# Does anyone dampen their sub enclosure?



## ghart999 (Feb 8, 2006)

I hear mixed reviews and opinions that it is necessary to prevent backwaves from canceling out the sub, etc. No matter how well braced the enclsoure is. Some say its not needed at all. 

I don't want to use polyfil due to its perceived effects of increase the volume of the enclosure. What about acuoustic foam panels or ensolite? Or would this only disperse freqs above 80Hz?

Just curious as to what everyone else does.

Thanks.


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## bobditts (Jul 19, 2006)

hmm never thought of doing anything like that. I wonder if lining the inside of the box with egg crate foam would help? Great topic ghart!


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## Antnee77 (Aug 1, 2006)

This is actually an excellent question. I was just about to post something similar to this. I have recently built a massive enclosure for W7's (see Install Gallery) which happens to also be a seat. I was wondering if anyone dampens their enclosures to reduce the vibration.


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## Beau (Oct 8, 2005)

One additional thought - would the benefit, if any, depend on whether the box was sealed vs ported?


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## bassfromspace (Jun 28, 2016)

I see no purpose in dampening your enclosure. As long as it's not perfectly square and braced properly you should be ok.


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## BlackLac (Aug 8, 2005)

i did notice it my parts express magazine, the Dayton MKIII home audio sub enclosure that comes unassembled has foam with it.


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## ghart999 (Feb 8, 2006)

Quotes from one of the tutorials posted by audionutz on ECA. Thoughts?

"Reflections are also a problem INSIDE speaker enclosures themselves. Speakers produce sound on BOTH sides of the cone. In an enclosure, the rear wave of the speaker is playing directly into a small, solid-walled chamber. When the sound waves reach the enclosure boundary, they can either be absorbed or reflected (we'll get to that). In a solid enclosure with no absorptive material, reflections from the back wave will occur, and the most devastating thing that can happen when they reflect happens when these sound waves bounce directly back at the cone. Since sound waves possess energy, when they strike the backside of the cone, their energy causes undue forces to be exerted on the speaker cone. This makes for distortion (both mechanical and sonic) as the reflected wave tries to force the cone backward. Side effects are resonation in the actual speaker itself, decrease in resolution of detail, cancellation at certain frequencies, and a basic "muddiness" of the overall sound (to name a few). Many guys use different tactics to battle reflections within enclosures. Some line the enclosure with fiberglass insulation, some use polyfill, wool, AcoustaStuff, or a derivative to "fill" the enclosure. Others use Acoustic Foam panels (you know the stuff(it's on the walls of recording studios) to line their enclosures. Cascade Audio even has special discs of damping material specifically designed to absorb the back wave of the speaker. They are called "DeFlex Pads" and work very well. In case you were wondering, I usually use deflex pads and/or polyfill to ensure absorption of the rear waves. No matter how you do it, the key is to absorb and dissipate the back waves of the speaker cones so they don't have a chance to alter your sonic performance in a negative way. "

Ideally, we want to be in a listening environment where we are surrounded by "acoustically dead" surfaces listening to speakers in "acoustically-dead" enclosures. By acoustically dead, I mean a surface that remains vibration-free in the presence of sound waves. A prime example is the hooptie box-chevy you likely passed on the road today with the loudest "trunk" you ever heard. I mean you hear the rattles OVER the bass, that's "trunk" bass! The sound pressure is causing loose stuff to vibrate and the metal to resonate. This also can happen at ALL frequencies, but as the freq goes up, it becomes less noticeable, almost to the point of us not needing to be concerned with the highs in this fashion. To expand on this a little further, body panels have their own "resonant frequency" and when that particular frequency is played at enough volume, these panels will vibrate and likely be heard. Even actual door panels and headliners can be affected this way. This is the very reason Dynamat and other like products were developed. Ever hear an interior trim piece rattle, but only on certain bass notes? This is exactly what I am talking about. It is a good idea to dampen as much of the vehicle as possible, and you will likely (I do!) continue to find little "rattles" here or there that need some sort of dampening to calm them. There are several types of dampening materials out there, and each type suits a different purpose. Resonations are also a BIG problem with the enclosures of the speakers. It is absolutely, positively VITAL that a speaker's enclosure resonations are dampened. When the enclosure vibrates at it's resonant frequency, it will emit sound waves of it's own. These waves can do several things. They can react with the backside of the speaker cone, cause cancellation, and even change the tonality of the speaker therein. On the outside of the enclosure, we can even hear the enclosure's "note" along with the speaker's note in severe cases. For this reason, enclosures and speaker baffles are often built extremely solid. Some guys even go to double-layers of MDF with Dynamat sandwiched between them. Others have even used sand and/or concrete to fill the space between the layers of double-walled enclosures for added resistance to resonation. In fiberglass applications, guys can add dampening layers to become part of the mold. Sometimes, thicker and stiffer enclosure walls can STILL resonate, so great care should be taken to use some sort of damping material inside the enclosures used in a high-end system. We can't get into all of these materials here, but these materials MUST be in direct contact with the inner surfaces of said enclosures. Sprays are the easiest to use, but self-adhesive damping materials work well too. If enough damping material is applied, virtually all unwanted resonations can be conquered inside an enclosure. Personally, I like to use non-hardening clay to deaden enclosures, as it sticks in direct contact with said enclosure and is easily pliable while offering excellent damping characteristics.

If we set out to make our own enclosure, we should consider trying to avoid a perfectly square box. A good way to do this with the standard "behind the seat, subs firing back" enclosure is to slope the front wall to form-fit the backside of the rear seat. Simply by having one large wall off-axis with the subs, we take away the "perpendicular" surface most responsible for standing waves. In any sealed enclosure, standing waves can occur at virtually any frequency, as ALL speakers produce second and third order harmonics (sound artifacts or notes which affect adjacent octaves in the freq spectrum) when they produce a sound, and for the most part, this is regardless of crossover frequency. Steep slopes do indeed help restrict these "unwanted" harmonics, however they should not be considered the "cure". Proper enclosure design is vital to combat standing waves, and the use of absorptive damping material is how I tackle them. I know there has been some debate lately on the topic "to polyfill or not to polyfill", but I believe strongly that ALL sealed enclosures can realize the benefits of using loosely stuffed polyfill throughout the interior. Polyfill serves to dissipate the rear sound waves of the speaker cones and hinders the chance of reflections and standing waves re-striking the cone. This results in greater detail resolution and the elusive "clean" sub bass, absent of artifacts and "sloppy sound". Polyfill is also known to make subs seem like they are in a bigger enclosure, but I believe the rear wave dissipation character of the stuff is responsible for the phenomenon. I'd like to see someone research the effects of polyfill inside sub enclosures to see if I am right. I believe I am.


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## bobduch (Jul 22, 2005)

There is a difference between cabinet resonation and the backwave hitting the cone. Ie you could have a totally non-resonant cabinet but still have the backwave bounce against the cone.
If your box is mounted to the floor and/or is a seat you will have lower resonance. (sitting on the seat/box is great mass loading!)
And a ported box will resonate less than a sealed since it is under less pressure. 
My box has non-parallel walls and acoustastuff. If you don't want the box to act bigger glue a brick in a corner to take up space and add filling. The filling will help avoid backwaves as it converts sound waves to heat. Tom Nousaine (spelling?) article on filling was very good too.

http://web.archive.org/web/20020808224043/integra.cyberglobe.net/caraudio/resources/fiberfill/

I wish we could get ahold of the Wilson Audio (you know, the X-1 Grand Slamm speaker) X material that they use for their bass cabinets. Supposed to be deaeder than concrete.
I've thought about the all out box. Non parallel walls, made of 3/4" or 1" 9 layer Baltic Birch (seems like the layers and glue make for less resonance than MDF to me), line the whole thing with 12" x 12" deflex pads, then stuff with Acoustastuff.
Oh, and plug those 2 big holes with Velodyne subs. lol


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## Diru (May 23, 2006)

Polyfill and/or opencell foam(eggcrate).

Note: Some high Xmax subs could pull poly into the VC assem. Should make a way for the poly to be kept off the back of the motor assem.

Opencell foam, (eggcrate). What I mean by open cell, you can blow through it, closed cell you can not(no good). Can be glued to interier walls. Not as good as poly, but can be used in combination.


Myself I used both at the same time. Before I stuffed the box. it rang at about 180hz(useing the tap test, 90hz was the second largest ring), and of course there were upper harmonics of 180hz, 360hz and so on at lessening levels as the frequency increased.

Even though I am xovered at 50hz, 45hz singals were enough to ring the box 180hz standing wave. So a note around the 45hz excited 90,180 and 360. So the box added this crap to the original sound(fundamental). Didn't sound to hot.

Stuffing method I used, opencell eggcrate all interier walls, then a pound of polyfill, then a flat sheet opencell foam that fit the width and height of the inside of the box, placed to hold the polyfill from laying on the back of the drive.


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## ghart999 (Feb 8, 2006)

Good ideas with the open-cell foam, etc. How do you guessitmate how much it changes the perceived volume of the box though? My box is tuned to specific frequency. If I add stuff to it and change the volume it will also change the tuning. How do I know how much this is effecting it? I like the brick idea, but again how would I know how much I am effecting the volume with the foam first off?


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## ocuriel (Oct 7, 2005)

Good info here.


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## Diru (May 23, 2006)

Just a guess.

If you used eggcrate foam with the 1 1/2 peaks glued to the walls only no stuffing. I would thumb a number of about 5 to 10 % increase of box volume would be shown to the driver. Not a huge change , but enough to lower the box tunning.

2 1/2 peaked eggcrate, again just thumbing a number, should closer to a solid 10% to maybe 13-14%.

Poly fill by itself can do 14-20%.

This is off the top my head so , yeah.


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## Tirefryr (May 15, 2005)

How can standing waves develop in an enclosure? They don't have the room to fully develop, so standing waves should never be an issue in a subbass enclosure. WHat is an 80Hz wave, 11ft.? Who has an enclosure with an 11' Long side?

If I'm wrong here, someone let me know.


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## dodgerblue (Jul 14, 2005)

ive cut and lined my sealed enclosures with eggcrate on all walls on 3 different enclosures,it did seem to tighten response some ,for 15.00 and a half hour you cant beat it!


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## bobduch (Jul 22, 2005)

So if I'm standing in the woods and the woofer is putting out an 11 foot wavelength and I'm standing 10 feet away does it make a sound?

Seriously though, it does not have to complete the wave to have energy (read backwave). This energy is what resonates the cabinet and hits the back of the cone causing distortion. Ever look at a passive radiator in a home speaker?

According to Tom Nousaine you can get up to a 40% increase in "box volume" with the right amount of fill. Some of the guys here should have the software to tell you what frequency you'll get out of a certain volume/port length.


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## typericey (May 13, 2006)

anybody tried putting dynamat on the inside panels of the box? i remember doing this when i was a car audio ignorant teenager in an attempt to make an inert box. I honestly didn't find out if it made a difference.


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## 3.5max6spd (Jun 29, 2005)

I spray Cascade VB1SPRO into all my enclosures. The material converts that energy /vibration created in the cabinet into low level heat. It also creates a perfect seal inside the enclosure. If you have a dual sub enclosure, i suggest you give this product a try and apply in in one side and test it out. Just giving it the good old knock test will show you changes.

I have yet to try using a Deflex pad behind the sub, or in combination with this product. Those pads arent cheap, but the VB1SPRO is like $11-14 a can tops and it will last several applications and have plenty left over to apply to some nook and cranies around the car. I use it inside door panels as well. Very effective.


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## ghart999 (Feb 8, 2006)

3.5max6spd said:


> I spray Cascade VB1SPRO into all my enclosures. The material converts that energy /vibration created in the cabinet into low level heat. It also creates a perfect seal inside the enclosure. If you have a dual sub enclosure, i suggest you give this product a try and apply in in one side and test it out. Just giving it the good old knock test will show you changes.
> 
> I have yet to try using a Deflex pad behind the sub, or in combination with this product. Those pads arent cheap, but the VB1SPRO is like $11-14 a can tops and it will last several applications and have plenty left over to apply to some nook and cranies around the car. I use it inside door panels as well. Very effective.


Where do you get the Cascade spray? SOunds like a good idea.


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## mikemareen (Apr 20, 2006)

all loaded enclosures by JL, Kicker, fosgate, etc all use stuffing or polyfill lining. In fact, I had a old school 8w6 triple box that was MASSIVELY stuffed with polyfill.


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## 3.5max6spd (Jun 29, 2005)

ghart999 said:


> Where do you get the Cascade spray? SOunds like a good idea.


http://www.cascadeaudio.com/aut7.html


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## rbenz27 (Mar 9, 2006)

Interesting thread. I'm also looking into this topic. Before I had my sub in a fiberglass enclosure, estimated around 0.9 cu. ft. 

I recently redid my cargo install and now the sub is in a 0.75 cu. ft MDF box. Cosmetically, it looks nicer but to be honest, I liked how the sub sounded in the old enclosure.

Even though the old enclosure was too big for the sub, it wasn't playing as tight, the sound was very clean and hitting low levels with ease. Now with the smaller box, its tight but it sounds boomy, I guess I'm getting a peaky frequency response?

Unfortunately, my setup doesn't have the capability to EQ the sub. What options do I have, polyfill, VBS1Pro, etc?


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## Pb2theMax (Aug 26, 2005)

Ensolite is closed cell, so I guess it would not be a good choice to use inside an enclosure?

I'm using AcoustaStuf now, but would like to experiment with some other stuff.


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## Chaos (Oct 27, 2005)

This topic is covered thoroughly in the Loudspeaker Design Cookbook by Vance Dickason. 

I have yet to find a more comprehensive explaination of subwoofer enclosure design and the relative performance which results from employing different methods of construction & dampening techniques. Not to say that the information in that book is absolute, but it does help to clearly illustrate these issues for the serious DIY speakerbuilers.


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## Pb2theMax (Aug 26, 2005)

Ah, I think I have that book in my house somewhere. I'll have to read it again.


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## FoxPro5 (Feb 14, 2006)

Weird. I just put a 1 sq ft piece of closed cell foam (camping pad) directly behind the sub today because I didn't have any polyfil. It was kind of boomy up around 100 hz. Afterwords the boomyness was gone and there was more of a identifiable thump that integrated better with the mids. Guess you never know till you try!!


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## Pb2theMax (Aug 26, 2005)

You let your sub play over 100 Hz? IMO 90Hz and up sounds better coming from mids.


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## FoxPro5 (Feb 14, 2006)

Pb2theMax said:


> You let your sub play over 100 Hz? IMO 90Hz and up sounds better coming from mids.


No I agree. That was just a guess. I think I had it LP at 60-65hz at 12 db/oct...and mids at 60hz or so. Anyway the boomyness is now gone


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## bassfromspace (Jun 28, 2016)

B-Squad said:


> No I agree. That was just a guess. I think I had it LP at 60-65hz at 12 db/oct...and mids at 60hz or so. Anyway the boomyness is now gone


Double-blind test's are your friend.


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## demon2091tb (May 30, 2005)

I'm not exactly sure from any tests or read anything about dampening sub boxes, etc. But what i will be doing most likely, is going to be a layer of deadening/spray on deadener (looking to be Cascades spray stuff from PE), a layer of ensolite, then a layer of acoustical eggshell foam, i've done this type of layering througout the whole car, the subbox will be done as well, and to mass load the FG as well as decreasing any audible inner noises/resonances.


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## effenay (Mar 2, 2006)

Chaos said:


> This topic is covered thoroughly in the Loudspeaker Design Cookbook by Vance Dickason.


Sixth Edition on clearance for $11 right now at Madisound!
http://www.madisound.com/cgi-bin/index.cgi?pid=2166


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## Pseudonym (Apr 17, 2006)

i tossed in some raammat but it was just to seal up some pre-existing holes from when i mounted some amps to the box.


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