won't be 100%, because only a fraction of the rear wave is 'leaking' into the cabin, and it's frequency dependent. But I've never seen a trunk that was perfectly sealed off, and the level of isolation varies wildly from car to car. I've owned Volkswagens where noise from the trunk seemed to leak right into the car, and I've driven Mercedes where the trunk seemed to be sealed off like a bank vault.


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## Spyke (Apr 20, 2012)

Subscribed. It's late, i'll read later.


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## chithead (Mar 19, 2008)

Would a dipole require large woofers to accomplish this? Or could multiple smaller subs be implemented for this effect?


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## RNBRAD (Oct 30, 2012)

What's cool about (newer) Mercedes is they use special materials and sound isolating designed trim panels in reflection prown area's like below the angle of the back window and distal area of the front dash directly under the windshield. This is where the magic happens. The trim pieces are an aesthetic compromise (many people prefer a full leather looking dash) but they have done well to blend them in but they are specifically designed to capture and cancel reflection off the glass. The technology in sound deadening in these cars is off the charts. The rear decks have an inch thick of like a memory foam material pinched in between inner and out layer of metal. They also started using a high grade all weather material in the fenderwell as well. This helps muffle the sound from the road and any debree that hits you fender wells. Cars literally as dead moving as it is stopped. Luckily I was able to get sub bass through the trunk into the interior.


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## Hanatsu (Nov 9, 2010)

What's the difference between this Helmholtz resonator and an ordinary bass trap and how do you calculate a Helmholtz resonator? Do these work for higher frequencies as well, like lower midrange/midbass?


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## Oliver (Jun 25, 2007)

How to make a Bass Trap Acoustic Panel (Tutorial) - YouTube

Small Studio Acoustic Treatment, Bass Traps, Acoustic Panels. - YouTube

Building a frameless broadband absorber - YouTube

couple of vids


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## trebor (Jun 30, 2008)

Patrick Bateman said:


> Now... Who can think of another way to absorb reflected bass? (Hint: foam won't do the job.)
> 
> 
> 
> ...


So....your talking about manipulating the listening environment by actively controlling/canceling reflections. Makes one wonder about 12" rear mounted mid-basses, or phased arrays.




Sent from my iPhone using Tapatalk


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## thehatedguy (May 4, 2007)

I think the midbass array would be as close as we could get to Toole and Geddes's approaches in the car...and would be more beneficial since this is where most of our car's problems lie IMO.

The best bass that I had in my old car was when I had a 10 mounted under the radio between the dash and the trans tunnel with the 3 12s across the back deck.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> I would posit that they are only feasible for midbass on up, as low bass is not going to react to an aperture too small to collect a wave 20 feet long or more...
> 
> any wave that long would be a compression mode as the wave attempted to double on itself in the confines of the car interior.
> 
> the "clean" response of a summed response is no doubt, due to the resonant modes of those speakers playing above the level of the subwoofers, and also the dominant ringing modes or "harmonic distortion" of the subs playing outside of their frequency fundamentals: these harmonics being acted upon by the helmholtz cleaning up the end result.


I'm no expert on room treatment - but it DOES seem that the Helmholtz resonator will work, even if the aperture is small. It SEEMS like the math to calculate one should be no different than for any ported box. 









For instance, if you have a two cubic foot tuned to 30hz, the air in the box and the air in the port interact at one frequency, augmenting that frequency.

I'm still left with a ton of questions, unfortunately:

1) The best calculator that I can find makes my head hurt in a huge way : Porous Absorber Calculator V1.59

2) Guys like Geddes are way smarter than me, and it seems like they've tried and rejected a lot of this stuff already. For instance, the first time that I heard about Helmholtz bass traps was from Geddes. If I'm not mistaken, he's currently using a much simpler solution. He uses multiple sealed subs, and a lot of EQ.

3) One thing that's really depressing is how unspectacular and unpredictable the results of this stuff is. There's a lot of threads on this and it seems like no one is getting 'great' results:

Super-Chunk Absorber test, this can't be right? | AVForums.com - UK Online - Page 3


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## Patrick Bateman (Sep 11, 2006)

I still think the tapped horn or front loaded horn is probably the most "pain-free" way to cancel that reflected energy

BUT...

Here's an idea for some of you, who prefer conventional boxes. *What if we used the entire trunk of the car to cancel out bass reflections?*










Above is Andy Wehmeyer's cabin gain measurement. Typically we visualize cabin gain as something that starts at 80hz, and continues at a linear pace down to 0hz. But it doesn't actually work that way; IMHO there are two big peaks and a dip that occur in a car. The first peak is at 65hz, the second peak is at 32.5 hz, and the dip is *also* at 65hz. These peaks correspond to the dimensions of the cabin, which is approximately 4' x 8'. (There's a peak *and* a dip at 65hz. You might wonder why they don't cancel each other out. The reason is that nulls in wavelength are infinite, but the maximum gain of a peak is 6dB. So the null at 65hz has a larger affect on frequency than the PEAK at the same frequency. Net effect is a dip.)

So here's my wacky idea, and it's a very simple one:

*In order to cancel out the reflections, what if we used a passive radiator?*

For instance, a 15" passive radiator tuned to 35hz would really obliterate that 35hz room mode.

One of the 'cool' things about this is that it's dead simple to construct, doesn't require a PHD in physics, and if it sucks, well you've only wasted $50.









Pyle PylePro PPA15 Professional Premium Woofer | Overstock.com

These puppies are $50.99 delivered to your door, and with a surface area of 800cm, they'll be VERY efficient at absorbing bass.

(If it's not clear where I'm going with this, you simply mount the subwoofer ifinite baffle *and leave it unpowered.* The woofer will act like a big efficient passive radiator, tuned to 27hz. Ideally, we'd want an FS of about 35hz, but I leave it up to the reader to find a big cheap efficient woofer with an FS of 35hz. Passive radiators won't work too hot because they're tuned too LOW. They often have an FS in the range of 10-20hz.


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## Navy Chief (Jun 14, 2010)

I never thought I would see Patrick Bateman recommend Pyle drivers for anything, lol. If you did use this driver or any other for a similar purpose, could you unmount the magnet to save space and just rely on the cone weight and spider for the FS.


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## Patrick Bateman (Sep 11, 2006)

I <3 cheap drivers! Some of the best bass I've ever heard was Eminence Alpha 15s in a dipole.

As for removing the magnets, YES, that would work. The only advantage to using a "working" speaker is that you can measure the FS.

Radiator efficiency is directly related to surface area, and one of the 'stranger' ideas I've had for passive radiators is to simply use a crappy panel for one side of the box. For instance, picture a six sided cube. Five sides of the cube are rigid, and one is weak and flexy. The weak and flexy side should act like a passive radiator.

The only problem is that it would be a complete p.i.t.a. to tune. But it would be a very cheap/clever/efficient option for a loudspeaker manufacturer, as it would be much cheaper than a 'real' passive radiator.

http://www.diymobileaudio.com/forum...ssion/133472-cheap-diy-passive-radiators.html

^^ Logitech does something similar in their computer speakers, which use a simple piece of cardboard and a foam surround for a passive radiator.


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## Patrick Bateman (Sep 11, 2006)

More anecdotal evidence *against* using Helmholtz bass traps:









1) Here's someone that built one, to unspectacular results: Acoustics Forum • View topic - Helmholtz formula, is this incorrect?









2) The Danley DTS-20 used helmholtz bass traps, built into the enclosure. But Danley has moved away from that, and I don't believe a box of his has used that technology since. Nearly all of Danley's subs use multiple drivers now *and I personally believe that one of the reasons is because multiple resonances smooth out the dips and peaks better than Helmholtz bass traps do.*


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## thehatedguy (May 4, 2007)

Wouldn't it act more like a tuned enclosure?

I see what you are saying, but off the cuff don't think it would work like how you are thinking.

Though I might be missing something.


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## Hanatsu (Nov 9, 2010)

What about those quarter wave tube basstraps? I have issues at 120-130Hz with high peaks. Can't such pipe be integrated below the dashboard to absorb those frequencies, if I understand it correctly I need a 60-70cm pipe? Would that work?


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> What about those quarter wave tube basstraps? I have issues at 120-130Hz with high peaks. Can't such pipe be integrated below the dashboard to absorb those frequencies, if I understand it correctly I need a 60-70cm pipe? Would that work?


From what I can tell, there's a couple options:

1) Take a piece of PVC, fill it with fiberglass, and seal it at one end. (Similar to the tubes in the Danley DTS-20 that I posted.)

OR

2) I think you might be able to put an unpowered driver with an FS of 125hz into a sealed box.

The downside to both approaches, as far as I can see, is bandwidth and efficiency. For instance, one of the articles indicated that a coke bottle works as a helmholtz resonator, but it has a bandwidth of a fraction of a hertz!

I think that may be the reason that these guys are getting crappy results. Due to the very narrow bandwidth, the effect is nearly unmeasurable.

That's a big part of the reason I have renewed excitement for dipoles. *In a dipole we basically have two sound sources with identical efficiency and bandwidth.* YES they're inefficient, but who cares? If you need more SPL just add more woofers. I could probably squeeze four 15" woofers into a three cubic foot cube. In a nutshell, it seems like people go nuts about the sound of dipole bass (and yes, FLHs and tapped horns are dipoles), but they never quite knew WHY it sounded so good. And EVERYONE griped about the crappy efficiency of dipoles. But it sounds like the bass-cancellation is a big part of the magic, and that cancellation comes at a price - reduced efficiency.

It also explains why people say things like this about dipoles:

_"I didn't realize what I was missing until I heard this beast, and I've owned or heard all the usual suspects -- JL, SVS, Revel, Aerial, eD, ML. Detail, detail, detail amidst tremendous output. It's like the ribbon tweeter equivalent on a subwoofer -- the clarity and resolution are astonishing. Everything else sounds muddy in comparison. It is the bass equivalent of going from 240i to 1080p, or as another owner commented, like "going from a receiver to separates. This is how major this DTS20 is."_ (Danley DTS-20 = LFE Nirvana)

_"Positioned correctly these dipoles really get going. The B200 produces an expressive and dynamic sound with authority and amazing three-dimensionality, exactly like we expected the performance to be. For some the low end might be a bit exaggerated, but we thought the sound was rather warm and pleasant, and - as mentioned already - the high pass filter can easily be adjusted. The dipole subwoofer was impressive, and when positioned and adjusted correctly produced a sound like no other cabinet type. Even the lowest bass is tight and dry and passed on without any sluggishness, displaying the "fast" bass that makes a dipole sound so attractive. Surely, the sound doesn't reach the ear quicker then with a standard cabinet subwoofers. But, especially compared to bass reflex cabinets, the dipole shows an incredibly fast excursion. This results in giving the bass more space and contour, making it easier for the ear to absorb the musical information. In conjunction with the B200 this subwoofer provides even more depth and power, sweeping away all reservations regarding the reasonably priced drivers. While some might be worried about the power handling, we, on the other hand, liked the dynamics and musicality at any time."_ (Strassacker: Speaker Building, Components)


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## Patrick Bateman (Sep 11, 2006)

Oh, one more idea for Hanatsu -

If you have a peak at 125hz, and you're interested in canceling it passively with a Helmholtz bass trap, how about an ACTIVE solution?

For instance, a small bandpass box under the dash could do the trick. The reason you can get away with a small box is that you can use a very narrow and efficient alignment. For instance, you could use an Dayton Neo-Syn 3.5" woofer tuned to 125hz, with a bandwidth of a fraction of an octave. It would actively 'null out' that peak.

Since it's small, you could also experiment with various locations in the car. For instance, putting the 'null' woofer in the rear of the car might improve soundstaging.


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## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> Oh, one more idea for Hanatsu -
> 
> If you have a peak at 125hz, and you're interested in canceling it passively with a Helmholtz bass trap, how about an ACTIVE solution?
> 
> ...


Cool idea. I sure have both amplifiers/DSP channels (14ch available) and quite a few speakers on the shelf. Why not give it a try? 

There's also some space under the seat. I'm posting a build thread soon, seriously interested in doing something "special". While EQ brings down the peak it doesn't 'fix' it and something still sounds off around that frequencies (120-130Hz).

Thanks!


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> Cool idea. I sure have both amplifiers/DSP channels (14ch available) and quite a few speakers on the shelf. Why not give it a try?
> 
> There's also some space under the seat. I'm posting a build thread soon, seriously interested in doing something "special". While EQ brings down the peak it doesn't 'fix' it and something still sounds off around that frequencies (120-130Hz).
> 
> Thanks!


Yeah this is something Jon and I spent a lot of time talking about. The fact that EQ can't fix these reflection problems in the same way that a bass trap can. (EQ definitely helps.)

Probably the best solution is a dose of both, kind of like using two different brands of painkiller to make a headache go away. Each one works in their own synergistic way.


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> 2) Guys like Geddes are way smarter than me, and it seems like they've tried and rejected a lot of this stuff already. If I'm not mistaken, he's currently using a much simpler solution. He uses multiple sealed subs, and a lot of EQ.


I don't want to stand in the way of good crazy, because good crazy is were innovation evolves (or at least it makes life worth while). But its nice to have perspective, and nice to reaffirm that a simple sealed box we all can make will go a long way. No fancy contortions needed. Just lots of power (and power is cheap and efficient, thanks to class D) and gratuitous use of EQ (everybody has one, right?)

Carry on


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## Nismo (Jan 10, 2010)

Patrick,
I'm interested in more info on the TH. I'm working with internal dimensions of about 12"H x 34"W x 15"D. I know that's not a perfect square, but I'd be interested in knowing if that might work with a Brahma 12.

I've been finalizing my ported box with dual 4" flared ports firing through the 6x9 holes in the rear deck, but I can't find a setup that seems reasonable to build and fits my needs. If the TH would fit with that, then it would be worth it.

Fs: 28
Qts: .45
Vas: 37.2 liters

Eric


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## Justin Zazzi (May 28, 2012)

I smile when Patrick starts down another crazy path to audio nirvana.


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## Brute71 (Jun 6, 2012)

sub'd! Lots of good info here to attack an issue I will run into when I finally get the sub stage in my car.


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## The real Subzero (Apr 13, 2010)

Subscribed. 

Interesting ideas and concepts that seem to have alot in common with my build. I have some focal 5ws subs in a small ported box tuned to 45hz firing up into my dash. ( I will eventually have them in the dash) and I also have a 27kx in the back in a sealed box in the back cargo area. and I must say, this combination has fullfilled the desired effects I have been looking for. There are some areas that I need to work out.


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## Patrick Bateman (Sep 11, 2006)

Yesterday I wondered if one could use a unpowered sub instead of a Helmholtz resonator, since an unpowered sub acts like a passive radiator, and a PR can be interchanged with a Helmholtz resonator in a box. I asked Dr Earl Geddes about this; here's the exchange.

_Quote:
Originally Posted by Patrick Bateman 
Dr Geddes - I know you've done a lot of research into bass traps and room treatment. You were the first person to clue me into the idea of using Helmholtz bass traps.

I have a question -

Can one use unpowered sealed subs as bass traps?

For instance, one could construct a helmholtz bass trap, but calculating the volume of the box and the volume of the helmholtz resonator is a mystery to me. (Is it the same math as a vented box? I do not know.)

But it occurred to me that one could simply build a sealed box, pick a woofer with the proper FS, and leave the box unpowered. It seems to me that the woofer cone would act like a passive radiator, and would cancel out sound in the room at that frequency.

Thoughts?
You could do that, but it would not be all that effective. Better is to use an amp and some electronics control to create an active absorber which would be much more effective, but better still is just to use the sub as a sub in a multi-sub setup. If done correctly, you will find that turning a sub on can actually reduce the sound level in some frequency range. Hence this sub IS acting as an absorber in that frequency range. You will find that all the subs do this over some frequency range. This means that a multi-sub setup IS an active absorber setup. 

Unless the absorption is built into the room walls its not going to be very effective - multi-subs simply works and trumps all of the other approaches IMO._

Geddes has tried a lot of this stuff already, so leveraging his expertise saves us a lot of time. (As noted earlier in the thread, I've never had better bass in the home than when I used a multisub approach. At the moment I'm using three, but I'll concede that using eight made an audible improvement.)


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## thehatedguy (May 4, 2007)

Didn't think that would work.

I have an idea. Big sub in the back, another smaller sub in front. Midbasses in each kick. Mibasses on the rear deck ala the midbass array.

Maybe not even need the sub in front if the midbasses can go low enough.


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## Navy Chief (Jun 14, 2010)

This thread makes me want to buy 8 of these 3" subs and run them all around the cab. 

Tang Band W3-1876S 3" Mini Subwoofer 264-909


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## Orion525iT (Mar 6, 2011)

So question is, how many subs, what kind (size, fs, ect) and how to get them to work in the auto environment.


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## thehatedguy (May 4, 2007)

Depends on if my Gedde's style approach works or not in the car...but I don't think for us mulitple subs in multiple locations is the trick as much as spreading the midbasses around.


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## thehatedguy (May 4, 2007)

Room Mode / Standing Wave Calculator

Calculator to see what your problem frequencies will be.


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## thehatedguy (May 4, 2007)

In my car, most of the modal problems are squarely in the midbass area, only one in the bass and one in the lower midrange.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Didn't think that would work.
> 
> I have an idea. Big sub in the back, another smaller sub in front. Midbasses in each kick. Mibasses on the rear deck ala the midbass array.
> 
> Maybe not even need the sub in front if the midbasses can go low enough.


I really have a 'knack' for visualizing wavelengths in my head, and I like your idea, but there's one 'tricky' thing about it. *The gap is about twice as long as we want it.*

For instance, the front to back distance in a car cabin is eight feet. That's equivalent to one quarter wave of 35hz. *But 35hz is too low for us; as noted earlier in the thread we want to focus on frequencies above the Schroeder Frequency. So I'd say the three octaves from 40hz to 320hz, imho.


Using that line of thought, I'm thinking locations like this:


sub in the back, with a second sub near the center of the car - about 4' away.
sub in the back, with sealed drivers in the doors. This is a bit too far - about 6' - but is likely superior to drivers in the kicks
sub in the back, with sealed drivers in the doors, but in edge of the door that's near the B-Pillar. For instance, in my Honda Accord there's plenty or room to put the drivers on the closer edge of the door. That moves the driver about 2' closer to the rear sub, which is just about ideal imho











Tapped horn with a pathlength of about 4-5' is by far the easiest though. You basically get two drivers playing with a built in time delay of 4ms, which is right where we want it.

*


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Depends on if my Gedde's style approach works or not in the car...but I don't think for us mulitple subs in multiple locations is the trick as much as spreading the midbasses around.


It might be an incredible mess, but I'm thinking about this for my Accord build:

1) dual reflex bandpass subs - (20hz - 160hz)
2) dipole midbasses under the dash (120hz - 500hz) 
3) back loaded horns for the midrange (300hz - 20khz)

lots of overlap on all the drivers - basically trying to encourage reflections, instead of avoiding them. And all drivers below 1khz are dipoles, so that we have both positive and negative waves

It would require a TON of EQ, of course, and efficiency would suffer. But it might sound clean (I hope!)

Also a sealed sub for infrabass would help add some 'weight'


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## thehatedguy (May 4, 2007)

Curious about the midbass idea under the dash.


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## Nismo (Jan 10, 2010)

Patrick,
Based on your drawing above, it would appear that as long as the design carries the right length and rate of enlargement, that it would be fine. I'm almost to the build stage, so I'd love to consider that.

Eric


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## Patrick Bateman (Sep 11, 2006)

Nismo said:


> Patrick,
> Based on your drawing above, it would appear that as long as the design carries the right length and rate of enlargement, that it would be fine. I'm almost to the build stage, so I'd love to consider that.
> 
> Eric


not sure what you mean by that - could you elaborate?

Glue is drying on my 'attempt' at implementing this in my Accord, so we'll see how that goes


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Room Mode / Standing Wave Calculator
> 
> Calculator to see what your problem frequencies will be.


A couple of things I noticed about this calculator:

1) It appears to only factor in the first reflection. For instance, in an 8' long room, it shows the lowest mode at 35hz. But there will be a *second* an octave lower, if I'm not mistaken.

I'm not 100% sure if that's correct though, because half of the modes are nulls and half are peaks.

2) I believe the calculator assumes that the listener or the speaker is exactly at the edge of the room. Location in the room really complicates all this; it's one of those things where it's really hard to predict unless you have a microphone.

On the upside, these wavelengths are soooooo long, if you move a foot or two it won't make a whole lotta difference.


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## audiguy (Jul 30, 2007)

Patrick Bateman said:


> It might be an incredible mess, but I'm thinking about this for my Accord build:
> 
> 1) dual reflex bandpass subs - (20hz - 160hz)
> 2) dipole midbasses under the dash (120hz - 500hz)
> ...


As a big time and phase coherent guy, this sounds like a mess.


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## oldschool4me (Feb 9, 2013)

Interesting thread. I have had good luck using midbass in rear of my cars. usually ran from roughly 40 to 400hz range. Im about to start an install in my cts 4dr. Will run midbass in rear doors and looking forward to playing with the 10" stock sub location in the rear deck for added midbass. First plan is trying a pro audio driver with baffle....this thread has me now also wanting to try putting an unpowered sub for use as a passive radiator.


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## The real Subzero (Apr 13, 2010)

thehatedguy said:


> Curious about the midbass idea under the dash.


I can say from my experiementing, the subs under the dash are awesome. I definately got what I had envisioned. and now its time to finish all the fabrication work and dial everything in.


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## MarkZ (Dec 5, 2005)

So your premise is that reflections steer the bass rearward? Presumably, those that "outlast" the reflections in the front of the car? I see an impressive discussion about how to tame these reflections, but I guess I'm not clear on why this is important...


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## Nismo (Jan 10, 2010)

Patrick Bateman said:


> not sure what you mean by that - could you elaborate?
> 
> Glue is drying on my 'attempt' at implementing this in my Accord, so we'll see how that goes


Pardon my poor description. My question was whether the shape of the box mattered [that] much, or if it could be folded in nearly any manner, so long as the throat started at a certain width, and expaned to a certain size at a given length (the ratio).

I am not liking the way my trunk is laid out, so I'm trying to figure out if I can stuff a TH into a 12Hx34Wx16D box.

Eric


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## Oliver (Jun 25, 2007)

Patrick Bateman said:


> Before I get into the technical details of my idea, I wanted to get into some things that *have* worked for making good musical bass, and what *hasn't* worked. (For me at least.)
> 
> First, things that *haven't* worked:
> 
> ...






> Year after year I keep trying to make something that exceeds the TH-Mini, but I haven't been able to do it. It's been my reference sub for something like three years now, and I've built easily four or five other subs in a (failed) effort to one-up it.


Is this is what you're asking about ?

[/B]The folds are what make this design !


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## mosconiac (Nov 12, 2009)

Could you not throw a well-designed passive circuit on the passive radiator/unpowered woofer to tune it precisely to your intended trap frequency? The circuit would resist cone movement outside the trap (higher impedence) and sink the energy when within (lower impedence).


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## quietfly (Mar 23, 2011)

mosconiac said:


> Could you not throw a well-designed passive circuit on the passive radiator/unpowered woofer to tune it precisely to your intended trap frequency? The circuit would resist cone movement outside the trap (higher impedence) and sink the energy when within (lower impedence).





DrGEDDES said:


> Better is to use an amp and some electronics control to create an active absorber which would be much more effective, but better still is just to use the sub as a sub in a multi-sub setup. If done correctly, you will find that turning a sub on can actually reduce the sound level in some frequency range. Hence this sub IS acting as an absorber in that frequency range. You will find that all the subs do this over some frequency range. This means that a multi-sub setup IS an active absorber setup.


i think that means that while i would work a little actively doing it would work much better.


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## GibTG (Mar 11, 2010)

Subscribed...


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## WrenchGuy (Jun 10, 2007)

Dont stop now...lol


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## Hanatsu (Nov 9, 2010)

I actually tried out an active approach to improve decay in the 120Hz area. A 4" in a 4th order bandpass enclosure, I set it 180deg out of phase. Guess what? I did actually work, it effectively canceled out the mode and the decay quite much. The immediate peak went down around 7dB and the SPL beyond 100ms went down almost 15dB. The annoying ringing at that frequency went away. Amazing how much difference it made actually.

Just a small issue, run out of both DSP channels and amplifier channels. Might add one DSP more, have an Audison bit.10 on the shelf and another PDX 4.150 amp (lol... it would mean 13 amplifier channels and 19 DSP channels in total). There are more problem frequencies than 120Hz that needs to be taken care of. The temporary box I made looks like crap too. The best placement was behind the driver seat the the port firing upwards, I could actually hear how the midbass "dried up" and moved forward.

Was too lazy to save the measurements I did in the garage, here's how it looked before, I'll post a before and after later on:


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## Patrick Bateman (Sep 11, 2006)

Innerworld Audio - Early days of Gradient


























I heard some Gradient speakers at CES, and their spaciousness was astounding.
Companies like Bose sell speakers which are designed to create reflections off of the listening room, in an attempt to add 'spaciousness' to the sound. But Gradient takes the opposite approach; they basically do everything possible to eliminate reflections in the room. And where reflections are impossible to eliminate, *they stagger them in time.* For instance, the Gradient Helsinki reflects energy off of the floor, ceiling, and walls, just as all loudspeakers do. But 90% of the loudspeakers out there do it at the same time, while the Helsinki's reflections are distributed throughout the room.

Might explain why they sound so 'spacious'


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## Patrick Bateman (Sep 11, 2006)

Cardioid bass


























Here's some information on how to make cardioid bass arrays. I've been raving about PK Sound lately* and cardioid subs is what they do. The Gradient speaker in the last post uses cardioid radiation for the midrange; same idea but higher in frequency.

* http://www.diymobileaudio.com/forum...ion/143420-louder-than-pk-sound-cx-800-a.html, PK Sound CX800: 95% efficient?? - diyAudio


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## SynRG (Jul 30, 2007)

The discussion regarding helmholtz resonators is interesting. I have wondered before about the possibility of tuning a car, with a separate trunk, by coupling an enclosed driver directly to the listening space in the car to isolate it from the trunk, and then using appropriately sized ports in the rear deck and the trunk space itself to create a helmholtz resonator that effectively tunes the listening space.


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## avanti1960 (Sep 24, 2011)

Rather than upfront bass the sub topic should be quality bass. 
The concept of band pass drivers delayed in phase to reduce nasty peaks and reflections in mobile environments seems like the basis for a paradigm shift in SQ and is an outstanding revelation.
As DSP and amplification gets smaller and cheaper it would not take too much to implement this on a mass aftermarket if not OEM scale. Why not a couple of strategically placed door peak cancelling drivers? Wouldn't this also help reduce resonance and rattle issues?


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## Patrick Bateman (Sep 11, 2006)

avanti1960 said:


> Rather than upfront bass the sub topic should be quality bass.
> The concept of band pass drivers delayed in phase to reduce nasty peaks and reflections in mobile environments seems like the basis for a paradigm shift in SQ and is an outstanding revelation.
> As DSP and amplification gets smaller and cheaper it would not take too much to implement this on a mass aftermarket if not OEM scale. Why not a couple of strategically placed door peak cancelling drivers? Wouldn't this also help reduce resonance and rattle issues?


A few observations:

1) I'm not 100% convinced that the drivers need to be up front. For instance, let's say that you have a nasty resonance at 150hz in your car. You *could* put a bandpass enclosure that's out-of-phase at 150hz, and stick it under the dash.

BUT - 

Another option could be to put an enclosure 45" away, that's IN PHASE.

The reason why you might consider the second option is that the waveform form the driver that's 45" away, that's playing 150hz, will be out-of-phase by the time that it reaches you. *This is because it's traveled one half of a wavelength.*


Obviously, once you think about this for a couple minutes, it will probably occur to you that a lot of muddiness in the midbass may be caused by the gap between the subwoofer in the trunk and the midbasses up front. Basically the two drivers are at a distance where they can create some nasty interactions with each other in the range of 100hz-200hz.


Another alternative to using bandpass drivers to 'null out' cabin resonances is to use a combination of sealed and ported woofers. This one is a bit trickier, but basically the idea is that the driver phase shifts as it gets closer to 20hz, so you could use this to your advantage. IE, if you had a resonance at 150hz, you might consider using a ported subwoofer with positive polarity. If the ported sub was 48" away from your sealed midbasses in the doors, the output from the upper end of the ported box would be out of phase with the door speakers at 150hz. So if there was a peak in the response curve, the output from the upper end of the ported box would 'null out' that peak.


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## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> A few observations:
> 
> 1) I'm not 100% convinced that the drivers need to be up front. For instance, let's say that you have a nasty resonance at 150hz in your car. You *could* put a bandpass enclosure that's out-of-phase at 150hz, and stick it under the dash.
> 
> ...


I tried a 4th order BP under the dash, under the seat, behind the seat, in the trunk facing forward and laying on the floor at the passenger side.

Found that these locations all changed the decay pattern. This is kinda weird to me, why is that happening?... 'Under the dash' location removed the 0-60ms portion more than behind the seat which cancelled out 60ms+ more but with less effect before 60ms (or so). SPL differed from 3-15dB down depending on location and relative phase. Nice thing is that you can adjust the decrease in SPL with T/A as the BP-box closes in towards full cancellation at the specific frequency. Too bad I never saved the measurements ;<


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## bbfoto (Aug 28, 2005)

Awesome thread.  It's going to take me a while to digest it all, but thank you to all who have contributed so far!


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## avanti1960 (Sep 24, 2011)

Patrick Bateman said:


> A few observations:
> 
> 1) I'm not 100% convinced that the drivers need to be up front. For instance, let's say that you have a nasty resonance at 150hz in your car. You *could* put a bandpass enclosure that's out-of-phase at 150hz, and stick it under the dash.
> 
> ...


For a mass market OEM approach the cancellation driver would go wherever is cheapest. If it can remain in phase at a specific distance without time delay processing then theoretically they could get away with a passive crossover network or ported enclosure. 

Which leads me to the question- have the OEMs already built in bass peak cancellation into their "from the factory" audio systems? 

The reason I ask is that my car had pretty decent full sounding bass as it arrived from the factory. Granted it lacked output and needed amplification (which is where the trouble could start) however the bass peak issues of your typical treated / sealed door aftermarket installs can be observed at lower volumes and are not easily / completely remedied with EQ. 

So the OEM system had full sounding bass without sealed doors- implying they may have used or tuned the leaking back wave to cancel peaks- or at the very least tuned the system to compensate for it. 

Although deading and sealing the doors improves "impact" and low frequency output of a good aftermarket midbass driver, in my experience it was not without bringing along some issues to deal with- namely too much bass at certain frequencies (bass peaks / resonances). 

So what about well tuned openings in the doors to allow key back wave frequencies to escape and cancel the peaks? Is this an ultimate "cheap" peak cancellation solution that the OEMs implemented?


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## thehatedguy (May 4, 2007)

I think you saw different results with the canceling system in different locations because the modal problem frequencies are located in different physical areas.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> my understanding of low bass in a vehicle is not that of a wave traveling.
> 
> Imagine the car is filled with heavy air.
> 
> ...



I'm hoping to address some of the points in your last paragraph in my Accord build - it's documented here. (sloooowly)

I'm doing a couple things to reduce delayed reflections:

1) Based on the data from John Kreskovsky, a dipole will basically 'fade to black' faster than a monopole. It's kinda like comb filtering, but in the time domain, not the frequency domain. I'd use a tapped horn if I could fit it, but I can't. So I'm using a dual reflex bandpass box. The one 'twist' is that the port isn't straight, it's shaped like a bowtie, so bandwidth is wider than normal. This is by design, basically to widen the frequency band of one chamber, in the hopes that we'll get close to the response of a TH

2) For the midranges I'm going to use cardioids or back loaded horns.

^^^ Note that 75% of the enclosure types are dipoles; the primary difference is the bandwidth of the output from the back of the cone. For instance, the output from the back of the cone in a ported box is narrower than the output from a tapped horn.


Oh, and I agree with you and Jason, all of this is fairly pointless below 35hz or so. Even the band from 35 to 70hz is a bit iffy, because there's only one dimension where a wavelength longer than 35hz can fit, and that's lengthwise.

But *above* 70hz we have a lot of problems. First off, 70hz is sixteen feet long, so a quarter wavelength is an even multiple of both the width *and* the length of the cabin. (Assuming most car cabins are about 4' x 8'.) And the fact that one dimensions is basically a multiple for the other creates one hell of a resonance. It's the same reason that speaker cabinets frequently use 'the golden ratio' for their dimensions. You *don't* want a box with two dimensions that are a multiple of each other, but that's *exactly* what you have in a car.

In fact, you basically have *three* dimensions that are a multiple of each other, because the *height* of the cabin is pretty close to the width, and the length is a multiple of both. Basically the worst case scenario is a cabin that measures 4' x 4' x 8', or some multiple thereof. (IE 3.5' x 3.5' x 7' would be bad too.)


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## jsketoe (Aug 8, 2008)

Patrick Bateman said:


> Jason has a point here; any type of bass cancellation will be ineffective below a certain frequency, simply because the wavelengths are so long. We can calculate this:
> 
> 1) Given a car cabin that's about 96" long
> 2) and given that we only want to address frequencies which are one quarter wavelength or shorter;
> ...



I bolded what I have found to work. Another tid bit to make the blend work is time relation response between subwoofer and midbass. You want the exact same mechanical response time as your midbass. Heavier woofers move slower. See where I'm going?


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## thehatedguy (May 4, 2007)

I dunno the statement heavier woofers move slower...


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## Nismo (Jan 10, 2010)

How does a heavier woofer move slower? If the moving mass is 20 lbs, and it is playing 40 hz, is it going to only play 20 hz? No. Heavier woofers are NOT slower. Higher inductance can slow response, which is why they are unable to play higher frequencies.

What you're saying is akin to saying you can't run a fast quarter mile in a heavy vehicle. Tell that to the guys running 8 sec times in old 60's sheetmetal. It may take more effort to get there (in the case of a speaker more power) to get a level of output from a heavier driver...but your statement is incorrect.

Eric


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## jsketoe (Aug 8, 2008)

I may have worded it wrong. If you send a pulse testing mechanical response time of a heavy pulp cone 15" driver and a paper 7" midbass/midrange and silk 1" tweeter, you will see the difference in response time across the 3. I'm talking about mechanical allignment.
Taking the few minutes to tweak this type of thing flat out works in most set ups.


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## thehatedguy (May 4, 2007)

I know what we are saying and mean though.


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## highly (Jan 30, 2007)

jsketoe said:


> I bolded what I have found to work. Another tid bit to make the blend work is time relation response between subwoofer and midbass. You want the exact same mechanical response time as your midbass. Heavier woofers move slower. See where I'm going?


Yep. I finally have mine working right from 125 down on the sub and 45 up on the midbass. Almost 1.5 octaves of overlap. No more bloom, just nice, smooth bottom with a kick. Yessir. That's the stuff.


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## CraigMBA (Nov 19, 2010)

pionkej said:


> Question: Why not just run multiple subs "Geddes style"?


My HT in my last house started out as the worst I ever had because the room was so bad. It had slap back echo like Mike Tyson in his prime, so I got on a kick of building acoustic wall treatments. Then I tried the multiple subwoofer thing and it got even better.

What was quite unexpected was the improvement in power response. When I got done the timbre didn't change from seating position to seating position in the HT (which I expected) but is didn't change in the hall or in a bedroom or the kitchen or anywhere else I listened to it.

From a pragmatic standpoint, I'm not sure how you'd go about it in a car because you can't construct appropriate treatments and multiple subwoofers and still drive it - which, IMO, is why Jon's bus works so well.


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## subwoofery (Nov 9, 2008)

highly said:


> Yep. I finally have mine working right from 125 down on the sub and 45 up on the midbass. Almost 1.5 octaves of overlap. No more bloom, just nice, smooth bottom with a kick. Yessir. That's the stuff.


Forgot to ask... The overlap is done with shallow slopes or steep ones? 

Thanks, 
Kelvin


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## SPLEclipse (Aug 17, 2012)

subwoofery said:


> Forgot to ask... The overlap is done with shallow slopes or steep ones?
> 
> Thanks,
> Kelvin


I'd like to know this as well. Planning on doing almost the same thing.


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## SynRG (Jul 30, 2007)

cajunner said:


> ...so, if you scale up, we maybe could attempt to re-create some of the success by using damping treatment behind IB drivers, that operate normally but with a succession of felt layers behind, to not only appear "aperiodic" but mostly to produce a cardioid front, so less of what is going on in the trunk makes it into the cabin.


Interesting concept...flight of ideas...
so are you essentially proposing a bass trap to capture the rear wave, as well as its harmonics which localize the sub and interfere with the primary front wave? 
We wouldn't be talking about damping the bass frequencies within the trunk, but rather muting or elimination of the generation of those frequencies. 
It's done with tweeters and midranges frequently by a combination of materials and enclosure - are the bass solutions for the same effect either cost or space constrained in an auto application? 
As I understand it an aperiodic membrane manages airflow as a frequency specific filter, how would you construct such a device to cancel most rear frequencies in a space efficient manner? 
Perhaps a constrained-layer/foam membrane or structure, suspended behind the driver?
In the end, would this differ in essence from an acoustically stuffed sealed enclosure?


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## jsketoe (Aug 8, 2008)

kelvin...in the GN i did 24db slopes.

I want to hear more about the ib rear wave treatment here...


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## subwoofery (Nov 9, 2008)

jsketoe said:


> kelvin...in the GN i did 24db slopes.
> 
> I want to hear more about the ib rear wave treatment here...


Did you overlap your sub with the midbass in the old system? In the new system (the one with the Focal KX)? 
I'm using 24dB/oct slope on the sub and 18dB/oct slope on the midbass and it works well but no overlap... Just an 80Hz Xover point and phase match using T/A...

Kelvin


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## jsketoe (Aug 8, 2008)

with the quart 15 I had the sub crossed over at 72hz. bottom of the midbass was 25hz .
With the Focals I crossed over the top end somewhere in the 60s (can't remember...sold car) and the midbasses played down to 30hz . All 24db slopes. I added power when I did the Focal sub change..that's when I went to Mosconi's and ditched the Tru Billet.
The Rane was infinite adjustement so I could crossover by ear. If there was something I heard I didn't like I could slide the crossover down or up to adjust. I was just trying to keep the uber low freq's from killing the midbasses since it was a 2 way.
Everything in that car was tuned one specific way with the car set up in a certain seating position, window treatment etc. Any one small change in any of that impacted it. The car is different now. By the scores at Daytona recently I figure it is still a work in progress as the new owner finds the learning curve on it. Once it gets dialed in I expect it to back on kill pretty strong. I expect that car to be one of three top contenders in Ultimate with IASCA and Supermod SQ with USACi at Huntsville.


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## subwoofery (Nov 9, 2008)

Thanks Joe for the info  

Kelvin


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## kaigoss69 (Apr 2, 2008)

Sorry, I may have missed it, but what purpose does the overlap between midbass and sub serve? What are the benefits? Assuming there is no T/A capability but the sub an midbass are all equidistant to the listener, would this still work?


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## hc_TK (Jan 18, 2006)

subscribed


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## kaigoss69 (Apr 2, 2008)

kaigoss69 said:


> Sorry, I may have missed it, but what purpose does the overlap between midbass and sub serve? What are the benefits? Assuming there is no T/A capability but the sub an midbass are all equidistant to the listener, would this still work?


 Anyone? Bueller? Bueller?...


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## highly (Jan 30, 2007)

kaigoss69 said:


> Anyone? Bueller? Bueller?...


I'll be frank and just say no, it wouldn't have the intended effect. By overlapping drivers in that region the intent is to smooth the overall frequency response by reducing modal issues through a distributed approach. Like running multiple subwoofers in a home environment to reduce response anomalies due to room geometry.

-T


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## brett (Apr 27, 2005)

not that i completely understand what was discussed here, but i think i took away enough information to get the gist of it. so, tonight i did another tuning session and played around with this idea using my 6.5's in the rear deck and the 8's in my doors. i did alot of overlapping, phase inversion, etc and really noticed a difference. at one point my sub sounded HORRIBLE and then with a little tweaking and overlapping it snapped into place!

patrick, i do have an idea that i'd like to try. after sitting in the magic bus i realized that most of the impact i was feeling was (to me anyway) coming from the doors and the subs really just rounded out the low end. in no way did i ever feel like the bass was coming from behind me and im assuming that it's because jon has a hefty amount of power going to his midbass in the doors, which if i remember correctly were 10's. that being said, i have a malibu with not alot of space, but im tired of being able to locate the sub every time i turn it up slightly. there are quite a few shallow subs out there these days. what do you think the effect of running a shallow sub on the floor, or footwell, of both the driver and passenger and giving it a ton of power bp'ed at, lets say, 60-200 on a 24db slope, and keeping my subs in the back taking care of 60 down?


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## thehatedguy (May 4, 2007)

How is that different than what you were experimenting with?


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## brett (Apr 27, 2005)

well, the morels in the doors are more of a midbass than subwoofer. they are in a less than ideal enclosure in the doors. but, you're right, it would be very similar to what it is now except my idea was more in line with the thought of a shallow 10 sub in a sealed (better built) enclosure. my intention was to have a driver that i could really sink alot of wattage into and have more control over than the 8's in the doors which are really just a crapshoot at this point. i was thinking by doing this i would be able to get close to what the magic bus has with that strong impact right up front.

at the end of the day, though, im just a guy who is trying very humbly to understand what more knowledgeable guys are saying.


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## subwoofery (Nov 9, 2008)

brett said:


> well, the morels in the doors are more of a midbass than subwoofer. they are in a less than ideal enclosure in the doors. but, you're right, it would be very similar to what it is now except my idea was more in line with the thought of a shallow 10 sub in a sealed (better built) enclosure. my intention was to have a driver that i could really sink alot of wattage into and have more control over than the 8's in the doors which are really just a crapshoot at this point. i was thinking by doing this i would be able to get close to what the magic bus has with that strong impact right up front.
> 
> at the end of the day, though, im just a guy who is trying very humbly to understand what more knowledgeable guys are saying.


Adding more driver, if you don't know what you're doing tuning wise, will only create more phase problems IME - especially if you add more drivers to play the freq range your other drivers are already playing... I can imagine the 30Hz-100Hz being a big mess with your subs playing 60Hz and below and 4 drivers playing 60Hz and up

Kelvin


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## jhnkvn (Mar 26, 2011)

Agree. But if you get it right, it should be equally rewarding. I'm actually attempting a similar setup but with just one 10-incher at front rather than two located in the passenger footwell supported by 6.5" midbass on the doors.


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## BigRed (Aug 12, 2007)

U can run big midbass's up front and if they aren't installed correctly, bass will still sound like its coming from the back based on energy transfer. Trust me, I speak from experience.


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## 14642 (May 19, 2008)

Interesting. 

I can answer a few questions posed here about what goes on in an OEM system.

Interior designers (the people who determine what the inside of the car looks and feels like) OWN the inside of the car. Unless it's a ridiculously expensive system, the OE providers don't have much say in the location of the speakers, unless the location doesn't impact the look and feel of the interior. This is changing slowly.

For the most part, all of these kinds of problems are "solved" in the EQ. Sometimes the "solution" is BS and doesn't work, as some system tuners are better than others. Usually, the attempt to fix these problems is the use of an all pass filter on the sub(s) or on the midbass/midrange drivers in the front. Sometimes, the all pass filter is used on rear speakers to suck up the resonance from a trunk mounted sub. 

Some of the guys where I used to work attempted to implement a multi-sub and DSP solution intended to eliminate resonances with delay, level and EQ set differently for each of the drivers (using the subs and all the 6" door mounted drivers). It as originally intended to eliminate the effect of room modes in the bass at home and it did that well. It flattened the frequency response at most of the seats, but absolutely screwed up the image because the big problems happen at frequencies where we hear the location pretty easily. Boosting 200Hz and delaying the left rear speaker, for example, really screws up the placement of vocals.

In my old car, I did the big overlap thing thinking that i could move the bass up front more easily if I used the front speakers all the way down as low as they would play and then filled in with the sub. I wasn't using much power, so even driving them with no high pass filter was OK. Using all pass filters in an attempt to put the sub and the front speakers in a phase relationship that eliminated the droning midbass worked, but only for one seat and typically made the other seats worse with either more droning, no midbass or a terrible image. Was there a solution set that would have improved all the seats? Probably, but not one that I could find in countless hours of manually implementing ideas. 

Some of the research guys at my old job developed an algorithm to do this automatically (computers can implement solutions sets much more quickly than people can) with only all pass filters using measured frequency responses in the two front seats. The measurements looked perfect, but when I got in the car, there were plenty of frequencies where the image fell apart. There was a lot of speaker movement and my pant leg was being blown all over the place, but no impact--obviously a cancellation that sucked out the drone, but that wasn't all that sucked. 

I suggested a conventional crossover scheme with the front speakers tuned first for the right performance and then adding the sub and adjusting only the EQ for it to blend the two. Then, the rear speakers were added, but with a twist. In the DSP, the signal was split through a high pass filter at 250Hz (this was processed with L7) for ambiance. A bandpass filter from 50-250 Hz was summed with the output of the high pass filter, but the bandpass filter was passed through a delay, level control and a separate EQ before the summer. That helped to eliminate the droning that was left in the front seats and to remove some of the annoying bass in the rear seats. 

This is similar to the bandpass box behind the seat experiment someone wrote about here, but didn't require an additional speaker. There aren't any DSPs available in the aftermarket that will do this, though. I've also done it with an AKM demo board and a 4 dollar DSP to be added to a head unit.


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## brett (Apr 27, 2005)

Andy Wehmeyer said:


> I suggested a conventional crossover scheme with the front speakers tuned first for the right performance and then adding the sub and adjusting the EQ for it only to blend the two. Then, the rear speakers were added with a twist. In the DSP, the signal was split through a high pass filter at 250Hz (this was processed with L7) for ambiance. a bandpass filter from 50-250 Hz was summed with the output of the high pass filter, but the bandpass filter was passed through a delay, level control and a separate EQ. That helped to eliminate the droning that was left in the front seats and to remove some of the annoying bass in the rear seats.



actually, this is almost exactly what i did last night, if i understand correctly. I already have my rear speakers summed to mono, so on my 360.3 i bp'ed them from about 80-200 and letting my sub take care of everything below about 80; both on 24db. i played around with different crossover points, but that was what seemed to be the best. i then inverted the phase on the rear deck and the bass just sounded tighter, louder and more efficient.

however, when i tried to implement my midbass up front, it started to muddy up again. which leads me to answer somebody elses question about my original idea. i would essentially just get rid of my doors/kicks if need be.


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## thehatedguy (May 4, 2007)

Run the rears stereo.


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## thehatedguy (May 4, 2007)

And running a sub 60-200? That's a midbass. Not too many would like playing that high, and would be a waste of the bottom end.


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## avanti1960 (Sep 24, 2011)

Andy Wehmeyer said:


> Interesting.
> 
> I can answer a few questions posed here about what goes on in an OEM system.
> 
> ...


Thanks Andy- so in my car (recent model Toyota, non-JBL option system) the decent bass that I heard from my OE system (with its paper cone drivers and wide open door panels) was most likely EQ built into the OE (Fujitsu) head unit? 
Would they have included the all pass filter as well? 
Is there anything valid about the idea that they used the open door panels to make use of the back wave to cancel some of the unwanted bass? 

BTW, "droning" bass is the perfect word for it. It is annoying as heck.


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## Hanatsu (Nov 9, 2010)

Is there some DSP unit available that has allpass filters btw?

Sent from my Samsung Galaxy 3 via Tapatalk.


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## 14642 (May 19, 2008)

avanti1960 said:


> Thanks Andy- so in my car (recent model Toyota, non-JBL option system) the decent bass that I heard from my OE system (with its paper cone drivers and wide open door panels) was most likely EQ built into the OE (Fujitsu) head unit?
> Would they have included the all pass filter as well?
> Is there anything valid about the idea that they used the open door panels to make use of the back wave to cancel some of the unwanted bass?
> 
> BTW, "droning" bass is the perfect word for it. It is annoying as heck.


The basic OE systems don't include much in the way of processing. Most of them make use of the DSP that's included in the basic audio controller in the head unit. In addition to programmable bass and treble controls, there's often a simple 3-band parametric EQ with some selectable EQ. There's often a parametric bass boost/cut, a midrange control and a treble shelf. These are often stereo filters (only one adjustment for left and right together) and a separate one for rear. That all pass filter is only available in higher-end DSPs and often not as part of the existing filter library. In many of the slightly upscale DSPs, there's a place to implement a biquad filter, and that's how it's implemented. Some of the DSPs don't include this and won't run phase EQ.

My guess is that the bass was the result of efficient paper cone speakers and some midrange attenuation in the head unit.


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## 14642 (May 19, 2008)

Hanatsu said:


> Is there some DSP unit available that has allpass filters btw?
> 
> Sent from my Samsung Galaxy 3 via Tapatalk.


Not that I know of--at least not for the aftermarket. The old Basslink 4sc amp from Infinity included an analog implementation designed to improve imaging for door and dash mounted front speakers, but it's no longer available and wouldn't work for this anyway.

You can fake this with an analog crossover and some resistors. For a bass cancellation experiment, get a simple analog crossover that will do 12dB/octave slopes. adjust the high pass and low pass filters so they cross at -3dB at the frequency where you want to reverse phase. Then, sum the outputs through a pair of resistors (use 4.7k, 1/4 watt). Since a 12dB butterworth filter reverses phase by 90 degrees, the sum of the two filters will be 180 degrees out of phase at the crossover point. You may want to tune this with an analyzer so you can get flat frequency response and the appropriate phase shift. It's a little tricky, but good for an experiment. Just pick up a cheap analog unit on sonic electronics. The slopes MUST be 12dB/octave and it's helpful to have a separate control for low and high pass.


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## Hanatsu (Nov 9, 2010)

Andy Wehmeyer said:


> Not that I know of--at least not for the aftermarket. The old Basslink 4sc amp from Infinity included an analog implementation designed to improve imaging for door and dash mounted front speakers, but it's no longer available and wouldn't work for this anyway.
> 
> You can fake this with an analog crossover and some resistors. For a bass cancellation experiment, get a simple analog crossover that will do 12dB/octave slopes. adjust the high pass and low pass filters so they cross at -3dB at the frequency where you want to reverse phase. Then, sum the outputs through a pair of resistors (use 4.7k, 1/4 watt). Since a 12dB butterworth filter reverses phase by 90 degrees, the sum of the two filters will be 180 degrees out of phase at the crossover point. You may want to tune this with an analyzer so you can get flat frequency response and the appropriate phase shift. It's a little tricky, but good for an experiment. Just pick up a cheap analog unit on sonic electronics. The slopes MUST be 12dB/octave and it's helpful to have a separate control for low and high pass.


Interesting... I'll try this 

Sent from my Samsung Galaxy 3 via Tapatalk.


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## Hanatsu (Nov 9, 2010)

Btw. Couldn't theoretically an allpass filter be used to counteract group delay at all frequencies with some automated algorithm (using a DSP). Wouln't that fix lots of these so called 'phase issues'?

Sent from my Samsung Galaxy 3 via Tapatalk.


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## thehatedguy (May 4, 2007)

There are not any car audio based processors that can do all pass filters. But there are more than several pro audio processors that can do all pass filters- Rane, Behringer, BSS, dBX, Lake, xta...


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## Neil_J (Mar 2, 2011)

thehatedguy said:


> There are not any car audio based processors that can do all pass filters.


MiniDSP does it. Sort of a gray area between car audio and home audio, but I think it's still perfectly relevant.


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## subwoofery (Nov 9, 2008)

Neil_J said:


> MiniDSP does it. Sort of a gray area between car audio and home audio, but I think it's still perfectly relevant.


Wondering if the PPI piece does it as well, would be cool  

Kelvin


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## MarkZ (Dec 5, 2005)

MarkZ said:


> So your premise is that reflections steer the bass rearward? Presumably, those that "outlast" the reflections in the front of the car? I see an impressive discussion about how to tame these reflections, but I guess I'm not clear on why this is important...


^^^ Asking this question again. 

I have an alternative theory about why the overlap thing is working to pull bass forward. It's because the front speakers are more likely to be generating harmonics that the ear can use as a cue for front/rear localization. Because they're highly correlated with the subwoofer frequencies, it's steering the bass percept forward by solving the front/rear ambiguity problem.

The ideal solution, then, would be to generate those harmonics in the front speakers WITHOUT the fundamental (so you don't overdrive your front speakers too much).

I describe this here and here.


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## 14642 (May 19, 2008)

While it seems plausible, in most instances I find that front sounding bass is easier to reproduce at lower listening levels. in some cases, cars that have rear-sounding bass IMPROVE as you turn the volume down. Hmmm...

I suppose you could try this in Adobe audition or Audacity or something. Take your favorite song, low pass it, add some 2nd and 3rd harmonic distortion to the low passed track, high pass it to remove the fundamental and mix the distortion back into the original track. Then, audition the two tracks in your car as an A/B comparison. this way, the distortion is present in the signal at all listening levels even when the sub and the front speakers are operating in a range where they're linear.


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## MarkZ (Dec 5, 2005)

Andy Wehmeyer said:


> While it seems plausible, in most instances I find that front sounding bass is easier to reproduce at lower listening levels. in some cases, cars that have rear-sounding bass IMPROVE as you turn the volume down. Hmmm...


But you're fighting several confounds here... e.g. the frequency-dependence of loudness perception as you change amplitude. Or the influence of tactile information on sound localization. It's hard for me to draw many conclusions from this observation.



> I suppose you could try this in Adobe audition or Audacity or something. Take your favorite song, low pass it, add some 2nd and 3rd harmonic distortion to the low passed track, high pass it to remove the fundamental and mix the distortion back into the original track. Then, audition the two tracks in your car as an A/B comparison. this way, the distortion is present in the signal at all listening levels even when the sub and the front speakers are operating in a range where they're linear.


The added distortion needs to be confined to just the front speaker(s) though. Not difficult to do with a car PC. I just haven't gotten around to it.


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## ultimatemj (Jan 15, 2009)

@MarkZ> You may be onto something with the higher frequency artifacts, but I'm wondering if it is not "just" the phasing of the 1st order artifacts and the intensities relative to the x-overs applied.

I found these 2 articles (about aligning subs) thought provoking and am now thinking most of us with "up front bass" are just getting lucky with phasing!


Optimally aligning subwoofers with main loudspeakers


Phase alignment of subs why I dont use the impulse response

A "pull to the rear" could be partially being caused by our x-overs not summing flat...as that appears to only be the case when perfectly in phase. An example image showing cancellation due to phase issues









Add to that the typical flawed assumption the x-over holds firm regardless of intensity...as shown in an image AndyW has shared here before...and you will have (rear) subs playing frequencies that provide ILD and ITD cues. Depending on how cranked up your subs are the 2nd and 3rd order artifacts may be louder than your mids 1st order :thinking:









So, it appears achieving in-phase at the x-over point and keeping 200Hz and up "louder" in your front located drivers is a key to "upfront bass".

Agree? Or am I over my skis here?


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## thehatedguy (May 4, 2007)

http://www.excelsior-audio.com/

Is the webpage of the company who Charlie Hughes owns...other interesting stuff on there too. Pretty smart guy, and local...lord knows what/how he found Gastonia, NC- not exactly the hot bed of audio.


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## thehatedguy (May 4, 2007)

I know the pro pieces can do odd (6dB) and even (12dB) order all pass filters.

In the miniDSP, you can only configure an all pass using the advanced biquad feature, right? I read somethings about folks trying to recreate the Linkwitz ASP using the miniDSPs, but couldn't because they couldn't do (maybe at that time?) the all pass filters Linkwitz has in his analog processor.

At any rate, it is cool to know you can do that with the miniDSP.



Neil_J said:


> MiniDSP does it. Sort of a gray area between car audio and home audio, but I think it's still perfectly relevant.


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## MarkZ (Dec 5, 2005)

ultimatemj said:


> @MarkZ> You may be onto something with the higher frequency artifacts, but I'm wondering if it is not "just" the phasing of the 1st order artifacts and the intensities relative to the x-overs applied.
> 
> I found these 2 articles (about aligning subs) thought provoking and am now thinking most of us with "up front bass" are just getting lucky with phasing!
> 
> ...


I only skimmed these so far because I found the titles intriguing. 

Seems like you should phase align _and_ time align the subwoofer if you have the tools to do so. I would think you could settle the group delay down if you play the phase, and that this is somewhat independent of time aligning it. It doesn't make sense to me to ignore the impulse response altogether, although maybe I should keep reading. 

I'm still not convinced that phase response matters a whole lot for the up-front-bass thing, except where it may throw your amplitude response all out of whack. Subs are kind of a special case because people want that thump, and they'll rape their FR to achieve it.

Anyway, I remain pretty convinced that the higher frequencies are driving front/rear localization, and that correlation with low frequencies is important. Whether phase (directly) affects that correlation isn't clear to me... I would think the brain is more interested in the temporal envelope here.


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## ultimatemj (Jan 15, 2009)

thehatedguy you weren't kidding! Great stuff on his site!


> Excelsior Audio Design & Services, LLC
> 
> Is the webpage of the company who Charlie Hughes owns...other interesting stuff on there too


Mark,



> I'm still not convinced that phase response matters a whole lot for the up-front-bass thing, except where it may throw your amplitude response all out of whack <SNIP>
> Anyway, I remain pretty convinced that the higher frequencies are driving front/rear localization, and that correlation with low frequencies is important. Whether phase (directly) affects that correlation isn't clear to me..


My take away from those 2 articles is _*exactly*_ what you just said you are not sure convinced...I'd be interested in hearing your views after doing more than scanning the articles


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## brett (Apr 27, 2005)

MarkZ said:


> But you're fighting several confounds here... e.g. the frequency-dependence of loudness perception as you change amplitude. Or the influence of tactile information on sound localization. It's hard for me to draw many conclusions from this observation.)


i am in no way as smart as you guys, but i find this to be an issue with me. i can only be satisfied with my sound at moderate listening levels. as soon as i want to crank it up (which is one of the reasons we do this, right?) bass starts sounding sloppy and easily located. i can definitely hear it coming from the rear but im not convinced that im also feeling it coming from the rear (thats what she said!). so, instead of using more traditional drivers up front in consoles, dash, doors, etc... wouldn't, then, a powerful tactile transducer effectively pull the stage up front with it's tactile cues?


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## Patrick Bateman (Sep 11, 2006)

bikinpunk and I were discussing The Magic Bus in another thread, and were arguing over the efficacy of the helmholtz absorbers that are in there.

My hunch (and it's just a hunch) is that Helmholtz absorbers have a bandwidth that's too narrow and a size that's too large to be practical for car audio. Even Jon W himself has argued that the sound of his Bus would not be possible in a car, due to the small size. (When we met at CES he said that the sound could not be replicated in a smaller vehicle.)

In my humble opinion, simply using another speaker that's out of phase has the following advantages:

1) it's smaller
2) the efficiency of a loudspeaker is higher than the efficiency of a Helmholtz absorber. For instance, if it was possible to get another sub to be 100% out of phase across it's bandwidth, *you would get a perfect null.* Zero dB. Now it's NOT possible to do that, but if you get close, you'll get a significant amount of cancellation from a second sub.









^^^ observe how certain bass notes linger for nearly a second and a half?!










Here's some data to chew on. The first pic is the decay of a sub with Helmholtz Absorbers.
The second is with eight subs, and four of them out-of-phase and delayed. *See how the decay on the second set is significantly improved?* Note the time scale in particular, and how the second sub 'fades to black' in a fraction of a second.

original source is Panel and Helmholtz resonators for studio - Gearslutz.com and Double Bass Array (DBA) - The modern bass concept!.

here's what they look like:









^^^ Helmholtz absorbers for a studio









half of an eight sub bass array (other half is on the opposite wall)


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## cajunner (Apr 13, 2007)

I was reading about helmholtz resonators the other day, and panel resonators. I thought about where there is a flat plane in the car, that one could use to make a panel resonator and it seemed to me that the sub box is about the easiest spot to make one.

it would increase the size of the box by a couple of inches, but it would be tunable to the muddying frequencies at the Schroeder frequency or transition area inside the vehicle, which could go towards reducing the 60 hz bloom in many vehicles, and reduce "chestiness" that comes from male speaking voices, which is irritating to me.

I think there are natural panel-type absorption with Luxury Liner type barrier and foam additions, and maybe the roof headliner is a place for something that attenuates certain frequencies for rear bias control?


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> I was reading about helmholtz resonators the other day, and panel resonators. I thought about where there is a flat plane in the car, that one could use to make a panel resonator and it seemed to me that the sub box is about the easiest spot to make one.
> 
> it would increase the size of the box by a couple of inches, but it would be tunable to the muddying frequencies at the Schroeder frequency or transition area inside the vehicle, which could go towards reducing the 60 hz bloom in many vehicles, and reduce "chestiness" that comes from male speaking voices, which is irritating to me.
> 
> I think there are natural panel-type absorption with Luxury Liner type barrier and foam additions, and maybe the roof headliner is a place for something that attenuates certain frequencies for rear bias control?


But it still suffers from the same fundamental problem. I hate to be Debbie Downer, but all Helmholtz devices have a bandwidth that's a fraction of an octave.

For instance, if you had one tuned to 62.5hz, if you were very very lucky you might get a bandwidth of a tenth of an octave. So that's about four hertz.

On the other hand, a plain ol' subwoofer wired out of phase has a bandwidth of two or even three octaves.

So there's two solutions to the same problem:

1) Helmholtz absorber

or 

2) sub wired 180 degrees out of phase and delayed

Obviously, second solution is more complex. But MiniDSP is what, $99? In this age of cheap and ubiquitious DSP, I think it's an easy call.


Another nice thing about solution two is that it doesn't necessarily have to be the same size as the main driver. For instance, if you have a twelve in the trunk you could put an eight in the front, or even a six. The reason you can get away with this is that it doesn't have to be a perfect null. An identical driver is *ideal*, and if the phase matched perfect, you'd get that perfect null. But if the output level is lower it's still going to give a hefty amount of cancellation. This is because two signals 180 degrees out of phase sum to zero decibels, while two signals perfectly IN phase sum to +6dB. So nulls are always deeper than peaks, if the output level of the two waves is the same.


^^^ This is basically a long winded way of saying that nulls are fairly easy to produce with two drivers and a little bit of delay.


A small driver in a bandpass box seems like The Ticket, since bandpass enclosures narrow bandwidth, increase efficiency, and lower excursion. All of which are good things if you're trying to null out room modes.


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## Patrick Bateman (Sep 11, 2006)

oh, one last thing -

If anyone is wondering why bandpass subs have a bandwidth that's an octave wide, while Helmholtz resonators have a bandwidth that's a fraction of an octave, *it's because the output of a bandpass sub isn't just from the Helmholtz resonator.* There's sound that's produced from both sources, the woofer cone *and* the port. The port only works over a fraction of an octave, because that's all Helmholtz resonators are good for. The rest of the output in a bandpass box is from the actual loudspeaker that's in the box.


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## cajunner (Apr 13, 2007)

the better mousetrap would be a headliner with panel absorption qualities, but made from Yamaha's special wood that resonates at pre-determined frequencies. This would make a large panel absorb at different frequencies...

or, how about like a guitar doing harmonics on the strings, you have a variable transducer in the panel absorption, that regulates a harmonic in the panel's resonance, that would be cool!

you know, like a magnetic field controlled by a motor, but not attached to the panel so the panel could still resonate at it's primary frequency...


but I like the use of a thin build, bass trap in areas of the vehicle that are normally wasted, instead of more electronic wizardry. However, I like my MS-2 so I guess I could learn to love a digital recurve as much as an original instrument one.


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## cajunner (Apr 13, 2007)

a panel absorber doesn't have such a narrow band of attenuation, though.

it may be less of a "helmholtz" device than the actual resonant tube with aperture, and therefore capable of much greater utility.

the Bus has multiple resonators, which presumably operate at different frequencies but it's possible that they only act over a small portion of the spectrum and they are all that's needed to get that "dead zone" quality to the interior, stretching for a span as wide as necessary to attenuate the main long-axis phase issue in a vehicle's acoustics.


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## Hanatsu (Nov 9, 2010)

I have issues at 41-42Hz in my car. There's massive ringing in the time domain, the note lingers for over a second. Would it be required to add massive delay to the active 'out of phase' driver? Think I can manage about 25ms with my DSP. At such low frequencies, does it matter where the speaker is located?

Sent from my Samsung Galaxy 3 via Tapatalk.


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> I have issues at 41-42Hz in my car. There's massive ringing in the time domain, the note lingers for over a second. Would it be required to add massive delay to the active 'out of phase' driver? Think I can manage about 25ms with my DSP. At such low frequencies, does it matter where the speaker is located?
> 
> Sent from my Samsung Galaxy 3 via Tapatalk.


Assuming that the two speakers are in phase at the frequency in question, then the delay is simply 1ms per 34cm. So if the gap between the front sub and the rear sub was 8ft long, the delay for the inverted sub would be 7ms.

If you don't have DSP delay you might be able to mimic the same thing by adjusting the phase of the inverted amplifier. I haven't seen these knobs on car amps, but they're pretty common on plate amps for DIY. My Kef subwoofer has a phase control.

Off the top of my head (and this may be wrong), here's how you do it without DSP using the phase knob:

step 1) figure out your frequency that's a problem. For instance, sixty hertz
step 2) figure out how long that frequency is. For instance, 60hz is 225" long.
step 3) Slice that wave up into 360 degrees. In this case, 225" divided by 360 is 0.625" per degree
step 4) Figure out the distance between the two subs. For instance, an eight foot gap between subs would be 96"
step 5) Now we know how far it takes to moved one degree (from step 3) and we know how far they're apart (from step 4). In this case, the sound rotates sixty degrees in the time that it takes to move from one sub to the other. (96" * 0.625 degrees per inch.)
step 6) Now invert one of the subs, and add an additional sixty degrees of rotation via the phase knob on the amplifier. Assuming that both of them have the same phase to begin with, the second sub will 'null out' the reflection from the first.


If I were going to do this, I would highpass one of the subs. The reason that you do this is that there's a point where the wavelengths are so long, they basically act like one driver. For instance, if you have two subs that are 8' apart playing sixty hertz, they're seperated by 0.43 wavelengths. But at 35hertz, they're seperated by just a quarter of a wavelength. Due to the tight spacing at 35hz and below, inverting the second sub is basically killing your bass output, with no real upside.

So the solution is simple; use the inverted sub to 'null out' the reflection above 35hz, but add a highpass to the inverted sub so it doesn't 'null out' everything below that frequency.

Of course, crossovers change the phase, but I can't do those maths in my head  If it were me, I'd use a first order filter just to be safe. Or better yet, just use a smaller sub for the inverted driver. For instance, a 12" sub in the trunk with a couple of 4" subs in the front of the car.


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## Hanatsu (Nov 9, 2010)

Does the acoustical natural rolloff of a bandpass box introduce the same phase shift?

Just responded in another thread regarding the same subject, so I'm just quoting myself:



> Interesting thread. I have not yet reached a point in my build where I start to tackle the acoustical problems fully. The active solution having a speaker 180 deg out of phase and somewhat delayed worked very efficiently and affected the the sound by a fair amount. I used a small driver in a 4th BP box around 120-150Hz area and experimented in cancelling out the massive ringing the time domain there related to room modes. It was very capable in reducing SPL by a pretty big amount and it was different from just EQ away it. It sounded "dryer" to me.
> 
> I discussed the usage of a Helmholtz resonator with my neighbor who've been an audio enthusiast for many years and he told me that a HR would be useless in the lows since it would be too small to do any good (because of limited space in a normal car). An active bass cancellation solution on the other hand works awesome. He proposed using a microphone to pick up the sound in front of the driver and amplify it 180deg out of phase but I find that to be a bit excessive, it should work just as good just delaying the signal to the driver electronically and use the same signal as your "ordinary speakers".
> 
> Wonder if it's possible to use the high group delay of a 6th order BP in conjunction with high amounts of digital delay to create a cancellation solution that cancels out modes 40ms+ in time. One thing I found out that it almost sounded "too dry" compared to the frequencies above the "treated" area, the derived T60 should probably be around the same for all audible frequencies. In a car there's massive high frequency absorption but massive low frequency ringing, this creates a mismatch which I believe to be ONE OF the cause why a car sounds like a car.


Here's a decay measurement of my car, posted in another purpose but you can see the issues.



Don't I have to account for the time delay of the ringing. Let's say that a note decays in time normally about 40ms down but then something happens and SPL increases at 60ms to a level above of that of 40ms. Mustn't the "cancellation driver" be delayed 60ms then so it only cancels out the SPL decayed more than 40ms in time?

I proposed using a DSP in conjunction with a high group delay enclosure design like a 6th order BP. 

Is it something wrong in my thinking here?


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## cajunner (Apr 13, 2007)

Hanatsu said:


> I have issues at 41-42Hz in my car. There's massive ringing in the time domain, the note lingers for over a second. Would it be required to add massive delay to the active 'out of phase' driver? Think I can manage about 25ms with my DSP. At such low frequencies, does it matter where the speaker is located?
> 
> Sent from my Samsung Galaxy 3 via Tapatalk.


I believe the ringing, even though not "driven" by voltage, would still be subject to diminishing by an absorber/trap/resonator, and with the attenuation would be the decrease in ringing length, time-wise.

An electrical signal driven acoustic counter-force similar to the active noise reduction in headphones, driven by the clamp time set, or gated or whatever you call it, would make an artificial dryness to the sound when the signal was more low bass tone than dynamic impact.

So, an acoustic control using absorption techniques, either through panel resonator or helmholtz design, may have a more musical outcome than a second speaker driven by an algorithm.


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## Patrick Bateman (Sep 11, 2006)

If I'm not mistaken, the big spikes at long delays like 40ms are due to the fact that *some frequencies are augmented by their own reflection.*

Here is an example of what I mean by this. Illustrations would help, but I'm too busy at work to do them at the moment.

First off, let's say you have a car cabin that's 100" long. And let's say the sub is in the trunk. When you play 33.75hz, here is what is going to happen:

1) At zero milliseconds, the sound is emitted by the sub
2) 7.4ms later, the sound hits the front windshield. That creates a reflection.
3) At 14.8ms, the initial wave AND it's reflected energy reaches the back of the car, right where it started. *Here's the interesting part.* The sound has traveled 200", which puts it 180 degrees out of phase. *So at the rear of the car, 33.75hz cancels, but at the front of the car, it adds.

now if we go down an octave, it's a different story. At 17hz, it adds in the front *and* it adds in the back, due to the wavelength being only 90 degrees out of phase by the time it reaches the back.


Same thing is true if we halve the distance. If we go from 100" to 50", then the reflected energy will be additive at both the first reflection, AND when it gets back to the woofer.








(And I think this is why we see 'spikes' in cabin gain which seem to be arithmetic, such as a peak at 18hz and also at 36hz. IMHO, that's because the width and depth of the cabin tend to be a multiple of each other, such as a cabin that's 4' wide and 8' feet deep.)

If I'm mathing right, there are some frequencies where you'll get a reflection off the front window that adds SPL at the front *and* the back. If I'm not mistaken, integer multiples of one-half wavelength will do this. So with a 100" cabin you'd see that at 67.5hz, 135hz, 202.5hz, etc.

What I really need to do is get one of those programs for simulating rooms, the ones that can do 'heat maps.'

*


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## Patrick Bateman (Sep 11, 2006)

If all of this makes your head hurt, a fairly simple solution is to just use a lot of drivers above the Schroeder Frequency. That's a brute force approach, but when you look at it you can see that it basically 'randmomizes' the frequency response and the phase response.

Another thing about this randomization, which I just realized yesterday, is that it should make the sound 'fade to black' faster. Here's why:

From looking at sengpielaudio.com, it looks like 'correlated' sound sources add up to +6dB. For instance, if you have two subs right next to each other, and they're in phase, you get +6dB.

But *uncorrelated* sources add +3dB.

And that's what the 'pile of subs' approach does. It creates a pile of uncorrelated signals.








So these peaks and dips in the time response should 'fade to black' faster when you have a pile of subs. That might also explain why dipole subs sound good; you basically have two subs playing 180 degrees out of phase right next to each other (since there's sound radiated from both sides of the cone.)
I've mentioned this before, but at one point I had eight subs. And the most noticeable thing was that the bass basically just blended in with the mains. You were no longer aware of particular notes standing out. And it was basically impossible to pinpoint where the subs were in the room.

Of course there's no free lunch. I'd say that dynamics suffered a bit. And this makes sense, since peaks and valleys in the dynamics get 'smoothed out' by all the subs.

So possibly the best of both worlds would be some middle ground between eight subs and one sub. I've been using three for a while now. (This is for the home; for the car it should work in the range of about 30-120hz, maybe even 240hz.)


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## cajunner (Apr 13, 2007)

but at some point, this resonant chamber we call the interior of the car, is subject to ringing modes in the metal of the body.


I'm thinking like a tuning fork, for those long modal peaks.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> but at some point, this resonant chamber we call the interior of the car, is subject to ringing modes in the metal of the body.
> 
> 
> I'm thinking like a tuning fork, for those long modal peaks.


That's an interesting point, and perhaps an argument for sound deadening. (I'm not a fan of sound deadening, and haven't used any for any of my last three cars.)

When the sound hits the windshield, the glass is poorly damped, and reflects the sound very well.
On the contrary, steel has better damping, and so does the foam in the seats.

And when you add CLD or mass damping to the metal, you raise the damping. I'd expect that this would reduce the amount of reflected energy.

So worst case scenario would be something like glass or concrete or aluminum, better case would be something like wood or lead.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> That's an interesting point, and perhaps an argument for sound deadening. (I'm not a fan of sound deadening, and haven't used any for any of my last three cars.)
> 
> When the sound hits the windshield, the glass is poorly damped, and reflects the sound very well.
> On the contrary, steel has better damping, and so does the foam in the seats.
> ...


but it's all still treating the body of the car like an enclosure for speakers, right?

you know how they do, using accelerometers to judge panel resonances for a commercial design, what's "thick" enough, dense enough, cost-effective enough...

and speaker designers have used a tuning fork to find where resonances are greatest, so they can add ribs in the most appropriate areas to damp the ringing modes.

We're talking about two physics lessons, an acoustic response "in the air" wave combination and destruction, and the panels of the car resonating from energy storage modes.


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## quietfly (Mar 23, 2011)

In theory, the more effective way would be to capture and convert the offensive energy to something less offensive, like heat. Almost as if we were using an acoustic trap/converter. Something that could convert the Vibrations to friction or Even better static electricity that could be "reclaimed". Just thinking " out loud"


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## Justin Zazzi (May 28, 2012)

quietfly said:


> In theory, the more effective way would be to capture and convert the offensive energy to something less offensive, like heat. Almost as if we were using an acoustic trap/converter. Something that could convert the Vibrations to friction or Even better static electricity that could be "reclaimed". Just thinking " out loud"


This is exactly what happens with a constrained layer damper, the mechanism we use for damping sheet metal with products like CLD tiles, mushmat, dynamat, etc. Sympathetic motion of the panels induce a shear strain on the tile sandwich, and the resulting friction transforms this motion into heat.

I think Cajunner gets it very close though, and I also believe modal ringing is a function of standing waves, not sympathetic vibratons of some interior component (though this may make the ringing worse).


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## cajunner (Apr 13, 2007)

Jazzi said:


> This is exactly what happens with a constrained layer damper, the mechanism we use for damping sheet metal with products like CLD tiles, mushmat, dynamat, etc. Sympathetic motion of the panels induce a shear strain on the tile sandwich, and the resulting friction transforms this motion into heat.
> 
> I think Cajunner gets it very close though, and I also believe modal ringing is a function of standing waves, not sympathetic vibratons of some interior component (though this may make the ringing worse).



ever hit a drum?

an oil barrel, it rings a bit like a bass drum, but the decay at a particular frequency can be attributed to what? Standing waves?

I read some research into how waves decay in enclosures, I think it was B&W's paper that was when they were describing their matrix enclosure, anyway the way different parts of the structure decay in their ringing makes more of an impact than a standing wave condition, to me, but excitation of and prolonging of standing waves by the panel resonances, makes this a synergistic combination of things that might best be treated with the brute force approach, and we see this with deadener application, MLV over CCF, the MLV creates a panel trap, dissipating much of the lower midrange frequencies in the CCF, and not allowing it to continue reverberating in the listening space.

The exact volume of the car can lead one to assume a resonant tone, and the actual dimensions of the car can lead one to assume various combine/null positions in the car, at the point where these waves can travel intact, but the resonance of a 41 hz tone does not seem to me, to be in this area of the FR that is dependent on wave propagation, and seems more likely to be a condition of resonance from the body of the car acting as an active producer of ringing due to the energy storage of metal and glass.

The natural decay of a helmholtz trap or resonator, or a panel absorber, wicks away at this resonant mode in analog based fashion, it's going to be logarithmic like our hearing, it's going to sound natural.

Trying to electronically diminish the ringing with some "anti-matter algorithm" that attempts to strike a balance between dynamic timbres and tympanic peaks with the natural tones of a bass guitar, is going to sound processed, there's going to be some artificial nature to the outcome, imho.

I can't say it's not going to sound great, and it sure is easier to put a small sub in a location in the cabin that works against the harmonics of the trunk, but at some point the whole cabin resonating is what makes those deep bass long reverberation times and it's what is muddying the sound, imho.

Something as simple as a re-configured headliner with a 1/2" of some mojo foam, doing the panel resonance thing can attenuate a rather large wave, maybe even enough to not need the additional electronic wizardry. Although, using panel exciters in the form of bass shakers, to attenuate what is ultimately metal ringing, strikes at the source of the problem and may be a better use of these interesting devices, if only someone would create an anti-feedback circuit that addresses the resonant modes....



hmm...


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## quietfly (Mar 23, 2011)

Jazzi said:


> This is exactly what happens with a constrained layer damper, the mechanism we use for damping sheet metal with products like CLD tiles, mushmat, dynamat, etc. Sympathetic motion of the panels induce a shear strain on the tile sandwich, and the resulting friction transforms this motion into heat.
> 
> I think Cajunner gets it very close though, and I also believe modal ringing is a function of standing waves, not sympathetic vibratons of some interior component (though this may make the ringing worse).



yeah however that heat is "wasted" my thought was more of like an acoustic version of a solar panel. very cursory ideas would be using some sort of diametrically charged metal/copolymer particle between to layers of laminate, then once exposed to sound the particles would vibrate/move crossing paths with the laminate between them. the laminate itself would be the electrode and power would flow through the laminate into what ever storage device chosen.


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## cajunner (Apr 13, 2007)

quietfly said:


> yeah however that heat is "wasted" my thought was more of like an acoustic version of a solar panel. very cursory ideas would be using some sort of diametrically charged metal/copolymer particle between to layers of laminate, then once exposed to sound the particles would vibrate/move crossing paths with the laminate between them. the laminate itself would be the electrode and power would flow through the laminate into what ever storage device chosen.


so basically, a big piezo panel? 

or, how about a small piezo pressure mic at the resonant surface, that can process a re-curve, and apply that re-curve to the underlying panel of piezo-charged resonant zones, in the headliner...


using a simple analog transverse, and the time between the piezo picking up the signal to putting out the cancellation vibe, is traveling at an electric speed and not an acoustic speed, so plenty of time to do it "real time"


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> so basically, a big piezo panel?
> 
> or, how about a small piezo pressure mic at the resonant surface, that can process a re-curve, and apply that re-curve to the underlying panel of piezo-charged resonant zones, in the headliner...
> 
> ...


There's some interesting work being done on this. On a small scale, imagine a set of tennis shoes that do this:

1) You step on the ground
2) that energy is transmitted to a piezo layer in the shoe
3) that energy is converted into electricity

It's not terribly efficient, but can be used to keep your phone charged and other odd stuff.

Where it gets really interesting is ideas like covering the entire side of a skyscraper with this stuff, then using the vibrational energy from the wind to power the building. Obviously not terribly efficient, but way more practical that putting a windmill on the top. (Plus doesn't look weird.)


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> There's some interesting work being done on this. On a small scale, imagine a set of tennis shoes that do this:
> 
> 1) You step on the ground
> 2) that energy is transmitted to a piezo layer in the shoe
> ...



cool.

I read about some of this too, if it's a green thing then great, but I don't like spending 12 to 1 on solar, for a theoretical clean.

this stuff is probably going to matter soon enough, may as well get used to it.

in the car, I could see a panel of say, 12 4" semi-spherical piezo transducers that are tied to a recombinant matrix that runs off of sensors that are strategically placed to approximate the waveform at the listening space.

your six measurements in the head area that make up an averaged RTA would be the same region that determines the way the grid delivers it's energy to the panel.

excite all piezos and you get a massive wave but excite the middle line and you bend the panel into two separate harmonic regions, and so on and so forth.

could be a way to "shallow mount" a corrective or cancellation circuit without having the bulk of motors or whatever, the panel could be made of zones of piezo fused to a PCB body, or hell, it could be one big ol' planar magnetic, haha...


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## Justin Zazzi (May 28, 2012)

Okay, you all are taking this in a completely different direction than I thought it was going.

Fantastic though, I love the discussion!

-J


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## subwoofery (Nov 9, 2008)

Patrick Bateman said:


> But it still suffers from the same fundamental problem. I hate to be Debbie Downer, but all Helmholtz devices have a bandwidth that's a fraction of an octave.
> 
> For instance, if you had one tuned to 62.5hz, if you were very very lucky you might get a bandwidth of a tenth of an octave. So that's about four hertz.
> 
> ...


Reminds me of this: 
Black Hole 

Too expensive for my blood but I'm sure it works great... 

Kelvin


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## Hanatsu (Nov 9, 2010)

Tried something today... sending the car away for repairs so I was experimenting some with the an active out of phase speaker solution. My rear door speaker have been disabled for a while since I've not tuned them yet, turned them on today and delayed them for about 25ms just for fun and played with the phase inversion control at little. At first it sounded kinda weird so I played around with levels and crossovers a bit, listened to some music and messed with the settings. Finally something happened, I was using a 40Hz/24dB HP and 160Hz/24dB LP and with the right driver 180deg out of phase and the left side "normal phase" IIRC and wow... I never ever had such a upfront bass. It sounded completely dead from behind, yet the sub was coming through loud and clearly. It was simply impossible to locate the sub until I pushed the volume quite high. I'm serious, it felt like the bass jumped 3-4 feet forward and 1 feet up. 

I hope I can make some measurements tomorrow to see what actually happened before I send the car away for 2 weeks... =/


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## goodstuff (Jan 9, 2008)

Subd


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## 94VG30DE (Nov 28, 2007)

Hanatsu said:


> Tried something today... sending the car away for repairs so I was experimenting some with the an active out of phase speaker solution. My rear door speaker have been disabled for a while since I've not tuned them yet, turned them on today and delayed them for about 25ms just for fun and played with the phase inversion control at little. At first it sounded kinda weird so I played around with levels and crossovers a bit, listened to some music and messed with the settings. Finally something happened, I was using a 40Hz/24dB HP and 160Hz/24dB LP and with the right driver 180deg out of phase and the left side "normal phase" IIRC and wow... I never ever had such a upfront bass. It sounded completely dead from behind, yet the sub was coming through loud and clearly. It was simply impossible to locate the sub until I pushed the volume quite high. I'm serious, it felt like the bass jumped 3-4 feet forward and 1 feet up.
> 
> I hope I can make some measurements tomorrow to see what actually happened before I send the car away for 2 weeks... =/


Yeah I'm in for the followup to this too, because it's something I can do in my car pretty easily.


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## cajunner (Apr 13, 2007)

expanding on my idea of resonating panels, riddle me this:


when going over railroad tracks, it shudders for a second or so after crossing the girders.

this is what I'm talking about.


this sympathetic vibration could be a function of the shocks, the bushings for the car body, the engine mounts, the actual monocoque of a uni-body or the frame's inherent springiness from a tempered steel construction.

this is to an extent, also part of the construction of crumple zones, and why certain parts of the car crush first in a collision.

so, it's not so far fetched that the car is contributing to low bass ringing modes, as much as recombinant sound wave congregations.


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## goodstuff (Jan 9, 2008)

I am hesitant to post this since it's sort of a "duh" thing but maybe is relevant here.
I was listening last night and I noticed when I mute the mids I can localize my sub. It's *really *obvious where it's coming from. When the mids are not muted bass is up front BUT it's not the mids however making the bass up front...I am trying to relate this to the discussion with phase, way over my head, but it seems like the mids play an important role in canceling the sub localization out, I know it's not the mids making the bass sound like it's coming from the front, it's the way they are setup that causes the sub to sound like it's up front. Hope you enjoyed my incoherent run on sentence about nothing. I'm sure that made no sense.

PS: relevant details are sealed Aurasound Ns10 in the trunk, side firing in the rear corner, ski pass folded down. Id xs 6x9 mids in the front doors from 2k-63hz , sub from 63hz down, t/a on sub 133cm, 2004 Subaru Legacy sedan.


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## kaigoss69 (Apr 2, 2008)

goodstuff said:


> I am hesitant to post this since it's sort of a "duh" thing but maybe is relevant here.
> I was listening last night and I noticed when I mute the mids I can localize my sub. It's *really *obvious where it's coming from. When the mids are not muted bass is up front BUT it's not the mids however making the bass up front...I am trying to relate this to the discussion with phase, way over my head, but it seems like the mids play an important role in canceling the sub localization out, I know it's not the mids making the bass sound like it's coming from the front, it's the way they are setup that causes the sub to sound like it's up front. Hope you enjoyed my incoherent run on sentence about nothing. I'm sure that made no sense.
> 
> PS: relevant details are sealed Aurasound Ns10 in the trunk, side firing in the rear corner, ski pass folded down. Id xs 6x9 mids in the front doors from 2k-63hz , sub from 63hz down, t/a on sub 133cm, 2004 Subaru Legacy sedan.


Someone correct me if I'm wrong but I think the mids play a crucial role in the sub's location. In my mind it is due to the fact that most bass notes carry along with them "cues" well into the midrange frequencies (kick drums or bass guitar, for example). Those cues help us hear the low frequency information in the front, since the cues are in the front, even though the response from the subwoofer is more or less unlocateable due to the wavelength. Your brain interprets the entire note to be coming from the front, even though a portion of it is not.


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## adamclark1 (Jan 20, 2014)

Patrick,
I just discovered DIYMA. What a great resource. I have been reading a lot of posts over the last few days as I plan out my next install. This will be my third install, all in personal vehicles. I stumbled onto your posts because I had some similar design ideas. Could I send you some sketches of my ideas? I'm not a professional installer. I don't have access to an RTA or other testing devices, but I will be able to test out a few theories before I call it "done". However, if my design is logical I should be able to take the finished product to a professional and say, "tune it the best you can". Let me know how best to keep in touch. Thx.


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## Patrick Bateman (Sep 11, 2006)

IMHO, the main thing that 'gives away' the location of a subwoofer is frequencies above the passband being generated where the sub is located.

For instance, I don't think that putting subs up front makes the subwoofer sound like it's up front; I think that when the rattles generated are up front, instead of in the back of the car, it preserves the illusion that the sound is up front.

I also think that one of the reason that infinite baffle subs work well is because they tend to have lower displacement than sealed box subs, because IB subs tend to be much larger in surface area, therefore *it takes less displacement to reach the same SPL.* This also reduces the effect of rattles in the back of the car.

Anyways, the reason I bring all of this up is that an engineer who's worked for Kef, McIntosh, JBL and Snell is divulging some data on what works and what does NOT work for isolating subs:

Interesting read I found on Lossy Cabinet designs by Harbeth - Page 20 - diyAudio

It's very technical, but a lot of this information has been rarely divulged. The AES is frequently focused on prosound, where rattles aren't much of a concern.

But for home, and very much for a car, rattles are a huge deal.


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## Hanatsu (Nov 9, 2010)

Yes. I can probably agree with that.

I noticed an improvement when isolating the enclosure from the chassis. Non-linear distortion can be an issue as well if it's tall order HD/IMD.

Sent from my Samsung Galaxy S5 using Tapatalk


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## Orion525iT (Mar 6, 2011)

Patrick Bateman said:


> IMHO, the main thing that 'gives away' the location of a subwoofer is frequencies above the passband being generated where the sub is located.
> 
> For instance, I don't think that putting subs up front makes the subwoofer sound like it's up front; I think that when the rattles generated are up front, instead of in the back of the car, it preserves the illusion that the sound is up front.
> 
> ...


Exactly why I have utilized manifold mounting for my subs; the opposed positioning allows for force cancellation. And I am using eight subs. Granted, there are still some inherent resonances that build up in the driver basket itself, so force cancellation only goes so far. But I have detachable front panels on the slot side which can be acoustically isolated and each manifold stack will be decoupled with isolation mounts. Most people will tell you to bolt everything down as firmly as possible, but I don't subscribe to that and I think decoupling is the way to go. It will be neat to see if/how it works. 

On a side note about lossy cabinet design (that thread is a great read). I brought this subject up here months ago, and it was kinda dismissed. I think manly because "lossy" was conflated with "flimsy" or "weak" or "poorly designed". In any case, the midbass door pods I built are as about as asymmetrical as they could be and do not have a single surface that is of the same size, shape or stiffness.


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## Patrick Bateman (Sep 11, 2006)

It's a bummer that Jon's bus turned into so much drama, because the bass in there is probably better than any I've ever heard, in a car or in a home.

(Jon puts the subs on isolation mounts designed for industrial generators. So it has the effect of having the sub "float" above the surface of the vehicle itself.)

I've heard dipole subs that sound close to that level of performance, but dipole subs don't have any "impact" because they don't compress the air in the room.

Actually, this has me thinking about my subs at home, I should really isolate them from the room. One of my subs has two 8" woofers in a tapped horn, and even at modest levels you can feel it flexing the walls that are close to it. This is likely due to the subwoofer transmitting energy from the enclosure and into the corner that surrounds it. The walls are more susceptible than the floor because the walls are drywall.


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