I need acoustic damping foam....

KramerBassFan · #1 08-08-2010, 06:47 PM

Where can i find it?

My Woodson with 2x15 Eminence Betas is almost done, except for its foam lining... can anybody help me out here?

Thanks.

SurferJoe46 · #2 08-08-2010, 06:57 PM

Wal-Mart has mattress foam padding that works just fine. Cheap.

If you buy 'bass speaker cabinet sound insulation' it'll cost you yards of money for the same effect.

Foz · #3 08-08-2010, 07:56 PM

unfaced batts of fiberglass [no paper liner] work perfectly.

billfitzmaurice · #4 08-08-2010, 08:15 PM

Quote:

Originally Posted by Foz

unfaced batts of fiberglass [no paper liner] work perfectly.

They work well but aren't exactly user friendly. Foam mattress pads as mentioned above work well with no itching. So does polyester batting (used for furniture upholstery) and carpet padding, both foam and felt.

Quote:

My Woodson with 2x15 Eminence Betas

I don't know what a Woodson is, but Beta 15s are best suited to sealed cabs. If that's what you have it will probably work best with the cab stuffed completely full of polyester pillow stuffing.

Growly Lytes · #5 08-08-2010, 08:54 PM

This ^
I did need some & was just about to buy the Acoustic Foam used in studios for heaps of cash.Then i tried a carpet shop.The guy their gave my about 5 meters of Foam carpet underlay & he gave it to me for free.It works great & just as good as the expensive foam.

JSK5String · #6 08-08-2010, 08:59 PM

The first suggestion about matress pads from Wal-Mart is right on. I used their 1" memory foam matress pad with an eggshell design on one side and it works great. I think I spend under $20 for a single and had a bunch left over.

Foz · #7 08-09-2010, 05:11 AM

Closed cell foam [like memory foam] would be decidedly inferior to a structure with interstices [little holes] and density sufficient to provide a reasonable acoustic impedance. Fiberglass batts are near perfect in acoustic properties for the task.

Unspecified/randomly selected foam products are likely much less effective - even many open cell foams with low densities [like typical polyfill upholstery bating products] will have very poor absorptive properties compared to a denser fiberglass batt. There are foams perfect for the job but properly engineered acoustic foams are often extremely expensive by comparison to fiberglass and are in no way superior in performance. Industrial and commercial construction requires millions of feet of acoustic absorptive material to be installed every year - its always done with a mineral wool product because such are cheap, safe, inert, fireproof, bug proof, and easy to install.

Working with a few feet of fiberglass batt off a roll is trivial in difficulty [opt for long sleeves - yes I know its cushy soft, but try not to roll around in it]. The difficulty/annoyance factor of working with this material is vastly overstated on the innertubes. If you have enough on the ball to be trusted with a open can of house paint, or spinning circular saw, you will be able to handle working with fiberglass batts without incident.

Fiberglass batts work great, are very cheap [for the super cheap - look in a few construction dumpsters - stuff a few clean lengths in a garbage bag and take it home = free cab liner], and the stuff is no more difficult to work with than other standard handyman materials.

billfitzmaurice · #8 08-09-2010, 06:51 AM

Quote:

Originally Posted by Foz

Working with a few feet of fiberglass batt off a roll is trivial in difficulty [opt for long sleeves - yes I know its cushy soft, but try not to roll around in it]. The difficulty/annoyance factor of working with this material is vastly overstated on the innertubes.

Fiberglass is an excellent damping material, but it must be the right type, and that's not insulation batts. Rigid fiberglass is the right material, as explained here:
http://www.ethanwiner.com/density/density.html

The article deals with room mode control, but the interior of a speaker cabinet is just a very small room.

The acoustic pressures inside a cabinet will cause fiberglass insulation to fall apart.

Foz · #9 08-09-2010, 08:16 AM

No Bill, that aint right.

The incidence angle element one encounters in a speaker cab usage versus architectural acoustic absorbers installed to address axial room modes makes the lower acoustic impedance of lower density mineral fiber superior for speaker applications. Also, the target frequency range for architectural acoustic/room mode absorbers is typically much lower than that desired in a speaker cab - which also makes the use of semi-rigid boards sub-optimal.

Of course this superior behavior at non-normal incidence also arises for lower density materials in architectural usages but there are practical reasons that semi-rigid boards can be more convenient. In short, none of these conveniences apply to the case at hand.

As to the idea that fiberglass batts will "fall apart" inside a speaker cab - this simply isn't true. I have opened up cabs that are old enough to join AARP that have perfectly stable fiberglass batts still in place. And I own some very high output cabs dampened with fiberglass that are holding up just fine - and will continue to do so. There is not more force encountered by lower impedance materials but less - the force of the pressure waves is much lower per unit volume with a lower density porous absorber - this is why it works so much better at non-normal angles of incidence.

You can review some reliable Sabine numbers on such materials here:

http://www.bobgolds.com/AbsorptionCoefficients.htm

but keep in mind that these are alpha Sabines measured in a specialized reverb chamber [diffuse field]... if you want to learn more about the incidence angle element of the problem I suggest post a query here:

http://forum.studiotips.com/viewforum.php?f=1

KramerBassFan · #10 08-09-2010, 09:50 AM

Quote:

Originally Posted by billfitzmaurice

They work well but aren't exactly user friendly. Foam mattress pads as mentioned above work well with no itching. So does polyester batting (used for furniture upholstery) and carpet padding, both foam and felt.

I don't know what a Woodson is, but Beta 15s are best suited to sealed cabs. If that's what you have it will probably work best with the cab stuffed completely full of polyester pillow stuffing.

Woodson was a brother company of KUSTOM back in the day, and made in Bolivar Missouri. Lots of parts were interchanged between the two companies.

The cabinet is sealed now, even if it was not originally... it had small "ports" which as far as my limited knowledge is concerned, did no real purpose. Four little holes that are maybe... two inches wide, placed about three inches away from each corner. And then there was a "port" in the middle of the baffle, that was two inches tall by about four inches.

Again, as far as i know, these ports serve no proper purpose, correct? My guess, somebody at Woodson back in the day saw a picture of some speaker cabinet with "ports" in the baffle, and said, "gee, it needs ports to sound good!"

The originals were Fisher 15 inchers, and one was bad. the other will go in a guitar cabinet some day.

And you say stuffed full, not just lining the walls of the cabinet?

knuckle_head · #11 08-09-2010, 10:15 AM

Quote:

Originally Posted by KramerBassFan

Woodson was a brother company of KUSTOM back in the day, and made in Bolivar Missouri. Lots of parts were interchanged between the two companies.

The cabinet is sealed now, even if it was not originally... it had small "ports" which as far as my limited knowledge is concerned, did no real purpose. Four little holes that are maybe... two inches wide, placed about three inches away from each corner. And then there was a "port" in the middle of the baffle, that was two inches tall by about four inches.

Again, as far as i know, these ports serve no proper purpose, correct? My guess, somebody at Woodson back in the day saw a picture of some speaker cabinet with "ports" in the baffle, and said, "gee, it needs ports to sound good!"

The originals were Fisher 15 inchers, and one was bad. the other will go in a guitar cabinet some day.

And you say stuffed full, not just lining the walls of the cabinet?

As ports go - there need be no tubes for them to have served an intentional tuning purpose. You can indeed calculate port size and length to match the thickness of the material the cab is made out of to achieve specific tunings.

billfitzmaurice · #12 08-09-2010, 12:35 PM

Quote:

Originally Posted by KramerBassFan

And you say stuffed full, not just lining the walls of the cabinet?

Yes, otherwise the cab could be quite boomy. That's assuming it's not optimal size for the Beta 15, which is 27 cubic feet per driver

...although 8 cubic feet will work fairly well.

KramerBassFan · #13 08-16-2010, 02:27 PM

Well, a trip to walmart later, and i got a couple feet of pillow foam.

Lined the whole thing, installed some handles, and then plugged it in.

With My Superbass, it sounded rather good, even if there was oscillation - a problem i still haven't sorted out. But thats due more to the amp, than the speaker.

And with my Coliseum 300, it sounded huge. Didn't fart out on any notes, even with the "62.5 hz" boosted.

So, it sounds good, yes, but Hi-fi, NO.

Good thing i prefer vintage tone. Its been a fun restoration project, but if i wanted to build one, i'd build a fearful.

Thanks all!

Oh, and don't tell anybody...but the cab has an internal volume of 5.6 cubic feet.