# Does Anyone Understand Cabin Gain



## Patrick Bateman (Sep 11, 2006)

Has anyone on this forum studied cabin gain?










This is JBL's measurement of cabin gain. I've used this jpg a million times, but I think I made some fundamental mistakes in my understanding of room gain. If what I've studied yesterday is correct, it leads to some surprising conclusions!

These conclusions include:

#1 - There's no good reason to use a ported sub box in car
#2 - There's no good reason to use a tapped horn sub in a car
#3 - Our estimates of 'cabin gain' cannot be applied to all box types - they only apply to sealed subs, single reflex bandpass subs, and front loaded horn subs.

I literally re-read my acoustics books in the past day, so I may be making some type of fundamental mistake here. But based on a re-read, I've found the following:


All rooms have a fundamental resonance, and below that resonance, a monopole will pressurize a room. A dipole WILL NOT. That's the key. (And vented boxes, tapped horns, and back loaded horns are dipoles below their passband.)
In a sedan, the lowest fundamental resonance is about sixty hertz. I calculated this figure using my Accord as an example. The longest dimension of the cabin is 110". According to page 110 of the Audio Recording Handbook, we calculate the frequency like this:
_room fundamental = frequency / 2 * length
= 13500 inches per second / 220"
= 61hz_

Now at this point, plenty of people will say "I've heard vented boxes produce tons of bass in a car."

But I think there's *another* thing going on here, which further complicates cabin gain. And that is standing waves.










The car's cabin is excited by a series of standing waves. These standing waves begin at one quarter wavelength, and occur at odd multiples. *Both monopoles and dipoles are effected by standing waves.*

So I think that's the key. If I'm grokking my acoustic texts properly, *both affects are laid on top of each other.*

But the key to all of this is that *only a monopole will pressurize the cabin below 61hz*, using the dimensions listed above.

The effect of standing waves is not subtle, and in the example of a Honda Accord, the standing waves will occur at odd multiples of one quarter wavelength. For a 110" long cabin, those frequencies are 30.7hz, 92hz, 153hz, etc.

Complicating this further, standing waves are created by from side to side, and top to bottom as well. With a width of 55", there are also side-to-side standing waves at 61hz, 183hz, 305hz, etc.

And just to really blow your mind, this all happens in three dimensions.










If you tried to visualize it, the car cabin is almost like a pressure map, with varying areas of high and low pressure. And this is why you can move a microphone (or your ears) a couple of inches and the frequency response changes dramatically.

*But the main thing, is that any type of dipole box has limited use as subwoofer in a car.* This includes vented boxes, tapped horns, and back loaded horns. YES, these box types can see an efficiency bump from the rear wave, but that efficiency gain will be swamped by the effect of cabin pressurization. If I'm reading my numbers right, pressurization would add 12dB at 30hz for a monopole, and 0dB for a dipole. The dipole subs would only become compelling if the vehicle was very large, or if the tuning was extremely low (sub 30hz, likely) But even that last case is dubious, due to the monopole's size advantage.

If anyone wants to fact check this, here's some reading:

Audio Recording Handbook : http://books.google.com/books?id=bb...a=X&ei=h-D1TsbZN-_WiALVpqySDQ&ved=0CEwQ6AEwBw

John K explores pressurization on dipoles : http://www.musicanddesign.com/roomgain.html

standing waves : http://hyperphysics.phy-astr.gsu.edu/hbase/waves/funhar.html#c3

Geddes weighs in : http://www.diyaudio.com/forums/gedlee/161630-geddes-bandpass-subs-multi-sub-approach-3.html


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## thehatedguy (May 4, 2007)

That might explain why the "unhorn" on DIYA acted the way it did.

Ported can be useful for exciting a room mode...ala what the SPL guys are doing.


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## 14642 (May 19, 2008)

Patrick,
I think you're on the right track, but there are a bunch of other things to consider and I'm not sure about the calculation of "room resonance"--that appears to me to be a calculation of some mode, not resonance. The resonance of the room MUST include all of the things that contribute to sustaining the energy that's applied. A square balloon that's been inflated would likely NOT have the same resonance as a cinder block box of the ssame dimensions--as Geddes suggests, leaks have to be considered and anything that isn't completely rigid is a leak. IF there are multiple surfaces that vibrate differently when the "room resonance" is excited, then those would contribute to the "spread the chaos around" idea and would serve to obscure the fundamental frequency and the Q of the fundamental. This will be exceptionally difficult in the car, since the seat is a filter between the cavity of the trunk (box appears to be larger at lower frequencies), the windows are MUCH stiffer than the sheet metal. Windows are also suspended using a rubber gasket or flexible glue--so they're passive radiators each with mass and compliance, and so on and so forth.

I suppose this would be easy enough to try to determine the resonance. Put a mic in the car and close it up. Make a recording of the sound inside the car when you:
1. Whack the window with your hand
2. Whack the sheet metal with your hand
3. Whack the windshield with your hand.

If you notice that there's a fundamental frequency at which the sound decays, then you've found the resonance of the car. If the fundamental is different depending on which surface you whack, then the fundamental depends on the surface that's used to excite the resonance. I don't know if this will be the case, as I've never done this. 

I also don't buy the idea that a vented box doesn't pressurize the cabin. I do, however buy the idea that the vented box doesn't do a good job of pressurizing anything far below Fb. The pressure inside the vented box is MUCH higher at Fb than the pressure inside a sealed at the same frequency--Richard Small wrote a paper that indicates that the anechoic response of the speaker can be modeled by measuring the pressure inside the box. I'll see if I can find it. I have it somewhere. It's no mystery why dipoles don't pressurize the room at low frequencies--there's no displacement at frequencies below the point at which the radiation patterns meet. At low frequencies, they radiate in all angles. Same for a woofer and a port--far below Fb. Same for a 6x9" speaker thrown onto the rear package tray of the car.

Vented boxes are beneficial in cars for other reasons, so let's be careful not to categorically rule them out simply because of what happens below Fb (in the same way that ALL AMPLIIFERS DO NOT SOUND THE SAME, despite the misunderstanding by so many of RC's "experiment").

In my experience, bass in the car is so easy that it really doesn't warrant much experimentation or explanation. It's between 60Hz and 1kHz Hz where all of the thinking and reading ought to be applied.


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## asota (Feb 7, 2011)

Have a perhaps dumb question but how does a true infinate baffle sub (vented outside) effect cabin gain?


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## Mirage_Man (Jun 29, 2007)

I always enjoy reading your posts Patrick. I try my best to follow what you're saying. I have one question though regarding this one. When you talk about "dipole" would it also refer to two sealed subs mounted in different locations (ala two corner loaded subs)? My guess is no because there is no back wave. However they should be exciting different but symmetrically the same points, yes?

My current build in my Accord coupe:


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## BigRed (Aug 12, 2007)

Floyd Toole's book is awesome. thanks for the suggestion Andy. It has changed my whole perspective about near field listening.


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## BlackFx4InTn (Apr 11, 2009)

Here's PWK's take on standing waves
Standing Wave Info | HexiBase.com


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## adrenalinejunkie (Oct 17, 2010)

Hmm... Can't get to the subscribe button. Thanks for sharing, can't wait to see what comes out of this.


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## The Baron Groog (Mar 15, 2010)

Patrick Bateman said:


> Has anyone on this forum studied cabin gain?




Not extensively, but I did use the graph below when designing my system. I implimented a Linkwitz Transform enclosure design and used the cabin gain for the LT EQ. F3 of enclosure is around 74Hz, Fb around 76Hz sub crossed at 63Hz. 1st pocket RTA of the setup showed flat to 30Hz-150Hz with zero tuning. Box volume 0.126cf and in the front kickwell of a 2003 Cooper S.












Patrick Bateman said:


> This is JBL's measurement of cabin gain. I've used this jpg a million times, but I think I made some fundamental mistakes in my understanding of room gain. If what I've studied yesterday is correct, it leads to some surprising conclusions!
> 
> These conclusions include:
> 
> ...




Good, glad I went LT



Patrick Bateman said:


> I literally re-read my acoustics books in the past day, so I may be making some type of fundamental mistake here. But based on a re-read, I've found the following:
> 
> 
> All rooms have a fundamental resonance, and below that resonance, a monopole will pressurize a room. A dipole WILL NOT. That's the key. (And vented boxes, tapped horns, and back loaded horns are dipoles below their passband.)
> ...


So large vented boxes will still have their place if tuned below the fundamental of the vehicle-but the gains below the fundamental will largely be from standing waves and the gains above the car fundamental will be from pressurisation of the cabin. 

Is extremrevolution (SP) still knocking about? He had some software for factoring in the vehicle boundaries when designing an enclosure-so perhaps he has a better understanding of standing waves within vehicles? (or maybe he just gets the softeware to crunch the numbers)


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## The Baron Groog (Mar 15, 2010)

asota said:


> Have a perhaps dumb question but how does a true infinate baffle sub (vented outside) effect cabin gain?


Under PB's proposed idea it would act as a sealed enclosure as you aren't using any of the back wave for increased output


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## thehatedguy (May 4, 2007)

60-1k is where I think a distributed system like Geddes and Toole recommend for subbass in the home should work in the car.


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## 14642 (May 19, 2008)

The Baron Groog said:


> Under PB's proposed idea it would act as a sealed enclosure as you aren't using any of the back wave for increased output


Right. And using the backwave is only a "not able to pressurize the cabin" condition when the front and back wave play the same thing out of phase at the same level. 

This is NOT the case AT Fb in a vented box. The port and the woofer do NOT play the same thing out of phase. At Fb, almost all the output comes from the port (if the port islarge enough) and almost nothing comes from the woofer. They are 2 separate radiators.

Below Fb, the port passes the backwave basically unobstructed and this is both the reason for the steep rolloff and the reason why a subsonic (infrasonic--whatever) filter ought to be used.


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## fish (Jun 30, 2007)

thehatedguy said:


> 60-1k is where I think a distributed system like Geddes and Toole recommend for subbass in the home should work in the car.


Are you thinking along the lines of an MS-8?


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## 14642 (May 19, 2008)

thehatedguy said:


> 60-1k is where I think a distributed system like Geddes and Toole recommend for subbass in the home should work in the car.


 
We actually tried this but there's one HUGE drawback that renders it useless--distributing the drivers to eliminate the modes doesn't necessarily place those drivers in spots that preserve the stereo image. Doesn't work. For subs or for a mono system and one in which imaging doesn't matter, it's fine.


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## stills (Apr 13, 2008)

*sealed isobaric makin' a comeback*

one thing not mentioned for the SPL'er

on the cabin gain chart look at the gap @ 60-70hz almost everything has.

many people run very low tuned ported boxes and wonder why their mids can't keep up. 
or think they need 10'' mids up front.

when maybe all they need are sealed enclosures.


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## Hanatsu (Nov 9, 2010)

Interesting post. Done extensive measurements on different boxes in my car. Small ported designs with low Fb (~30Hz) and sealed designs tend to work best. Cabin gain was more linear with the sealed enclosure than the ported even though they modeled pretty much alike in WinISD (same rolloff slope but lower f3 point). Cabin gain became more unpredictable as I increased tuning frequency, with more dips/peaks below 60Hz or so (still manageable though). Car's well damped btw... I measured FR outside the car and I was able to differentiate the in-car FR with the "anechoic" freq response and discovered that the sealed design had a very smooth and predictable FR below 30Hz, where the ported design had a narrow dip with like 10dB amplitude directly below Fb but went up again at normal levels around 25Hz. Must have been caused some cancellation of some kind, no idea if its related to this phenomena though.

It's close to impossible to integrate 6,5" and smaller midbasses with ported subs in my experience. They simply don't have enough output at lower frequencies and as you increase highpass, sub localisation becomes an issue. You probably need a pair of 8"s to keep up, another reason to go with sealed designs... or bigger mids hm.


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## 14642 (May 19, 2008)

*Re: sealed isobaric makin' a comeback*



stills said:


> one thing not mentioned for the SPL'er
> 
> on the cabin gain chart look at the gap @ 60-70hz almost everything has.
> 
> ...


What does a sealed sub enclosure have to do with midbass?


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## thehatedguy (May 4, 2007)

Just seems like that extra set of speakers in the center really changes the output of the system.


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## 14642 (May 19, 2008)

thehatedguy said:


> Just seems like that extra set of speakers in the center really changes the output of the system.


What? Oh, a center channel? Wll, sure, especially since the signal is steered and not just the acoustic sum of right and left. That's not the same as placing drivers in antinodes.


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## stills (Apr 13, 2008)

i was thinking along the lines of using a higher lowpass freq w/ a sealed subs than ported basically.


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## Patrick Bateman (Sep 11, 2006)

*Re: sealed isobaric makin' a comeback*




stills said:


> one thing not mentioned for the SPL'er
> 
> on the cabin gain chart look at the gap @ 60-70hz almost everything has.
> 
> ...


For literally twenty years I thought the gap at 60hz was a null, but after sitting down for a few hours, and seriously studying how standing waves work, I'm now convinced that the gap at 60hz isn't a null; it's just a trough between a pair of standing waves, one at approximately 30hz, and another at 90hz.

This is because standing waves are harmonic, so they occur at multiples.










Also, this last part is complete conjecture, but *I wonder if the harmonic nature of standing waves is one of the reasons that 'lumpy' bass doesn't sound offensive?*

IE, in nature, there are harmonics everywhere. Tap a milk carton or pluck a string on a guitar, and you'll hear a fundamental and harmonics. *And even the car cabin has harmonics.*

But when you EQ your system to fill in the troughs, it often sounds unnatural.









*Could it be harmonics?*

Here's what I mean by this statement. If you study standing waves, you'll understand that they create points where there's HIGH pressure and LOW pressure. If you look at the gif above, you can see them. *These points do not change - they're fixed and based on the geometry of the string, the pipe, or the car cabin.* So when you equalize your car, it creates a couple of problems. The first problem is that your microphone may be sitting in a high pressure node, and it that pressure will be seen in 'lumpy bass.' The second is that the waves are harmonic, so we may be naturally attuned to 'filter' them out. (That last part is complete conjecture by the way - so take it with a grain of salt.)

The nature of standing waves might explain why people have such a tough time 'tuning' their systems. Obviously, tuning at multiple locations in the cabin will help a lot. Jason's idea of using multiple midbasses has merit too I think. I know that Andy said that JBL found it screwed up imaging, but I believe there are ways to 'fix' that. Basically at low frequencies we localize sounds based on phase, so it's possible to use multiple midbasses *as long as they're in phase.* For instance, there's an overlap between your midbasses and your subwoofers, and I think that's one of the reasons that paying attention to the phase at the crossover point between the two is important for creating the illusion that the sub is up front.


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> It's close to impossible to integrate 6,5" and smaller midbasses with ported subs in my experience. They simply don't have enough output at lower frequencies and as you increase highpass, sub localisation becomes an issue. You probably need a pair of 8"s to keep up, another reason to go with sealed designs... or bigger mids hm.


Perhaps a sealed sub to take advantage of pressurization below 60hz, and ported midranges to increase power handling at the low end. Off the top of my head, I cannot think of any famous cars that used ported midbasses, except for the Buick Grand National


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## 14642 (May 19, 2008)

But vented boxes DO pressurize the cabin. They just don't pressurize anythig below their own Fb very well.


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## captainscarlett (Mar 15, 2011)

Hanatsu said:


> It's close to impossible to integrate 6,5" and smaller midbasses with ported subs in my experience. They simply don't have enough output at lower frequencies and as you increase highpass, sub localisation becomes an issue. You probably need a pair of 8"s to keep up, another reason to go with sealed designs... or bigger mids hm.





Patrick Bateman said:


> The nature of standing waves might explain why people have such a tough time 'tuning' their systems. Obviously, tuning at multiple locations in the cabin will help a lot. Jason's idea of using multiple midbasses has merit too I think. I know that Andy said that JBL found it screwed up imaging, but I believe there are ways to 'fix' that. Basically at low frequencies we localize sounds based on phase, so it's possible to use multiple midbasses *as long as they're in phase.* For instance, there's an overlap between your midbasses and your subwoofers, and I think that's one of the reasons that paying attention to the phase at the crossover point between the two is important for creating the illusion that the sub is up front.


I'm still having an issue with sub localisation with some of my subs. Some, like my JL Audio CP108 and DDLE308 (8") do well, whilst my bigger subs area still quite localised despite lowering LPF to 60hz and reversing polarity. 

My problem is that I want to stick my speakers back into the factory mountings which for my tiny Toyota, its 4" in the dash (see picture). So i'm thinking 4" mids just won't take on a 10 or 12 sub without the help of something a little more potent up front. 
*
Front:* 4" mids in dash (High passed)
*Tweets:* on dash or A pillar
*Midbass:* 1, 6.5 or 8 sub (in passenger foot well) to boost around 50hz+











So far i'm getting the feeling that a sealed sub is winning the vote here

Sorry for hijacking. As for Cabin gain

http://www.diymobileaudio.com/forum/diyma-sq-forum-technical-advanced/116923-cabin-gain.html


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## 14642 (May 19, 2008)

At frequencies above roll-off, there's no difference between a sealed box and a vented box.


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## Hanatsu (Nov 9, 2010)

Andy Wehmeyer said:


> At frequencies above roll-off, there's no difference between a sealed box and a vented box.


Exept it might have higher output, making it harder to integrate with mids. 

I'm using high output 8"s crossed at [email protected] to keep up with my dual sealed 12"s (also at [email protected]). This is the area where many ported subs have their highest output. Of course this might not be an issue if you have an low tuned enclosure or an EQ to flatten the peak out. Everyone might not cross as low as I do, but down at 40Hz there are no localisation issues at all. Also, love the simplicity with sealed enclosures, so predictable


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## The Baron Groog (Mar 15, 2010)

captainscarlett said:


> I'm still having an issue with sub localisation with some of my subs. Some, like my JL Audio CP108 and DDLE308 (8") do well, whilst my bigger subs area still quite localised despite lowering LPF to 60hz and reversing polarity.


When you've fitted the larger subs have you dropped the amp gain? If the sub (in the enclosure) is more efficient than the one it replaced then the crossover point will shift up in freq, if the sub is less sensitive it will shift down-as you can see in my basic skills sketch below


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## Mirage_Man (Jun 29, 2007)

Is there some reason that there have been no responses to my question in post #5. Is it not relevant to the topic?


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## ErinH (Feb 14, 2007)

Andy Wehmeyer said:


> We actually tried this but there's one HUGE drawback that renders it useless--distributing the drivers to eliminate the modes doesn't necessarily place those drivers in spots that preserve the stereo image. Doesn't work. For subs or for a mono system and one in which imaging doesn't matter, it's fine.


wasn't sure if anyone really saw this or not. it intrigued me. most of our problems are in this range. I'm interested in more discussion of what you guys may have found (if there's anything more to say, really).

You're talking in context of distributed midbass; not subbass. Our problems are in the region above (assumedly) where cabin gain takes over. 1/2 wavelength of the longest dimension in the car will get you the first boost, but there are other modes, correct?


Topic 2: Modes (standing wave) vs. Transfer Function
Does the TF start at the first mode? Modes being fractions of the fundamental... 1/2, 3/4, etc. 
There's online calculators that can be used to generate the modes caused by the enclosed volume; specifically in home theater application. I've not yet seen specific discussion relating these to an overall cabin gain affect, though.



I asked the same of Mark E but since I was basing it off your post above, I figured I'd toss it in here, too:
_What really sucks is that, while I have a huge suck out in response at the driver's seat from the driver's side midbass (kick mounted) in this region, I also have a cabin mode at 71hz (give or take a couple hz). There's no way to boost the null and on pink noise it shows up as a problem. However, when listening to bass guitar, the car lights up like a firework. So, the issue then becomes that I have to cut the 60/80hz region to help soften this mode but I lose some of the impact. Luckily the midrange tuning really helps bring out the midbass so the issue isn't immediately noticeable. This is actually what has made me consider building my own bass traps and trying them in the corners. It's interesting that Todd found the trouble spots to be the corners; I'd imagine so as corner loading is a double edged sword, IME. And that's exactly how my midbasses are: corner loaded in the kicks._



Topic 3: The subject in the subject of infinite baffle output being limited by which volume (if any):
What I'm personally wondering and plan to start researching is how an IB alignment is affected by cabin gain. Does the IB alignment "see" the smallest volume (the trunk, typically) or the largest (the cabin)? I'd guess the trunk simply because it is the most limiting. The reason I think you'd split the two up is because you've essentially (assuming you did your best to do a good install) got two independent volumes (again, trunk and cabin) due to the separating baffle.
If that's the case, then you'd probably have a length of about 4' or so, which should give a rise starting at 140hz. Well, I've not noticed this in my car, but I've also not ran them up that high to test this. I do, however, notice a good gain in response starting at about 60hz, which then tells me that it's "seeing" the entire car's volume. I just don't know if I trust that sole piece of data so I'm not going to say that there isn't 2 distinct volumes for the IB setup.
If I assume that the smallest volume is the limiting factor, then you would expect to have cabin gain noticably in your plots, which you don't. That's causing me to question my theory of 2 different volumes.
Taking it a step further, is it also possible the subs' "see" the trunk as the enclosure, and the car's cabin acts as the encompassing enclosure? Therefore, the cabin would be the driving factor in the gain, and let's say the cabin length is something like 6'... you get a rise at 93hz. I don't see this in my setups, so I don't really think it's the case, but it is another way of looking at it.




Note: Please forgive the brain dump. I had to go back to posts made elsewhere to get some of these.


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## captainscarlett (Mar 15, 2011)

The Baron Groog said:


> When you've fitted the larger subs have you dropped the amp gain? If the sub (in the enclosure) is more efficient than the one it replaced then the crossover point will shift up in freq, if the sub is less sensitive it will shift down-as you can see in my basic skills sketch below


Cheers!

Sorry for the newbie comment, but it seems that if we're going for SQ, and the LPF is set .. low 55-60hz, and most modest 5.25's or 6.5 won't do much down there anyway, isn't the crossover @60Hz (for example) always going to be a weak spot anyway?

I was thinking about MrDave and the comment about the Dynaudio MW182 subs and localising. As MrDave has got the LPF set at 40hz for the 1200 (if I remember rightly), and the 182's from 40hz until the Esotar 430's start to do their thing, I thought the 182's were overkill. maybe not! 

http://www.diymobileaudio.com/forum...0-esotar-110-430-1200-tru-billets-ssld6i.html



MrDave said:


> My choice of using the MW182's came after I already had purchased Esotar 650's, which were never installed. Simply, I wanted to be able to have all my sound coming from the front with little need for a subwoofer, other than adding a little extra pop when I wanted, and strengthening the bottom most octaves. Plus, I had the space in my doors. Some people don't. What I'd say about the Esotar 1200 I can to some degree about the 182's. They are merely an extension of each other to accomplish the same goal. Typically, the midbass in most installs outperforms the subwoofer. They tend to appear quicker, and the subwoofer is usually what needs tweaking to match the front stage, not the other way around. Even when I ran the Esotar 1200 in a 1.25cu enclosure, it had seeamless integreation and zero localization. Now that I have it IB, it's everything you could possibly want the sub stage in your car to be.


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## Hanatsu (Nov 9, 2010)

bikinpunk said:


> Topic 3: The subject in the subject of infinite baffle output being limited by which volume (if any):
> What I'm personally wondering and plan to start researching is how an IB alignment is affected by cabin gain. Does the IB alignment "see" the smallest volume (the trunk, typically) or the largest (the cabin)? I'd guess the trunk simply because it is the most limiting. The reason I think you'd split the two up is because you've essentially (assuming you did your best to do a good install) got two independent volumes (again, trunk and cabin) due to the separating baffle.
> If that's the case, then you'd probably have a length of about 4' or so, which should give a rise starting at 140hz. Well, I've not noticed this in my car, but I've also not ran them up that high to test this. I do, however, notice a good gain in response starting at about 60hz, which then tells me that it's "seeing" the entire car's volume. I just don't know if I trust that sole piece of data so I'm not going to say that there isn't 2 distinct volumes for the IB setup.
> If I assume that the smallest volume is the limiting factor, then you would expect to have cabin gain noticably in your plots, which you don't. That's causing me to question my theory of 2 different volumes.
> Taking it a step further, is it also possible the subs' "see" the trunk as the enclosure, and the car's cabin acts as the encompassing enclosure? Therefore, the cabin would be the driving factor in the gain, and let's say the cabin length is something like 6'... you get a rise at 93hz. I don't see this in my setups, so I don't really think it's the case, but it is another way of looking at it.


I believe IB can be concidered a closed enclosure, just a very big one. Since VAS is the volume of air that has the same compliance as the woofer's suspension, the speaker shouldn't "see" an enclosure on the front side as long as the cabin volume's greater than the woofer's VAS. Believe it's no more complicated than that.

Might be completely wrong though, perhaps you shouldn't listen to me xD


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## traceywatts (Jun 2, 2008)

bikinpunk said:


> Topic 3: The subject in the subject of infinite baffle output being limited by which volume (if any):
> What I'm personally wondering and plan to start researching is how an IB alignment is affected by cabin gain. Does the IB alignment "see" the smallest volume (the trunk, typically) or the largest (the cabin)? I'd guess the trunk simply because it is the most limiting. The reason I think you'd split the two up is because you've essentially (assuming you did your best to do a good install) got two independent volumes (again, trunk and cabin) due to the separating baffle.
> If that's the case, then you'd probably have a length of about 4' or so, which should give a rise starting at 140hz. Well, I've not noticed this in my car, but I've also not ran them up that high to test this. I do, however, notice a good gain in response starting at about 60hz, which then tells me that it's "seeing" the entire car's volume. I just don't know if I trust that sole piece of data so I'm not going to say that there isn't 2 distinct volumes for the IB setup.
> If I assume that the smallest volume is the limiting factor, then you would expect to have cabin gain noticably in your plots, which you don't. That's causing me to question my theory of 2 different volumes.
> ...


if you measured the external response of a boxed sub in atmosphere, there would be no cabin gain. if you varied the box size, you eq the low end. so small side affects low end, large side affects gain. right?


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## The Baron Groog (Mar 15, 2010)

Mirage_Man said:


> I always enjoy reading your posts Patrick. I try my best to follow what you're saying. I have one question though regarding this one. When you talk about "dipole" would it also refer to two sealed subs mounted in different locations (ala two corner loaded subs)? My guess is no because there is no back wave. However they should be exciting different but symmetrically the same points, yes?
> 
> My current build in my Accord coupe:





Mirage_Man said:


> Is there some reason that there have been no responses to my question in post #5. Is it not relevant to the topic?


It's not really relevant, your speakers aren't dipole or using the rear wave to re-inforce the front wave so that's why no one bothered replying. Nice looking install though.


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## The Baron Groog (Mar 15, 2010)

double post


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## The Baron Groog (Mar 15, 2010)

captainscarlett said:


> Cheers!


No worries



captainscarlett said:


> Sorry for the newbie comment, but it seems that if we're going for SQ, and the LPF is set .. low 55-60hz, and most modest 5.25's or 6.5 won't do much down there anyway, isn't the crossover @60Hz (for example) always going to be a weak spot anyway?
> 
> I was thinking about MrDave and the comment about the Dynaudio MW182 subs and localising. As MrDave has got the LPF set at 40hz for the 1200 (if I remember rightly), and the 182's from 40hz until the Esotar 430's start to do their thing, I thought the 182's were overkill. maybe not!
> 
> http://www.diymobileaudio.com/forum...0-esotar-110-430-1200-tru-billets-ssld6i.html


Having a 4-way set up (3-way front + sub) should always allow better integration of the mids to the bass region(otherwise there'd be little point in going for it). In a 3-way set up (2-way front + sub) you can get a great sound and integration between your mids and subs-but you are output limited by your mids. The problem is bass is very easy in a car, midbass isn't. Stick with 2-way fronts and up your midwoofer size to 8" then you have issues with beaming-if you can get the buggers in-or getting a tweeter to play low enough to cross suitabley with the 8" for you to avoid it beaming. Car audio = compromises!


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## Patrick Bateman (Sep 11, 2006)

Yesterday I was trying to shoot a video of my Summas, which are in my bedroom, and got COMPLETELY frustrated trying to get a good recording. So frustrated that I dragged one down to my deck, and recorded it out there. *The idea was that eliminating two of the six walls would clean up the recording.*

But even OUTSIDE, on a deck, you can still hear reflections in the recording. It's particularly noticeable at the 1:00 mark, and at any point where I'm more than a meter from the loudspeaker:

johnny cash on summa outside - YouTube

Clearly, there has to be some type of 'cocktail party effect*' going on, where our brains are 'filtering' out a lot of garbage that the microphone doesn't.

Cocktail party effect - Wikipedia, the free encyclopedia


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## Patrick Bateman (Sep 11, 2006)

Hanatsu said:


> I believe IB can be concidered a closed enclosure, just a very big one. Since VAS is the volume of air that has the same compliance as the woofer's suspension, the speaker shouldn't "see" an enclosure on the front side as long as the cabin volume's greater than the woofer's VAS. Believe it's no more complicated than that.
> 
> Might be completely wrong though, perhaps you shouldn't listen to me xD


What you say is true, but we also enjoy a few more benefits with IB. Check out the measurements I did in the kick panels and in the quarter panels. (It's somewhere in this thread.) You'll see that location in the car can change the response quite a bit. So an advantage of IB mounting is that it gets the woofer closer to the center of the car, and that can increase output by pushing the frequency of the standing waves higher. If your trunk is *very* well sealed, it would likely increase the frequency that the cabin is pressurized.

A lot of this is stuff the SPL guys already figured out. The use of small cars and pickups to increase bass and the idea of moving subs and ports around to change the response.


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