# Infinite baffle manifold in a trunk.



## bradsworth (Jul 3, 2013)

Hey guys. Ive been running infinite baffle in my car for the last few months using a 12inch Infinity 1262W sub. I absolutely loved it when I first installed it, Much more detailed bass, and it gets much lower than my previous sealed and ported boxes. (granted I've learned a lot about tuning since those days). 

Anyways, I've gotten annoyed with the chassis vibrations I get when I am demoing the system. Under normal listening loads I don't have any rattles to speak of, but when I get some excursion going it sounds terrible.

I have 2-3 layers of raamat BTX II on my deck lid and near where my sub baffle is attached. The baffle itself is 2 layers of 3/4 inch MDF with a third layer for the center section where the sub itself mounts. And the sub fires through my skii pass through in my rear seats. 

I was looking at some home theater installs the other day and came across IB sub manifolds. Meaning there are an even number of subs mounted on opposing sides of a cube(or rectangular cube) With the goal of canceling out the vibrations created by cone movement. This is a slight compromise of absolute sound quality, but may be the cure for my annoying rattles. 


I have ordered a second infinity 1262 and plan on making a 5 sided cube the same width as my skii pass through with one sub on the driver and passenger side, I will then mount this manifold to the back of my existing baffle, and cut the hole in the baffle to be the same size as my skii pass through. 

If anyone has trouble visualizing I can whip something up in MS paint, I'm a pro at that 


Has anyone heard of or seen this being done? I would like to see what others have tried and either failed or succeeded. I have a narrow window to have my car nonoperational this weekend to get this project done and would like to have as few delays and re-works as possible. 


Any Ideas? 
Thanks guys.


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## thehatedguy (May 4, 2007)

It's not going to help the rattles in your car.

But it would be cool to do if you could stick the magnet of one sub in front of the cone of the other sub...would decrease distortion that way.


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## Coppertone (Oct 4, 2011)

Whip it up so that we can visualize what exactly you are planning to do please.


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## damonryoung (Mar 23, 2012)

Coppertone said:


> Whip it up so that we can visualize what exactly you are planning to do please.


I think this is what he is talking about...



Hopefully that is visible enough.

Edit: Or I could have just found an image...


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## bradsworth (Jul 3, 2013)

That is what I am talking about, thanks! I should specify the rattle in my car is mostly my seatbelts that are mounted to the rear deck lid. The retraction mechanisms themselves vibrate... There is also a vibration where the baffle comes in contact with the body of the car.... I think the nature of the manifold, which cancels out physical vibrations from the woofer cone. Should take care of both of those...

I see now that i may still have some of these vibrations due to the sound pressures produced. I can't imagine this not being a vast improvement though.


Also mounting one woofer with its magnet facing the cone of the other is a possibility. I had read that distortion is reduced in this manor, but wonder weather the slight differences in cone movement would make it less effective at canceling vibrations.


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## thehatedguy (May 4, 2007)

It's not going to help those vibrations because the backwave of the sub(s) is escaping to the entire trunk...and the baffle is attached to the car. There is nothing you can do on that end of things to reduce the vibrations.


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## bradsworth (Jul 3, 2013)

I don't follow. Are you talking about vibrations due to air pressure?


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## thehatedguy (May 4, 2007)

Yeah, the whole trunk is being pressurized by the back wave of the sub and that is going to cause vibrations that cause your rattles. And then the baffle is rigidly coupled to the car and the cone movement itself will cause vibrations that cause rattle.

Your problems can't be fixed from this method, you will need to fix the rattles at the source.


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## Orion525iT (Mar 6, 2011)

I am running eight 8" subs IB in a PPLS manifold in my tire well. I did that to get maximum cone area in the smallest space. I think the force cancellation apsect has merit, but I also think that it may not solve your issue. There is the distortion reduction aspect too.


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## BlkRamRt (Nov 27, 2013)

I HAVE SEEN PEOPLE USE THE CAN OF FOAM THAT EXPANDS THEY FILL IN THE HOLES CRACKS OR WHATEVER IS RATTLING.


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## Orion525iT (Mar 6, 2011)

You can also alter fs and q with a manifold. It can act as band pass if designed to do so.


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## cajunner (Apr 13, 2007)

sounds like the rear deck needs bracing, because that's the main issue.

If you build a manifold and put it under the rear deck, and it is attached to the rear deck and the trunk floor or parcel shelf, you'll also reinforce the rear deck and reduce that vibration from transmitting to the seat belt retractors.


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## bradsworth (Jul 3, 2013)

Great idea mounting to the floor and my rear deck. I'll do that. 

I was unaware that you could alter sub dynamics with a manifold like this, any suggestions on where I can learn more? 

I may do some reinforcing of the deck lid while I have everything apart, anything to reduce vibrations. Isolating the vibrations caused by the back wave should help my output some as well....


As far as the air pressure itself causeing the vibrations I have, it seems like a bit of a stretch... My trunk is far from perfectly sealed from the outside of the car... The cabin though is very well sealed. But I still don't think 2 12's will pressurize my cabin to the point where it moves my decklid. I could be wrong though..... Time will tell!


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## cajunner (Apr 13, 2007)

bradsworth said:


> Great idea mounting to the floor and my rear deck. I'll do that.
> 
> I was unaware that you could alter sub dynamics with a manifold like this, any suggestions on where I can learn more?
> 
> ...


2 twelve's can easily create enough pressure to make your rear deck resonate, and that would excite the adjusters' internals to rattle.

also, the baffle attachment point at the rear deck may have worked by vibration, to a condition of looseness that isn't apparent by just pushing on the baffle to test for movement.

that juncture, and the rear deck's stiffening supports from behind the seat back, could have some issues that need addressing, no matter how solid the baffle you built "feels" to the touch or knock.


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## Woosey (Feb 2, 2011)

I have a build posted on here with a manifold, search Alfa Romeo posted by me and you'll see how it can be done.. We do this a lot in BMWs 


Sent from my Lumia


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## bradsworth (Jul 3, 2013)

I see, a reinforcement for the deck lid is in order then, I'll also see what I can do about bracing my baffle more against the floor of the trunk, thanks for all the help so far guys! And I will take a look at your build, thanks!


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## thehatedguy (May 4, 2007)

There is just as much pressure being made on the backside of the speaker as the front side.


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## t3sn4f2 (Jan 3, 2007)

Push-Pull benefits

http://www.mobilesoundscience.com/showthread.php/716-2001-Honda-S2000-Single-Seat?p=17175&viewfull=1#post17175

Cvjoint:

"*Subjective impressions:*

I have once again proved to myself that the LAT700s are a beauty of a driver. Right away, the Peerless drivers brought back the honk, dullness, and the long forgotten rattles and vibration. It makes little difference what conventional drivers I use, they all have the common drawbacks: AE IB12, Vifa NE 12", and now Peerless XXLS 12". The reason why these conventional drivers hit "hard" it's because they litterally hit the chassis, not in a good way. The seat resonates, the rearview mirror rattles on the windshield. At low volumes it sounds honky and generic. A lot of the detail in bass lines is smoothed out with noise. Every bass note excites the car, and now that I have experienced mechanical Push-pull with the Tympany LATs, this is simply... unacceptable. 

I will be going back to LATs soon!!

Pros:

It does get louder, downright brutal. There is no sign of strain no matter how much I push them but the car itself cringes. To get the additional output over the LATs you really have to accept an unsurmountable amount of rattles and vibration. So for 0.000001% of the time the extra output can make you happy, but the loss of quality...oh my. 

For those that want some feedback on the 12s, in order of best to last:
Vifa NE 12"
Peerless XXLS 12"
AE IB 12"

The NE dug the deepest, was the most efficient, can be crossed the highest, was the lightest, used the most advanced materials, etc etc... The XXLS may keep it's composure a little better at high SPL but low to mid the Vifa was a better driver imo. The AE IB12s suspension makes the Tympany drivers a better choice for sub use. As a midbass I'd reconsider the AE but a good suspension is more important than the improvement in inductance management (the Danish drivers still have very good farraday shielding)."


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## Woosey (Feb 2, 2011)

http://www.diymobileaudio.com/forum...all-gallery/125256-alfa-romeo-ib-project.html

here it is..


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## Orion525iT (Mar 6, 2011)

bradsworth said:


> I was unaware that you could alter sub dynamics with a manifold like this, any suggestions on where I can learn more?


There are some long threads on some of the hifi sites. I am sure that some people can find a good way to model subs in a manifold, but to be honest, the calculations and sims are beyond me. I think you can get some idea by modeling a truncated horn with a single driver. I took a somewhat educated guess with my manifold design, and chose low qts subs knowing that the manifold and the semi-IB (we all know trunk IB is not _true_ IB) would raise Q. I hope to measure fs when finished. Manifolds can push fs lower, but there is no free lunch here.

The thread I started when I was looking into this.
http://www.diymobileaudio.com/forum...sion/154600-plenum-volume-slot-area-ppsl.html

The maelstrom that is my build log.
http://www.diymobileaudio.com/forum...4-three-way-kicks-cement-board-baffles-3.html


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## TOOSTUBBORN2FAIL (Jan 31, 2011)

I have to back up cvjoint on his view. His car has almost no audible resonance from the subs, and as far as I know, nothing in his trunk or his car is deadened. All future projects I do sub-bass related will be push-pull if there's room for it.


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## bradsworth (Jul 3, 2013)

Hornresp absolutely baffles me. (haha. baffle. ha.  ) Orion, your thread was a great read. My plan is to basically make my manifold as small as possible so that I don't encounter to many problems with 1/4 wave resonances, Using 12's isn't going to help me to much there though. I think I will also run a higher crossover than I do now. my little 7 inch mid basses will appreciate it 

BTW the link in your thread called more bass less space. is kinda mind blowing. http://www.diymobileaudio.com/forum...io-discussion/82304-more-bass-less-space.html for anyone interested. 

And your build is absolutely insane. Full custom dash...  jesus. when I grow up can I do a build like that? :laugh:


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## thehatedguy (May 4, 2007)

I modeled the manifolds I was thinking about using for midbass in Hornresp last year. It is a really great free software and not too hard to use, just a little different than your basic winISD type programs.

What I did to model mine was to use the offset driver on a horn function like you would do for a midrange entering a Unity horn. I made the "horn" a square in my case (you can use the sliding wizard to change the segment lengths and angles, in this case I only used a 2 segment horn...maybe I 1 segment) though you can change the horn to a pyramid though Hornresp will not do asymmetric horns. Then for the mid entrance hole size I made that the size of the cone diameter. And the volume of the front chamber was zero. Though if you are inclined, you can play around with those numbers to see how smaller entrance ports/taps and thus adding a front chamber would affect the response- keep in mind the front chamber volume is default to cubic centimeters. As far as the rear chamber volume, I set that equal to roughly half the volume of the trunk since I was using it on 2 sides. With a sub setup just a rough estimate of the trunk volume will do. Then you can add speakers to the horn/duct/tap (whatever you want to call it here) using the wizard. Keep in mind when you add speakers, the program is going to share the back chamber volume, front chamber volume, and duct area (if you aren't using a front chamber then don't worry about that).

And that was pretty much it.

You can use the sliders to see how making the duct smaller or larger, changing the angles, and speaker placement on the duct will effect the response. I would use a 2 segment horn to let you move the physical location of the drivers up and down the duct especially if you are thinking about midbasses...with a sub I don't think it would make much if any difference in the response.

I know it sounds like a lot, but it really isn't that bad and only takes a few minutes to get everything entered into the program.


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## Orion525iT (Mar 6, 2011)

bradsworth said:


> And your build is absolutely insane. Full custom dash...  jesus. when I grow up can I do a build like that? :laugh:


Lol, I wouldn't recommend it for 99.99% of people.

With my manifold, there is some vibration in the manifold by itself, but almost none on the actual baffle. There is some asymmetry of forces with push-pull. With push-push, the forces cancel completely, but you don't get 2nd order distortion reduction. Also keep in mind, some people like distortion.


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## bradsworth (Jul 3, 2013)

I'll keep that in mind. With my manifolds I will not be limited to one configuration.


My sub showed up today, and unfortunately it is the wrong one. I now have one dual 4 ohm voice coil sub, and a single voice coil 4 ohm sub... What a pain in the A**! 

Do you guys think I'll be alright only using one voice coil from the DVC sub? I know power handling will suffer, but Its not like I'll be using that much power in IB anyway. Thoughts?


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## bradsworth (Jul 3, 2013)

Well, the manifold is built and installed. It seems to have solved my rattling issue, as well as providing a better place to mount my amps. I am however getting a rather large peak in my frequency response above my lowpass filter. Which is set at 60 hz 12db\oct. Using a frequency generator and my ear I have pretty linear response from 25 hz up to 55hz. It tapers down to 65hz, then at 67 all the way to 87hz I have a pretty large peak. Which is strange to me, the quarter wavelength at these frequencies are like 4 feet. My manifold is 14x11x8 inches.... Is this what is causing my problems? The drivers are mounted to the 14x11 if that matters.


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## Orion525iT (Mar 6, 2011)

^cabin gain.

Cut sooner, steeper. Dont worry if there is a gap between where you cross the subs to the midbass.


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## t3sn4f2 (Jan 3, 2007)

edited


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## t3sn4f2 (Jan 3, 2007)

I'd say it's a loading effect. Look green and red responses in the graph below. There is a small bump in the same region as yours for 2 15" when the leather back seat is up versus down. I imagine a manifold will load that region and higher more significantly, as well as it having a direct path to your ears.



cvjoint said:


> Here is my previous setup with 3 IdMax 12s in the same IB configuration, 100hz LP so judge from there down, no EQ. A total of 3 identical 500w amps were used. The only noteworthy aplication difference is driver orientation, IDmax dirvers were facing the cabin while the AE IB15s are facing the trunk. Polarity was reversed in the IB15 case. To keep variables fixed observe the green test where seats where up and trunk was closed for fair comparison.


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## Saturnsl2lover (Mar 26, 2017)

What happened to this thread


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## bradsworth (Jul 3, 2013)

I kept this setup for a while, I think a larger (wider) manifold and some better quality drivers would have gone a long way toward making this configuration sound better. And I definitely should have spent more time equalizing the Midbass/bass crossover region. I plan on doing another build in my 535i taking advantage of some of the lessons learned. 

The state of the old manifold is a bit sad


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## Saturnsl2lover (Mar 26, 2017)

Did you find the opening to small? I was advised to have tue drivers at least 12 inches apart face to face even though my ski pass opening is only 8 inches wide.


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## bradsworth (Jul 3, 2013)

I honestly don’t think the manifold opening is nearly as big a factor as being able to Integrate your subs into the rest of the system. I am convinced that more time spent tuning and refining could have made my system sound a lot better over a wider range of music. Saying your manifold width should be 12”or larger sounds kinda arbitrary. I still don’t know the physics that affect a sound wave in this situation. Maybe someone will chime in that knows more of the theory behind it. Keep in mind the wave lengths we are dealing with are 12+ feet long, I think the opening just has to be able to get all your air through it without weird compression or anything.


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## Saturnsl2lover (Mar 26, 2017)

The distance apart was recommended to reduce the air load on the drivers. Placing them close togeather generates resistance i guess so having them at least 12 inches apart was a good rule of thumb. I know dropping in a couple of 15s would deffinately flex the baffle and anything its bolted to if its not in a manifold lol. It works but you know how it is.


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