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Sound dampening material

 

New member
Username: Lbeckner

Tulsa, Ok Usa

Post Number: 6
Registered: Oct-04
I'm installing 2 15" L7's. I was wondering how much sound dampening material I should use inside the box. Can it just lay in there loosely or does it need to be glued to the walls of the box? Also what kind of material should I use? I was thinking of that synthetic cotton looking stuff that you can get a Wal-Mart in the sewing section. Thanks for any help.
 

BlownRiv
Unregistered guest
lining and stuffing the box are two different things.

"stuffing" is the technique of filling the entire enclosure with a fibrous material such as the fluffy stuff used in pillows. the purpose is to make the box sound a little "bigger" by delaying the rear waves inside the box. the polyfill that is used for fish tank filtration works well, and can be found in most pet stores sold in fairly large bags. you just cram the stuff in the box until the volume is near full, then install the sub.

lining the walls with acoustic insulation is a whole different idea. if you were thinking of doing this, you really don't need to. for the deep bass frequencies that a sub plays, it won't improve the sound much.

the reason for the linings that you see in a lot of home speakers is to absorb the midrange reflections produced by mids and woofers that play into the higher frequencies. in a car, you will cross the sub over so low that you don't have to worry about these reflections.

in my current set-up, i'm running a kicker L7 without any stuffing material in the box at all. it sounds fine to me.
 

Bronze Member
Username: Lbeckner

Tulsa, Ok Usa

Post Number: 18
Registered: Oct-04
so its just a matter of taste then? thanks for all the info. i didn't know any of that stuff. by the way how do you like your l7?
 

New member
Username: Blownriv

OH USA

Post Number: 1
Registered: Nov-04
it's more a matter of how much space you have, really. if you build an enclosure to fit a certain space, and it ends up a tad too small, you can stuff the box to gain back about 10% that you don't really have. a stuffed box will "sound" like a 10% larger box (although that's not much).

lining the walls with soft sound absorbing materials won't do you any good, but if you line the interior with dynamat or some other mass-adding material (roadkill, concrete, lead, tar, shingles, etc.) you will decrease cabinet resonance, which is a really good thing.

internal bracing also helps reduce cabinet resonance. i seriously recommend extensive bracing, especially on larger enclosures.

despite what people say on this forum, the L7 is a good sub. it's piston area is 20% bigger than a round cone of the same diameter. mine is an eight incher, but it can get as loud as most tens out there, and is even on par with many good twelves. the xmax spec could be better, but it's still respectable.

i do think the L7s are overpriced for what you get. part of the reason i have mine is because i found it at 60% off. i would not have paid the MRP of $230 for this sub. you can get a JL 8W7 on ebay starting at $300, and the W7 will stomp an L7 in every catagory.
 

Silver Member
Username: Deathshadow

Post Number: 162
Registered: Oct-04
You can get a 5 pound box of polyfill at Wal-Mart for eight dollars and change.
 

Bronze Member
Username: Lbeckner

Tulsa, Ok Usa

Post Number: 20
Registered: Oct-04
hey, thanks alot. by the way i got my speakers from tecbuyz.com for $281 each. Aaron do you have any more tips for bracing the box? i built the box myself so that sounds like a really good idea, but ive never done it.
 

New member
Username: Blownriv

OH USA

Post Number: 3
Registered: Nov-04
there are different ways of bracing. one is to use crossmembers (1" dowels or similar). the other way is to insert walls with cut-outs.

interior walls are my preference, but you have to plan for these before you build the box. any extra materials you put into the box will effect the volume, so you may need to increase the overall size of the box. the idea is to insert two or three walls evenly spaced within the enclosure. these walls should run the direction of the two shortest box dimensions, and they must have a few holes or cut-outs to allow all of the air inside to act as a single volume.

using crossmembers is an easier method, but not quite as effective as internal walls. one advantage is that you can brace in multiple directions. another advantage is that dowels don't take up as much space, so they won't affect your box's internal volume as much. the more braces you use, the more effective this technique is. also, strategically placing them in the correct locations will make a diffence.

however you choose, bracing can make the differenct between a good-sounding and a bad-sounding box. here is a test: take a sub box and tap your knuckle on the biggest side, noting the sound it makes. now, tap the smallest side of the box. notice anything different? if the larger panel makes a lower-pitched "bonk" sound, that means that panel is actually moving. if you brace that panel, it will no longer make that sound because you've stopped its movement. a well-braced enclosure will sound as dead as a rock because none of its panels can move.
 

Bronze Member
Username: Lbeckner

Tulsa, Ok Usa

Post Number: 23
Registered: Oct-04
Thanks for all your input. I'll put it strait to work.
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