# One of The Reasons Your Midbass is Anemic



## Patrick Bateman (Sep 11, 2006)

Over on Facebook there was a discussion about anemic midbass.

Facebook isn't a great forum for technical discussion, there's not enough space to post a proper reply. So here goes:

When two sources of sound are one quarter wavelength apart, they'll reinforce each other, and when they're half a wavelength apart, they'll nullify each other. This is how transmission lines work; basically we separate the front and the back wave by one quarter wavelength, to make it louder _at one narrow band of frequencies._










Here's an example of this in action.

A typical sedan is about six feet wide, and the cabin is about 54" wide, or 1.37 meters wide.

The width of the cabin leads to two critical frequencies:

At 63hz and below, the two midbasses will reinforce each other.

At 126Hz, the two midbasses will be out-of-phase.

IE, the sound from your LEFT midbass radiates to the right side of the car, and when it arrives at the right side, the RIGHT midbass is 100% out of phase with the wavefront radiated from the LEFT, and vice versa.

A typical midbass is high passed at 80Hz, so this means that your midbass has a big ol' null right where you'd want it the least, at the very bottom of it's bandwidth.

Note that this isn't an "all or nothing" thing. It's not like we have a suckout that's super narrow at 126hz. It basically means that our left and our right midbass will _augment_ each other as the two approach 63hz, but as you travel an octave higher, they'll interfere with each other.

One thing that's a bummer about waves, is that when two waves augment each other you get 6dB more output, but when they interfere with each other you get a null. IE, _destructive interference is a way WAY bigger problem than constructive interference._ With destructive interference, you can potentially have no output whatsoever at a given frequency. Of course, in the real world, that rarely happens. But you WILL see dips that can be as big as 10-15dB.

If you've ever wondered why those speakers you have on your desk have nice midbass and they're tiny, while the speakers in your car are twice as big and aren't as punchy, the answer is geometric.










On top of all that, we also have cabin gain kicking in at around the same frequency. (I'll get into cabin gain in the next post.)


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## Patrick Bateman (Sep 11, 2006)

Cabin gain is (fairly) simple:










The way that horns work, for the most part, is that they take sound and radiate into into a narrower beam. For instance, 500Hz is 24" long (0.6 meters) so when a horn has a mouth that's bigger than that, all the frequencies above 500Hz are radiated into a narrow beam. This raises the output on axis. Basically you have the same amount of energy radiated into a smaller space. You can get crazy high efficiencies because the space is so much smaller. For instance, if you reduce the angle of radiation from 180 degrees to 90 degrees, your efficiency goes up 6dB, which is like quadrupling your amplifier power. If you reduce it from 360 degrees (radiating in all directions) to 90 degrees, you get a 'bump' of 12dB.

*In a car, it's like you're sitting inside of a bass horn.*

For instance, 60Hz is 18.75 feet long (5.7 meters.) Due to that size, the wave is constrained by the size of the cabin.


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## Patrick Bateman (Sep 11, 2006)

If your subs are in the trunk, and your midbass is in the doors, there's going to be a significant delay between the subs and the door speakers.

For instance, my Accord is over SIXTEEN feet long. Subs in the trunk are about eight feet away from the door speakers.

So, let's do the math:

140Hz is eight feet long. But the critical frequencies are at one-half-wavelength and at one-quarter-wavelength.

1) at one-half-wavelength, the sub will be out of phase with the midbasses. This frequency occurs at 70Hz in my Accord, but your frequency will depend on the distance from your subwoofer to your midbass.

2) at one-quarter-wavelength and below, the output of the sub will augment the output of the midbass, because the two speakers are nearly in phase with each other. This means that the subwoofer will augment the midbass at 35Hz and below. Of course, this is fairly meaningless, because your door midbasses aren't generating much output at 35Hz.


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## Patrick Bateman (Sep 11, 2006)

If all of this is making your head hurt, it should, it's hideously complex.

In a nutshell, the octave from about 80hz to 160hz is a freaken' mess. We have one midbass cancelling out the other midbass, we have the sub cancelling out the midbass, and then we have a tremendous amount of _constructive_ interference that starts to happen below 80hz.

It's this weird car audio paradox, where it's ridiculously easy to produce gobs and gobs of output in the two octaves from 20 to 80Hz, but producing sound between 80 and 160Hz is a bit of a nightmare.

There are about a hundred different ways to fix this:

1) The simplest solution by far is to simply use REALLY BIG midbasses and lots of EQ and just power through it.

2) We know that the left and the right midbass will be out-of-phase at a specific frequency based on the width of the car. Due to this, we can use asymmetrical high pass filters. Basically the high pass filter introduces a delay. By making them asymmetrical, we can improve the midbass on one side of the car at the expense of the other side. The asymmetrical slopes move the null from one side of the car to the other. You will never get this right without a microphone, so go buy one and tinker with this. Thanks to Erin H on the FB group for mentioning this solution.

3) We know that the left and the right midbass will be out-of-phase at a specific frequency based on the width of the car. So you can use an all-pass filter to introduce a delay to one speaker. I believe Audiofrog may have a patent on this, so do your research before you go and use this solution.

4) You could use DSP delay to address it. Note that DSP delay works across all frequencies, so if you improve things at one frequency, it will likely degrade things at another.

5) You could use multiple midbasses.


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## dgage (Oct 1, 2013)

Good stuff Patrick. Thanks for the nice summarion and thanks to you and ErinH for the potential solutions. 

I hadn’t thought of an all-pass filter but that is interesting and one I might have to play with. 

I’m assuming multiple midbasses would bring about their own issues even if they’re right next to each other.

I’m thinking of rebuilding the bottom of the door panel in my Acura TL to be an enclosure for an 8”.


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## ckirocz28 (Nov 29, 2017)

Patrick Bateman said:


> 3) We know that the left and the right midbass will be out-of-phase at a specific frequency based on the width of the car. So you can use an all-pass filter to introduce a delay to one speaker. I believe Audiofrog may have a patent on this, so do your research before you go and use this solution.


I'm pretty sure they can't patent all-pass filters or their usage for this or any other purpose, they could patent a one button midbass "fix" in their dsp software that uses all-pass filters for the fix. But this midbass problem is a perfect fit for an all-pass filter.
Multi Sub Optimizer kind of does this sort of fix of midbass and bass using any eq or crossover type you tell it to use, although I haven't tried it for anything, yet.


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## dgage (Oct 1, 2013)

I haven’t tried an all pass on the midbass but would that really fix both sides or just one seat?


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## ckirocz28 (Nov 29, 2017)

dgage said:


> I haven’t tried an all pass on the midbass but would that really fix both sides or just one seat?


Most likely, just one seat, but that's why dsp's have different selectable presets.


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## tonny (Dec 4, 2010)

OR just fix it with one mono midbass in the centre off the car

Playing those frequenties at least up to 150 mono is no problem in most cases even for SQ competition....


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## bnae38 (Oct 3, 2015)

I have a fairly narrow apf on my right midbass to address this at about 170hz. It works to fix the null but I often wonder if it's worth it since it seems to affect staging a bit.


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## Patrick Bateman (Sep 11, 2006)

dgage said:


> I haven’t tried an all pass on the midbass but would that really fix both sides or just one seat?


It depends 

The "conventional" solution to fixing the center image in a car is to use delay.

Delay affects _all_ of the frequencies.

But, realistically, it might be better to only delay the frequencies that are _really_ out of phase.

This is one of those subjective things where you really need to try it and see which solution you prefer.

Here's an example:

Let's say you have a sedan, and in your sedan the left speaker is 51cm closer than the right speaker. The "traditional" solution would be to delay the left speaker by 1.5 milliseconds. The reason that this works is that sound travels 34cm in one millisecond, so delaying the left speaker puts the soundstage in focus.

But here's another solution, pioneered by Audiofrog. (Andy, chime in if I got this wrong.) We know that the left speaker is 51cm closer. 333hz is 102cm long. (speed of sound is 34,000cm per second, which means that 333Hz is 102cm long.) Because of the path length difference, we know that the biggest issue with the midbass in our car is going to occur at 333Hz. Basically at that frequency, the left and the right midbass are out-of-phase. This is because the pathlength is 51cm, 333hz is 102cm long, therefore the left and right are out-of-phase at 333Hz.

Therefore, one solution, instead of using DSP delay, is to use an all pass filter on ONE side that's centered at 333Hz. Basically delay it about one quarter wavelength (0.75 milliseconds) so that the left and the right side are no longer out-of-phase at 333Hz.

This solution probably won't sound as awesome as traditional DSP delay, but it won't wreck the soundstage as badly for the passenger. It's basically applying delay at the frequency where the pathlength difference is most offensive.

And if all of that makes sense, you can see why there's a lot of good reasons to try and equalize your pathlengths as much as possible. Basically the closer you get to equal pathlengths, the lower in frequency you can apply the delay, which will make the left AND the right seat sound more consistent.


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## dgage (Oct 1, 2013)

Good stuff guys. 

Can you guys speak to multiple midbasses? I know in home audio, if you keep the drivers within half the cone diameter, they act as one. But with the short path lengths in the car, I don’t think that is necessarily the case. Has anyone played with multiple midbasses in the car? Maybe 3 5.5” instead of an 8”.


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## ckirocz28 (Nov 29, 2017)

dgage said:


> Good stuff guys.
> 
> Can you guys speak to multiple midbasses? I know in home audio, if you keep the drivers within half the cone diameter, they act as one. But with the short path lengths in the car, I don’t think that is necessarily the case. Has anyone played with multiple midbasses in the car? Maybe 3 5.5” instead of an 8”.


It's actually based on quarter wavelength distance, not cone diameter. Coupling is the term for that effect. And, for the same reason it could help with low frequency nulls (pathlength differences), it will also hurt imaging/staging. But I haven't tried it, and T/A may correct the imaging/staging while still helping with nulls.
I just think the all-pass approach is better all around.


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## 209555 (May 3, 2019)

Stop making my brain hurt. 

Thanks for the write-up. I'm brand new to active with DSP and am putting together a system as we speak. I need to learn everything I can between now and sometime next month when I turn the power on for the first time.


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## ckirocz28 (Nov 29, 2017)

Gen5.7Max said:


> Stop making my brain hurt.
> 
> Thanks for the write-up. I'm brand new to active with DSP and am putting together a system as we speak. I need to learn everything I can between now and sometime next month when I turn the power on for the first time.


The brain pain is far from over my friend, it's just getting started, welcome to DSP land! Just go ahead and plan to spend several hundred hours of quality time with your dsp, and buy a battery charger.


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## ckirocz28 (Nov 29, 2017)

And an inverter to keep your laptop plugged in in the car.


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## 209555 (May 3, 2019)

ckirocz28 said:


> And an inverter to keep your laptop plugged in in the car.


Damn, I didn't even think about a battery charger! Makes sense. May as well test and tune without burning tank after tank of fuel. I had no idea it would take so long to dial it in. Do you have any suggestions? I am converting to LTO. I have 18 Yinlong cells for a total of 120ah of Lithium. This chemistry likes to rest at a little above 14V. What would you recommend? I'm buying a DC power supply as well, I suppose I could just build a lead to the battery with a plug and use that?


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## 209555 (May 3, 2019)

I'll delete my posts so as not to clutter the thread after ckirocz28 responds.


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## ckirocz28 (Nov 29, 2017)

Gen5.7Max said:


> Damn, I didn't even think about a battery charger! Makes sense. May as well test and tune without burning tank after tank of fuel. I had no idea it would take so long to dial it in. Do you have any suggestions? I am converting to LTO. I have 18 Yinlong cells for a total of 120ah of Lithium. This chemistry likes to rest at a little above 14V. What would you recommend? I'm buying a DC power supply as well, I suppose I could just build a lead to the battery with a plug and use that?


I don't know about LTO, but check NOCO chargers, they're pretty damn good and may have a setting that works for those.


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## ckirocz28 (Nov 29, 2017)

Gen5.7Max said:


> Damn, I didn't even think about a battery charger! Makes sense. May as well test and tune without burning tank after tank of fuel. I had no idea it would take so long to dial it in. Do you have any suggestions? I am converting to LTO. I have 18 Yinlong cells for a total of 120ah of Lithium. This chemistry likes to rest at a little above 14V. What would you recommend? I'm buying a DC power supply as well, I suppose I could just build a lead to the battery with a plug and use that?


It doesn't have to take that long to tune, I was kind of joking, kind of.


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## 209555 (May 3, 2019)

ckirocz28 said:


> It doesn't have to take that long to tune, I was kind of joking, kind of.


I understood your sarcasm. I also understand it will take some time, especially because I am a perfectionist. My OCD and pathologically fastidious nature is going to turn it into 100hrs whether I want it to or not, I'm just ignoring that part right now and focusing on the build. I don't even have a mic yet or downloaded REW. I'm staying as blissfully ignorant of all that until the very last minute!


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## 209555 (May 3, 2019)

Just checked the edit function to delete posts. Not there? How do I delete this tangent?

Edit: Maybe a mod can delete posts #15-22 please?


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## Focused4door (Aug 15, 2015)

dgage said:


> Good stuff guys.
> 
> Can you guys speak to multiple midbasses? I know in home audio, if you keep the drivers within half the cone diameter, they act as one. But with the short path lengths in the car, I don’t think that is necessarily the case. Has anyone played with multiple midbasses in the car? Maybe 3 5.5” instead of an 8”.


I have done it testing, but not as a permanent install. I tried as many as sixteen 3.5" midbass, in various places. Since it wasn't a permanent install I also tried lots of not practical locations. It works, but you are going to need multiple channels of DSP and amplification. You don't necessarily need a big midbass, nor do you need a lot of per channel power.

If I ever do it as a permanent install, I think it would be worth trying as an simple underseat or under dash line array. Wouldn't be perfect, but would be far easier.

Patrick has some really good threads on midbass arrays, worth a search.



tonny said:


> OR just fix it with one mono midbass in the centre off the car
> 
> Playing those frequenties at least up to 150 mono is no problem in most cases even for SQ competition....


Unfortunately it isn't that easy, as it can collapse the sound stage. It is like the opposite of the Opsodis setup, which is worth reading up on if you really want to try a center only midbass.

Everything about car audio is a trade off and a compromise.


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## tonny (Dec 4, 2010)

Focused4door said:


> Unfortunately it isn't that easy, as it can collapse the sound stage. It is like the opposite of the Opsodis setup, which is worth reading up on if you really want to try a center only midbass.
> 
> Everything about car audio is a trade off and a compromise.


I have a centre midbass for almost a year now, and it works perfect and absolute no collapse off the stage, als long as you have mid on the corners in stereo that play down to inbetween 125/150hz, below that the wave lengts are to large to fit in the car and create a good stereo midbas.... This setup I have now gives me much more left and right balance in the lower mid and midbass area then I ever had in any off my cars with kick's or door builds or so.


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## Bnlcmbcar (Aug 23, 2016)

Patrick Bateman said:


> Therefore, one solution, instead of using DSP delay, is to use an all pass filter on ONE side that's centered at 333Hz. Basically delay it about one quarter wavelength (0.75 milliseconds) so that the left and the right side are no longer out-of-phase at 333Hz.
> 
> This solution probably won't sound as awesome as traditional DSP delay, but it won't wreck the soundstage as badly for the passenger. It's basically applying delay at the frequency where the pathlength difference is most offensive.


Hey Patrick,

What happens when instead of using TA or an All Pass Filter and simply employ a phase shift.

I was exploring the sengpielaudio phase calculator (I believe ErinH posted it somewhere)






Phase angle calculation time delay frequency calculate phase lag time shift between voltage difference time of arrival ITD oscilloscope measure two signals formula angle current voltage phi phase shift time difference - sengpielaudio Sengpiel Berlin


Phase shifting phase angle time delay frequency calculation phase lag time shift between voltage calculate phase difference time of arrival ITD oscilloscope measure two signals formula angle current voltage phi phase shift phi time difference - Eberhard Sengpiel sengpielaudio




www.sengpielaudio.com





It calculates in order to accomplish a .75ms delay at 333hz the phase shift needed would be 89.91 degrees or ~90 degrees on a DSP.

*It would be ~180 degrees to delay 1.5ms









Would this solve the null at 333hz but cause another in a different octave?

Definitely not as precise a solution as employing an All Pass Filter filter, I just want to understand more the shortcomings of just employing phase shift to addreas the null.


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## minbari (Mar 3, 2011)

isnt this the idea behind using TA? (which is really just adjusting the phase of the speaker across all freqs) you cant fix every freq peak or null but if you can de-emphasise the worst one, then it can sound pretty good.


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## josby (May 8, 2011)

Patrick Bateman said:


> There are about a hundred different ways to fix this:


Will angling the mid-basses toward the listeners alter the null frequency (at the listener's head, that is)? And if so, how much angle would it take to shift the cancellation up or down to a less bothersome range?


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## ckirocz28 (Nov 29, 2017)

Let's just give up on these elegant eq/ta solutions and just use 12 inch midbasses with 500 watts each.


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## dgage (Oct 1, 2013)

josby said:


> Will angling the mid-basses toward the listeners alter the null frequency (at the listener's head, that is)? And if so, how much angle would it take to shift the cancellation up or down to a less bothersome range?


Angling down in the door or pointing in the kick panel won’t help with the nulls. It probably would help if you were able to put something like Illusion C6 coaxials up on the dash.


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## dgage (Oct 1, 2013)

ckirocz28 said:


> Let's just give up on these elegant eq/ta solutions and just use 12 inch midbasses with 500 watts each.


That’s a little overkill I think. A 10” should be fine.


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## Jscoyne2 (Oct 29, 2014)

Ran two 10s from 20-150hz on 150rms. I straight up didn't need a sub.

Sent from my XT1710-02 using Tapatalk


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## Patrick Bateman (Sep 11, 2006)

dgage said:


> Good stuff guys.
> 
> Can you guys speak to multiple midbasses? I know in home audio, if you keep the drivers within half the cone diameter, they act as one. But with the short path lengths in the car, I don’t think that is necessarily the case. Has anyone played with multiple midbasses in the car? Maybe 3 5.5” instead of an 8”.


I don't think I can see any scenario where I'd ever use a single midbass per side. There's just so many advantages to multiple midbasses.

First off, two midbasses will generally be about 3dB more efficient with twice the power handling. Even if you don't need that, it will still have more headroom. Third, it allows you to get the impact of a larger midbass without turning your car door into swiss cheese. For instance, two 6.5" midbasses have about as much output as an 8" midbass.

There is nearly no impact to stage depth if you run one 6.5" midbass in the door and another in the firewall. But if you're worried, you can simply attenuate the midbass in the door, and it will basically sound like you're only using the midbass in the firewall. (But you'll still have higher output and power handling.) For instance, if you have two woofers and each one is playing 90dB, they sum to 96dB. But if you reduce the power to ONE woofer by half, _you still have 94.649dB._ IE, even cutting the power on one by half, the sum of the two is STILL much louder than one. (Total dB level adding of coherent correlated sound sources combining decibels or SPL sound pressure level audio logarithmic decibel scale loudspeaker add signal noise levels incoherent noncoherentt - sengpielaudio Sengpiel Berlin)

But the biggest 'bang for the buck' by far is that multiple midbasses smooth out the frequency response and the impulse response. For instance, if the geometry of your car is creating a big null at 125Hz, if you add another midbass, the additional midbass will 'fill in' the null because the pathlength is different. 

In most cars with multiple midbasses, people generally put them side-by-side, but I personally prefer to put them about a quarter of a wavelength apart. This one is super tricky because a lot is going to depend on how high the midbass is playing. If you have a three-way stage up front and the midbass is only playing form 80-320Hz, then you can spread them quite far apart because the wavelengths are so long. (320Hz is over a meter long.) If you're front stage is a two-way, multiple midbasses get super tricky, because *the higher you need the midbass to play, the closer together they need to be.[/i] For instance, with a crossover point of 1500hz or 2khz, multiple midbasses largely won't work (unless they're small and packed tightly.)

Basically it all boils down to how high you want the midbass to play.

Subjectively, I find multiple midbasses to sound smoother and I find that it's harder to determine where they're located. Basically our brains 'fuse' together the two sounds as if they're one.*


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## seafish (Aug 1, 2012)

I am curious if mounting dual mid basses vertically, within a quarter wavelength of each, would still help eliminate nulls??? .... or only still add to output??


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## dgage (Oct 1, 2013)

Thanks for that Patrick. So it sounds like you have a lot of experience running multiple midbasses in a car, is that correct? For my home theater mains, I have 2 12” pro audio midranges in my speakers to (try to) keep up with the efficiency of the horn-loaded compression driver. Works great but of course at those distances, the speakers have the same path lengths. In a car, say two midbasses in the lower door, one midbass will be closer to another. So I guess that means I need to have 2 more channels of amplification and DSP To have the most control over them. Sounds like something to look at as I also like running multiples to share the load, which means better sound quality (lower distortion) running two drivers instead of working one harder.


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## dgage (Oct 1, 2013)

seafish said:


> I am curious if mounting dual mid basses vertically, within a quarter wavelength of each, would still help eliminate nulls??? .... or only still add to output??


What Patrick is saying is, regardless of orientation in the doors (though mounted close) will have slightly different pathlengths to your ears. These slightly different pathlengths will have slightly different nulls in the car, which when combined, will partially improve upon each others nulls. Between 4 midbasses, the nulls should be largely attenuated, at least compared to 2 drivers. Now I think one of the issues is that these slightly different pathlengths may result in midbass that is ever so slightly less accurate (on time) than a single pair of midbasses, which is where Patrick’s idea of attenuating the nearest midbass comes into play. Definitely something more to play with so wouldn’t be for someone trying to keep it simple, which is also a goal in audio; use the fewest drivers to most easily reproduce the frequency range. In this case, extra midbass drivers are meant to combat the unique nulls of a car audio environment.


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## Luis Rivera (Jan 8, 2020)

tonny said:


> I have a centre midbass for almost a year now, and it works perfect and absolute no collapse off the stage, als long as you have mid on the corners in stereo that play down to inbetween 125/150hz, below that the wave lengts are to large to fit in the car and create a good stereo midbas.... This setup I have now gives me much more left and right balance in the lower mid and midbass area then I ever had in any off my cars with kick's or door builds or so.


 Hi just wondering if its possible to get a pic on the center mono midbass your talking about and what size midbass your using and how much power or if it's sealed or ported would love to try this pretty please??


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## Patrick Bateman (Sep 11, 2006)

dgage said:


> Thanks for that Patrick. So it sounds like you have a lot of experience running multiple midbasses in a car, is that correct? For my home theater mains, I have 2 12” pro audio midranges in my speakers to (try to) keep up with the efficiency of the horn-loaded compression driver. Works great but of course at those distances, the speakers have the same path lengths. In a car, say two midbasses in the lower door, one midbass will be closer to another. So I guess that means I need to have 2 more channels of amplification and DSP To have the most control over them. Sounds like something to look at as I also like running multiples to share the load, which means better sound quality (lower distortion) running two drivers instead of working one harder.


I mean, even at home I can't think of many good reasons to run a single midbass. My current project :






Nexus - World's Easiest Controlled Directivity Loudspeaker


Here's Nexus 3 on it's baffle Here's the polar response WITH a baffle and without. The addition of a baffle makes the beamwidth significantly wider, about 25% wider. Without a baffle, the beamwidth is about 110 degrees, WITH a baffle it appears to be about 135 degrees. (I only measure out...




www.diyaudio.com





But that project is definitely pushing the limits of how much bandwidth you can squeeze out of an array of midbasses. Even I was shocked that I could run four midbasses up to 1khz.


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## dgage (Oct 1, 2013)

Patrick Bateman said:


> I mean, even at home I can't think of many good reasons to run a single midbass.


I was actually saying the opposite, it makes a lot of sense to run multiple midbasses at home since you can minimize pathlength differences to a negligible amount. 

In a car where you’re closer to the midbass drivers, pathlength differences are a potential real issue but one worth pursing due to the nulls in a car audio environment.


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## seafish (Aug 1, 2012)

dgage said:


> What Patrick is saying is, regardless of orientation in the doors (though mounted close) will have slightly different pathlengths to your ears. These slightly different pathlengths will have slightly different nulls in the car, which when combined, will partially improve upon each others nulls. Between 4 midbasses, the nulls should be largely attenuated, at least compared to 2 drivers. Now I think one of the issues is that these slightly different pathlengths may result in midbass that is ever so slightly less accurate (on time) than a single pair of midbasses, which is where Patrick’s idea of attenuating the nearest midbass comes into play. Definitely something more to play with so wouldn’t be for someone trying to keep it simple, which is also a goal in audio; use the fewest drivers to most easily reproduce the frequency range. In this case, extra midbass drivers are meant to combat the unique nulls of a car audio environment.


But mounting them vertically changes the lobing effects of the multiple speakers and I am wondering if that will enhance or reduce the effect that he is talking about.


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## gijoe (Mar 25, 2008)

My understanding is that lobing isn’t the problem, it’s the dimensions of the car. A vertical orientation won’t be any different than a horizontal orientation. The reason the midbasses need to be within a 1/4 wavelength is to avoid creating destructive interference while trying to fix the null caused by the length, width, and height of the interior.


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## Patrick Bateman (Sep 11, 2006)

The thing that sucks... is that both counts.

I kinda hate doing midbass because my brain has a bad habit of trying seventy different solutions to the same problem (I've literally built a hundred Unity horns.)

And multiple midbasses is one of those things where there's about a hundred ways to 'skin a cat.'

If you arrange the midbasses on the same vertical plane, like 99% of car audio people do, they're largely going to act like a single device.

But I'd argue that there's a lot of reasons you DON'T want them to act like a single device. In particular, if you're trying to fill in that damn null we get due to the cabin dimensions, you DON'T want them close together.

But then you open up a new can of worms, which is that *the further apart they are, the lower the xover point has to be.*

I generally do three-ways (it's not gay in a three way) so I can generally get away with having the midbasses 30-50cm apart.

One "neat" thing that I learned from the Nexus project is that you can stretch the distance further and further when you have more midbasses. IE, with two midbasses your upper limit might be as little as 40cm, but with four it might be as much as 60cm.


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## dcfis (Sep 9, 2016)

Since you only need to go up to 3-400hz if you had a 2 way playing 80hz or so on up would those under seat flat subs like jbl, kicker, pioneer, ect be a solution playing up to 400 or so?


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## gijoe (Mar 25, 2008)

Right, if they are super close together, and act as a single source then you he same null will be there. The way you fix the null is by putting them in different locations, but then you have to worry a out pathlengths, or have separate DSP for each pair.


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## Patrick Bateman (Sep 11, 2006)

dcfis said:


> Since you only need to go up to 3-400hz if you had a 2 way playing 80hz or so on up would those under seat flat subs like jbl, kicker, pioneer, ect be a solution playing up to 400 or so?


I have subs under my seat.

Because our perception of *width* is determined by phase at low frequency, we _really_ want to maximize the time difference between our left and our right ear.

This makes underseat subs tricky. If the sub is right underneath you, then there's an equal amount of energy going to your left and your right ear.

A couple of things I do to address that:

1) I would never use an underseat sub alone. In my car, one sub is under the seat, the other is under the dash. I use DSP delay to get the wavefronts in-phase. Ideally, I should attenuate the underseat sub by 50% or so.

2) I use bandpass subs. This allows me to put the ports as far to the side of the car as possible. The port on the bandpass box is just 10cm away from the edge of the car.


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## Jscoyne2 (Oct 29, 2014)

Patrick Bateman said:


> I have subs under my seat.
> 
> Because our perception of *width* is determined by phase at low frequency, we _really_ want to maximize the time difference between our left and our right ear.
> 
> ...


Do you time align based on farthest driver or do you always consider sub 0 as it has so much modal issues.

Sent from my XT1710-02 using Tapatalk


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## gijoe (Mar 25, 2008)

Another reason to attenuate the under-seat sub is because the tactile feeling of the seat vibrating makes it tough to have unlocalizable bass. If your ass is shaking, that’s a dead give away.


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## Vx220 (Nov 30, 2015)

dcfis said:


> Since you only need to go up to 3-400hz if you had a 2 way playing 80hz or so on up would those under seat flat subs like jbl, kicker, pioneer, ect be a solution playing up to 400 or so?


Most of these have a LPF at 120hz or so, so they won't do midbass


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## Patrick Bateman (Sep 11, 2006)

Jscoyne2 said:


> Do you time align based on farthest driver or do you always consider sub 0 as it has so much modal issues.
> 
> Sent from my XT1710-02 using Tapatalk


I use the tape measure method, with the near sub delayed to meet the far sub. Andy W would know more about this than I do, I'm not an expert on delay at low frequencies.

At midrange and high frequencies I have it down cold, but that's because I build Unity horns, and any kind of phase or delay problem becomes super apparent with those, because all the drivers are so close together and the radiation is symmetrical. (IE, doesn't matter if the mic is on the ground or on the ceiling or on the door, phase is just about identical.)


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## seafish (Aug 1, 2012)

Patrick Bateman said:


> 2) I use bandpass subs. This allows me to put the ports as far to the side of the car as possible. The port on the bandpass box is just 10cm away from the edge of the car.


That said raises yet another question for me...

Does the port exit equal another "speaker diaphragm" that will help reduce the null if the end of the port is placed correctly ??


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## Patrick Bateman (Sep 11, 2006)

Nope, because it's pretty hard to get the ports in a bandpass box really far apart. With a horn you could do something like Voxativ does:



















Or what the late great Terry Cain did.

I've heard both, they sound really awesome. Definitely different than a conventional horn with a single mouth.


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## josby (May 8, 2011)

Patrick Bateman said:


> 2) I use bandpass subs. This allows me to put the ports as far to the side of the car as possible. The port on the bandpass box is just 10cm away from the edge of the car.


This is something I wondered about from your post about the problem caused by a sub in the trunk and the mids in the doors. Could you have the port extend outside of the box and make it longer so its output is much closer to the midbass? IIRC, lengthening a port also requires increasing its cross-sectional area, though,so maybe it wouldn't be possible to extend it very far without its area becoming gigantic.


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## Patrick Bateman (Sep 11, 2006)

josby said:


> This is something I wondered about from your post about the problem caused by a sub in the trunk and the mids in the doors. Could you have the port extend outside of the box and make it longer so its output is much closer to the midbass? IIRC, lengthening a port also requires increasing its cross-sectional area, though,so maybe it wouldn't be possible to extend it very far without its area becoming gigantic.


It would be way easier to align things via DSP


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## Patrick Bateman (Sep 11, 2006)

The 'multiple midbass' idea isn't mine, I largely stole it from Earl Geddes.

Multiple subs in a room smooth out each other's response. In a car, because the 'room' is smaller, the effect is shifted UP about an octave.

For instance, in a room that measures five meters x 2.5 meters, multiple subs will smooth out the response of the octave from about 50Hz to 100Hz. In a car that measures 2.5 meters x 1.25 meters, multiple midbasses will smooth out the response of the octave from about 100hz to 200Hz.

Some observations and simulations are here:


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## seafish (Aug 1, 2012)

Thank you and what a great idea to do a video on this. 
I was avidly watching it and unfortunately your microphone cuts out at 6:28 and never comes back on!
At least AFAICT.


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## Babs (Jul 6, 2007)

So was it my post that sparked the thread where I was lamenting about the difference in phase slopes between left and right sides causing phase to be off at the bottom if I was well timed at the top?










The conclusion was because of placement and car “room” of course and the resulting wraps from left midbass at the seat. And of course the amazing model cancellations such as the usual 150-160hz which the left driver has where it completely dips out. 

I’m still considering trying an APF on left or right side to attempt to not loose alignment at the top but try to mate them up down near the high pass area, allowing better sub integration. From the looks of it, some version 1st or 2nd order in my Helix Pro-2 might be able to possibly induce another wrap (steeper phase slope) on right side (blue) in that 70-160 region. 

At the moment I re-EQ’d and am powering through it, but of course it’s awful sub integration. 

In effort to show my particular example which may be typical or not unusual a couple better shots hopefully:

Wrapped and up wrapped
















Sent from my iPhone using Tapatalk Pro


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## Focused4door (Aug 15, 2015)

Patrick Bateman said:


> Nope, because it's pretty hard to get the ports in a bandpass box really far apart.


Bandpass with multiple passive radiators should work, but I don't know of any software that lets you model a bandpass using passive radiators. 

Polk power port would do it too, but might be hard to put anywhere other than under seat or in a full up custom door panel


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## few35t (Dec 10, 2014)

This is probably a stupid question and I know I'm way out of my league here.. but could this void be filled in with another driver say in the trunk? Specifically an 8" subwoofer that could be band passed to play around that range?


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## ckirocz28 (Nov 29, 2017)

w35t_fg2 said:


> This is probably a stupid question and I know I'm way out of my league here.. but could this void be filled in with another driver say in the trunk? Specifically an 8" subwoofer that could be band passed to play around that range?


It's not a stupid question, and exactly that has been done, with varying locations, and varying results.


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## few35t (Dec 10, 2014)

ckirocz28 said:


> It's not a stupid question, and exactly that has been done, with varying locations, and varying results.


Interesting. I'm currently working on a build in my Civic Type R and have been wondering if I could somehow put the stock subwoofer enclosure to good use. I've got lots of unused amplified channels available after all.


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## ckirocz28 (Nov 29, 2017)

w35t_fg2 said:


> Interesting. I'm currently working on a build in my Civic Type R and have been wondering if I could somehow put the stock subwoofer enclosure to good use. I've got lots of unused amplified channels available after all.


It is preferable to have the midbass up front.


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## ckirocz28 (Nov 29, 2017)

Patrick Bateman said:


> The 'multiple midbass' idea isn't mine, I largely stole it from Earl Geddes.
> 
> Multiple subs in a room smooth out each other's response. In a car, because the 'room' is smaller, the effect is shifted UP about an octave.
> 
> ...


Have you ever used MSO (Multi Sub Optimizer)?








Multi-Sub Optimizer Freeware for Multiple Subwoofers


Optimize bass performance of multiple-subwoofer audio systems. Reduce seat-to-seat frequency response variations.



www.andyc.diy-audio-engineering.org


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## josby (May 8, 2011)

I wonder how much a center-steering upmixer with a center mid the same size as the L and R would help with this. Bass from instruments placed in the center of the soundstage would only play from the center mid, so no constructive/destructive interference. Except with the sub, of course. Same for far-left and far-right instruments. 

You'd still get interference when the placement is anywhere in between left and center or right and center, but I wonder how common that is for bass notes in recordings.


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## Izay123 (Jun 9, 2009)

Does the midbass speakers’ placement control the frequencies of the null and peak? 

What would happen to the null and peak frequencies in a BMW where the midbasses are under each seat? Would the null be higher in frequency because the midbasses are closer together? 

I used a midbass array in my first BMW, putting two 8” midbasses in each front door on 150watts RMS each. During tuning I had to reduce the midbass gain by 6db relative to my 5-1/4” mids on 500watts RMS each. (The second component set in the front doors was not powered; It functioned as a spare set in case I blew something at a competition.)


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## Patrick Bateman (Sep 11, 2006)

seafish said:


> Thank you and what a great idea to do a video on this.
> I was avidly watching it and unfortunately your microphone cuts out at 6:28 and never comes back on!
> At least AFAICT.


What the heck!

I made the video in four clips and assembled them with ffmpeg.

Let me see if I still have the original clips, and I'll re-upload. The video definitely needs audio!


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## Patrick Bateman (Sep 11, 2006)

Bnlcmbcar said:


> Hey Patrick,
> 
> What happens when instead of using TA or an All Pass Filter and simply employ a phase shift.
> 
> ...


All three solutions have drawbacks:

1) With a DSP delay, you're delaying everything by a fixed amount of time. For instance, 200hz is five milliseconds long. So if you use 1.25ms of DSP delay, you'll delay 200Hz by one quarter of a wavelength. At the same time, you'll be delaying 400Hz by one half of a wavelength.

2) With an all pass filter, you're delaying one frequency by a fixed amount of time. For instance, 200hz is five milliseconds long. So if you use a 1.25ms all pass filter that's centered at 200Hz, you'll delay 200Hz by one quarter of a wavelength. At the same time, the other frequencies will be largely intact. (Because the all pass is centered on a single frequency.)


3) With a phase shift, you're delaying everything by a fixed amount of cycles. For instance, 200hz is five milliseconds long. So if you use 90 degrees of phase shift, you'll delay 200Hz by one quarter of a wavelength. At the same time, you'll be delaying 400Hz by one quarter wavelength.

All three options are different, the one that works best for you really depends on if you're using a three-way or a two-way, and where your speakers are located.


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## Jscoyne2 (Oct 29, 2014)

Wasn't this all discussed on a rear fill thread years ago? Just throw some midbass on the rear shelf and delay them the same as any other driver and you now have filled gaps in the FR?

Something about the cone of confusion

Sent from my XT1710-02 using Tapatalk


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## Focused4door (Aug 15, 2015)

Since there is little point to trying to fill a null, I am curious if you simply put a bandstop on the midbass that has a null, and then placed only a second midbass bandpassed to that gap if it would be sufficient.


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## tonny (Dec 4, 2010)

Focused4door said:


> Since there is little point to trying to fill a null, I am curious if you simply put a bandstop on the midbass that has a null, and then placed only a second midbass bandpassed to that gap if it would be sufficient.


That would work, only very hard to get the phase right between the midbass and just the cancelation cancel channel... 


The best way is just to find the spot in the car with the least problems and just use that....


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## Jscoyne2 (Oct 29, 2014)

Focused4door said:


> Since there is little point to trying to fill a null, I am curious if you simply put a bandstop on the midbass that has a null, and then placed only a second midbass bandpassed to that gap if it would be sufficient.


I think you'd have phase issues introduced by crossovers that were different than the original midbass.

Might work with Dirac really well.

Sent from my XT1710-02 using Tapatalk


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## Whiterabbit (May 26, 2006)

Jscoyne2 said:


> Wasn't this all discussed on a rear fill thread years ago? Just throw some midbass on the rear shelf and delay them the same as any other driver and you now have filled gaps in the FR?
> 
> Something about the cone of confusion
> 
> Sent from my XT1710-02 using Tapatalk


And since I like bookmarks for selected interesting topics,









midbass arrays revisited


This is going to be one long thread. Inspired by the interesting work that Patrick has been doing :) Lots to cover, for anyone interested. We're going to end up covering : the fundamentals of Blumlein's stereo, vector math, a variety of already-marketed technologies including SRS and...




www.diymobileaudio.com





In my case, I used the rear doors for the second midbass set.

I could never get them to pair how I liked as advised by that thread. I still run them, but I ended up tuning them, each mirrored to the other, to match and augment the center channel instead. As per earlier in this thread, I DO in fact have yet another midbass in the center console of my car, but the output capability is very low, basically a failed experiment. But, combined with the two midbass in the rear, and center channel which is already a passive 2-way on the dash, all 5 come together just fine. It's just a matter of getting the phasing right at the driver's seat via RoomEQ Wizzard. The effect is very subtle because the three midbass are on super low to avoid localization, but it's a much better effect than trying to get the phasing right to the front midbass, feeding them L and R rather than C.

It doesn't mess up the passenger seat nearly as much as the fact that L and R are tuned to be a 1-seat car, even given that there is a great center channel. That alone also drastically improves the performance in the driver's seat, so I roll with it. Worthy sacrifice.

Noone here will get a free lunch. the problems are too severe.

I'd like ot see a thread discussion sometime about the next frequency sinkhole challenge, in the 750-1000 Hz region depending on car size. That is a much more severe problem to deal with for everything from tonality through imaging.


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