# Sealed Box versus Infinite Baffle



## Patrick Bateman (Sep 11, 2006)

On this forum I've documented tons of horns that I've built. My horn subs have been kind of 'hit and miss' and I think the reason for that is that *our cars basically horn load our subs already.* For instance if you build a sealed sub and place it in the car carefully, the geometry of the car is going to act like a horn does. *So what's the point of building a horn sub when the car itself is bigger, stronger, and more efficient?*

In this thread I want to explore that; basically determine if programs like Hornresp can be used to figure out which works better:

sealed or infinite baffle?

Before reading any further, keep in mind that it might not be possible to model a car's interior with hornresp. I'm hoping that it CAN though, and I'm particularly curious if we can optimize the response so that it's improved at the drivers seat. (Due to all the reflections in the car, the frequency response can change if you move the seat forward or backwards an inch or two.)


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## BuickGN (May 29, 2009)

IB is better/ thread.

Looking forward to this one. On a more serious note I haven't found a sub yet that didn't sound better and require less power when used infinite baffle vs sealed.


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## Patrick Bateman (Sep 11, 2006)

BuickGN said:


> IB is better/ thread.
> 
> Looking forward to this one. On a more serious note I haven't found a sub yet that didn't sound better and require less power when used infinite baffle vs sealed.


My 'hunch' is that you're right.
Basically when you have a loudspeaker with a TON of displacement potential, it sounds really dynamic and effortless. I know it's fun to hit 140dB with an eight in a ported box, but there's something really *satisfying* about a couple of fifteens that are just loafing, and have a ton of headroom to burn.

But let's see what the sims say...


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## BuickGN (May 29, 2009)

Looking forward to it.


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## cajunner (Apr 13, 2007)

what would you call an IB using a horn mounting configuration?

basically, it's a way to mount 18's in a trunk's parcel shelf, while still being IB but using the loading scheme to "throttle" or compress, the front load of the sub into the cabin.

this would achieve two objectives:

it would suspend the sub physically in a down-fire on a reinforced baffle, and control excursion while providing some acoustic lever to the larger listening area of the cabin, providing a resistance, that a normal infinite baffle wouldn't. This would in turn make the possibility of rear chamber (trunk reverb) standing wave interference, less able to distort the output.

All the speed of a horn, all the smooth and deep response of an IB, and much reduced drops or nulls from the mid bass transition region affected by through-cone distortion modes.


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## Patrick Bateman (Sep 11, 2006)

here's some sims I did, using my new car (2014 Mazda6) and some of my favorite subs (Apline SWS-10D2)









We can model the cabin of a car using Hornresp. It's basically a big horn, which you happen to be sitting in. (I hope! Again, I'm not 100% sure this will work.)

The pic above shows how a conventional horn is modeled in hornresp. More info on how to do that here: Simple Offset Driver HornResp Tutorial - How to design your own Bass Horn









Here's my cheezy model of a 2014 Mazda6. The driver is mounted underneath the rear deck, inside of the trunk. Output of the woofer feeds into the car. *You could do the same thing across the rear deck, like in a conventional car, but you'll get more horn loading if you use the rear window for part of the path.*









Here's the frequency response of two of the Alpine tens in an infinite baffle (the grey line) and the same box horn loaded by the interior of the car (the black line.) Power is 1000 watts into 8 ohms (89.44 volts).









Here's the excursion of the two 'boxes'

Here's some things I notice here:
1) Excursion is completely out of control. Any big note below 80hz is going to make the woofer blow through it's excursion limits
2) When you put a sub in the trunk you usually get a big peak around 40-50hz, depending on the car. In this config, I'm seeing a big bump around 60hz. I think the reason that it's at 60hz instead of 40-50hz is because it's about 2-3 feet closer to the driver than it would be if it was inside the trunk instead of hanging off the rear decklid. (we have some ways to fix that, stay tuned...)









Here's a cabin gain measurement from John Janowitz at Acoustic Elegance that shows the gain in a Buick Regal and a Toyota Camry. Note the big bump at 40-50hz.

In the next few posts I'll see if reducing the box size fixes the issue with excursion, and I'll see if there's anything we can do to move that peak at 60hz to 50 or even 40hz.


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## Patrick Bateman (Sep 11, 2006)

My hypothesis is that the interior of the car can 'horn load' a sub, similar to the way that a horn sub works. In my last sim, it looked like most of the gain was at 60hz, which is too high in frequency for a real subwoofer.

In the sim above, I tried adding a 20" segment to the throat. Basically this would fit between the cone of the woofer and the rear deck of the sedan. *The purpose is to make the pathlength longer, extending the low frequencies.*

It looks like this works a little bit; but you need a much longer segment to get real bass. (Basically the segment is too short / too small.)


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> My hypothesis is that the interior of the car can 'horn load' a sub, similar to the way that a horn sub works. In my last sim, it looked like most of the gain was at 60hz, which is too high in frequency for a real subwoofer.
> 
> In the sim above, I tried adding a 20" segment to the throat. Basically this would fit between the cone of the woofer and the rear deck of the sedan. *The purpose is to make the pathlength longer, extending the low frequencies.*
> 
> It looks like this works a little bit; but you need a much longer segment to get real bass. (Basically the segment is too short / too small.)



that's what I am proposing.

I'm no good at posting drawings.

the way I want to do it is extremely simple, I'm going to use 2 pieces of MDF to make a first transition through the rear seat metal openings, and sheet metal welded to the back seat metal and rear deck, creating an expanding gap that begins at 0 where the subs' mounting panel ends in the interior of the trunk at the angle where the parcel shelf dips down over the fuel tank.

then the wave passes through the rear seat openings, into a gradually expanding wedge of horn to the turn at the rear deck in the car, which then travels most of the way towards the rear window. The area above this angled piece forms the last part of the horn, and fires directly into the cabin space at head level.

I'd use a little butyl caulk to stabilize the sheet metal portion, done right it would strengthen the area of the car that is subject to large signal deflection and vibrations.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> that's what I am proposing.
> 
> I'm no good at posting drawings.
> 
> ...


The thing I'm trying to figure out is whether it's practical.










One big horn can basically be visualized as a series of small horns stacked on top of each other. Similar to the layers in the pyramid that's pictured above.

The tricky thing is that making a dramatic change in the expansion rate causes issues.









For instance, in the pic above we have a nice slooow expansion that's caused by the sloping rear window. But as soon as the wavefront moves past the seats, the expansion rate jumps dramatically, and the wave basically 'detaches'.

Basically it looks like you can use the rear window to horn load a driver, but you're not going to get a lot of horn loading beyond the edge of the back seats, due to the rapid expansion that occurs as the wave moves towards the front of the car.

That's not the end of the world though; you can still use the cavity above the rear deck to form the last half of a bass horn.


One way that you can investigate this is by looking at the impedance curve of the sub; if there's no dip in the impedance curve, then you're not getting horn loading.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> The thing I'm trying to figure out is whether it's practical.
> 
> 
> 
> ...


and you'd have to tune it, each transition can be 'massaged' with liberal use of the low-expansion foam until you get a nice even response, I understand that the changes in expansion rate are to be the more carefully predicted indicators of a quality install.

take your pic, and turn your subs firing down. Then leave a little angle for them to fire forward, into the car. Partition in front of the seat back, going up with the next fold. Then fold to the rear of the rear window, leaving the last expansion from the window forward.

a long, tuned bass horn?

and if it's IB, it's using the trunk as an enclosure. If necessary to create compression you could enclose the back with a small enclosure but I would like to see it run IB first.

It's gotta be feasible, my experience tells me that hatchback cars with a sloped rear window and slight widening, (280ZX, 300ZX etc, 240SX, the little Honda, the Corvette, and especially the Camaro, '95 or whatever) always had a prominent bass load, and the resonant peak had to come from that expansion rate. Taming the resonant peak by using a longer horn, should govern the response at the driver's seat, and when we're using basically an 11 foot folded horn, it's got to be pretty decent.

I'm hoping you get this worked out, I want to liquid nails some 1/4" luan for a low power testing bed....


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## BuickGN (May 29, 2009)

Plexiglass to extend the rear seats upward/forward?


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## cajunner (Apr 13, 2007)

BuickGN said:


> Plexiglass to extend the rear seats upward/forward?


right, they would still be basically attached at the bottom in the same place, but the top moved forward into the cabin space about 2.5" at the point where you would make the next fold towards the rear window, and above the rear deck metal. There would be a small rise of a new false rear deck, that angles up towards the rear window, with a gap at the window where the last turn, or fold occurs in the horn.

very lightweight, and with bracing probably gaining a reduction in bass passing through the rear deck/back seat metal transmission area, due to it being used as part of the enclosure or horn mechanics.


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## Patrick Bateman (Sep 11, 2006)

cajunner - I *think* we're talking about the same thing here. I'm not willing to make any changes to my shiny new car though  I guess I'm willing to cut a hole in the rear deck, but that's about it.









Basically the last foot or two of a bass horn takes up the most volume, due to the rapid expansion at the mouth. Picture that pyramid that I posted yesterday, and then fold it like a snail, and you get the idea.

Since the last couple feet are so huge, I'm thinking you could use the entire car cabin.

The trick is that you can't have the expansion get too big too fast. For bass it's probably better if it expands too slow than if it expands too fast. If it expands too fast, you're F3 on the bass horn will be very high.

The thing will still work, but it will only give you gain at high frequencies, where we don't need it.


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## Patrick Bateman (Sep 11, 2006)

I was thinking about this for a bit, and it seems like we have a problem with this design. Basically the expansion rate is too fast, which makes it act like a horn at high frequencies, but like a sealed box at low frequencies.

So it's kind of a ****ty design, because we don't need any gain at high frequencies, since it's a sub, and if it acts like a sealed box at low frequencies we might as well save ourselves a lot of work and just build a sealed box.

But it occured to me that there's a lot of horn subs out there that use a really rapid expansion and a short pathlength.

Sound Physics Labs BDEAP is a good example of this:
























http://www.diymobileaudio.com/forum/1821521-post27.html

And the new Danley BC412 sure looks like an array of four BDEAPs:








Danley sub demo - YouTube

And I have a pretty good idea of how these subs work; basically the last 25% of the horn sub is 'outside of the box.'

So it's a huuuuuuge front loaded horn, with the last 25% of the path removed. And that last 25% takes up a LOT of volume, as much as 50% of the entire box, due to the very long wavelengths down low.

So maybe you can do the same thing in a car.

Hmmmm...


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## Patrick Bateman (Sep 11, 2006)

OK, I made some progress on this idea. I'm starting to think it might actually work.









Here's a layout of a bass horn, before it's been folded.









My idea was to use the car to form the horn, similar to the pic above. The driver hangs off the rear deck, or just below it. *But the sims didn't look good; basically the horn was expanding too rapidly, and that was making it suck.* (See explanation of why we don't want a rapid flare in my last post.)









It occurred to me that a Sound Physics Labs BDEAP works on the same principle as what I'm trying to do. Basically it uses a boundary to extend the pathlength. I think the Danley BC subs use the same trick, and that's why "BC" stands for "boundary constrained" IIRC.









So what if we took a BDEAP, sliced it in half, and crammed it in the trunk?

Here's why I think this might work well:

1) the rear window makes a really nice horn segment
2) it shouldn't be too difficult to re-arrange the segments in a BDEAP so that they fit in a trunk. The pic above is drawn to scale, and you can see that even with dual 12" woofers, there's still lots of trunk space left
3) We should get 'real' horn loading down to 40 or 50hz. This is an improvement over the other well known car horn, the Fitzmaurice Autotuba. (IIRC, the Autotuba is good to 60hz, and below that it basically acts like a sealed box.)
4) This shouldn't be a terribly difficult horn to build, unlike some of my other monstrosities ----->


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## Patrick Bateman (Sep 11, 2006)

I used Xara and the pictures from the patent to figure out the dimensions of the BDEAP.
We can use these dimensions to simulate the subwoofer in Hornresp.
And once we have a model in Hornresp, we can plug in various subwoofer drivers, to see which ones work and which ones DON'T.

And once we have *that*, we can then 'slice' the enclosure in half, then cram it into the trunk of the car.

In the next few posts I'll posts some sims of the BDEAP with various sub drivers.


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## cajunner (Apr 13, 2007)

yes!

all I was proposing was your idea, with 2 extra folds in the horn, extending it's length to get more powah...

or, gain at lower frequencies.

that pic where the BDEAP is super-imposed on the pic of your car, is similar. The beauty of what I am proposing (for a Panther Chassis, Grand Marquis/Town Car/Crown Vic) is that there's no extra holes to cut, you don't weaken the car's structure, you strengthen it, and you use the rear deck and parcel shelf to make up two of the panels that make up the horn, saving weight.

this is looking good!


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## Patrick Bateman (Sep 11, 2006)

In an earlier post I said I'd sim the response of the SPL BDEAP sub. I've finished the sims.

In order to make it a fair fight, I am comparing one HALF of a BDEAP, versus FOUR vented boxes. That might sound a bit nutty, but I figure that most of us are more concerned with the size of our subs than the cost of our subs. So if four vented boxes will get louder in the same footprint, I'm sure most of us would just use four vented subs, not some weird ass front loaded horn that's going to be a ***** to build.









Here's the excursion of half a BDEAP versus four vented boxes. The driver is the Alpine SWS 10-D2, which runs four about $80. The vented box is the one recommened by Alpine. Power is 500 watts into 4 ohms, or 44.72 volts. Here's some observations:

1) If you highpass it at 30hz, four of the vented subs can handle the power, but the BDEAP is going to exceed the drivers excursion by about a third of an inch. Then again, it's an $80 driver so you can't expect miracles.
2) Below 40hz the sealed back chamber really keeps excursion nice and low in the horn. You might even run this box without a high pass. The whole reason I'm considering building this box is I want that bass that makes the car shake, and that means LOW BASS









Here's the impedance. The vented box is the one that dips to one ohm at 40hz. If you high pass the horn, it's basically a 1.5ohm load. That's 50% higher than what it would be in a vented box, due to the air load on the cone. That bump in impedance lowers the demand on your amp, which means you can squeeze about 50% more power out of your amp, everything else being equal.









This is my favorite graph. It's the phase response of the vented box, versus the BDEAP. In the vented box we see that the phase shifts by 180 degrees as we get lower and lower in frequency. That introduces a hefty delay; at 40hz that's like moving the subwoofer FOURTEEN FEET. This wonky phase response is why vented boxes rarely sound 'tight.'

Compare that phase curve to the BDEAP, which basically fits within a window of 45 degrees in the two octaves from 40hz to 160hz. Admittedly the BDEAP sees phase shift below 40hz, but I'd argue that the octave from 40-80hz is a lot more important than the octave from 20-40hz.









And of course, the frequency response.

Yeah, I know this looks atrocious, but I can explain! 

Basically hornresp tends to exaggerate peaks and dips. If it shows a dip that's 10dB, in the real world it's usually a third of that. And the same thing goes for peaks. So I know this graph looks awful, but I've been building horns long enough to know that it never measures this bad in the real world. I wish hornresp had some type of 'smoothing' function to make these peaks and dips look less severe.

*Having said that, the output level of half a BDEAP exceeds four vented boxes.*

That's pretty crazy when you think about it; that means that four BDEAPs have a higher efficiency than THIRTY TWO vented boxes. We're talking sick output potential.


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## Patrick Bateman (Sep 11, 2006)

In my last post I claimed that the "real world" response of something like the BDEAP wouldn't be as atrocious as the sims predict. Basically saying that hornresp exaggerates peaks and it exaggerates dips, and in the real world the actual response is much smoother than predicted.









Here's the measured response of the Danley BC412, which seems very similar to a pair of BDEAPs in my humble opinion

















Here's the predicted frequency response and impedance of four of the BDEAPs, if they use the Eminence Lab12 woofer. (Which seems like a safe bet.)

We see:

1) Crazy high sensitivity. A subwoofer with a sensitivity of about 113dB.
2) Smoother response than my sims with the Alpine. This is because I simmed it with two BDEAPs, a total of four woofers. (More drivers smooths out the response.)
3) The measured response of the BC412 is basically flat in the octave from 50-100hz. With a lowpass you could probably squeeze an octave and a half out of this sub. (40hz-120hz.)


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## cajunner (Apr 13, 2007)

wow!

I don't know if that will translate into final pressure numbers being high or not, but starting off at say, 104 db/Watt, in a slightly compromised car installation, makes a pretty strong argument for giving it a try.

I saw where they made some styrofoam Imperials, and Scoops get up pretty high in the deebeez before they lost their integrity. IF the car's interior can handle the pressure, (the back window might just "pop" out) then there's no reason (seemingly) you couldn't come up with better numbers *and sound!* than a plain IB installation.


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## Oscar (Jun 20, 2010)

how are your simulations getting around the fact that horn simulation programs (like almost any other modeling software) uniquely specify that the output of the horn itself is into the _atmostphere_, where the wavefronts are indeed _maintained_ as wavefronts? (IOW, once you're below the cabin-gain frequency, the entire "atmostphere" within the cabin completely pressurizes and de-pressureizes, as opposed to having bass frequencies as traveling _waves_)


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## cajunner (Apr 13, 2007)

ouch, the fly in the ointment...

let's hope that this works at least, above the transfer function of the vehicle and total length of the interior including trunk, contributes...

then maybe the mid bass gets the gain, and below cabin Schroeder you get IB-type response?


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## Patrick Bateman (Sep 11, 2006)

OK I juggled the variables, and this is what I've come up with so far:










Basically it's a twelve foot long horn, but only the first five feet of the horn are in the box. The last seven feet are formed by the rear window and the back seat of the car.

Response should be similar to the BDEAP.

The driver is an Alpine SWS-10D2, but nearly any woofer will work. The box seems very insensitive to driver parameters. The response with the Alpine 10", the B&C 12PS100 and the Lab12 12" were all virtually identical.

Basically pick your favorite ten or twelve and start cutting!

I'll post some more refinements to this later, but right now it's time for dinner!


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## Patrick Bateman (Sep 11, 2006)

Oscar said:


> how are your simulations getting around the fact that horn simulation programs (like almost any other modeling software) uniquely specify that the output of the horn itself is into the _atmostphere_, where the wavefronts are indeed _maintained_ as wavefronts? (IOW, once you're below the cabin-gain frequency, the entire "atmostphere" within the cabin completely pressurizes and de-pressureizes, as opposed to having bass frequencies as traveling _waves_)


Check out some of my threads from 2009, particularly the Triple8 thread. In my measurements I saw that horn subs do indeed work in a car. Some things I noticed:

1) Cabin gain still kicks in big time below 40hz, so if the sub is falling off below 40hz, it will basically be flat in the car. A good example of this is the Fitzmaurice Autotuba. Measured outside, it falls off at about 50hz. In the car, it's basically flat to 20hz.
2) The big "X Factor" is the response from the rear of the cone. I found that tapped horns don't get a bump from cabin gain the way that front loaded horns do. John Kreskovsky and Earl Geddes have written a number of articles about this. Earl Geddes uses sealed boxes exclusively now. (I own a set of his speakers, the top of the line Summas.) As I understand it, Geddes uses sealed boxes mostly because vented boxes and dual reflex boxes and tapped horns do not pressurize a room the way that a sealed box or a front loaded horn does.

Check out the Danley videos of the BC412 and you'll see what I mean; it moves air in a way that vented boxes and tapped horns do not.


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## Oscar (Jun 20, 2010)

I'd love to see final end results/empirical testing on this FLH.


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## subwoofery (Nov 9, 2008)

Just saw this thread... Anyone tried it? 

With I could but I don't have a trunk - SUV and hatchback only 

Kelvin


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## req (Aug 4, 2007)

this seems perfectly tailored to a trunk car. 

saying that, i have two 18's in my hatch baffle. im thinking that i could build some kind of contraption that sits atop the baffle - shaped like a large letter "D" (yellow area below) where the flat part of the D is sitting over the cones and baffle (orange), and one corner is resting against the seat (red) back, and the other corner is a few inches (depending on the design) shy of the rear window. the flat part is the first segment of the horn over the subs, the rest of the segments form with the shape of the car and the curve of this "D".

the question is - does the horn need a sealed enclosure for the back wave of the subwoofer - or can it remain IB (well, as close to it as i can get)










i think this would be something that should be fairly easy for me to build using a a piece of scrap wood and some foam or something.

it should be easy to put in\take out too. something i can drop in for a car show or whatever that i dont need to drive around with.

imagine if i had this made from clear plexiglass? that would be rad.


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## Patrick Bateman (Sep 11, 2006)

Thought I'd resurrect this thread, since I'm getting sick of not having any subs in my car.

Before I build anything, I wanted to explore if it's possible to improve upon the Fitzmaurice 'Autotuba' design.



















Here's a pic of the Autotuba










By tracing the Autotuba, I can figure out the dimensions










Here's the predicted response of the Autotuba with the MCM 55-2421 driver. *Horn loading it bumps up the efficiency by about 15dB in the sims.* Then again, the gain only affects frequencies above 40hz and it's kinda lump. (note the trough.)









Here's about as much output as you can squeeze out of one Autotuba. 120 decibels or so. Not too shabby for a single 8. Keep in mind that some of the SPL boxes with one driver exceed this, but their response is often very peaky.









Here's the displacement. It's going to need a high pass filter. Note that this sim is with 500 watts into a 4ohm load. (44.72 volts.)


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## thehatedguy (May 4, 2007)

If you could kill that 40 hertz bump, cabin gain would fill in the rest pretty well. A tapped horn would/could fill in that dip...I guess it could, I'm not very good at designing tapped horns.

Then again, a ported enclosure might be easier to do and have similar gain and a wider FR.

Then again, I would if you could port the chamber in the autotuba to bump that hole up like how Danley ports the midbasses in the Synergy horns...or gain extension like the old Altec horns?

Been reading that thread on DIY about the bass horns...you looking at something based on that thread?

I see someone peaking at the thread...


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## Patrick Bateman (Sep 11, 2006)

Basically I think that a plain ol' sealed box or vented box will offer more output in the car. This is for a simple reason - *the car itself basically horn loads the sub.* And a tapped horn offers the smoothest output from small horns.

So a front-loaded-horn is anything but ideal.

Danley new BC412 subwoofer - YouTube

But there's one thing that front loaded horns can do, that other boxes struggle with, and that's the 'punch' you get. And this is for a really simple reason, when the back chamber isn't sealed you can't compress the car or the room. (IE, in any box type with a sealed back chamber the subwoofer can 'push' the air right out of your lungs.)

At home I have some tapped horns, but I can't really crank them up because I live in an apartment these days, but in the car I can go crazy.


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## Thumper26 (Sep 23, 2005)

Patrick, I have an 07 Cobalt SS with a pair of shallow mount 10" subs IB in the rear deck, and am looking to redo the setup. Let me know if you need a guinea pig!


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## thehatedguy (May 4, 2007)

Is the punch from the sub or the midbass?

Sealed or ported can compress the car itself provided the cabin is sealed from the trunk and the sub is firing directly into the cabin.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Is the punch from the sub or the midbass?
> 
> Sealed or ported can compress the car itself provided the cabin is sealed from the trunk and the sub is firing directly into the cabin.


Yeah I'm mostly doing this for a goof. At home I have the tapped horn that was actually designed for my old car, a bandpass sub, and a vented box. I'll be adding a couple of sealed boxes once I finish my Synergy horns.

But I don't have any front loaded horns at all, since I gave away my Autotuba clone about a year back.


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## Patrick Bateman (Sep 11, 2006)

Thumper26 said:


> Patrick, I have an 07 Cobalt SS with a pair of shallow mount 10" subs IB in the rear deck, and am looking to redo the setup. Let me know if you need a guinea pig!


I'll post some plans for the box, but it's going to be tricky to build.
I am using ultra thin plywood, just 0.2", and using a matrix construction to make it work. Something like this:










Most of the shelves and shelving units at Ikea are actually made out of cardboard, so you can get a very rigid and strong enclosure with a matrix.


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## Patrick Bateman (Sep 11, 2006)

Here's some pics of a 'real' Autotuba.









Here's some pics of the 'shell' of my hornsub.
Note the wash machine below it, for scale.​
It uses some tricks I learned from my last horn sub:
1) It's bigger than most of the sub boxes I would normally put in a car
2) I'm using the lightest construction I can possibly get away with.
Basically the idea is that the sub is huge, but it's light enough to yank out of the car when needed. For instance, I've had small heavy subs in my car and I was always reluctant to move them out, because it's such a hassle. But when they're light, the size of the sub is less annoying because it can be moved as needed.









I'm building the 'sealed' portion of the horn independently of everything else, so that I can make it as strong as possible.









It's not complete, but here's some pics showing the 'matrix' construction.


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## MetricMuscle (Sep 16, 2013)

In a basic IB configuration with a 15" mounted on the rear deck facing up towards the back glass, is the angle of the glass relative to the subwoofer important? The factory 8" IB sub was canted forward slightly. This was not necessary for fitment or installation. I'll measure the angle of the back glass to the rear deck later.


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## SynRG (Jul 30, 2007)

Just curious Patrick, did you consider the newer flat version of the auto tuba?


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## thehatedguy (May 4, 2007)

Angle of the sub not important given the wave lengths we are talking about here.


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## Patrick Bateman (Sep 11, 2006)

MetricMuscle said:


> In a basic IB configuration with a 15" mounted on the rear deck facing up towards the back glass, is the angle of the glass relative to the subwoofer important? The factory 8" IB sub was canted forward slightly. This was not necessary for fitment or installation. I'll measure the angle of the back glass to the rear deck later.


The initial idea of this thread was to examine if you could truncate half of a horn by carefully using part of the car to form the last few inches.









If you look at a horn, the last five or ten inches is half the volume of the entire thing.

But I lost enthusiasm to do that, because I've tried to do that before, and the effect is unpredictable. You definitely get more low frequency output when you use a boundary, but there's a lot of variables involved and things can go sideways.

So, due to that, I decided to just stick with folding the whole thing in a box.

As for the angle, no, it doesn't matter. The wavelengths are too long. Even up to 250hz the angle doesn't matter. (250hz is 54" long, so the length exceeds the diameter of the loudspeaker by quite a bit.)

I know that some people have noticed that subwoofers sound different if you face them forwards or backwards. But I think that effect is mostly because you're moving the sub in the interior of the car when you do that, and that changes the frequencies that are excited by the car itself. (IE, if you put a sub in your trunk, and it's 1' from the end of the car, the combination of the sub *and* the car will excite a specific set of frequencies. But if you turn the sub around, it's now a foot backward, and the combination of the car and the sub excite a *different* set of frequencies.


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## Patrick Bateman (Sep 11, 2006)

SynRG said:


> Just curious Patrick, did you consider the newer flat version of the auto tuba?


It's funny, I keep screwing around with various folds, and they all end up looking like the Autotuba for the most part. I probably would have saved myself a lot of trouble if I just dropped my sub into Bill's design


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## thehatedguy (May 4, 2007)

He has the trucktuba now...that's the flat one he is talking about.


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## cajunner (Apr 13, 2007)

in his defense, Bill's been at it a while now..


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> He has the trucktuba now...that's the flat one he is talking about.


Here's a look at the Trucktuba:









Assuming that the layout is the same, here's a comparison of the Autotuba and the Trucktuba. Basically switch to a back loaded horn from a front loaded horn fills in the low frequency trough, but at the expense of output below 30hz. (In my experience, tapped horns and BLHs are usually tuned to a lower frequency than FLHs, so it's possible that Bill used a longer path.)























































Here's some pics of the Trucktuba, from this forum:

BillFitzmaurice.info - View topic - (My) First TRT


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## thehatedguy (May 4, 2007)

Lot of work for that result.


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## SynRG (Jul 30, 2007)

It's been worth it for me just for the learning.


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## cajunner (Apr 13, 2007)

I like the down-fire as it must quasi-slot load the sub, giving it heft and weight to the response.

slot load always puts a bit of group delay into the response, and it may match up better with the additional group delay of the horn.

I wonder if this could be managed in a phase-coherent physical positioning in a large vehicle, like if you'd do a long cabinet horn that coincides the group delay of the horn with an adjustable all pass filter, analog even, to make the wave coincident at the listening position.

basically, gettin' 'er done with math and geometry instead of electronic wizardry.


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## Patrick Bateman (Sep 11, 2006)

Moar pics of my horn sub coming together:






























































​


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> I like the down-fire as it must quasi-slot load the sub, giving it heft and weight to the response.
> 
> slot load always puts a bit of group delay into the response, and it may match up better with the additional group delay of the horn.
> 
> ...


The phase response of loudspeakers is something I can barely wrap my head around. So take this with a grain of salt, I may be wrong:

1) Sealed boxes have flat phase, *but only in their passband.* As the response rolls off on the low end, the phase rotates. For instance, if a sealed box rolls off at 12db/octave at 80hz, then a note played at 40hz will not be in phase with a note played at 80hz. This is problematic because musical notes have harmonics. For instance, a 40hz bass line will have harmonics at 80, 120, 160, etc.

2) Bandpass boxes and front loaded horns are a variation on sealed boxes. You basically have a resonant chamber in front of the sealed box that amplifies certain frequencies. So they suffer from the same problems as sealed boxes. But sealed boxes generally have wider bandwidth than FLHs and bandpass boxes. So if you have to rank them in terms of phase, it would probably go from widest bandwith to narrowest. (Because the phase response is flat when the response is flat.) So it goes Sealed > FLH > bandpass

I know that Geddes argues that basshorns are pointless in the home, and he makes some good points. You can squeeze four twelves into one cubic foot sealed boxes, and they'll deliver more output than my eight in a four cubic foot horn.









But horns sound 'tight', and I think the reason may be that the delay is harmonic. *The pic above shows the same woofer in two boxes. One is a front loaded horn, one is a sealed box.*

Here's what I mean by this:
A horn resonates at harmonics. For instance, in the pic above, you can see the resonance at 45hz, 90hz, 135hz, etc.
Bandpass boxes don't do this; they resonate at a single frequency. For instance, if a bandpass is tuned at 45hz, the second harmonic at 90hz may 'lead' the fundamental by ten milliseconds. Now let's say you're listening to an EDM track with a 140bpm bass line. That's one beat every 428 milliseconds. *If the fundamental 'leads' the harmonic by ten milliseconds, then the beat will be 'off' by about two percent.*
Now two percent probably doesn't sound like a lot. But humans are ultra sensitive to timing errors. For instance, if you took a record and varied the pitch by five percent over and over and over again, the effect would be unmistakable.
Bandpass boxes do something similar to that.

Long story short - front loaded horns have higher group delay than sealed boxes, but the delay is harmonic. So the fundamental *and* it's harmonics are both delayed, and my guess is that's why horns don't sound 'slow' the way that a bandpass subwoofer often does. In fact, I've heard bass horns that sound 'tighter' than a sealed box.


Also, there's one way to 'fix' the group delay problem of bandpass boxes. And that's to use them across the entire frequency spectrum. IE, a bandpass box for subs, a bandpass box for midrange, a bandpass box for tweeters. In some respects, this is how multi-range horns work. There's a group delay, but *all* of it is delayed, not just one part of the spectrum.


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## cajunner (Apr 13, 2007)

right, but the slot load of a down-fire is also causing group delay, so that the effect of a BLH having two distinct zones of out-of-phase response, is minimized in comparison to the plain BLH doing an up-fire or normal orientation.

slot loading adds additional air mass, and BLH also adds air mass but knowing how much delay is involved in each instance is an engineer's exercise.

this is apparent in the Power Port, or whatever JBL and Polk call their little dimpled loading schemes for their ported systems.

I have to believe that the slot loading delay, brings the horn's delay, closer together instead of farther apart.

Whether or not this is a moot point at sub bass frequencies can possibly be debated, but like you point out, we are extremely sensitive to timing errors and a ported box that displays excessive group delay is certainly detectable and not a pleasing characteristic.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> right, but the slot load of a down-fire is also causing group delay, so that the effect of a BLH having two distinct zones of out-of-phase response, is minimized in comparison to the plain BLH doing an up-fire or normal orientation.
> 
> slot loading adds additional air mass, and BLH also adds air mass but knowing how much delay is involved in each instance is an engineer's exercise.
> 
> ...


Yeah I intentionally left out back loaded horns and tapped horns because their phase response makes my head hurt. Since it's a complex interaction of two signals, one from the front of the cone, one from the rear. Sealed boxes, single reflex bandpass boxes and FLHs are easier to wrap my brain around, because you basically have one signal which is delayed at certain frequencies, not two.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> Yeah I intentionally left out back loaded horns and tapped horns because their phase response makes my head hurt. Since it's a complex interaction of two signals, one from the front of the cone, one from the rear. Sealed boxes, single reflex bandpass boxes and FLHs are easier to wrap my brain around, because you basically have one signal which is delayed at certain frequencies, not two.


you could get lost in theory, haha...

and never find your way out of 2pi.


I like your observation that because there's harmonic convergence in the delay, your horn isn't detected like a port's single resonant peak.

I still wonder if delaying sound by passing it through a porous medium like the charcoal, actually can cause a speaker to become cardioid in polar plots or that is just some marketing copy.


maybe it's something that can be calculated using HornRESP as well, and if that's true maybe loading the horn with a reticulated foam of some low density variety, might be able to put all the phase, all the way...


I'd like to know more about how horns can or cannot be believed in the automotive capsule, and in the lower registers.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> you could get lost in theory, haha...
> 
> and never find your way out of 2pi.
> 
> ...


David Smith is one of the smartest loudspeaker engineers in the world. He's worked for Snell, JBL, PSB, A/D/S, and Kef. According to David, plain ol' fiberglass is the best:

Box colourations - really ? - Page 23 - diyAudio

As for the cardioid behavior, yes, that definitely works. The fiberglass doesn't make it a cardioid by delaying the sound; the fiberglass makes it a cardioid by absorbing the sound. So the cardioid behavior is frequency dependent. Basically at high frequency it's very directional and then it starts to radiate like a dipole at low frequency. At low frequencies it's a little iffy because you need a lot. Probably the easiest way to make a cardioid at low frequency is with digital delay and two drivers. In my new Synergy horns I'm only doing cardioid for the midrange. At low frequencies the wavelengths are so long, it's semi-useless in a living room or a car. You'd probably want a room that's big enough to form at least 5-10 wavelengths. In a car cabin that's 8' long, that works out to a frequency of 700-1400hz.

Another dead simple way to make a cardioid is to simply but a dipole on top of a sealed box. When you do that the following happens:
1) The front wave of the two speakers combine, yielding six more decibels of output
2) The back wave of the two speakers nullify each other, reducing output backwards
3) The nulls to the left and to the right of the dipole are 'filled in' by the output from the sealed box

The net effect is cardioid. It's basically directional in the forward lobe, but not the rearward lobe. It's a neat trick, would be very handy for midranges mounted up high on the dash, like this:










http://kotisivu.dnainternet.net/anukaa/CardSub/CARDSUB.html was by far the best reference for these enclosures, and it appears to be gone. Sucks! Here's an old copy from the wayback machine:

http://web.archive.org/web/20130403...u.dnainternet.net/anukaa/CardSub/CARDSUB.html


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## Patrick Bateman (Sep 11, 2006)

I finally settled on a horn fold. It's a fairly standard 'snail' fold. *This type of fold offers extended response, because all of the bends are 90 degrees.* (180 degree bends tend to roll off the highs and can introduce peaks and dips, it's the reason that a lot of classic bassbins light the Cerwin Vega L36 and the Labhorn are snails.)









Here's the predicted response of *four* of the TC Sounds eights, versus *one* of the TC Sounds eights in this horn. *We're getting about 6-11dB of gain across the passband.* I designed this very specifically to have a slow rolloff, because of cabin gain.









Here's the expected response, with 400 watts into 4ohms, and the expected 'bump' from cabin gain. Once you factor in cabin gain, *one of these boxes should be good for about 125dB.* The box is good for two octaves, about 30hz to 120hz.









Here's the excursion with 400 watts into 4ohms.
I'll be using a miniDSP and running a high pass at 25 or 30hz to keep excursion under control. Should be good to 600 watts, but my amp craps out at 400 per channel.









Here's the specs. This uses the values that I measured for the woofer, using the WT2, which are quite a bit different than the published values.

Here's my measurements, versus the Soundsplinter measurements, versus the published specs from TC Sounds. (I believe this woofer is the same as the "Epic 8" that is currently sold by Parts Express.)

FS = 31hz / 25.7hz / 24hz
QES = 0.37 / 0.32 / 0.26
QMS = 4.27 / 2.5 / 7.2
QTS = 0.34 / 0.28 / 0.25
VAS = 23 liters / 22L / 16L


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> Here's the specs. This uses the values that I measured for the woofer, using the WT2, which are quite a bit different than the published values.
> 
> Here's my measurements, versus the Soundsplinter measurements, versus the published specs from TC Sounds. (I believe this woofer is the same as the "Epic 8" that is currently sold by Parts Express.)
> 
> ...


the specs from TC Sounds, look better for horn use than your measured specs?

and I would expect your horn to have less excursion at the lower frequencies than the Xmax graph you posted, simply because I believe real world boxes tend to be able to play deeper than their sims.

On pop music with very little content below 30 hz, you may never stress the suspension even at full tilt, but don't hold me to it.

definitely interested in seeing your results and explanations when you compare this snail configuration with a simple sealed box, or IB results.


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## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> The phase response of loudspeakers is something I can barely wrap my head around. So take this with a grain of salt, I may be wrong:
> 
> 1) Sealed boxes have flat phase, *but only in their passband.* As the response rolls off on the low end, the phase rotates. For instance, if a sealed box rolls off at 12db/octave at 80hz, then a note played at 40hz will not be in phase with a note played at 80hz. This is problematic because musical notes have harmonics. For instance, a 40hz bass line will have harmonics at 80, 120, 160, etc.
> 
> ...


Interesting idea with the delay of harmonics. I wonder if harmonic distortion is affected in the same way. Flat group delay in the passband would fix this issue, "an absolute" low GD wouldn't matter since that can be compensated with T/A. Modal dips screws GD though.

Sent from my Samsung Galaxy 3 via Tapatalk.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> the specs from TC Sounds, look better for horn use than your measured specs?
> 
> and I would expect your horn to have less excursion at the lower frequencies than the Xmax graph you posted, simply because I believe real world boxes tend to be able to play deeper than their sims.
> 
> ...


The specs from TC sounds never made much sense to me. Here's an example of this:









In this corner, we have a TC Sounds Epic 8.
This driver is all motor, and has a very heavy cone.
The main reason that the motor is deep is to accomodate the high excursion.
(IE, if it was short and fat it would concentrate the force of the motor into a single spot. You see this in a lot of prosound drivers; the motor looks like a pancake, whereas carsound woofers like the Epic 8 and the Sundown SA-8 have a motor that looks like a paint can.)









In this corner, a B&C 8PS21.
Both drivers have the same voice coil diameter. The diameter of the magnets are fairly similar, the TC may be a little wider. The TC is *dramatically* deeper, but I believe that's because of it's excursion, not to raise the motor force. (Again, pancake vs paint can.)

B&C claims a qts of 0.33, and TC claims a qts of 0.25.

But here's the catch: *The moving mass of the B&C is less than one quarter of the TC.* (23g vs 108g)


So *that's* the part where I honestly think that TC exaggerates their specs. I don't see how it's even *possible* to get the QTS down to 0.25 when the moving mass is so heavy. It *might* be possible with a lot of neodymium, but with a ferrite motor? Uh uh.

Sundown advertises an even *higher* MMS for their 8" driver; it's 176 grams. *But the Sundown's QTS is advertised as 0.48*

That sounds about right for a motor that size and a cone that heavy.

Then again, it's very possible that my measurements suck! Or that TC's equipment is just faulty. Or that they ran their drivers in longer. I can make the QTS of a driver change ten percent just by pushing on the cone for about fifteen seconds. (Loosens everything up.)


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## thehatedguy (May 4, 2007)

Both Qes and Qms have Fs in their terms including Mms. So a higher Fs will allow you a lower Mms to keep the numerator in the factions about the same...and Re is a factor there too- the TC has a lower Re and the B&C.

The motors are roughly the same strength, but for the calculations you square the terms, so differences get larger.


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## thehatedguy (May 4, 2007)

double post


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## cajunner (Apr 13, 2007)

the TC has multiple rings stacked, and although it isn't doubling the motor strength, there is an incremental increase in gap flux with each successive layer added on.

I also believe the metal's content and magnetic properties play into it, along with whether a shorting sleeve is included, which could decrease gap strength, and also the weight of the copper on the coil is a big factor in this.

You typically need more room to allow a humongous coil to move, so the gap gets wider, and you lose a lot of flux that way...

but I'd have to agree, the Qts of the Epic can't be down in the .26 range, there's just not enough motor there to support it.

it's still good for a horn project at .3 or slightly above, though.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> the TC has multiple rings stacked, and although it isn't doubling the motor strength, there is an incremental increase in gap flux with each successive layer added on.
> 
> I also believe the metal's content and magnetic properties play into it, along with whether a shorting sleeve is included, which could decrease gap strength, and also the weight of the copper on the coil is a big factor in this.
> 
> ...


Agreed. I really like the Alpine Type R eights for tapped horns, but for front loaded horns, the TC Sounds Epic Eight works better. They have a QTS and an FS that's similar to the typical 12" prosound woofer, maybe even a 15".

So you basically get the output of a prosound FLH, but in a smaller footprint. There's a price to pay, which is lower efficiency.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> Agreed. I really like the Alpine Type R eights for tapped horns, but for front loaded horns, the TC Sounds Epic Eight works better. They have a QTS and an FS that's similar to the typical 12" prosound woofer, maybe even a 15".
> 
> So you basically get the output of a prosound FLH, but in a smaller footprint. There's a price to pay, which is lower efficiency.


would it be worth getting one of the custom spec'ed eminence built woofers, that were purpose built for horn use, or something like the Alpine would also work for a snail?

I have an old issue of speaker builder with the plans for the Siamese Snail, that was a long time ago, lol... Think it was from '98!


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## Patrick Bateman (Sep 11, 2006)

Here's some pics of the horn coming together.
As noted earlier in the thread, I'm using wood that's 3.75 times thinner than what's typically used in a subwoofer. (It's 0.2" thick.)

Due to the extremely think wood, I'm using an insane amount of cross braces, basically the entire subwoofer is a matrix of braces.

That's also the reason that all of the angles are 90 degrees. If they weren't it would be really difficult to make everything line up.


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> would it be worth getting one of the custom spec'ed eminence built woofers, that were purpose built for horn use, or something like the Alpine would also work for a snail?
> 
> I have an old issue of speaker builder with the plans for the Siamese Snail, that was a long time ago, lol... Think it was from '98!


I think if you're going to do a FLH, the Fitzmaurice plans and cabinets are tough to beat.

My horn ended up a lot like the AutoTuba, but with two changes:

1) I'm using a much more expensive driver than the MCM
2) The footprint is designed to fit on my back seat
3) I'm using 0.2" wood instead of 0.75"

If these requirements aren't important to you, I'd just build an AutoTuba.

Note that those speaker builder articles were written by the same dude.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> I think if you're going to do a FLH, the Fitzmaurice plans and cabinets are tough to beat.
> 
> My horn ended up a lot like the AutoTuba, but with two changes:
> 
> ...


the siamese snail had the PVC ports, I don't know if you know the one I'm talking about, it used the backwave to load the horn I think?

I wonder if the horn craze had just begun to take off, when he did those designs or if the complexity of the snail was just too much for the average DIY to attempt.

It looks like the tapped horn craze took over the esoteric horn designs because of it's simplicity and effective output.

I've still got my DecWare Imperial plans, and a stack of 3/4" cabinet ply, just haven't brought myself to build them.. although they would work great on a Mardi Gras float!

do you plan on glassing the shell of your horn, semi-monocoque construction?


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> the siamese snail had the PVC ports, I don't know if you know the one I'm talking about, it used the backwave to load the horn I think?


Yep. Bill has mentioned a few times that venting into the horn throat doesn't work. It was a failed experiment.

The reason it doesn't work is that the gain from the horn swamps the output of the vent.

So you basically get all of the bad parts of a vented box (steep rolloff) without adding much SPL.

Bill did those before hornresp existed, so we didn't understand horns as well back then.

If you want the output from the rear of the cone, probably better to do a TH or a BLH.



cajunner said:


> I wonder if the horn craze had just begun to take off, when he did those designs or if the complexity of the snail was just too much for the average DIY to attempt.
> 
> It looks like the tapped horn craze took over the esoteric horn designs because of it's simplicity and effective output.
> 
> ...


Probably not. If the box 'buzzes' a lot I'll do it, but it seems quite rigid.


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> Yep. Bill has mentioned a few times that venting into the horn throat doesn't work. It was a failed experiment.
> 
> The reason it doesn't work is that the gain from the horn swamps the output of the vent.
> 
> ...


funny how far things have come along..

those siamese snails reminded me of the Klipsch La Scala.

I've heard La Scalas in a dance club, suspended with no boundary loading and they still managed to sound good, back in the eighties.

of course, the time of boom permeating the club with huge subs hadn't come around just yet, down on the bayou..

how much gain you think you'll get out of that snail, in the 50-100 hz region?


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## Patrick Bateman (Sep 11, 2006)

cajunner said:


> funny how far things have come along..
> 
> those siamese snails reminded me of the Klipsch La Scala.
> 
> ...












Due to Hoffman's Iron Law, one Epic 8 in a horn loaded cab produces about as much output as six Epic 8s in a sealed box. (The graph above is for four in a sealed versus the box I'm building, with the same amount of power for both sims.)

The foot print for both is about the same.

The sealed enclosure has more maximum output, but also costs $900 :O

Though the efficiency of six sealed and one horn loaded is similar, the sealed gets louder because it has more displacement and higher power handling.

But watt for watt? It's about the same.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Both Qes and Qms have Fs in their terms including Mms. So a higher Fs will allow you a lower Mms to keep the numerator in the factions about the same...and Re is a factor there too- the TC has a lower Re and the B&C.
> 
> The motors are roughly the same strength, but for the calculations you square the terms, so differences get larger.


I just leave everything to my WT2.
But I looked up the formula and I don't see MMS in the calculation for QMS or QES:

mh-audio.nl - Measuring Loudspeakers

Not saying it's not there; it's very possible that you can infer the parameters from the others. I know hornresp offers that.


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## cajunner (Apr 13, 2007)

that can't be right... 





it increases area in steps, there's no smooth graduated wave...

is it not really important, if you're dealing with subwoofer frequencies only?

That the wavelengths are so long they don't notice the stepping, and end up with a relatively smooth response?


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## Patrick Bateman (Sep 11, 2006)

No need for angles. Just get the length and the volume right.










This is the layout for the sub that was originally in my car, and now sits here underneath my chair. Works great. All angles are right angles.

I think the 180 degree bends are a little iffy; a fraction of the wavefront will get reflected back when it hits the bend.

This isn't a huge deal with one bend, but in the box above *eighty percent of the bends are 180 degree bends.*


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## thehatedguy (May 4, 2007)

Thiele/Small - Wikipedia, the free encyclopedia


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## cajunner (Apr 13, 2007)

and that works?

looks a lot simpler than a lot of horn layouts I've seen.

I think I would have built a couple of these easy horns if I had known that they were feasible.


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## cajunner (Apr 13, 2007)

thehatedguy said:


> Thiele/Small - Wikipedia, the free encyclopedia


very informative, hadn't read that concise list of definitions before.

thanks for posting, the large signal section is good.


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## thehatedguy (May 4, 2007)

See the Mms term in the numerator now?


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> See the Mms term in the numerator now?


Yep.

So you could increase MMS by 25% and as long as FS is reduced by 20%, *QES would stay the same.*

That's interesting, because it actually gives me another reason to use woofers with small voice coils. (I've noticed that small voice coils reduce inductance, and that widens bandwidth. Less wire in the voice coil = less inductance.)

Obviously there's a point of diminishing returns, but it definitely makes a case for using cheap drivers in some situations, particularly if you're not using a lot of power.

On the flipside of this argument, it also makes a case for using large woofers with large voice coils when you ARE running a lot of power.

Basically I could see some scenarios where you might want larger voice coils for your midbass than for you subwoofer. For instance, in my home theater I use multiple subs. Due to this, it's hard to find space for all the subs. Right now I have one in a corner, one up on a shelf, and my tapped horn is basically a raised platform for the chair that I work in front of the computer on:


















Since there are multiple subs, and each one is getting a fraction of the power that would go to a single sub, *it might be a good idea to use small voice coils.* Because small voice coils can't take a lot of power, but it *does* appear that they would lower QTS, which is useful in a horn.[/b]

OTOH, the speakers that are currently in my living room have a single midbass per side, so one might want to use a larger voice coil, to keep up with the power handling of the subwoofer array.


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## cajunner (Apr 13, 2007)

you need stable motor force to apply the kind of pressure a horn demands.

That said, you *could* decrease voice coil diameter, and keep motor size the same, resulting in more motor force but at the expense of stability.

I mean, if we're talking about going from a 1.5" coil in an 8" driver, to a 2" coil, that's not that big of a change. But go down to 1" coil, and you start to get away from that geometry that supports a cone with the larger tube, to one that may deform in a tight gap and rub or fail.

Even so, it looks like you need a pretty decent motor to do horns nowadays, probably because the bar has been raised, technology supports really novel motor strategies.

when I think of a strong motor I think of Lowther's design, but at 1mm Xmax, it's not that useful to put on a horn woofer.

Maybe the answer is in a front/back motor on a horn, where you can double motor strength in a small diameter cone area.

That would allow you to decrease the Qts of the motor while fitting inside a tight compression chamber, unlike that humongous Epic 8.

I would go so far as to do it with neo-radial motors, so it can be compact yet have that high BL over stroke.

like, take the 8" shallow Aura, and put another motor on the back side. 


that would be a powerful, yet compact presentation with legitimate Xmax and linearity, and really low intrinsic inductance numbers.


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## luisc202 (Oct 29, 2013)

subd


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## Patrick Bateman (Sep 11, 2006)

Patrick Bateman said:


> Here's some pics of the horn coming together.
> As noted earlier in the thread, I'm using wood that's 3.75 times thinner than what's typically used in a subwoofer. (It's 0.2" thick.)
> 
> Due to the extremely think wood, I'm using an insane amount of cross braces, basically the entire subwoofer is a matrix of braces.
> ...


^^^ You can see from my pics from earlier this week that I went kinda nuts with the crossbraces.

Last night I hooked up the sum to an amp for the first time. *The results were a bit disappointing.* The bass is melodic, there's no real buzzes or rattles... but the efficiency was terrible.[/b] Even with the amp cranked to 100% the system could only be called 'polite.'

I was really starting to freak out. In twenty years of building sub boxes, I don't think I've EVER built a sub that was this time consuming. I've literally invested about thirty hours into this box, and it's only 80% done.










Here's a graph that shows the simulated response of the horn, along with the impedance. In this graph, you'll notice three deep impedance peaks. They basically occur at octave intervals, beginning at 38hz.

*Each one of these dips is a frequency where the horn resonates.* At those dips, the horn draws maximum power from the amplifier, and that's why horns are so loud. It's almost like a vented box, but with multiple resonances. (Again, the phase is different.)

This is the whole reason we build these big complex heavy boxes. A vented box resonates at one frequency, and it's 180 degrees out of phase. *A horn resonates at multiple frequences, and they're only 90 degrees out of phase.*

The thing that sucks about these enclosures is that they're easy to screw up. A buzzing panel or a leak in the box will screw it all up.










^^^ Here's an example of how you can screw up a horn. The orange impedance curve is an 8" woofer in a sealed box. *The red line is my hastily assembled autotuba clone, using the exact same woofer.* You'll notice it doesn't have the deep dips that you see in the Hornresp sim.

Because the dips aren't deep the woofer won't draw a lot of power.
This probably explains why I was able to dump what *appeared* to be a crapton of power into the MCM. Basically if the horn was airtight it would have been getting about 800 watts, but since it wasn't, it was only getting about 200.

(Here's the link to that discussion, from nearly five years ago, after I built my Autotuba 'clone': http://www.diymobileaudio.com/forum/849405-post60.html)





Anyways, I didn't intend for this post to take an hour.

To make a long story short, my new horn is quite sturdy, and it doesn't SEEM to be leaking. I'll need to run some impedance sweeps to be sure.



The main problem, it turned out, was my crappy Dayton amp. I have one of those Dayton Class T amps on my workbench, the ones that are *supposed* to make 100 watts. Turns out that's more like 20 watts, and THAT is why the sub was so quiet. I swapped out the Dayton for a Class D sub amp and the new sub got plenty loud.

*phew*


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## Patrick Bateman (Sep 11, 2006)

Here's some more pics of the horn coming together.









Here's the plan that I made in Xara




























^^^ Here's some pics of the sub coming together. There are a LOT of braces so it's kinda difficult to see the layout.









Compression ratio is about four to one. The gap in front of the sub is just 1", just enough to accommodate the 3/4" of xmax.










Halfway through the project it occured to me that cross-shaped braces were the easiest to build.



















Cats <3 subwoofers.


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## Hanatsu (Nov 9, 2010)

Holy crap... what an advanced enclosure.


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## Patrick Bateman (Sep 11, 2006)

Aargh. I don't think I've ever been so frustrated with a car audio project.

This is literally the most time consuming subwoofer I've ever built, *and it simply doesn't work.*

I had a three day weekend and I nearly spent every waking hour on this stupid sub. There's probably sixty hours invested in this box, because it's so hideously complex.

I'll upload some data and a post-mortem, but it looks like this box is a bust.
Basically it's supposed to be about 5-10dB more efficient than a single eight in a sealed box. Unfortunately, my measurements show that it's not even as efficient as a plain ol' ported box. And it doesn't sound good either.


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## Hanatsu (Nov 9, 2010)

That's too bad with all that work ;(


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## cubdenno (Nov 10, 2007)

So there is no taper to the passage? or am I missing what you did? Did you account for that in hornresp?


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## cubdenno (Nov 10, 2007)

Plus are you sure all that bracing isn't causing issues? It looks like you are running varying dimentional ports. pictures aren't clear.


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## Patrick Bateman (Sep 11, 2006)

Hoffman's Iron Law rules over all, so I'm going to do some quick stats on the two boxes I have here.

The first box is my sad failed horn sub experiment. It's 3.75 cubic feet.
The second box is my trusty Kef sub, from my home theater. It's 1.27 cubic feet.

I'm considering doing another horn sub, but this time using a Sonotube. I have a 20" diameter Sonotube onhand, that's 32" long. That works out to a whopping 5.8 cubic feet.

The Sonotube approach has some advantages:

1) The main reason that I want the "box" to be light is that I want the whole system to be removable. Basically I have a four seat car but I barely use my car at all. 95% of the time my family uses my Hyundai Genesis, my Mazda6 is barely used at all. *So I want a sub that can be yanked out of the car at a momen't notice, in the event I need to haul four people.*
2) A Sonotube is lighter than a conventional box.
3) A Sonotube can be rolled.
4) One big concern of mine is that a big heavy plywood box on the back seats could leave a permanent impression. One way to reduce that possibility is with a lightweight box. But a Sonotube should be less susceptible to this problem, due to the shape.


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## Hanatsu (Nov 9, 2010)

You seem very fond of these horn subs. Ever tried building a pure transmission line? Can those be modeled in Hornresp? A TL sounds a lot like a sealed box but more "effortless" somehow. TH subs sound more "live" if I would describe it with words. The efficiency of a TL would be close to sealed though, so it might not be very interesting for you. Dunno how the typical phase response looks in a TL either.


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## Patrick Bateman (Sep 11, 2006)

cubdenno said:


> Plus are you sure all that bracing isn't causing issues? It looks like you are running varying dimentional ports. pictures aren't clear.


Here's my hunch on why this box and my Triple 8 box were ****ing disasters:









^^ This is a clone of a Danley TH-Mini. I made something similar, *and it's probably my favorite sub.* It's five cubic feet and it's tuned to 50hz.









^^ This is my 'Super Autotuba.' A disaster of a project. It's 3.75 cubic feet and it's tuned to 38hz.

*I think the main issue I'm having is a combination of high pressure, crummy construction, and horn losses.*

What I'm about to type is just a theory, so if this doesn't make sense, please correct me 

Okay, let's think about what's happening in a ported box and in a horn. *At certain frequencies, the subwoofer box is suppressing the motion of the cone, and then the box is making sound, not the woofer.* For instance, in a ported box tuned to 30hz, *the combination of the port, the box, and the subwoofer are making sound at 30hz.* If everything works out right, the subwoofer cone simply does not move at the tuning frequency.

*** Now what happens if there are leaks, or if the panel flexes? ***

If that happens, your resonance is basically gone. For instance, if you have a ported box with a leak, *the more it leaks, the less it's going to act like a ported box.*









Easiest way to picture this is a wine glass. If you hit the right frequency, you can break it via it's resonance. *But what if you applied some Dynamat to the glass?* As you can imagine, it would damp the resonance, and it wouldn't be possible to excite the resonance fully. The same thing is happening with my horn. Due to leaks and wall flex, it's not resonating like it should.

So, *that* is the first part of the puzzle. If you're building a ported box, or any type of horn, that box needs to be as tight as a drum. And due to my crappy construction, and the complexity of the box, I didn't fulfill that requirement.

*** Now why did my TH-Mini work alright, but my 'Super Autotuba' worked like crap? ***

I think the answer to THAT question is PRESSURE. The 'Super Autotuba' and the 'Triple 8' exert higher pressure, for a number of reasons. First, the woofer is smaller. Due to the smaller woofer, it has to move further to reach the same SPL as the twelve that's in my TH-Mini clone. IE, to generate the same pressure, it has to move further. The second reason is that the box is smaller. The TH-Mini is about five cubic feet, the 'Super Autotuba' and the 'Autotuba' are a bit under four cubic feet. So, again, they need to generate more pressure to hit the same SPL. (Because there's simply less air in the horn.) The third reason is that the Autotuba and the Super Autotuba are tuned to a lower frequency than the TH-Mini. *Due to the lower tuning, the Super Autotuba generates nearly double the pressure at tuning than the TH-Mini, for the same SPL.*

The last part of the puzzle, and this is something that I don't think is well understood, is the difference between front loaded horns and everything else. If you look at the TH-Mini, you'll notice that it's facing high pressure when pushing INTO the box, but low pressure the other way. In a front loaded horn, *the pressure is higher going in AND going out.* As the cone goes in, it's pushing against a sealed box. As the cone is going out, it's pushing against the horn.

This is different than a tapped horn because in a tapped horn it's basically pushing against nothing as the cone moves out.

I'm not entirely sure what the effect of that would be, but it *seems* that the cone is subject to much higher pressure.




I'll post some data soon.
In my measurements, I found that some very basic things made a difference of SIX DECIBELS. That's like quadrupling your power! For instance, wrapping the enclosure in saran wrap made a huge difference in output. (Which would confirm that there are leaks.)

It's a bummer, because I can't imagine that I am the only person who's built a horn that leaks. And if I'm getting losses of as much as six dB, then other people are too, and they probably don't realize that they're not getting the full potential of their box.


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> You seem very fond of these horn subs. Ever tried building a pure transmission line? Can those be modeled in Hornresp? A TL sounds a lot like a sealed box but more "effortless" somehow. TH subs sound more "live" if I would describe it with words. The efficiency of a TL would be close to sealed though, so it might not be very interesting for you. Dunno how the typical phase response looks in a TL either.


Yeah I used to build TLs before I got into horns.
I had a TL with dual Dayton DVC 12s in my silver Accord for a while, around 2005ish.
My main gripe with them is pretty much what you describe; they sound a lot like a sealed box but they're a lot more work.
I prefer the impact of horns to TLs.


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## Patrick Bateman (Sep 11, 2006)

^^ Here's a sim comparing the Alpine SWS-10D2 in a five cubic foot front loaded horn, versus my 'Super Autotuba' which featured a TC Sounds 8" in a 2.1 cubic foot horn. *I did the sim at one watt into the first sub, versus four watts into the second sub.* The Alpine is much louder because it is also much bigger.

So I think I might build this thing. It's going to be BIG but that's what it takes to get loud.


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## Patrick Bateman (Sep 11, 2006)

Here's some pics of the new horn coming together.









First off, I'll post a diagram of the horn soon. But it's basically set up like pieces of pie, or like slices in an orange. It's a big sonotube and the horn path consists of 'slices' of the circle.





































Here's the throat of the horn.
No, I didn't INTEND to build The Vagina Horn.
It was an accident.














































The bottom half of the sonotube is the sealed part of the box. (Front loaded horns are basically a sealed box firing into a horn.) This horn includes a 'coupling chamber' which does a couple things here. First, it rolls off the high frequencies. Second, it reduces the amount of compression. (I wanted to minimize compression since leaks were such a huge issue with the 'super autotuba' project.)


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## Hanatsu (Nov 9, 2010)

"Vagina horn" rofl.

Looks interesting. Can you post a FR plot how it performs in the car after you're done? 

Sent from my Samsung Galaxy 3 via Tapatalk.


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## thehatedguy (May 4, 2007)

A 15 or two on a removable baffle in the trunk is looking better and better I bet. Not a lot of space, light weight, easy to build, and lots of displacement.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> A 15 or two on a removable baffle in the trunk is looking better and better I bet. Not a lot of space, light weight, easy to build, and lots of displacement.


Agreed. I have a couple of TC Sounds fifteens gathering dust in the garage, and throwing them into a simple sealed box has some nice benefits:

1) Dead simple construction
2) The main reason I'm trying a front loaded horn is I want a lot of 'impact.' Basically a FLH and a sealed box can pressurize a car in a way that a vented box or tapped horn can't. (Because it's literally compressing the air in the car.) But two fifteens in a sealed box might do that better, because they move so much air, due to their sheer size.

But i'm definitely learning a lot in this project. If someone had told me that it's possible to make a horn that's LESS efficient than a vented box, I wouldn't have believed them. But it's true! The rigidity of the horn and airtight construction is SO IMPORTANT, it can literally add five or even ten decibels of output.


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## thehatedguy (May 4, 2007)

Oh, I wasn't even talking about building a "real" sealed enclosure...lol. Just a removable IB setup if you needed to take it out of the car.

I know what you mean by the impact. While I love IB because it is easy to build, I have never found the impact attack of a sealed box has. Which makes me want to experiment with EQing the IB setup to mimic the roll off of a sealed box on the bottom end to see if I could recreate that midbass impact a sealed box has.


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## cubdenno (Nov 10, 2007)

Patrick Bateman said:


> Agreed. I have a couple of TC Sounds fifteens gathering dust in the garage, and throwing them into a simple sealed box has some nice benefits:
> 
> 1) Dead simple construction
> 2) The main reason I'm trying a front loaded horn is I want a lot of 'impact.' *Basically a FLH and a sealed box can pressurize a car in a way that a vented box or tapped horn can't. (Because it's literally compressing the air in the car.)* But two fifteens in a sealed box might do that better, because they move so much air, due to their sheer size.
> ...


Is there any measurements that agree with this statement. I have seen you type this before. 

I would think a simple pressure sensor would be an easy validation for this. 

Don't get me wrong, In a sealed chamber, I would say it makes more sense. But a vehicles interior is far from sealed so the compression does not happen like we think it would. 

Isn't the term lab sensor a simple pressure sensor?


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## cubdenno (Nov 10, 2007)

thehatedguy said:


> Oh, I wasn't even talking about building a "real" sealed enclosure...lol. Just a removable IB setup if you needed to take it out of the car.
> 
> I know what you mean by the impact. While I love IB because it is easy to build, I have never found the impact attack of a sealed box has. Which makes me want to experiment with EQing the IB setup to mimic the roll off of a sealed box on the bottom end to see if I could recreate that midbass impact a sealed box has.


Just use a high pass filter. pretty much what the sealed enclosure does.


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## cubdenno (Nov 10, 2007)

Patrick Bateman said:


> Halfway through the project it occured to me that cross-shaped braces were the easiest to build.


I agree that it's possible that the thickness could contribute to the losses, I really think it's your bracing that really screwed up the response. There is to much restriction with those small holes


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## Patrick Bateman (Sep 11, 2006)

cubdenno said:


> Is there any measurements that agree with this statement. I have seen you type this before.
> 
> I would think a simple pressure sensor would be an easy validation for this.
> 
> ...


Logically, it would seem that anything with a sealed back chamber will pressurize the car more. These designs include sealed, front loaded horns, and single reflex bandpass.

The reasoning is simple:
*If the car is perfectly sealed, the subwoofer will change the air pressure in the car.* As the cone moves OUT the pressure will increase, as the cone moves IN the pressure will decrease.

Now, obviously this is all theoretical, because a car ISN'T perfectly sealed.

But I haven't built a front loaded horn in half a decade, so this gave me an excuse to.

Danley new BC412 subwoofer - YouTube
^^^ This video from Danley was a bit of an inspiration. In the video the subwoofer blows out a candle from a distance of two feet. It's a front loaded horn; one of the few that the company sells. Most of their subs are tapped horns. Theoretically, FLHs should have an easier time doing this than a FLH.

I've been running tapped horns for quite some time now, and subjectively, they don't "hit" the way that other subs do. Basically you can feel the air vibrate, but it doesn't punch you in the chest.

I want that 'hit in the chest' effect.


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## cubdenno (Nov 10, 2007)

My single 15 will punch your chest. it dislodged a friends kidney stone, And when in a ported enclosure, I will see how far it will blow out a candle. I am betting 2 feet is doable. I know it had no problems blowing out a lighter at at least a foot.

That chest punch feeling is upper bass. So bigger midbass drivers and a great 60-200 response. This is why i think so many people love the "sound" of a sealed sub in a car. The sub starts rolling off around 60 hertz. The 20-40 hertz region does not overwhelm the upper bass like it can do in a ported enclosure tuned to 30-40 hertz. To have it all (low bass pressurization and chest impact) you have to have solid midbass drivers or the sub playing higher than the usual 80 hertz we all use as the standard starting point.


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## Patrick Bateman (Sep 11, 2006)

cubdenno said:


> My single 15 will punch your chest. it dislodged a friends kidney stone, And when in a ported enclosure, I will see how far it will blow out a candle. I am betting 2 feet is doable.


We've all seen 'hair trick' videos, where an SPL car blow dries someone's hair. In that scenario, the entire car is basically a dual reflex bandpass box, and the window of the car is the port.

Blowing out candles in a 10,000 square foot auditorium with 20' ceilings is trickier than doing it inside a car 



cubdenno said:


> I know it had no problems blowing out a lighter at at least a foot.
> 
> That chest punch feeling is upper bass. So bigger midbass drivers and a great 60-200 response. This is why i think so many people love the "sound" of a sealed sub in a car. The sub starts rolling off around 60 hertz. The 20-40 hertz region does not overwhelm the upper bass like it can do in a ported enclosure tuned to 30-40 hertz. To have it all (low bass pressurization and chest impact) you have to have solid midbass drivers or the sub playing higher than the usual 80 hertz we all use as the standard starting point.


I agree. It's one of the reasons I'm using a relatively high F3, about 35hz, and I'll likely run the sub all the way to 200hz. IMHO any modern sub with shorting rings or an underhung voice coil is good to 250hz, even 1khz in some cases. (The Alpine Type S are very odd drivers; cheap but underhung. The Type Rs are overhung but have an aluminum shorting ring.)


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## cubdenno (Nov 10, 2007)

Have you ever built this? Lower tune but handles an 8 or ten. 1 sheet 1/2" ply. Great for music. In car with the Alpine or Sundown, should easily approach 140db

Lilmike's Cinema T-6


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## Patrick Bateman (Sep 11, 2006)

I need a name for this thing.
Vaginahorn?
The Depth Charge?

This pic shows the scale of it, compared to my Kef sub, which is 1.25cf









Here's one way I found leaks in the box. I used an LED light from Ikea and shined it into each chamber. If everything is working right, the light will only go ONE way - into the adjacent chamber. If there's a leak, you'll see 'pinholes' of light where the leaks are.

Very handy.









The top and the bottom panels are not even glued in, but I couldn't resist the chance to run some measurements. In this pic you can see there's a *significant* gap. (Obviously I'll fill this in once the whole thing is sealed up.)



























^^^ Here are three impedance plots. The first plot is the PREDICTED impedance of The Super Autotuba. The second is the *measured* impedance of the Super Autotuba, after I braced it, covered it in fiberglass, ran over it with a fine tooth comb looking for leaks. The last measurement is The Depth Charge Horn, with a leaky top and bottom plate. Here's what I see in these measurements:

1) Even with a slavish attention to leaks and rattles, my Super Autotuba never had a deep resonance at 38hz. [b]Without that deep resonance, you're losing TONS of output.[/b] You can see in the impedance plot why it was no louder than a vented box; at 38hz it's only drawing a fraction of the power that the amp can provided.
2) Even with some really obvious leaks, The Depth Charge Horn is already resonating at 42hz. Hopefully, sealing off the sub will drop the resonance and give me those three deep troughs that will draw gobs of power from the amp.

[/font]


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## Patrick Bateman (Sep 11, 2006)

cubdenno said:


> Have you ever built this? Lower tune but handles an 8 or ten. 1 sheet 1/2" ply. Great for music. In car with the Alpine or Sundown, should easily approach 140db
> 
> Lilmike's Cinema T-6


The subwoofer I'm sitting on is fairly close to a mirror image of that. It was originally intended for my Accord, but then I sold it, which is why it ended up in my living room.









Here's the T-6









Here's the sub I'm sitting on. Basically the same fold, but rotated ninety degrees. I'm using the Alpine Type R instead of the Exodus Audio Anarchy because the Type R delivers more output. I'm using push-pull because it lowers distortion.


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## thehatedguy (May 4, 2007)

I know...I just haven't seen anyone comment on actually doing it and being convinced it is like a sealed enclosure, and I don't have anything in the car at the moment to try it myself.



cubdenno said:


> Just use a high pass filter. pretty much what the sealed enclosure does.


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## Patrick Bateman (Sep 11, 2006)

I made a big breakthrough yesterday.
Remember how frustrated I was, because I spent sixty hours building a four cubic foot subwoofer, only to find that it was no louder than my tiny little Kef sub?
It turns out there was a problem with my measurements. Here's the story:

Yesterday I was measuring that big ass sonotube sub. The one that's the size of a barrel. And guess what my measurements said? *They said this six cubic foot horn was no louder than my 1.25cf Kef.*









^^ here's a measurement of the two subs at one meter. *see how the measurements are almost identical below 100hz?* This makes NO SENSE. Due to Hoffmans iron law, the bigger sub should be SIGNIFICANTLY louder. The Hornresp sims say it should be 5-10dB louder. 

At this point there were three option:
1) set both subwoofers on fire
2) tie my ankle to the subwoofer and throw myself off a bridge
3) get a second opinion

I strongly considered option one, but opted for three. 









Here's a measurement of the tiny Kef sub, and my new 'Depth Charge' horn. See the difference in output? About five to ten decibels, *exactly what Hornresp predicted?*










So here's what I think happened here:
I believe that the program that I normally use to measure speakers is scaling the measurements. For instance, if you measure a speaker that's ninety dB, then measure one that's 100, it scales both measurements to zero. (Check out the first graph, and note how the maximum SPL of both measurements is almost exactly the same. 

WAY ANNOYING.

To confirm my hypothesis I did the following:
1) I measured a speaker in Arta with the amp turned up to five
2) I repeated the measurement at a volume of 2.5
3) then I did the exact same thing with HolmImpulse

Thus test confirmed my fear: in Arta the two measurements were virtually identical. In HolmImpulse they differed by about five decibels. Which confirmed that Arta was scaling its measurement. 

By the way, the SHAPE of the two measurements in thus thread are different because one was done at one meter and the other was done at one inch. I did a measurement in Arta at 1" but I didn't save it. The peaks and dips in the Arta measurement are due to the influence of the room.


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## Patrick Bateman (Sep 11, 2006)

I'm sure a LOT of people have wondered why I invest so much effort into these horn subs and these synergy horns. God only knows it would be a LOT easier to throw that sub into a ported box and be done with it. 

To my ears, horns are great at percussion, intelligibility and dynamics. The difference is not subtle. When I was barely twenty years old I built a bandpass box with a couple of Blue Thunder tens, and I remember how the synthesized machine gun percussion on 'Eye of The Beholder' sounded completely different than a ported sub.* So this obsession isn't new - I've been hooked on this sound for a looooong time. I built about four different variations of that sub, and I remember the owner of the local stereo shop in San Bernardino kept telling me to just throw in the towel and build a ported box. They just sounded muddy to me.




























Here's the frequency response and phase of the Kef and The Depth Charge. The latter is definitely louder. But the thing that really grabs my attention is that phase plot. If you're listening to a bass guitar at 40hz, there's going to be harmonics at 80 and 120hz. In the Kef ported box, the second harmonic is a hundred and forty degrees out of phase. (Look at the pink curve, and note that 40hz is at 145 degrees and 80hz is at five degrees.) *in the Depth Charge Horn, the second harmonic is 35 degrees out of phase!* (Look at the blue curve, and note that 40hz is at zero degrees and 80hz is at -35 degrees.) That's a HUGE difference IMHO, and might explain why horn sound subjectively tighter to me. Their fundamentals and their harmonics are closer together in time. In a ported box, there is a large variance. My calculator says that 145 degrees of phase rotation at 40hz is equivalent to a hundredth of a second. Can everyone hear a timing difference of 0.01 seconds? I don't know. I can. A quick google search indicates that people can hear a timing difference of 0.007 seconds. So ten milliseconds is nearly fifty percent above this threshold. 

TLDR: I personally like the tightness, intelligibility and dynamics of horns. Google says humans can perceive a timing difference of seven milliseconds. The measurements above demonstrate that the Kef ported box has a time delay of ten milliseconds at 40hz, in comparison to the harmonic at 80hz. The Kef is also five to ten decibels quieter, yielding a dynamic advantage to my Depth Charge sub.


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## Patrick Bateman (Sep 11, 2006)

i am no expert at analyzing an impulse response. I know that Dunlavy and Vandersteen obsess about it. I have a set of Vandersteens in my living room. 









Here's the impulse response of a Dunlavy sc-iv, a speaker that's popular in recording studios, and designed to be time coherent. 

















Here's the impulse response of the Depth Charge Horn, and my 8" Kef Ported sub. 
*Check out the symmetry and the shape of the first impulse?*

I'm not exactly sure WHY the horns impulse is so much better than the ported box. Is it the phase response? Possibly. But there's no mistaking that the horn's decay is much closer to ideal.


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## cajunner (Apr 13, 2007)

in another way of describing what you're saying, a horn presents a static load at any frequency in the horn, to the driver.

a port is essentially another speaker, doing it's own thing and relatively confined by the resonant energy excited by the cone's resonance, from the Qtc of the box.

the "springiness" of the horn, is like a parabolic curve compared to the vent, which is like a square wave battering the air inside the enclosure at exactly the same frequency, dictated by the cone's physical measurements of mass and ringing.

so the horn would be acting on the cone in a much more uniform fashion, and present a much less diabolic, and more parabolic force inside the box, and consequently, on the speaker's cone.

that's what I'm thinking when you show the differences in the impulse response, you have the horn decay essentially an even energy distribution and the vented box is mucked up. Like the horn is analog, and the vent is digital in nature, one mimics the way sound decays in the natural environment and the other is a disconnect.


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## Hanatsu (Nov 9, 2010)

Experiment; EQ the vented and the horn to the same response. Measure again, would be interested in how the phase response looks then. 

Sent from my Samsung Galaxy 3 via Tapatalk.


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## thehatedguy (May 4, 2007)

Build Your Own Q-Pie Bass Horn - diyAudio

Looks like it could work using the back deck/rear glass.


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## Patrick Bateman (Sep 11, 2006)

My wife will definitely leave me if this appears in my living room


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## cajunner (Apr 13, 2007)

Patrick Bateman said:


> My wife will definitely leave me if this appears in my living room


but the numbers are good, it's only got 135 degrees of bend...


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## Hanatsu (Nov 9, 2010)

Patrick, can't you start a "how to build a successful TH-mini sub" thread  ? 

Messed with hornresp and a few drivers but I don't comprehend it fully yet... everything I model appear to become huge and the low-end seem to be non-existent. Not possible to build a TH in the size of a "larger" vented box with some output below 40Hz?


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## thehatedguy (May 4, 2007)

Nope, not really possible.


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## Hanatsu (Nov 9, 2010)

thehatedguy said:


> Nope, not really possible.


Sucks :<


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## thehatedguy (May 4, 2007)

I haven't seen one.

Not one that used a driver worth (IMO) to use as a sub.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Nope, not really possible.


Oh c'mon now!
Ported boxes and sealed boxes are probably capable of more sheer output, as long as you have unlimited power.

But if you *don't* have unlimited power, or you have a thing for tight bass, horns are tough to beat. Due to their efficiency advantage, a single 8" woofer in a horn is about as efficient as two twelves. Now, admittedly, the box is about as big as a dual 12" ported sub. So there's no free lunch, you can't escape Hoffman's Iron Law.

If I wanted to make a really small tapped horn sub I'd probably look far and wide for a 6.5" woofer with as much xmax as possible, a nice BL curve, and an FS around 40hz or so. The Exodus Audio Anarchy is the obvious choice, but I still prefer the Alpine 8". 
















The cone on the two woofers is about the same size, the Alpine just has a larger flange and deeper motor to accomodate it's higher xmax. Long story short, the Alpine doesn't need a box that's much bigger but it will produce about twice as much output.

I re-ran my subwoofer measurements, with EQ, as Hanatsu requested. *And the phase response is even better.* This FLH may just be the 'tightest' sub I've ever built.

I had to tear up the sealed part of the sub because it was generating a huge amount of pressure, and it was rattling a bit. But besides that, this project is going splendidly. (knocks on wood.)

I'll post the new phase measurements (with EQ) later today.


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## thehatedguy (May 4, 2007)

I haven't seen a TH that could get below 40 in an enclosure that could fit a 12. You would need 2.5-3 cubic feet on the very minimum to get that kind of extension. You could load a lower 80 dB sensitive 6 in there and pick up the sensitivity to where a 12 would already be...and go lower, be easier to build, and louder.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> I haven't seen a TH that could get below 40 in an enclosure that could fit a 12. You would need 2.5-3 cubic feet on the very minimum to get that kind of extension. You could load a lower 80 dB sensitive 6 in there and pick up the sensitivity to where a 12 would already be...and go lower, be easier to build, and louder.


All true.
But the horn will have higher efficiency and better phase.

So pick your poison:

1) sealed : easy to build, excellent phase, needs a lot of power, smallest box
2) ported : nearly as easy to build, terrible phase, doesn't need a lot of power, second smallest box
3) tapped horn : hard to build, phase is nearly as good as sealed, sometimes better, doesn't need a lot of power, second largest box
4) front loaded horn : hardest to build, phase is nearly as good or better than sealed, doesn't need a lot of power, largest box


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## thehatedguy (May 4, 2007)

You of all people should know how it pains me to say bad things about horns...you like them as much as I do.

lol


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## Hanatsu (Nov 9, 2010)

Patrick Bateman said:


> All true.
> But the horn will have higher efficiency and better phase.
> 
> So pick your poison:
> ...


As far as I understand, what we want is a flat group delay to cover the fundamental + harmonics. If we use let's say a vented box in the range where GD remains somewhat flat and compensate the absolute delay with T/A against mids wouldn't that give us the same effect?

Sent from my Samsung Galaxy 3 via Tapatalk.


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## cubdenno (Nov 10, 2007)

From what I understand, for subs, group delay is not as important. Especially the lower you go.


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## MetricMuscle (Sep 16, 2013)

Patrick Bateman said:


> Here's my cheezy model of a 2014 Mazda6. The driver is mounted underneath the rear deck, inside of the trunk. Output of the woofer feeds into the car. *You could do the same thing across the rear deck, like in a conventional car, but you'll get more horn loading if you use the rear window for part of the path.*
> 
> https://lh4.googleusercontent.com/-...AAAAAAGN0/alFfabjcCS0/s800/mazda6-horn-01.jpg
> 
> ...


What would happen if the woofer was mounted vertically on a more narrowly tapered horn section that extends below the rear deck? Essentially rotate the woofer in the picture above clockwise around the rear most point of the mounting flange. It would mount to a vertical baffle panel which is one side of the horn. The panel opposite the baffle panel will taper up and forwards to meet the top of the back seat.

- The horn will be longer.
- The woofer will not be mounted horizontally which allows for sag.
- The woofer cone will not be facing upwards towards the glass and sun.

- This will take up more room in the trunk.
- Will this just improve an IB configuration or will it add other problems?

The back glass in my sedan is at a 20 degree angle to the rear deck.
The rear deck is around 18" deep and over 48" wide.


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## thehatedguy (May 4, 2007)

I think that is what he was working on with his last project.

The thing is you can not load a bass horn in a car, there isn't enough air to load the throat...and you can not separate the horn from the interior of the car, so you are just sitting inside the throat of the horn.

That's just my opinion.


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## MetricMuscle (Sep 16, 2013)

I went to a couple of those links posted on how to configure the sections taper, area and length etc. but didn't really get it. Is there a Cliff's Notes version or simpler approach?
Would a horn for a 15" woofer be HUGE?

In a couple of IB threads folks have posted that they installed the woofer in a manifold mounted under the rear deck so as not to have it mounted horizontally, for sag reasons and maybe some other fitment issues. Would a tapered horn shaped manifold have any advantages and/or would it's dimensions have to be figured out for each specific application?
I would be building it this way for reasons other than maximizing SPL.
- Better, more protected location for woofer to live, no sag issues.
- I've read a horn has less distortion due to the panel in front of the cone compressing it's output, IIRC.
- Since the back glass forms a horn shaped configuration anyway, it might be advantageous to start the path correctly.


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## thehatedguy (May 4, 2007)

Actually with horns, the larger the speaker the shorter the horn needs to be. Horns are an area progression from (almost) a finite point. The size of the speaker determines where you start at on that area progression.


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## cajunner (Apr 13, 2007)

I look at professional mid bass horns, and they're pretty short, all things considered.

the pressurization of the cabin below the Schroeder frequency, can add to a horn's output.

this frequency isn't absolute, there are overlapping resonant tones by directional waves.

Paolo's News - SOUND IN A CLOSED ENVIRONMENT - INTRODUCTION

it's interesting that a car's interior can be like a horn, I remember putting a box with 2 eight's, in an enclosure firing down into the hatch of a '96 Camaro and there was room on the front and back of the box, to let the sound "grow" out of it and it wanged for what it was, but there was a resonant note around 65 hz, that I attributed to the hatch glass making up a natural horn and amplifying the sound. 

so, I don't believe that the horn is useless in bass frequencies, but the harmonics of a 40 hz horn is easily "acoustic levered" to an increased gain, which could make one believe the horn was contributing at all frequencies affected by the horn.


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## thehatedguy (May 4, 2007)

http://www.diymobileaudio.com/forum...had-patrick-bateman-pwk-horn.html#post1505765

There are midbass horns that I used in my house in the back seat of my old car...one horn. It was an 80 hertz horn, and it was about 3/16th sized.

How is that not large?

A horn in a car does not work for bass. There is not enough air inside the car to load the throat of a horn for those frequencies. Anything below the Fc of the horn just blows right through the horn with no gain, and considering how small the rear chambers are in these horns, you aren't going to get much output there.


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## cubdenno (Nov 10, 2007)

thehatedguy said:


> http://www.diymobileaudio.com/forum...had-patrick-bateman-pwk-horn.html#post1505765
> 
> There are midbass horns that I used in my house in the back seat of my old car...one horn. It was an 80 hertz horn, and it was about 3/16th sized.
> 
> ...


Building a 6 cubic foot horn called the T-6 Cinema for my daughter. Uses a Sundown E10. It's for her room. I am going to throw it in my car for a quick listen. I am wanting to see how it stacks up to in car response.

Going to post pics of the build in the HT section and may have some pics in the car.


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## Patrick Bateman (Sep 11, 2006)

thehatedguy said:


> Actually with horns, the larger the speaker the shorter the horn needs to be. Horns are an area progression from (almost) a finite point. The size of the speaker determines where you start at on that area progression.


The 'horns' that we build in the real world are actually just quarter wave resonators. 









That's why you see these periodic spikes in the frequency response; basically the 'horn' is too small, so it's only working at certain frequencies.

If the bass horn was full size, you wouldn't get these peaks, but it would also be the size of the entire car.

Once you accept that it's just a quarter wave resonator, you can make them much smaller than a 'true' horn, and you can also reduce the box size by using a smaller driver. This is because a smaller driver will produce less pressure at the throat, which means the response will be smoother.


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## Patrick Bateman (Sep 11, 2006)

Patrick Bateman said:


> i am no expert at analyzing an impulse response. I know that Dunlavy and Vandersteen obsess about it. I have a set of Vandersteens in my living room.
> 
> 
> 
> ...


Here's a video of the sub playing outside

https://www.youtube.com/watch?v=1jJQhF25URE

As silly as this sounds, I haven't hooked it up to an amp in the car yet. I used it as the sub at my wedding last Saturday.

The video does a pretty good job of showing the integration with the mains. The whole thing was completely set up 'by ear' so it could probably use some fiddling at the xover point and maybe a little delay for the mains.


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## Patrick Bateman (Sep 11, 2006)

This is what happens when I leave horns in the house.


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## Jscoyne2 (Oct 29, 2014)

Patrick Bateman said:


> This is what happens when I leave horns in the house.


1. Lol

This thread is interesting but goes really in depth into something i barely understand. I do have a question i'd like answered if you could. For the sake of simplicity. Lets just use the idea of 1 sub. Do you think you would net a gain in spl from mounting an IB sub in the rear deck vs mounting them in a traditional trunk wall set up?

This is assuming all rigidity and sealing was done correctly. This is purely a horn question and not so much on build process or issues with back deck rigidity.










VS










Ignore size and multiple subs.


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## Patrick Bateman (Sep 11, 2006)

Assuming that both setups are equally sealed, the trunk wall setup will win because the woofer sags when it's mounted vertically. The 'sag' isn't a huge difference, but it costs you about a dB of maximum output.

If you want maximum output from minimum space in a car, go with a manifold setup. Car trunks are REALLY big, so you can basically cram in as many woofers as you can fit. There's no need to worry about not having enough air space, the only limiting factor is displacement.

BTW, I've been thinking about 'putting my money where my mouth is' and doing a couple of eighteens in a manifold for my Mazda. I've been rockin' a SWS-15 in a tapped horn for well over a year, but I'm getting kinda tired of having nearly no trunk space.


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## Jscoyne2 (Oct 29, 2014)

I was reading about 15s or 18s in a tire well with a 6in hole cut into the bottom. Seems interesting and i guess has worked. What ur opinion 

Sent from my SGH-M919 using Tapatalk


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## zacjones99 (May 11, 2009)

Jscoyne2 said:


> I was reading about 15s or 18s in a tire well with a 6in hole cut into the bottom. Seems interesting and i guess has worked. What ur opinion
> 
> Sent from my SGH-M919 using Tapatalk


I've been wondering about doing that too... This gentleman seems very happy with his setup.

https://www.youtube.com/watch?v=NLsvAVM_vxA

He's not using a sedan so cabin gain will be different. His setup is pretty linear from 10hz to 35hz in the front seat, then it dips quite a bit. So firing into the floor in a larger vehicle is good if you only need 35hz and below. I wonder what kind of frequency response people are seeing with standard trunk baffle setups... do they get flat usable response up to 60hz?


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## Patrick Bateman (Sep 11, 2006)

A member on the forum asked to buy the subs from this project about four months ago. I finally carved out some time to extract them from this subwoofer box. It took about four hours to cut them out, and another hour or two to measure them and figure out what it would cost to ship them.










Unfortunately, I'm not a merchant, and I don't get discounts. It's nearly $100 to ship these things. 

So I won't be able to sell them to the person who wanted them originally. But if you're in SoCal, they're up for grabs. 

I paid $200 for the pair. I lost the gaskets a million years ago, so I'd say they're worth about $180 now. (For the pair.)

I'm not in a big rush to sell these, because they're pretty awesome, but thought I'd put them out there since I put in the effort to clean them up. I currently use TC Sounds in my home theater and I'm a big fan. TC Sounds R.I.P.



















I measured the Thiele Small of each driver to be sure they work as expected. Pictured above.


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## Theslaking (Oct 8, 2013)

zacjones99 said:


> I wonder what kind of frequency response people are seeing with standard trunk baffle setups... do they get flat usable response up to 60hz?


I have 3 10s (TC Sounds)IB rear deck and run them 15-60. I get these to rumble the car at 15hz. I don't get nothing nasty out of them until about 75ish. But they are real comfy under 60.

They really play low well with this setup. That was my surprise as this is my first IB install.


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## Patrick Bateman (Sep 11, 2006)

Theslaking said:


> I have 3 10s (TC Sounds)IB rear deck and run them 15-60. I get these to rumble the car at 15hz. I don't get nothing nasty out of them until about 75ish. But they are real comfy under 60.
> 
> They really play low well with this setup. That was my surprise as this is my first IB install.


I really like them. I currently have one TC Sounds 12" (Eclipse), two eights (Soundsplinter), and two fifteens (TC Sounds).

My only real grip is that you can't really hear them, you just FEEL them, because they're so damn clean. I sometimes consider replacing them with something that has some distortion lol!

In my home theater there's three subs:

1) a tapped horn with dual Alpine eights

2) a vented box with a cheap Orion 12"

3) a bandpass box with dual TC fifteens

The Orion is the easiest to localize. Then the Alpine. With the TC sub, it's seriously difficult to tell if it's even on. It's right behind the couch and you can't hear it at all, you just feel it, the array of subs flexes the walls.

I sincerely think that TC Sounds largely went kaput because their subs are just so darn clean. People don't like clean.


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## Patrick Bateman (Sep 11, 2006)

If anyone's interested in taking them off my hands, here's some videos showing the thiele small params that I measured today:

https://youtu.be/M89yN220hF0

https://youtu.be/ndL6S3Q0DrA


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## Theslaking (Oct 8, 2013)

I couldn't agree with you more about TC Sounds. I have over 20 different of their subs. The original 8" was the most impressive sub I've owned. The hands down best subwoofer ever made to me is the SW8000. It's linear coil, tc9 variant motor, and 30 mm of xmax is simply amazing. It has to have 400w + to sound right but when it does it will rip your vehicle apart at 15hz then play up to 90hz in the same stroke. All while giving out zero distortion or even getting warm. To me the sub was unbelievable. I did SPL comps for years and never seen another 10 do that. But the downfall is/was the sub is huge, heavy, and power hungry.

Aw-well those days are gone ......


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## dcfis (Sep 9, 2016)

Theslaking said:


> I have 3 10s (TC Sounds)IB rear deck and run them 15-60. I get these to rumble the car at 15hz. I don't get nothing nasty out of them until about 75ish. But they are real comfy under 60.
> 
> They really play low well with this setup. That was my surprise as this is my first IB install.


How is everyone only getting 60hz out of ib? I'm crossed at ~100 and would take the additional midbass spl but it gets localized and thick on piano and guitar is not down to near flat by 165/70


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## ciaonzo (Feb 5, 2009)

Patrick Bateman said:


> I'm not in a big rush to sell these, because they're pretty awesome, but thought I'd put them out there since I put in the effort to clean them up.


*edit 

Nevermind, I see the drivers in the video.


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## Theslaking (Oct 8, 2013)

dcfis said:


> How is everyone only getting 60hz out of ib? I'm crossed at ~100 and would take the additional midbass spl but it gets localized and thick on piano and guitar is not down to near flat by 165/70


I feel like mine played lower better not necessarily higher. I only needed it to get to 70 so I didn't really try.


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