# Do you deaden the inside of your sub box?



## [email protected]

Just curious, I have seen it done before and I am trying it on the box I am currently building. I am usign 3/4" MDF rabbited on the edges to give me a 50% increase in surface area to be glued. I then put 45's where each panel meets up to another, and finally I applied Damplifier to the rest of the exposed wood on the inside. Not really sure if its gonna help with anything or not, but I was bored and had the time so I figured **** it if for some reason I dont like it I am only out the $32 bucks for the teklite mdf. 

So what does the sound deadening do inside a sub enclosure? Just slow the waves down more so the sub thinks its in a larger enclosure?


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## Megalomaniac

I deadened my sub enclosure. But I deadenedit on the outside of the box though. My reason was to eliminate some trunk rattles from the box hitting the tire spare well in my situation. 

I did notice if i tap on the box its not as "hollow" sounding as before. my box is made out of birch ply .5"


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## [email protected]

Megalomaniac said:


> I deadened my sub enclosure. But I deadenedit on the outside of the box though. My reason was to eliminate some trunk rattles from the box hitting the tire spare well in my situation.
> 
> *I did notice if i tap on the box its not as "hollow" sounding as before*. my box is made out of birch ply .5"


I noticed that right away also


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## bretti_kivi

... mine isn't quite dead but I'm going to put some Buytl on the top before the whatever surface. It doesn't resonate, but it's still not as dead as I'd like. Plus it's around 0.8cuft and 500W 

Bret


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## GlasSman

I use extensive bracing in my enclosures.....no need for deadening.


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## circa40

I used liquid deadening for my previous enclosure. Its a must for fiberglass enclosures, along with poly fill.

Edit: are you using for structural integrity? or to help kill standing waves (as I did, indicated above)


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## James Bang

I don't see the need for any deadener in mdf boxes, I'd rather add bracing. Fiberglass enclosures are a diff story like circa40 said.


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## Rudeboy

James Bang said:


> I don't see the need for any deadener in mdf boxes, I'd rather add bracing. Fiberglass enclosures are a diff story like circa40 said.


I agree. Sound deadener is intended for thin resonant materials like sheet metal and plastic. It shouldn't have any functional benefit on MDF.


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## FoxPro5

BeatsDownLow said:


> So what does the sound deadening do inside a sub enclosure? Just slow the waves down more so the sub thinks its in a larger enclosure?


Applying ANY type of viscoelastic material to MDF will change it's resonant properties at least some. The question is: will they result in an audible benefit or greater SPL?

That depends on the size, shape and density of the MDF. If you have a long, flat face on your box with the sub at the far end, for ex, it will impart a flexion/extension force and vibration nodes along that face. An extensional damping product like a liquid "deadener" can do a few things for you...
- dynamically stiffen the surface and help reduce the formation of those resonant nodes (especially dead center if the panel.) 
- convert higher harmonic resonances to heat (you cross your sub at 80 with a 12 db slope, but it still plays 160 hz, for ex).
- soak into the porous surface of the MDF, thereby giving the sub a more solid structure to play in. 

Yes, I used liquid deadener on my box and I feel like it works like it should. I'd recommend it to anyone. 

Also, I find it funny that the same people that recommend the use of deadener on a baffle build also say using deadener (in the generic sense)on a sub box is worthless. Is the mounting surface of a sub box not a baffle?


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## Rudeboy

FoxPro5 said:


> Applying ANY type of viscoelastic material to MDF will change it's resonant properties at least some. The question is: will they result in an audible benefit or greater SPL?
> 
> That depends on the size, shape and density of the MDF. If you have a long, flat face on your box with the sub at the far end, for ex, it will impart a flexion/extension force and vibration nodes along that face. An extensional damping product like a liquid "deadener" can do a few things for you...
> - dynamically stiffen the surface and help reduce the formation of those resonant nodes (especially dead center if the panel.)
> - convert higher harmonic resonances to heat (you cross your sub at 80 with a 12 db slope, but it still plays 160 hz, for ex).
> - soak into the porous surface of the MDF, thereby giving the sub a more solid structure to play in.
> 
> Yes, I used liquid deadener on my box and I feel like it works like it should. I'd recommend it to anyone.
> 
> Also, I find it funny that the same people that recommend the use of deadener on a baffle build also say using deadener (in the generic sense)on a sub box is worthless. Is the mounting surface of a sub box not a baffle?


I don't buy it. If you have resonance or movement in the box, you didn't build it properly in the first place. Same goes for high frequency harmonics. Liquids soaking in might increase the density of the MDF, but we'd need to know the densities of the two materials. Deadening an MDF baffle doesn't make sense to me either.


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## FoxPro5

Rudeboy said:


> Deadening an MDF baffle doesn't make sense to me either.


If polyresin isn't available, keeping MDF away from the elements with a coat or two of liquid deadener does wonders and really helps extend the life of it. Same could be said with a layer of foil-backed butyl (if you get a good seal.) Also, adding some aluminum to the baffle it can improve it's function by delaying the rear wave (blocker) more than the MDF alone. There's a bit of mass added, which probably won't hurt. In a world obsessed with back waves, these are all good things.

But yes, if you cannot build a box, then they seem to be band aids. Not always bad things for guys with limited budgets and fabrication skills.


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## Megalomaniac

you guys still using mdf? 



edit: just to be clear i used the deadener on the outside of my box to stop it from rubbing on my spare tire well floor making noises while driving, kinda bounces even though its bolted down.


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## RedGTiVR6

ABSOLUTELY!

We have used 6 sheets of Black Hole 5 on the inside of the sub enclosure.

Reducing and/or completely eliminating resonance is the absolute KEY to having a good sounding car.

You would be surprised just how much of a difference you will hear by properly deadening an enclosure of ANY kind.

Just adding 3/8" of mounting baffle (aluminum/plexi/aluminum) to our pillars allowed us to drop the XO point a full octave.

If you're NOT adding mass to your enclosure and only relying on internal bracing, you're only doing half of the job.

I'm not saying that everyone should run out and plaster Black Hole 5 everywhere, unless you want to...then I won't stop you...

I'm saying that to NOT do it, and to say it doesn't make a difference is a gross wrong statement.


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## theRESONANCE

Just wondering, How about full glassed boxes?


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## RedGTiVR6

Sure thing. Fiberglass isn't really a great material for stuff like this.

I will say this...use sand in your fiberglass next time you build a box with it...or anything that needs to be dead.

It works a treat.

We just built/are building a new set of pillars for the GTi and used about 2 cups of sand per side. I'm amazed at how dead it's made these things.


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## circa40

theRESONANCE said:


> Just wondering, How about full glassed boxes?





circa40 said:


> I used liquid deadening for my previous enclosure. Its a must for fiberglass enclosures, along with poly fill.



To stiffen up FG enclosures Duraglass does wonders.


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## theRESONANCE

-.- .. 
sorry, i totally missed your earlier mentioned comment circa.

Red, you mentioned sand ? how is this done lol.


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## jdsimons

My sub enclosure is full fiberglass enclosure, I would strongly suggest using sound deadening material. The enclosure is about .55. It only took about half maybe 3/4 of a sheet of Damplifier Pro sheet to do the entire inside of the enclosure. Definately made it sound more solid even though the glass work was built pretty thick I thought would keep from flexing at all but I did notice quite a bit of difference from before and after.


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## Rudeboy

Let's get down to basics here. Nobody is questioning the benefit of dense materials for baffles, so let's leave that out of the discussion for now. Blackhole 5, at 1.375" thick (and $12/ft²) for lining an enclosure brings all sorts of variables into the equation that may or may not be relevant. Let's talk about typical sound deadener on MDF.

We choose MDF because it is pretty dense and rigid to start with. I started with a small scrap of 3/4" and calculated its density to be 7.81 grams/in³. Regular Damplifier's density is roughly 22.18 grams/in³. Big difference, but keep in mind that we aren't replacing the MDF with deadener, just supplementing it. One layer of Damplifier on 3/4" MDF yields a combined average density of 8.74 grams/in³ - a decent improvement.

Foxpro5 mentioned applying a liquid deadener to MDF to increase density, do a few other things and waterproof the surface in case Poly resin isn't available. For waterproofing, I'd suggest that it is always available since you can buy a quart at HD for a few bucks and a quart will go a very long way the way I apply it. I learned this technique from a boat builder and use it for any MDF that goes into a car. I dilute the resin 1:3 or 1:4 with acetone and then a quantity of hardener that I'd use for the total volume. U.S.Composite's resin call for 10 drops of hardener per ounce. I mixed 2 ounces of resin, 6 ounces of acetone and 80 drops of hardener. This makes a very liquid mixture that soaks into MDF really well. I slathered it on my test scrap of MDF and let it cure. It's important to do this after you have drilled holes in the MDF so that every exposed surface is treated. I've cut previous test pieces in half and found the mixture had penetrated about 1/8".

The treated MDF sample has a density of 8.69 grams/in³ versus the MDF/Damplifier density of 8.74 grams/in³. That's extremely close and has the added benefit of completley waterproofing the MDF. Nobody has provided any evidence that the marginal density increases we are considering have any effect at all. It seems likely that if MDF alone needed augmentation, other materials would be used instead.

Applying sound deadener to the surface of a box and tapping on it proves nothing about the box's performance. If somebody wants to build two boxes, one with and one without, put identical drivers in them and ABX them, we'll have something to talk about. I don't think you can do Oberst bar testing with MDF, but if somebody can devise a similar test to evaluate resonance, I'd love to see the results. As it is, all we have are anecdotal accounts.


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## Attack eagle

mdf is used because it is cheap, has no grain, and is easy to work. It is still sawdust mixed with a binder, not magically stiff or acoustically dead. especially in large flat panels. 
I have deadened mdf enclosures internally (using textured undercoating) and found that it reduced the amount of 'reflectivity' inside... a large sealed mdf box, no matter how well braced, is a big echo chamber. It sounded better (cleaner) to me, so I will keep doing it  After all I only care about the sound... the science is just a stepping stool to get me there


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## RedGTiVR6

Attack eagle said:


> mdf is used because it is cheap, has no grain, and is easy to work. It is still sawdust mixed with a binder, not magically stiff or acoustically dead. especially in large flat panels.
> I have deadened mdf enclosures internally (using textured undercoating) and found that it reduced the amount of 'reflectivity' inside... a large sealed mdf box, no matter how well braced, is a big echo chamber. It sounded better (cleaner) to me, so I will keep doing it  After all I only care about the sound... the science is just a stepping stool to get me there


Very well put.


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## Rudeboy

Attack eagle said:


> mdf is used because it is cheap, has no grain, and is easy to work. It is still sawdust mixed with a binder, not magically stiff or acoustically dead. especially in large flat panels.
> I have deadened mdf enclosures internally (using textured undercoating) and found that it reduced the amount of 'reflectivity' inside... a large sealed mdf box, no matter how well braced, is a big echo chamber. It sounded better (cleaner) to me, so I will keep doing it  After all I only care about the sound... the science is just a stepping stool to get me there


This sounds like directional speaker wire logic to me. MDF may be cheap, grain free and easy to work with, but while I've seen alternatives discussed where weight is a concern, I've seen no one suggesting better performance from other materials. Cost may be a factor, but with the extremes many people on this board go to, I'd be very surprised if a clearly superior, but more expensive material wouldn't be the new forum boner. For that matter, if there was a demonstrable advantage to be had in doubling up or using thicker MDF, plenty of people would be flocking to it.

Exactly which frequencies produced by a subwoofer are we worried about having bounce around in the "echo chamber" that is a sealed MDF box? What can undercoating do beyond sealing leaks in a poorly constructed box? Can it absorb or deflect an 11 foot long 100 Hz wave? Volume is key and anything you put inside the box will have an impact but undercoating applied at 1 mm inside a 12" cube will only amount to .00003051 ft³. Will that make an audible difference? 

The treated box may have less "reflectivity" when you shout into it, but that's dealing with a completely different frequency range and without the driver in the box, a completely different application. Science may just be your stepping stool, but without a plausible scientific explanation (and I'm not saying there isn't one I have missed), it is many times more likely that you are only hearing what you expect to hear.


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## C5!

Double layer face n back, Lots of resin, 45's in corners, and threaded rod (front to back, top to bottom, side to side) it "aint" moving!


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## Attack eagle

Rudeboy said:


> This sounds like directional speaker wire logic to me. MDF may be cheap, grain free and easy to work with, but while I've seen alternatives discussed where weight is a concern, I've seen no one suggesting better performance from other materials. Cost may be a factor, but with the extremes many people on this board go to, I'd be very surprised if a clearly superior, but more expensive material wouldn't be the new forum boner. For that matter, if there was a demonstrable advantage to be had in doubling up or using thicker MDF, plenty of people would be flocking to it.
> 
> Exactly which frequencies produced by a subwoofer are we worried about having bounce around in the "echo chamber" that is a sealed MDF box? What can undercoating do beyond sealing leaks in a poorly constructed box? Can it absorb or deflect an 11 foot long 100 Hz wave? Volume is key and anything you put inside the box will have an impact but undercoating applied at 1 mm inside a 12" cube will only amount to .00003051 ft³. Will that make an audible difference?
> 
> The treated box may have less "reflectivity" when you shout into it, but that's dealing with a completely different frequency range and without the driver in the box, a completely different application. Science may just be your stepping stool, but without a plausible scientific explanation (and I'm not saying there isn't one I have missed), it is many times more likely that you are only hearing what you expect to hear.


New forum boner: 3/4" appleply...  I like it better than mdf for my own stuff. 

I think the textured finish, more so than the mass or sound absorbtion qualities is at play. MDF by it's nature is flat uniform panels. flat panels reflect not diffract. You can hear this in a room when you sheetrock the walls and ceiling before applying textured finish, and the reflections go away after. Same reason why we use textured foam, or deflect pads, behind smaller drivers in doors. 
I find it particularly useful when the driver to rear wall is very short.

It really helps with FG enclosures... 

I learned this from a blind A/B test one of the shop's installers did with two identical enclosures, there were no unwanted harmonics and reflections (to my ears) in the treated box. It sounded cleaner... and I was puzzled as to why until he took the driver out.

I always say, try it for yourself, make up your own mind. 

It sure as hell isn't going to HURT you by losing volume, and if it does nothing then it can't hurt you either, right?


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## trunks9_us

so does adding some deadener all over a sealed box help out on a fiber glass or mdf box at all? If it does I plan on doing the entire box inside.


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## RedGTiVR6

I cannot stress how important it is to prevent resonance. It seems like people don't understand the impact that this has on a audio system.

if panels or enclosures are resonating, they are drawing the resonant frequency from your ears.

Deaden, deaden, deaden. Another fact that most people skimp on is the mounting baffle. You need to make 100% certain that your mounting baffles are as solid and dead as possible.

These two things will make the biggest difference for the least amount of money, IMO.

Remember, non-hardening modeling clay is your friend.


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## zGhost

I must have woke up on the wrong side of the bed this morning. But instead of laughing at this thread I frowned. Rudeboy has made the only intelligent informed reply here. So called painting or sound deading the inside of of Box made "correctly" (well cut ,well glued and correctly braced) Make absolutely no sense to me either. I have made many boxes in my days and never had or even felt the need to apply any so called deading to them. Sure I could and charge the extra $ for it. Not saying it would hurt anything and if you enjoy the process (as many people would being they are building the box theirselves) go ahead and do it. You'd be better off do something that actually makes a difference like adding some fill to the the box. The "its a big echo box" made me smile though. Where did that come from? Sure a empty box might echo or sound hollow when you shout into it, But its a whole different beast once you seal it with the driver. I don't need any measurements to tell me that, a little acoustical knowledge, and over 20 years experience tells me. Either or enjoy painting your boxes I'm sure they sound much better to you ears and that what counts in the end. The reason why though i fell has much more to do with the fact the you know its been done (power of the mind) than actual measurable differences in the sound. Feel free to flame me here. I'll still sleep well at night.


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## SQCherokee

I agree with what jan said...alot of people work the sides and back of the box...but don't do much to the baffle...probably because you can't see what your doing so it gets neglected. 

I always build my boxes adding the back panel last. that way you can get to the back of the baffle...and the sides and then add deadner to the back panel from the front once your done.

My enclosure in my sentra was a 1.33 cuft common chamber originaly built for a pair of old 10" kicker comps. I put dynamat over the whole interior...and then sprayed truck bed liner on top of that. Those two things combined with screws every inch instead of every two made that enclousre sound very good with those subs.
However when I upgraded to some alpine type R's and I noticed that it was a little boomy because it was a bit to small. Adding a bit more polyfill helped but I think that if I could have rebuilt it with a bit more airspace it would of sounded better.


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## FoxPro5

zGhost said:


> I must have woke up on the wrong side of the bed this morning. But instead of laughing at this thread I frowned. Rudeboy has made the only intelligent informed reply here. So called painting or sound deading the inside of of Box made "correctly" (well cut ,well glued and correctly braced) Make absolutely no sense to me either. I have made many boxes in my days and never had or even felt the need to apply any so called deading to them. Sure I could and charge the extra $ for it. Not saying it would hurt anything and if you enjoy the process (as many people would being they are building the box theirselves) go ahead and do it. You'd be better off do something that actually makes a difference like adding some fill to the the box. The "its a big echo box" made me smile though. Where did that come from? Sure a empty box might echo or sound hollow when you shout into it, But its a whole different beast once you seal it with the driver. I don't need any measurements to tell me that, a little acoustical knowledge, and over 20 years experience tells me. Either or enjoy painting your boxes I'm sure they sound much better to you ears and that what counts in the end. The reason why though i fell has much more to do with the fact the you know its been done (power of the mind) than actual measurable differences in the sound. Feel free to flame me here. I'll still sleep well at night.


Let me get this straight. You've been building boxes for 20 years and have never "deadened" any of them and therefore conclude that it's "unintelligent" and makes no sense to you? How about on your next box you actually _try it_ and then form an opinion?  Seems like _that _might be more intelligent.

Again, many of us are DIYers and not expert builders with 20 years under out belt. Hence, we need to get as far as we can "doing it right" with our skills and knowledge. There is nothing wrong with creativity and compromise in this hobby. IMHO its _necessary_. 

Jan, I don't have any regret in saying this but I think I <3 u!  Keep up the good work!


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## RedGTiVR6

We deadened the sub enclosure in our car after it was recommended to us.

Since then, the most frequent comment we get about the car is that the sub bass is the best they've ever heard. These are people who have no idea the lengths we've gone to on that sub box just to deaden it.

I don't have the science to back it up, but as I've mentioned elsewhere on this forum in other, I've listened to it and heard the difference....therefore I choose to believe it.


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## zGhost

Hehe . I never stated I've been building boxes for 20 years nor am I a professional. I started out in 1981 building my first box outta plywood and proceeded form there. After gaining some knowledge and a lot of research I finally learned the correct way. I again state yes you are correct I have never deadened any of the boxes i built nor do i have any plans to do so if i built another. I would rather build it correctly with super clean cuts, correct bracing and well glued joints (along with trying to follow the 'golden ratio' as far as dimensions go). As far as your "Again, many of us are DIYers and not expert builders with 20 years under out belt. Hence, we need to get as far as we can "doing it right" with our skills and knowledge." comment that was the whole reason for my post. The point is build it correct with the correct materials and you do not need to stick ,paint or spray anything on it. Being that money is often an issue for many member reading this forum, I cannot condone wasting money on deadening material for a sub box. When it has negligible effects. Again if you want to go ahead, like I also said many might enjoy the effort doing it and that what counts most. I'm sorry though I still see no beneficial gain from doing this besides the 'I know its deadened so my mind tells me it sounds better' If you think deadening your "correctly" (note the quotes as correctly built is critical) box make a difference. You better strip down your car and paint, stick., spray rhino liners all over it cause your getting much more resonances out of your vehicle than the box its self.


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## FoxPro5

zGhost said:


> You better strip down your car and paint, stick., spray rhino liners all over it cause your getting much more resonances out of your vehicle than the box its self.


Now that I agree with. 

I'm not trying to give you a hard time and I definitely agree with you about proper box construction and doing it right the first time. I'm all for that. Thing is, bracing will raise the RF of the box and "deadening" will lower it. Nothing wrong with using that to help you achieve the best sound possible, is there? After all, as it's been said a few times, it's about controoling the _noise _created by our sound. 

Jan, with all the BH5 in your enclosure, it sounds like (from a "scientific" standpoint) that the barrier layer is really helping you out in terms of not being able to locate the subbass location. I'm not entirely convinced on the positive effects of open cell materials and sub-length frequencies. MR's, yes but not up to 80-100 hz with huge wavelengths. 

What would be interesting is to build two identical enclosures - one with a decoupled barrier on the inside and one with a damped decoupled barrier (Black Hole 3) and see if the deadening layer really does make a significant difference. I'd guess not.


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## RedGTiVR6

I agree...though I'm not sure I follow your comment about open celled foam and 80-100 hz.

The BH5 has more than just opened cell foam, and any sub that plays up to 80-100 Hz in a car is going to be localized no matter what.

Our sub only plays up to like 35 Hz.

Also, what's this BH3 you speak of?

I think that the description of BH5 helps to explain a bit:




> Blackhole 5 is a complex multi-layered system which addresses three key functions: cabinet damping, isolation, and absorption. Blackhole 5 attaches to the enclosure interior via extremely strong PSA (pressure sensitive adhesive). It will take the guess work out of tweaking your enclosure. You will spend more money (not to mention time) building enclosures with excessive bracing, disproportionately thick panels, and exotic materials just to approach the performance of Blackhole 5 in an inferior enclosure!




So in short, yes, the same end result is possible by building a completely rigid, 100% correct enclosure. However, in a car, that's not always feasible. Fiberglass isn't exactly a great enclosure material to begin with, and in most car audio systems, fiberglass is necessary to fit many of the complex shapes and areas that one must work with. BH5 effectively negates that downfall.

If we're talking about a home cabinet, the I'm sure the differences are quite negligible, but for someone looking for that minute improvement, deadening their enclosure for a home cabinet is the way to go.

Why else would super high end home speaker companies do it? They are looking for the few percentage points that make them that much better than others on the market.


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## keithace

great discussion...

to me it would all matter on size of the panels...the smaller the panels the less chance of resonation they have...larger panels would be more apt to resonate...i would assume good bracing and clean soild joints would all but eliminate resonance in larger boxes...

and the placebo effect also takes place...its like putting a cold air intake on your car...looks cool, makes you feel good, sounds different...but does it make the engine run better than the stock intake?


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## keithace

damn double posts...


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## RedGTiVR6

keithace said:


> and the placebo effect also takes place...its like putting a cold air intake on your car...looks cool, makes you feel good, sounds different...but does it make the engine run better than the stock intake?


You know...that's not really a great analogy...lol


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## [email protected]

keithace said:


> great discussion...
> 
> to me it would all matter on size of the panels...the smaller the panels the less chance of resonation they have...larger panels would be more apt to resonate...i would assume good bracing and clean soild joints would all but eliminate resonance in larger boxes...
> 
> and the placebo effect also takes place...its like putting a cold air intake on your car...looks cool, makes you feel good, sounds different...*but does it make the engine run better than the stock intake*?


Yes it does, make the cars cpu redo the fuel/air ratio and makes more hp, simple as that


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## keithace

BeatsDownLow said:


> Yes it does, make the cars cpu redo the fuel/air ratio and makes more hp, simple as that


not true...

sorry i opened that can of worms...


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## FoxPro5

RedGTiVR6 said:


> I agree...though I'm not sure I follow your comment about open celled foam and 80-100 hz.




BH5 has 1" OCF as the absorptive layer. There's not a chance in hell that 1" CCF can do anything to a 100 hz wave that's 11 feet long. 1" OCF is probably only going to significantly affect ~3khz and above (if you go by the 1/4 wavelength vs velocity theory. In the real world, things are a bit different, though). As an example, your standard Owens Corning Acoustical Blanket lets 90% of 125hz right through. You'd have to go up to about 4" to get significant (above .65 NRC) absorption at 100 hz. 



> The BH5 has more than just opened cell foam, and any sub that plays up to 80-100 Hz in a car is going to be localized no matter what.


It's a deadener, decoupled barrier and absorber all in one. 5 layers: VE damping mat, CCF, vinyl, OCF and magic sprinkles/film covering. You can make a 1x1' tile for $15 if you have the materials. 



> Also, what's this BH3 you speak of?


BH5 minus the OCF absorber and the facing. It was to drive home the point that the OCF isn't doing anything in that box by way of absorption. Ok maybe something, but physics says a definite 'no' in terms of significance. 



> Why else would super high end home speaker companies do it? They are looking for the few percentage points that make them that much better than others on the market.


Because they are subject to the same physical laws as cars are. In order to successfully "kill" the back wave it has to be delayed by a properly-built baffle. The bigger the speaker, the bigger the baffle and the more impedance mismatch between the forward and rearward waves is needed.


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## Rudeboy

I think people are thinking too hard about this.  What's the resonant frequency of the enclosure? I'm pretty sure it would have to be enormous to be excited by any of the fundamental frequencies produced by a sub. That means we're only concerned with resonance from harmonic frequencies. I'm sure someone can explain how much energy is available there.

Bracing is going to raise the resonant frequency of the enclosure, taking it further away from the sub's fundamentals. Adding vibration damper may lower it.

Adding 1" OCF may perform like polyfill, letting you get away with a somewhat smaller than ideal enclosure, but FoxPro5 is certainly correct that absorbing frequencies >= 3.4kHz shouldn't be wildly beneficial in a sub enclosure. Applying vibration damper and OCF inside the enclosure of a home speaker might be helpful because of the frequencies involved. You can't extrapolate from that to a sub enclosure.

If you are considering doing any of this (and maybe even if you haven't considered it yet), build your enclosure and mount your sub(s) in it. Play it outside the car, sending it just the frequencies it will have to deal with. Hear enclosure resonance? Do something about it. Don't? You're all set. It seems crazy to spend money and effort to solve a problem that you don't know you have.


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## SQCherokee

if it works do it


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## jeff33702

trunks9_us said:


> so does adding some deadener all over a sealed box help out on a fiber glass or mdf box at all? If it does I plan on doing the entire box inside.



I'm planning fiberglass, spare-tire box. Is there a "correct" deadner to use on glass? Can I use a spray-on for the inside? Will I need polyfill?

Thanks
Jeff


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## RedGTiVR6

Use sand in the fiberglass.

1:1 ratio worked for us. Buy the more uniform grain like would be used in a playbox, not the general purpose sand. The cost difference is something like $1 for a 60 lb bag...which you'll end up using a few cups of...lol

But for less than $4.00 it's worth EVERY penny.

It deadens the enclosure.


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## SQCherokee

this is whats great about audio....its so subjective. There are so many things that can be done and alot of them work...while other things only make you think they work. Its mostly subjective...and most people build to what they like.

As I was saying about my enclosure in my sentra...when I switched to the type R-s...that enclosure was to small for those subs...it sounded great with techno, and rap. But for tracks on the usaci disc it sounded to boomy.

So an undeadned enclosure may sound ok for heavy kick drum, or synth bass...but with stand up bass it just dosn't work. This dosn't mean that Jan's wrong for all the work she put into her enclosure. And it dosn't mean that anybody who thinks that adding more bracing is wrong. Hell, I've seen people use the card board box that their sub came in as an enclosure...we know whats going on...we know how to do it right...so move on and agree to disagree.


----------



## hibuhibu

I only use deadener inside the box only to make sure that I do not have a leak. Most likely on corners or mounting hole etc etc.


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## jeff33702

RedGTiVR6 said:


> Use sand in the fiberglass.
> 
> 1:1 ratio worked for us. Buy the more uniform grain like would be used in a playbox, not the general purpose sand. The cost difference is something like $1 for a 60 lb bag...which you'll end up using a few cups of...lol
> 
> But for less than $4.00 it's worth EVERY penny.
> 
> It deadens the enclosure.


Added to my list 

I just realized that I've seen some of your posts over at mp3car. I don't compete, but I'm interested in the possibility of great sound from a PC....heading over there now to search your name, lol.


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## RedGTiVR6

heh - you'll find a lot of posts where I'm telling people to search.



Read the FAQs first, it will get you a ton more info, especially the FAQs in the navbar over there.


----------



## jeff33702

RedGTiVR6 said:


> heh - you'll find a lot of posts where I'm telling people to search.
> 
> 
> 
> Read the FAQs first, it will get you a ton more info, especially the FAQs in the navbar over there.


I've been reading them. There's very little info on spdif output directly to a processor like the 701. I guess I don't know enough about the optical signal because I thought that would be the most basic 1's and 0's - then the 701 could take it from there, but I guess there's more too it....still figuring it out - i'll leave it alone in this thread, as Im de-railing it fast.


----------



## RedGTiVR6

search for "bit-perfect".

In short, you basically just take the tos-link out of the computer and go into the 701.

Not much more to it other than getting pretty detailed as far as the technicalities of the software, etc.


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## trunks9_us

Ok so ppl here say they use deadener then on a box what are you guys using? damplifer pro or spectrum or somthing else? See I would think damplifer pro for the major areas but what about the edges and corners what would you guys use there? If it is sprectrum I would perfer not to use it but buy somthing rather small since I am just doing edges and corners. Another question I was looking at what about these here 
These dynaxorb as the same as ants except there square instead of circle. Well would these be better off in the back of the box in a sealed enclosure over the damplifer pro mat? Take note In my box setup I will be having polyfill in my box as well.

http://dynamat.com/products_car_audio_dynaxorb.html


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## RedGTiVR6

BlackHole 5: ORCA Design & Manufacturing


----------



## AVIDEDTR

RedGTiVR6 said:


> BlackHole 5: ORCA Design & Manufacturing


Jan,

I just picked up a Morel Ultimo 12" and I'm designing the temp box right now. I have two sheets of Black Hole Five which I bought last year and I want to incorporate them in to the box.

My question is: Do I have to take in the account the size and thickness of the BH5 and subtract them for the overall volume???


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## RedGTiVR6

Here's a bit of info from a page:



> Blackhole 5 is 1.375" thick, but it only displaces 0.250" of incompressible air.


----------



## AVIDEDTR

RedGTiVR6 said:


> Here's a bit of info from a page:


Thanks for the link - so I'll add .125 to enclosure to offset the bh5 sheets
14.6x14.6x14.6/1728+1.801


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## AVIDEDTR

jeff33702 said:


> I'm planning fiberglass, spare-tire box. Is there a "correct" deadner to use on glass? Can I use a spray-on for the inside? Will I need polyfill?
> 
> Thanks
> Jeff


Make sure you bolt it to the car! this will help


----------



## trunks9_us

RedGTiVR6 said:


> BlackHole 5: ORCA Design & Manufacturing


not to be doing a vs here but is there really any difference in this product over luxery liner or over kill pro?

Also what would I use to glue this to the box? and would I use some damplifier followed by the black hole 5 or just the black hole 5?


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## RedGTiVR6

Apples and oranges really...


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## trunks9_us

Hey so I can use this black hole 5 on my doors and floors as well correct? I mean i like the idea of it having its own way to stick on. That being said I would like to use black hole 5 on my doors and floor if it is ok over another barrier product.


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## FoxPro5

trunks9_us said:


> I would like to use black hole 5 on my doors and floor if it is ok over another barrier product.


So you want two barriers?


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## trunks9_us

FoxPro5 said:


> So you want two barriers?


NO I am sry for the confusion I meant would black hole 5 be ok to use on doors and floors instead of over kill pro and luxery liner pro.

Also I am about to do my head liner and deaden it I only have enough room for one layer So Should I use some blackhole five or damplifer pro on the headliner?


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## FoxPro5

trunks9_us said:


> NO I am sry for the confusion I meant would black hole 5 be ok to use on doors and floors instead of over kill pro and luxery liner pro.
> 
> Also I am about to do my head liner and deaden it I only have enough room for one layer So Should I use some blackhole five or damplifer pro on the headliner?


Don't know anyone that can fit something as thick as BH5 on an outer door skin without the window tearing it off when it goes down. 

Yes, LLP on your floor, not OKP. 

Yes, deaden your headliner with DP.

Also, re-read the thread and understand what BH5 is and does. Also, search the site - tons of great info here.


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## RedGTiVR6

BlackHole 5 is not designed to go in areas where it can get wet - like it would in a door.

They make a product called BlackHole Tile. Which is essentially 4" square tiles of BH5 covered in a rubber coating to make it water proof.

We have used 48 tiles total in our car (24 per door).

It makes all the difference in the world, and yes, it will clear windows is most vehicles when added to an outter door skin. There's no need to cover the entire door solid.

We have used the blackhole mat on the roof and on the floor of the car, and on the doors as well. We have used the Blackhole seal on the back side of the headliner its self as well as for seals for speakers and in other areas of the car.

We've also used the Blackhole stuff in enclosures (like polyfill but works better, also more $$, naturally).


----------



## AVIDEDTR

Can you use BH5 and BHstuff together???

Especially for my application?





RedGTiVR6 said:


> BlackHole 5 is not designed to go in areas where it can get wet - like it would in a door.
> 
> They make a product called BlackHole Tile. Which is essentially 4" square tiles of BH5 covered in a rubber coating to make it water proof.
> 
> We have used 48 tiles total in our car (24 per door).
> 
> It makes all the difference in the world, and yes, it will clear windows is most vehicles when added to an outter door skin. There's no need to cover the entire door solid.
> 
> We have used the blackhole mat on the roof and on the floor of the car, and on the doors as well. We have used the Blackhole seal on the back side of the headliner its self as well as for seals for speakers and in other areas of the car.
> 
> We've also used the Blackhole stuff in enclosures (like polyfill but works better, also more $$, naturally).


----------



## Rudeboy

RedGTiVR6 said:


> They make a product called BlackHole Tile. Which is essentially 4" square tiles of BH5 covered in a rubber coating to make it water proof.


Putting a rubber coating over acoustic foam will compromise it's ability to absorb sound. How can this be anything but a marketing guy's attempt to move a high priced "audiophile" product into the car? At the very least, the "thin diamond pattern embossing" that "dramatically improves performance of the whole acoustical system" is totally ****ed once you coat it in rubber - as if it every did anything close to what it claims in the first place.



RedGTiVR6 said:


> It makes all the difference in the world, and yes, it will clear windows is most vehicles when added to an outter door skin. There's no need to cover the entire door solid.


Not covering the entire door surface means you are compromising the barrier layer.

As frighteningly expensive as these products are, willingly discarding the performance of ANY of the layers, let alone 4 of the 5 in the sandwich seems absurd.


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## RedGTiVR6

yeah - how did I know that I would run into the naysayers as soon as I even mentioned a product that cost more than the dirt on your shoes....*sigh*....

as for the question about using BH5 and BH stuff...no reason to use the both of them really. Focus more on getting enough air space first.


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## AVIDEDTR

RedGTiVR6 said:


> as for the question about using BH5 and BH stuff...no reason to use the both of them really. Focus more on getting enough air space first.


my box is 1.80 right now without the bh5 in it!


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## Rudeboy

RedGTiVR6 said:


> yeah - how did I know that I would run into the naysayers as soon as I even mentioned a product that cost more than the dirt on your shoes....*sigh*....


Not sure how pointing out that a product that cost $25.00 per square foot ought to perform to a certain standard. Regardless, your colorful objection doesn't address any of the points I raised. I'll assume that you don't know what characteristics contribute to a material's ability to absorb or block sound or that you are secretly promoting this stuff and don't care what characteristics are important.


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## trunks9_us

I cant seem to find info on the bh stuff or bh tile or bh seal. COuld you tell me the differences in these?


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## Rudeboy

FoxPro5 suggested that we could build our own BH5 comparable material, so lets look at that and then consider how often that exact configuration is the best approach to the issues we face in automotive applications. Zaph evaluates BH5 and Whipermat for speaker enclosure lining - a distinctly different application. Since he mis-identifies the function of a some of the layers, I take his review with a grain of salt.

I've seen BH5 priced online at $25.00/ft². After looking around, I found SonicCraft offering 24"X27" sheets for $54.00 - $12.00/ft².

To set about building our own, let's start from the substrate up. The first layer is described as: "High loss black flexible viscoelastic damping layer. Backed with a super strong pressure sensitive adhesive". Since Zaph describes this layer as the same as the barrier layer (incorrectly I believe) and other selling sources describe it as vinyl, we can assume it is comparable to Cascade VB-2 or PE's Lightweight Vinyl Sound Damping Sheet. Let's go with the more expensive and highly regarded VB-2, $4.50/ft²

Next up are the "Vibration Isolation layer made with polyurethane flexible open cell foam" and the "FLoating Wall sound barrier made with linp flexible vinyl copolymer loaded with non-lead Inorganic fillers". I've grouped these together since it is so easy to find barrier/OCF composites already assembled. Second Skin Luxury Liner fits the bill. The foam layer is 3/8" istead of BH5's 1/4 inch, but that is to the good. $3.34/ft².

Finally, BH5 has a 1 inch acoustic foam with the famous "diamond pattern embossing". Parts Express sells a single 18"X24" sheet of 1" acoustic foam with surface embossing for $12.23 - $4.07/ft². It's also got a PSA, so we don't have to worry about glue for that layer.

Add it up:
4.50 - 1ft² Cascade VB-2
3.34 - 1ft² Second SKin Luxury Liner
4.07 - 1ft² PE 1" acoustic foam (embossed!)

Comes to $11.91 for 1ft². We've saved 9 cents and we still need adhesive to bond the vibration damping and barrier isolation layers. If you can find a good price on BH5, it is not a bad deal versus buying all of the components in the minimum quantities available and assembling them yourself. This is a pricing structure that works really well for the relatively limited quantities needed for home speaker cabinets. The larger quantities needed to treat a car introduce economies of scale that should increase the savings for those taking the DIY approach.

*Here's the important point*. BH5 is designed to be used inside the cabinet of a full range speaker to address the following problems:

Resonant cabinet walls.
Sound escaping through the cabinet walls.

That's all. If the cabinet walls don't resonate, the vibration damping layer contributes nothing. If sound isn't escaping through the non-baffle faces, adding a barrier and acoustic foam that will absorb frequencies above 3.4kHz won't add anything either. Getting any benefit from lining a subwoofer enclosure with this assumes the same deficiencies AND reduces the possible efficacy of absorbing frequencies > 3.4kHz.

The value proposition really breaks down when you start to use a product like this in doors and other general automotive applications. Let's leave the performance compromises introduced by whatever waterproofing process is used to make this stuff durable enough to go into a car. The real problem is that complex composites like BH5 assume that there is an ideal 1:1:1 ratio between vibration damper, barrier and absorber. This is seldom going to be the case outside of a home speaker cabinet. Even there, it probably isn't ideal, but for such a small application, who cares?

Uniform coverage is never the best approach with a vibration damper. Some areas need more, some need none. High performance products can achieve optimal performance with 25% coverage.

Unbroken, uniform coverage is essential for the proper performance of a barrier. The barrier MUST completely shield the listener from the noise source. Any breaks or gaps and the sound just goes around. Using a checkerboard pattern for a barrier is like using a sieve for a cup. Using the same pattern for a applying a vibration damper may be the most efficient use of materials. The same thing goes for adding a 1" acoustic absorber everywhere you need a vibration damper or a barrier. 

Others can argue about whether there is any real benefit to be gained by adding products like BH5 to the inside walls of a home speaker cabinet. The question here is whether there is any to be gained from adding it to a subwoofer enclosure or to the sheet metal of a car. The answer is complicated but can only be "yes" if the ideal solution consists of a treatment made up of the predefined quantities of acoustic treatments included in the composite. In most automotive applications, I believe that the result will be either insufficient or overkill. Insufficient means the problem hasn't been solved and overkill means you are wasting money. Intentional overkill is an error, not a virtue.


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## FoxPro5

^^^ 

I have to say, I do admire Jan's fortitude and "whatever it takes to win" attitude, but she's obviously sponsored by Focal by the comments she's made. 

But, I'd expect nothing less because when it comes threads about treating cars for noise and vibration on any forum, science and understanding usually takes a back seat to anecdotes and random smatterings of outright sillyness.


----------



## RedGTiVR6

I'm sorry, but I *do *resent the comment about 'obviously being sponsored' by Focal. I believe in the products we're running. We've had a few offers for FULL sponsorships from other manufacturers. I've not accepted them because I don't believe in the product.

That's right, we're *NOT *fully sponsored by Orca Design (the importers of Focal and Steg). Please read that again and note how I have never said that we are sponsored by Focal directly. We still pay for a number of things in the car. We still pay for our entry fees, our hotel rooms, gas, the material to build the car, etc. Orca (and Nick) help us where they can and when they can. We've stuck by them because I believe in the product.

However, UNlike a lot of people, I don't immediately assume that just because something is expensive, or just because something doesn't immediately make sense, then it's all snake oil. If I don't respond immediately, chances are, I'm researching....or that I'm busy with something else....or any number of things.

I don't know the answers to everything, contrary to popular belief.....*confused* I'm learning, just like many of you on here. I have my knowledge in different areas from many of you. Tuning for starters....I know CarPCs, I know fabrication.

Some of the things we've done in the car have been suggested to us by those who have been in the industry for decades. Some of the things we've done in the car have been done by others with world titles. Some of the things are us going overkill on the car....sure....but who doesn't?

The checkerboard pattern done on the outter skin of the car was done over an older layer of rammat. It was also done when we ran the speakers in the doors. It's also one of about 6 different layers of products total on all of the different surfaces in the door cavity.

I could go on and on....but I'm sure it's falling on deaf ears anyways...have fun guys.


----------



## Rudeboy

RedGTiVR6 said:


> yeah - how did I know that I would run into the naysayers as soon as I even mentioned a product that cost more than the dirt on your shoes....*sigh*....





RedGTiVR6 said:


> However, UNlike a lot of people, I don't immediately assume that just because something is expensive, or just because something doesn't immediately make sense, then it's all snake oil.





RedGTiVR6 said:


> I could go on and on....but I'm sure it's falling on deaf ears anyways...have fun guys.


I really don't understand where this is coming from, but it seems unnecessarily personal when we are all just looking for good solutions. I don't see anybody questioning your use of BH5 because it is expensive. The closest I or anyone else has come is questioning the expense when the configuration doesn't match the requirement. I'm sure you'd agree that using the wrong material to gain a small advantage is very different when one is paying for the privilege. 

Since you seem to be saying that you aren't paying more for BH5 than you would for the dirt on your shoes, it will be easier for people to evaluate your recommendation when they do have to pay for it. That's an important piece of knowledge. Do most people prefer the least expensive path that meets their requirements? Sure, but that's very different than the sort of reflexive reverse elitism you are suggesting. My cost breakdown above actually demonstrates that BH5 is a decent value - when the configuration meets the requirement.



RedGTiVR6 said:


> The checkerboard pattern done on the outter skin of the car was done over an older layer of rammat. It was also done when we ran the speakers in the doors. It's also one of about 6 different layers of products total on all of the different surfaces in the door cavity.


This is very simple and has nothing to do with unthinkingly characterizing your advise about partial coverage being adequate as snake oil. If you need a barrier, you need a contiguous barrier. If you don't need a barrier, BH5 or similar composites is not an appropriate solution - unless you are happy to throw away a big chunk of what you paid for.


----------



## t3sn4f2

Found this post while research mid enclosure shapes, slightly off topic but not really. Not putting it here for any reason other then it looked interested at a glance. So if it goes against anyones beliefs, oh well. 

""""""""In answer to the question "does the shape of the cabinet matter" Yes it can matter a great deal, if you know enough to use it to your advantage - or you can just keep stuffing those boxes full of peanuts, fiber fill, black hole, or whatever the latest and greatest whiz-bang stuff the car audio store is trying to sell this week.

First you need to know a wee bit about what goes on in an undamped resonant space (your sub cabinet or any finite baffle transducer cavity.)

Of course, you are aware that the acoustical power of your bass transducer compresses and rarifies the air in your vicinity (including your eardrums and the neighbor's too, along with his windows and furniture and so forth) If you think about it, it also compresses and rarifies the air inside the sub box, right? Yes, but that's NOT all that's going on in there. There is another neat little gremlin in the box called "resonance". Now, resonance is word derived from Herman Von Helmholtz's coined term -"resonator"...Its' taken from his work "On the Sensation of Tone", which is the definitive work on the topic for almost a hundred years, by the way. You might check it out, but be warned that it is pretty tough sledding.
Anyway, to understand reasonance on the cheap, here's an easy illustration. Ever blow on a bottle of your favorite beverage and make it whistle? THAT'S a resonator. We engineers still sometimes call them "Helmholtz resonators". Guess what, transducers in finite space cabinets do about the same thing and that resonance is related both to cabinet volume AND shape. (negating the internal resonances of the materials themselves - which, compared to cabinet surface resonances and volume resonance, are puny variables.) With all due respect to the other posts here, within reasonable limits, the wall-material is the MINOR factor in cabinet resonance, compared to the acoustical albedo of the internal surfaces at their resonant peak frequencies. Sorry guys...that's just the way it is in acoustical engineering world where the real heavy lifting related to the audio sciences gets done. Yes, I know-your megadon 1500 made out of andalusian spruce sounds "awesome", yes, I know you made a sub out of eleven layers of marble and it was divine...yes yes YES! I've heard it all before. Hate to break it to you, but the resonance of your andalusian spruce is called a sympathetic secondary resonance. It induced by the energy of the primary resonance of the fundamental resonant peak of the cavity contained by said spruce! No primary? no sympathetic. So...

Now back to reality - the resonance of any rigid finite baffle sealed cabinet is primarily and overwhelmingly determined by the internal dimensions of the reflective surfaces as they sympathetically resonate at the frequency represented by that dimension (or that frequency's partial.)

Resonance inside boxes with parallel surfaces is just an acoustical fact of life. So...ready to go outside the stupid zone, where everyone stuffs the sub cabinet full of turkey feathers? Ready to stop doing just like the kid who flunked out of math and now works at the stereo store tells you? Ready to apply your brain plus hard acoustical science? Have you chosen?

Great! Let's explore! First the principles -

Just for fun, let's imagine a 12" square cabinet, with a 10" transducer - built from say...MDF. No ports, no stuffing, just a transducer and a box. Let's say you've actually read the spec sheet and see that the transducer is rated at 88db efficiency 1watt/1meter. So, what do you suppose will happen when I put 1 watt worth of white noise power into our 1 foot cube sub? Why out will come something like 88db of white noise conforming to the performance curve of the transducer as the spec sheet rates it, right?

If you think so, then you don't understand resonance. You see, transducer is exciting air inside a 1 foot cube which has an internal fundamental resonance of 644 Hz. Each pair of resonant surfaces (top-bottom, side-side and to a lesser extent, front-back) will resonate at a particular frequency, in this case, 644Hz. Why? because parallel reflective surfaces bounce the acoustical energy back and forth between them...but not all the energy, a resonant cavity will re-concentrate a portion of all available energy at the acoustical wavelength that is best represented by the distance between those two parallel reflective surfaces! (plus, in descending order of efficiency, the harmonics) Are you starting to get it? Do you see how the idea that the shape of a sub cabinet (or any cabinet) can make a HUGE difference in the sound makes sense? Great, you're getting somewhere.

So returning to the foot-cube-sub...that 1watt of white noise in our 12x12x12 cabinet will have what we engineers call an emphasis peak at 644 Hz. That emphasis peak is generated (at the expense of energy stolen from other frequencies - there is no free ride) by the acoustical coupling of the transducer's output to the resonant peak of the cabinet.

So your sub is hotter than a pepper - at 644 Hz. Not exactly earth shaking...644 HZ is about the fundamental frequency of the second mounted tom on a drum kit. But at least you're not wasting that energy as heat with your horse feather stuffing!

Now, armed with your basic knowlege, let's imagine you get very ambitious and decide to make another sub cabinet. This one is bigger though. It is 36 inches on a side! Put the same signal at the same power through the same 10" transducer and you will now see a resonant bump of 12 db at 196 Hz. Why? Because the resonance of a 36 inch cavity is 196Hz. Ah...that resonance again!

If you made it twice again as big - 72 inches, can you guess what the resonant frequency will be? Multiple choice

1.) 19.6 Hz
2.) 12,000 Hz
3.) about 90 Hz

If you chose 3.) congratulations, you're learning.

You may notice that the calculated resonant frequency has roughly halved, though it is shifted upwards slightly. Why? As the cabinet gets larger, the relative displacment of the transducer motor itself becomes less significant, causing a slight shift up towards absolute values in the resonance. (the transducer motor is a smaller percentage of the total affected volume)

Now, let's make a sub 144 inches...wait, that's bigger than my car. So what gives? How do those guys get those gut thumping lows out of cabinets that fit in cars (sort of fit, anyway) For that matter, how come my semi-cheap little 18 inch square sub in a cube can still thump my car. That sure isn't 600 and something Hz I'm hearing, is it?
You are right, and there is a simple reason. While your little 18" square sub WANTS to resonate at 410Hz the sub builder stuffed it full of horse hair or fiber fill or whatever the heck they thought was best or found was cheapest that day...and that stuffing is absorbing the 410 Hz resonant energy and turning it into heat. (second law of thermodynamics) Since shorter wavelengths are more prone to absorption than long ones, the energy resonant at 410 Hz is wasted more efficiently by the stuffing than it's first sub-harmonic. See, there is what we call a lower partial at 205 Hz, and another one at 102.5 Hz, and yet another one at 51.25 Hz, and so forth, each is less affected by the absorption, though of course, each lower partial is down 3 db in acoustical power compared to the the one right above it, because each wave is progressively less of the total acoustical energy. Do you see why? The 18 inch resonant cavity can contain one 410 Hz wave, but only 1/2 of one 205 Hz wave, and only 1/4 of a 102.5 wave, and so forth. The total energy is therfore reduced proprtionally.

So your little sub box can sort of make thumps...but are you starting to understand why people sell you 1000 watt amps to get that low bass thumping? It is the stereo shoppe's version of Dr. Seuss's Star Bellied Sneeches. Wrong shaped, cheap to build boxes stuffed full of power robbing horse feathers or whatever need MORE AMPS... and who's going to sell you those amps? Why your friendly neighborhood stereo sneech!

Ports - We're not going to talk about ports here - except to say that ports are nothing more than resonators. Just like the hole in the top of your favorite beverage bottle is a port. Same principles apply. Ports are wonderful high-Q (narrow bandwidth = high Q) resonators, and I'm going to presume that you can do the math to get there on the port part of the design I'm about to hint at.

Yes, there is a better way (TRUMPET FANFARE)- but it requires some for-real engineering. I mean the kind you fell asleep for during geometry and physics class. It requires that you understand acoustics a bit, plus have some math skills, patience with carpentry, and the guts to go against the parking lot wisdom of the ignorant masses. You will have to go out and find the resources. They're out there - Theile and Small's work on resonances is still a standard work. Helmholtz is good background too. There are plenty of resonance calculators for free on the web, too. A college physics book and your little sister's t/i 83 calculator can come in handy as well.

O.K. I'm not going to do all the work for you, but here are the critical hints...

Imagine two surfaces that are parallel on only one axis. Think of a "V". Can you visualize that these two surfaces are in fact a wide-band resonant cavity? Each single axis parallel surface represents a small amount of opportunity for resonant coupling, expressed over a range of dimensions that create a "bandwidth resonator". Got it? If one end of the V resonates at 400 Hz (and 200 and 100 and 50, in partials) then the other larger end might resonate at 500 Hz (and 250 and 125 and 62.5) are you starting to get it. Use this design reality to your advantage to TUNE your sub cabinet to deliberately resonate at the partials of the desired efficiencies.

1. determine the desired bandwidth performance of your sub cabinet. Be realistic. Determine the bandwidth of the low frequency spectrum of the music to which you listen. (this is for music, right? not noise and bragging rights in the parking lot wars...right?) Do NOT get into an idiotic contest over how low can you go. Kick drums are NOT 5 Hz, o.k? A five string electric bass' lowest note is 30 Hz. BE REALISTIC.

2. Now build your bass cab around an entire set of strictly one-axis asymetrical surfaces which dimensionally represent the range of desired resonances. (or their first subharmonic partials - if you want it to fit in your vehicle). You'll have to do some figuring to determine these exactly. DO NOT ALLOW ANY TWO AXIS PARALLEL SURFACES.

3. Build, brace, seal and wire but DO NOT DAMP THE CABINET (yet)

Now install your transducer in your asymetrical cabinet, put your cabinet in your car, and carefully and slowly sweep the cabinet with a calibrated sweep sine wave. You'll find that the cabinet is now capable of producing vastly more acoustical output in the desired frequency range than exactly the same transducer / amplifier combination that is suffering from the stuff it like a Christmas turkey syndrome that they recommended at the stereo shop. As you sweep the performance bandwidth, you'll note the out-of bandwidth frequencies that still jump out at your ears. Don't fret - these are the frequencies that require still require what we call "critical damping". We'll get there, but DON'T damp yet. Now, do your Theile/Small parameter calculations and install a properly calculated port. Leave it movable, for by-ear tuning adjustments...don't just cement it in at the recommended dimension. Even the best calculators don't have adequate input from you to account for every brace, the vagarities of transducer dimensions, etc.

NOW, sweep it again - See how your port has changed the swept efficiencies of the various frequencies? fine tune the port to the desired primary LF resonant point. (the window thump point, for your brainless types 

No, DON'T GLUE IT YET!

Now, noting the swept frequencies you wrote down (you did write them down, right?) and those undesired upper resonances (the ones above your design's preferred bandwith output) calculate, build, and install inside your cabinet parallel absorptive surfaces placed at those precise dimensions which will absorb that resonance and only that resonance. Clever designers with multiple resonance issues may be able to use both sides of an internal damper plate and place a single damper at the distance representative of the two critical frequencies. These dampers will be free-standing flat surfaces with highly absorptive surfaces. They'll representing a percentage of your total cabinent interior surface area which remains undamped. These tuned dampers will absorb the stray resonances (and ONLY the stray resonances, without wasting acoustical power by the stuff the turkey method the stereo shoppe wants you to use so they can sell you some more amplifiers, and wire and terminals and really cool neon glow tubes, etc.) Congratulations - you now have a critically damped subwoofer cabinet.

Listen again. You should be close to happy. You may still need to install a small amount of additional damping, to make up for the corners you cut in your cyphering. Remember non-critically applied damping wastes power! Avoid it.

Properly executed, this method can produce 9-12 db gains in the desired performance range...all other things being equal, without a single watt of additional electrical power. Remember 6db is a doubling of acoustical power! Put that in perspective, 6db of gain requires a ten-fold increase in electrical power. Does the work on a critically damped sub cabinet sound more appealing now? Imagine how much more thunder you can make with a tuned-resonant critically-damped cabinet!

Science is fun!

Cheers,
CBG""""""


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## RedGTiVR6

Some more technical information about the BlackHole 5 tile from the guys who designed it, hopefully it will help to explain some things.

If anyone has any questions, feel free to _ask_ and I'll see if I can get the answers.



> We had to make some changes so Black Hole Tile can survive inside a rain soaked car door. The home version of Black Hole 5 placed inside a car door holds water too long so has potential to grow mold.
> 
> 1) The plastic film on the face is very thin and reduces absorption only for frequencies higher than 8000 Hz. These frequencies have been removed from the 6.5 inch woofer by the crossover network. The diamond pattern surface texture only affects frequencies above 15,000 Hz.
> 
> 2) The 2nd 0.125 foam floating layer was changed from an open cell "spring" to a viscoelastic closed cell "damper". The closed cell prevents water absorption. We traded some barrier isolation for better damping of the steel. The end result is less steel vibration and faster vibration decay.
> 
> 3) The biggest sound reflection problems are the walls closest to the
> woofer. So this area must be treated first. It treats both the acoustic reflections and the steel vibration at the source where it has the greatest damping effect.
> 
> 4) Using nine Black hole tiles in each door fixes about 80 percent of the problem and covers about 20 percent of the car door area. Ideally 75 percent or greater of the door area should be covered to raise absorption to 95 percent. That is a large cost and weight increase for a small improvement. For a no compromise system it is worth covering the entire door to further improve the 60 Hz to 240 Hz frequency band.


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## FoxPro5

^That's about putting BH5 in a door. This tread is about damping a sub enclosure. Good info for this thread, though: http://www.diymobileaudio.com/forum...has-anyone-made-their-own-black-hole-5-a.html

It's true, if you put a film such as foil or mylar over an OCF absorber it changes the NRC figures. Basically, you trade some high end absorption for low end, which _might _ help you near a sub, but probably not. This is addressed here: http://www.diymobileaudio.com/forum/diyma-tutorials/27-simple-cheap-effective-door-treatments.html

It's nice to see them admit that their magic sprinkles does the product good at frequencies you can't even hear. 

Like it has already been stated, a barrier is only as good as it's continuity. If you REALLY think you can block 100 hz and down with the barrier layer in BH5, you have to ensure that are no flanking paths for that sound to squeeze through. A 10% gap is said to allow 90% of the sound through. 

Every acoustic factor that BH5 addresses.....damping, refraction, absorption, and diffusion...are all dependent on frequency. In a sub box playing up to 100 hz max, for example, the only thing that can affect that long of a wave is the barrier. A 1/8" layer of mass at 1lb/sqft has an estimated transmission loss of about 10dB at 100hz. At 50 hz it will be 0 dB. This is why you can hear your sub playing in your car from inside your house. How do you think it gets through all that metal, glass, wood, concrete etc to your ears? What makes anyone think some foam will have any affect on this? You have to have a ton of mass or a very thick open cell matrix to affect low frequencies with any significance.


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## RedGTiVR6

Yes, it is, but it was brought up in this thread (iirc) so I was finishing the subject rather than just leaving it hanging.


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## RedGTiVR6

And the response about using BH5 for a sub enclosure, hope it helps to clear up some confusion:



> If you take a perfect speaker and put it in a cabinet there are 3 primary kinds of distortion that lead to typically ± 6 dB frequency ripple.
> 
> 1) Diffraction at the edge of the front baffle.
> When the sound reaches the edge of the baffle, the corner causes diffraction. Typically there will be a +4 dB bump at the wavelength of the baffle width and a -4 dB dip at 2X this frequency. For all frequencies 1/2 this frequency there is a -6dB loss of efficiency called "Baffle Step". Mounting the speaker in a large house wall has no diffraction ripple or baffle step. A sphere, egg or "Olsen Wing (similar to Avalon)" cabinet reduces the ripple to ± 1dB, but it still has the 6dB efficiency loss. Mounting the speakers off center at 1/3 of baffle width reduces the problem to ± 2 dB. The -6 dB Baffle Step is fixed with a parallel resistor/inductor equalization circuit called "Baffle Step Compensation". In a three way speaker, Roy Allison solved the baffle step problem in 1971 by placing the woofer as close to the floor as possible and placing the crossover frequency to the midrange above 300 Hz - a HUGE improvement without any penalties. Subwoofers do not have these problems because the crossover frequency is several octaves below the diffraction frequencies.
> 
> 2) Internal acoustic reflections and acoustic resonance.
> For internal acoustic resonance a "golden rule" rectangle is the best with typically ±3 dB ripple when used in combination with 1 inch foam lining the walls. A sphere is the worst with typically ±12 dB ripple. A cylinder has typically ±6 dB ripple. Non parallel walls have no effect because the wavelength difference is too small. The total solution is open back DiPole with equalization but it has very poor efficiency and requires about 4 x cone area to reach the same loudness. A close second is a transmission line with typically ± 0.5 dB ripple. Transmission line bass extension falls midway between a sealed box and a vented box. There is very little wall resonance because there is very little pressure inside the transmission line. A transmission line box is also larger than a vented box. Power handling is similar to a large sealed box with Qts around 0.5. Transmission line woofers need to be very tough and have Qts between 0.5 and 0.7 - just like car door speakers and most car subwoofers.
> 
> 3) Cabinet wall resonance from internal air pressure.
> The stiffest wall is a curved surface like a sphere and the most flexible wall is a flat surface. Wall movement can add ± 4 dB resonant spikes, but the most noticeable sound effect is long sustained resonance that sounds cloudy and indistinct. Every doubling of wall thickness decreases the problem by about -3 dB. By adding shelf braces, every halving of free wall length reduces the problem by about -6dB. I like to put shelf braces every 4 to 6 inches to push flex to a very high frequency where it is more easily damped and hopefully higher than the crossover frequency. Building a double wall box with 1 inch air between the walls reduces the problem by -15 to -20 dB !!! A floating barrier like in Black hole 5 has a similar effect with about -6 dB improvement throughout midrange frequencies.
> 
> 4) Cabinet wall self resonance from standing wave vibrations.
> If you hit a bell it always rings at the same frequency, regardless of how fast you hit it or how hard you hit it. Both curved and flat walls have a self resonance frequency like a bell. Reducing wall size by adding braces raises the resonance frequency but does not eliminate the problem. Higher frequencies are easier to damp through wood loss or adding viscoelastic dampers like Black Hole Pad. Metal has the lowest damping and rubber has the highest damping. Polyurethane, uncured Butyl rubber, natural latex, vinyl copolymer and asphalt are the most popular damping materials. The best choice is based on operating temperature, weight and stiffness of the wall to be damped and cost. For cars, the two best candidates are Vinyl copolymer and uncured Butyl Rubber. Vinyl has more stiffness and viscosity so it is best for thick things like wood, fiberglass and aluminum castings. Butyl has more damping so is best for thin things like sheet steel and sheet aluminum. Using a stiff material like Baltic Birch plywood or fiberglass raises the resonance frequency and reduces flex. There can be a huge resonance reduction by not using glue, instead bolt the walls together with 1/4 inch thick EPDM rubber gaskets. The same is true for fiberglass, make it in sections that bolt together with rubber gaskets. It can sound like a solid rock when you tap on it! Making these decoupled sections is FAR more effective than adding damping to the surface.
> 
> So, how can damping be used to reduce the problems?
> From the above you can see that a sphere fixes two problems in exchange for another problem that is unfixable. A Rectangle is the best all around compromise that we can fix with some acoustic Band-Aids - curved sphere like front, round corners, drivers mounted off center, lots of braces, wall damping and acoustic damping.
> 
> Stuffing a cabinet full, like in a transmission line gives the clearest midrange but over damps the bass. So the acoustic compromise is to line the walls, thick enough to absorb the midrange but thin enough not to damp the bass resonance. For a vented box, acoustic foam about 1 inch thick is the sweet spot. A sealed box and use the foam on the walls plus polyfil stuff at about 0.25 pound per cubic foot. A transmission line will typically be filled with polyfill at around 1 pound per cubic foot - adjusted for woofer Qts and line length.
> 
> Black Hole 5 combines three functions into a single easy to apply acoustic treatment. 1 inch thick acoustic foam top layer, a floating barrier to reduce energy transfer to the cabinet wall and the wall damping layer.


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## FoxPro5

Good stuff, thanks for posting that.  Really says a lot about maximizing the enclosure build and design, especially to reduce the baffle step effects. 

I'd still like to do see test with BH5 in one box and a decoupled barrier in the other. Not so convinced about the foam.


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## Rudeboy

I really don't know what to say about this, except that in lieu of performance testing numbers, slinging BS is an insult to our intelligence.



> We had to make some changes so Black Hole Tile can survive inside a rain soaked car door. The home version of Black Hole 5 placed inside a car door holds water too long so has potential to grow mold.


Fair enough.



> 1) The plastic film on the face is very thin and reduces absorption only for frequencies higher than 8000 Hz. These frequencies have been removed from the 6.5 inch woofer by the crossover network. The diamond pattern surface texture only affects frequencies above 15,000 Hz.


That means we have an absorber, being touted for use inside doors that is effective between 3.4 and 8kHz. MOST or all of that range is not going to be sent to door mounted speakers.



> 2) The 2nd 0.125 foam floating layer was changed from an open cell "spring" to a viscoelastic closed cell "damper". The closed cell prevents water absorption. We traded some barrier isolation for better damping of the steel. The end result is less steel vibration and faster vibration decay.


Using closed cell foam for a barrier in a car door makes absolute sense,but what is viscoelastic closed cell foam? It's memory foam. Fine, probably no better or worse than any other CCF foam. Where it gets silly is extrapolating from the word "viscoelastic" that it is a vibration damper. Memory foam is viscoelastic in a MUCH coarser sense than viscoelastic vibration dampers. I'd be absolutely shocked if it added any vibration damping to the underlying vinyl layer. Playing with words.



> 3) The biggest sound reflection problems are the walls closest to the
> woofer. So this area must be treated first. It treats both the acoustic reflections and the steel vibration at the source where it has the greatest damping effect.


Fair enough. The vibration damping layer damps vibrations and the absorber absorbs frequencies that aren't significant in that application anyway.



> 4) Using nine Black hole tiles in each door fixes about 80 percent of the problem and covers about 20 percent of the car door area. Ideally 75 percent or greater of the door area should be covered to raise absorption to 95 percent. That is a large cost and weight increase for a small improvement. For a no compromise system it is worth covering the entire door to further improve the 60 Hz to 240 Hz frequency band.


These numbers are completely made up. 20% coverage fixes 80% of the vaguely defined problem? If the problem is solved by a vibration damper and absorbing frequencies between 3.4 and 8kHz, then OK, some of it will be solved. Remember that anything less than 100% coverage negates any significant barrier effect, so you completely waste that expensive component of the product at either the recommended 25% or the "ideal" 75% coverage. How does 100% coverage suddenly impact the 60Hz to 240Hz frequency band? 

BH5 is a vibration damper, a barrier and an absorber PERIOD. All of these functions can be quantified. Instead we get pure marketing blather - viscoelastic, frequency bands, blah, blah, blah. I'm shocked that a reputable company would allow an explanation like this out the door.


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## t3sn4f2

Rudeboy said:


> I really don't know what to say about this, except that in lieu of performance testing numbers, slinging BS is an insult to our intelligence.
> 
> 
> Fair enough.
> 
> 
> That means we have an absorber, being touted for use inside doors that is effective between 3.4 and 8kHz. MOST or all of that range is not going to be sent to door mounted speakers.
> 
> 
> Using closed cell foam for a barrier in a car door makes absolute sense,but what is viscoelastic closed cell foam? It's memory foam. Fine, probably no better or worse than any other CCF foam. Where it gets silly is extrapolating from the word "viscoelastic" that it is a vibration damper. Memory foam is viscoelastic in a MUCH coarser sense than viscoelastic vibration dampers. I'd be absolutely shocked if it added any vibration damping to the underlying vinyl layer. Playing with words.
> 
> 
> Fair enough. The vibration damping layer damps vibrations and the absorber absorbs frequencies that aren't significant in that application anyway.
> 
> 
> These numbers are completely made up. 20% coverage fixes 80% of the vaguely defined problem? If the problem is solved by a vibration damper and absorbing frequencies between 3.4 and 8kHz, then OK, some of it will be solved. Remember that anything less than 100% coverage negates any significant barrier effect, so you completely waste that expensive component of the product at either the recommended 25% or the "ideal" 75% coverage. How does 100% coverage suddenly impact the 60Hz to 240Hz frequency band?
> 
> BH5 is a vibration damper, a barrier and an absorber PERIOD. All of these functions can be quantified. Instead we get pure marketing blather - viscoelastic, frequency bands, blah, blah, blah. *I'm shocked that a reputable company would allow an explanation like this out the door.*


Anything is possible.......

What's wrong with the first pic?


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## TacoSQ

This is a long thread but of potential value. Starts of a little off-topic but bear with me here..

For the last 2-3 months our project @ UH Mech. Engineering undergraduate Design Class was to construct a benchtop wind tunnel, with low operating noise as one of the main requirements. (wind tunnels are inherently very very loud - 95dB and up! due to motors, fan, and lots of CFM flowing) 

The addition of a "muffler" which routes the 'exhaust' air through *a maze of special sound reduction foam was a KEY* in making the wind tunnel quieter.

A top view of the muffler is shown in 2 photos attached below. We were under flow constraints, otherwise the foam sound reducing area would have been greater (i.e. the maze would have been longer) to allow more sound absorbtion. 

We achieved a *minimum *sound reduction of over 8 dB across the whole operating range. In certain operating regimes the noise reduction was over 11dB !! THAT IS HUGE GUYS. 

The foam we used was 1" thick and had a NRC (noise reduction coefficient) of 0.75. 

There are many different variations of this foam, with varying thickness, self-adhesive and not, and even waterproof. We got ours from McMaster-Car, a popular engineering supply online warehouse. Go to McMaster-Carr and type "sound absorbing foam" into their search engine. 

*The price we paid was just a hair over $2.24 per square foot,* and we didnt even order a full roll. If you order 2+ rolls I think its even less.

Anyhow, this foam could possibly help in 'replicating' BH5, or at least some of its components. It could also be used a sub box lining.

The difference with the foam maze and without was huge, 11 dB sound reduction at the same operating CFM. (tested under same condition within almost same tim frame.)

Another point I'd like to propose but not fully address (it is almost 4 am here lol).. Can a structure similar to this maze be used to objectively TEST the different noise reducing products we have.

I know this has been off topic, but on the other hand, if you look at our wind tunnel, it is made of PLYWOOD, as in sub box plywood. We used 3/4" thick birch ply. (would have used MDF but we had to stain it to make it look nice)

I have some of the foam left I think. Maybe enough to at least cover a couple sides of my sub box. My system is not tuned at all but I will test the idea and see if the bass gets better.

Lastly, we did not have any resonance issues, thank God. The foam is proposed as absorbing material only. 8-11 dB reduction is nothing to scoff at.


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## TacoSQ

In the 2nd picture you can see the maze entrance and the 5th picture shows the exit hole.


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## Rudeboy

The important question (related to a sub box) is which frequencies did you attenuate and which frequencies did you attenuate with the baffle lined with foam versus without it? Regardless, the baffle itself adds a significant variable that makes it difficult to extrapolate from your project to a sub box. Cool project, BTW


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## chad

Or did the big ass vent just naturally attenuate the noise in general? Folded "venting" is commonly used in isolated computer racks, with no foam, but I have found that isolating the fan from the enclosure face REALLY makes a big difference.


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## TacoSQ

We tried the muffler with no foam and got nowhere near the results we had WITH the foam. I cant tell you the exact frequencies of noise we reduced. But this stuff WORKS amazingly well. 

The reason I posted this is if you're trying to build something similar to DH5 you might want to consider this type of foam..

We got up to 40 mph inside the wind tunnel, and it was still quiter than the old ones (no muffler) at 20 mph!


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## GlasSman

I've always suggested bracing an enclosure well and rigidly coupling the walls together rather than using any form of wall dampening products.

When I explain this to newbs I say "pick the largest wall in you enclosure and put on a layer of BRand X whatever.....hit it with you knuckle"

Now take that same wall minus the BRand X whatever and attach a full span wooden brace thats glued and screwed."

Hit it with your knuckle.

Which one feels and sounds more dead?


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## GlasSman

Now design the enclosure as JAn suggested in his reply where there are smaller spans that are attached together you take this concept several steps further.

Think of one of those HUGE autoclaves that are shaped like a submarine and built in modular sections...that would be the easiest ways of building a *VERY* dead enclosure thats *extremely* expandable.


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## jingle-jangle

if your box walls are flexing you need (more) bracing. I use triangular braces as well as dowels to hold the walls together.


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## Q-Authority

Wow, what a touchy subject!
I'm almost afraid to post.
As far as the original question goes, I would say it really depends upon box construction (material and design wise). Every box is liable to have at least two issues, resonance and reflections. You might or might not want a deadener depending upon your goals.
I personally only use sealed boxes and would definitely use some sort of relatively thin deadening material, even though I would already be using a decent mdf and polydacron stuffing. It never hurts to make sure you have reduced as many possible issues as you can, as long as you can afford it.
I haven't actually used any yet, in my car's sub box, but I have on my home sub and it definitely made a difference. The sub is a 200 watt bass reflex model, in which one would not normally assume that you would want to alter wave reflections. However, after having installed Dynamat on all interior sides of the sub, I was quite pleased with the results. It sounded as though the subs peak output was lowered by almost an octave and it was able to produce seemingly greater output with less audible strain. Hardly a scientific explanation, but the ears don't lie. I have however, done 1/3 octave testing on it, when matched to and crossed over with my front speakers at both 40& 60 hz and the results have been very good. When properly placed, the sub is virtually flat down to 20 hz, at about a 110db output. That's just at my testing volume level, not actual playing levels, which could be quite louder. Not too bad for a relatively cheap 12 year old Klipsch sub.
I would have immediately done the same to my car's sub box, which is a sealed type, but it is screwed and glued shut, and access through the speaker hole is very limited due to the box shape (bummer).
So, from my limited experience with it, I would definitely vote for at least trying it, depending upon your goals.


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## Leno

sealed box = poly fill 
ported or band pass = egg crate foam


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## temposs

Upon reading this thread I decided to go and add mass to my glassed kick panels. I already had poured quite a bit of resin in and let it dry to build up mass - I found some of the flat surfaces were still flexing quite a bit though, and I was getting some nasty resonance during extended deep midbass sections. I added rougly 4 layers of RAAMmat, followed by a layer of linacoustic (a popular material used by home audio enthusiasts to eliminate high freq reflections. The linacoustic is roughly 1.25 inches thick, with layers of fiberglass insulation of varying densities.

I must say, this made a HUGE impact on the overall sound quality, especially the midbass response in the vehicle. The mids seem louder overall at lower volumes to me. It also allowed me to lower the crossover point on my Dyn mw162 mids down to 63hz from 80hz - before I was just getting a TON of buzzing/resonance when attempting to run them down that low. This has brought a lot more of the bass towards the front of the vehicle, really improving the overall quality.

I plan to treat my subbox in a similar fashion tomorrow after work. It's roughly 1.1ft^3, with a 12w6v2 installed. Perhaps I'll snap some photos of the process.

Just wanted to thank all contributors for sharing their tricks/info regarding this subject.


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## jingle-jangle

TacoSQ said:


> This is a long thread but of potential value. Starts of a little off-topic but bear with me here..
> 
> For the last 2-3 months our project @ UH Mech. Engineering undergraduate Design Class was to construct a benchtop wind tunnel, with low operating noise as one of the main requirements. (wind tunnels are inherently very very loud - 95dB and up! due to motors, fan, and lots of CFM flowing)
> 
> The addition of a "muffler" which routes the 'exhaust' air through *a maze of special sound reduction foam was a KEY* in making the wind tunnel quieter.
> 
> A top view of the muffler is shown in 2 photos attached below. We were under flow constraints, otherwise the foam sound reducing area would have been greater (i.e. the maze would have been longer) to allow more sound absorbtion.
> 
> We achieved a *minimum *sound reduction of over 8 dB across the whole operating range. In certain operating regimes the noise reduction was over 11dB !! THAT IS HUGE GUYS.
> 
> The foam we used was 1" thick and had a NRC (noise reduction coefficient) of 0.75.
> 
> There are many different variations of this foam, with varying thickness, self-adhesive and not, and even waterproof. We got ours from McMaster-Car, a popular engineering supply online warehouse. Go to McMaster-Carr and type "sound absorbing foam" into their search engine.
> 
> *The price we paid was just a hair over $2.24 per square foot,* and we didnt even order a full roll. If you order 2+ rolls I think its even less.
> 
> Anyhow, this foam could possibly help in 'replicating' BH5, or at least some of its components. It could also be used a sub box lining.
> 
> The difference with the foam maze and without was huge, 11 dB sound reduction at the same operating CFM. (tested under same condition within almost same tim frame.)
> 
> Another point I'd like to propose but not fully address (it is almost 4 am here lol).. Can a structure similar to this maze be used to objectively TEST the different noise reducing products we have.
> 
> I know this has been off topic, but on the other hand, if you look at our wind tunnel, it is made of PLYWOOD, as in sub box plywood. We used 3/4" thick birch ply. (would have used MDF but we had to stain it to make it look nice)
> 
> I have some of the foam left I think. Maybe enough to at least cover a couple sides of my sub box. My system is not tuned at all but I will test the idea and see if the bass gets better.
> 
> Lastly, we did not have any resonance issues, thank God. The foam is proposed as absorbing material only. 8-11 dB reduction is nothing to scoff at.


You might have overkilled a little there... back when i used to smoke and grow my own mary-jane (legally via california MD recommendation), i had built a stealth box (just because i was legal doesnt mean i wanted to advertise my grow) with a GIGANTIC exhaust blower to exchange cool room air for hot grow-box air. The blower was EXTREMELY loud before I treated the exhaust with a foam liner. I had only about 12" of duct length after the blower exhaust. The actual output of the blower fan was a rectangular section about 2.5" x 7", and it WHOOSHED mightily by itself. This dumped into a larger box which was about 12x16" in section. What I did was just line the box with foam (old couch cushion foam) so that the 2.5x7" section carried through the larger box, effectively making a muffler out of the remaining volume. The 2.5x7" open area then did a 90-degree bend within the confines of the larger box towards the ground (formed by the foam).

This alone made the box virtually silent from the outside, probably a 10-20db drop in sound levels as percieved when standing directly in front of it. It was probably about 50db before (which is fairly noticeable in an otherwise silent room), and dropped to almost silent as in you had to "tune in" and listen for it to be able to notice it. 

FWIW...


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## hallsc

I have nothing usefule to add to this thread. I just wanted to subscribe. Sorry to interrupt thread flow


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## RedGTiVR6

Up at the top of the thread -> thread tools -> subscribe to tread

no need to post at all...unless you just want to...


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