DIY Speakers and Subs > Cheap foam?
russofris's Avatar russofris 03:08 PM 02-22-2009
Good afternoon,

I had a chuckle when I saw the prices for 4x8 convoluted (egg-crate) foam on PE and other DIY audio sites. Is there a cheap source that anyone can suggest? The stuff usually sells for $20 for a 4x8 at Home Depot, but my local HD does not seem to carry them (nor does their web site).

Thanx Much,
Frank

michael hurd's Avatar michael hurd 03:10 PM 02-22-2009
Difference being is fire rating, one is and one is not. Guess which one is cheaper? Google 'great white club fire'.
michael hurd's Avatar michael hurd 03:19 PM 02-22-2009
Here's a picture, the club owner installed foam, but cheaped out. He had noise complaints, and bought a foam that was not fire rated. The band used pyro effects that was not mentioned to the club owner. The foam caught on fire, and it spread very quickly. In the ensuing panic, many people were trampled and people were killed, it was a downstairs club.
LL
SlickmisterN's Avatar SlickmisterN 03:36 PM 02-22-2009
Tragic, Yes. Worth the money for a smaller home installation...you decide!
russofris's Avatar russofris 03:40 PM 02-22-2009
Thank you for the explanation. I assure you that I have no intention of installing pyrotechnic devices inside (or on the outer shell) of the cabinets I am finishing. They are purpose built for audio reproduction, without the flashy novelties that you seem to build into your speaker cabinets.

So the question remains,

Where should I look for cheap foam?

Frank
Uklit's Avatar Uklit 03:55 PM 02-22-2009
Walmart, sold as a mattress pad.
NoBS's Avatar NoBS 04:00 PM 02-22-2009
Foam mattress pads are all but worthless when it comes to absorbing sound. That's why acoustic foam exists..

http://bobgolds.com/AbsorptionCoefficients.htm
russofris's Avatar russofris 04:36 PM 02-22-2009
Thank you UKLit, I will take a look. I'd like something that is only a inch thick though.

@NoBS, almost any convoluted foam (or cardboard) will have a absorption CE of .8 from 400hz - 20Khz. Of course, you know this, as you linked material that supports this. Are you able to elaborate on what "all but worthless" means, as it is possible that I am misinterpreting your statement to mean "generic convoluted foam is not good" when you mean the opposite.

Frank
pochoboy's Avatar pochoboy 04:42 PM 02-22-2009
why not fiberglass insulation from Home Depot? it seems to be cheap enough and its manufactured to be insulation. I'm going with fiberglass from HD as its cheaper and made to be used for insulation than the high priced fiberfil/eggcrate from partsexpress. The material is going into a box, so I don't see it making anyone itchy sitting/standing around it after the build is done. Of course you may itch filling the box during construction but its a one time deal, right?
russofris's Avatar russofris 05:08 PM 02-22-2009
@poch

My intention is not to absorb the sound, but to break up the standing wave in a ported cabinet without significantly diminishing the volume (cubic inches, not spi). Hence, the use of convoluted foam instead of a high density dampening material. I tend to use fiberglass only in closed-back guitar cabs. I do a number of AC-30 and Bassman clones as a side hobby.

The current project is the finishing off of an old Packard Bell tube stereo.

http://russofris.tripod.com/

I'll be tossing up pics of the finished product when complete. I re-work about 2 old consoles per year and give them as gifts when friends get married. I rework the tube receivers (sometimes optimizing the circuit, but usually doing cap-replacement duty), modernize the speakers (usually with Dayton components unless I'm feeling special), isolate the turn-table, and re-do all of the wood work.

The only thing that is unique about this project is that the speaker cabinets are on hinges. This presents two challenges. I have to keep the weight of the cabinets as low as possible so not to stress the hinges, and I have to come up with a rigid locking mechanism for when the cabinets are extended.

Have a good one,
Frank
pochoboy's Avatar pochoboy 06:11 PM 02-22-2009
Quote:
Originally Posted by russofris View Post

@poch

My intention is not to absorb the sound, but to break up the standing wave in a ported cabinet without significantly diminishing the volume (cubic inches, not spi). Hence, the use of convoluted foam instead of a high density dampening material. I tend to use fiberglass only in closed-back guitar cabs. I do a number of AC-30 and Bassman clones as a side hobby.

The current project is the finishing off of an old Packard Bell tube stereo.

http://russofris.tripod.com/

I'll be tossing up pics of the finished product when complete. I re-work about 2 old consoles per year and give them as gifts when friends get married. I rework the tube receivers (sometimes optimizing the circuit, but usually doing cap-replacement duty), modernize the speakers (usually with Dayton components unless I'm feeling special), isolate the turn-table, and re-do all of the wood work.

The only thing that is unique about this project is that the speaker cabinets are on hinges. This presents two challenges. I have to keep the weight of the cabinets as low as possible so not to stress the hinges, and I have to come up with a rigid locking mechanism for when the cabinets are extended.

Have a good one,
Frank

Thank you for the explanation as I didn't know there was a sound difference between different materials used to stuff the box. I almost went to get the fiberglass thingy. So its either polyfil or that convoluted foam that resembles the PE's offering?
russofris's Avatar russofris 08:59 PM 02-22-2009
Depends on what you're trying to achieve. If you want dampen the sound inside the cabinet, go for something with a high absorption coefficient. If you just want to break up the mids and clarify the highs, go for something that's convoluted. The stuff that PE sells does both well, and is flame resistant to boot. With packing foam, you "may" get both, but don't count on it. A good rule of thumb is the the denser (more lush) and less rigid foam will have a higher ACE, but isn't always true.

Regardless of whatever other magical properties the PE stuff possesses, $25 for a 1ft square is absolutely crazy.

The link that NoBS posted will show you the ACE of many different materials, including the insulation you're already using. Granted, the figures there are more beneficial for dampening a room than lining the inside of a cabinet.

I'm going to run to the UPS store tomorrow and see what they have to offer.

Frank
russofris's Avatar russofris 10:40 PM 02-22-2009
After a bit of googling, I have found a supplier.

They sell 1.5" 1.8pcf convoluted foam at $34 for a 82" x 76" sheet. For external applications, you will also find the fire-retardant variety on the site for 3x the cost (DO NOT USE THE CHEAP STUFF FOR EXTERNAL APPLICATIONS!)

Frank
Uklit's Avatar Uklit 07:38 AM 02-23-2009
Quote:
Foam mattress pads are all but worthless when it comes to absorbing sound.

Not true. The purpose of lining the cabinet walls of a ported sub is to damp the back wave of the sub, which open cell egg crate foam or fiberglass insulation does.
russofris's Avatar russofris 11:13 AM 02-23-2009
@UKLit

I was unaware that fiberglass, or any flat surface, could be used for this purpose. I was under the impression that an uneven surface (and port length/positioning/diameter) was used to break the standing wave so that any sound emitted through the port was not out of phase with the audio emitted from the front of the speaker. I guess I thought that using a convoluted surface had the same effect as a baffle.

I guess I learn something new every day.

Do I still get a DB boost if I use high AC materials in my ported cabinets? Does fiberglass solve the phase problems?

Frank
flashEE's Avatar flashEE 11:29 AM 02-23-2009
Quote:
Originally Posted by russofris View Post

After a bit of googling, I have found a supplier.

They sell 1.5" 1.8pcf convoluted foam at $34 for a 82" x 76" sheet. For external applications, you will also find the fire-retardant variety on the site for 3x the cost (DO NOT USE THE CHEAP STUFF FOR EXTERNAL APPLICATIONS!)

Frank

Great find! I was looking for 3" or thicking egg crate foam to put behind my false wall. Thanks.
penngray's Avatar penngray 01:14 PM 02-23-2009
Quote:


Great find! I was looking for 3" or thicking egg crate foam to put behind my false wall. Thanks.

False wall, as in HT room wall?

If your are talking about acoustical treatments and sound absorption, it will not do a damn thing...sorry but its a complete waste of money.
penngray's Avatar penngray 01:15 PM 02-23-2009
Here is the definitive thread on acoustical treatments in any room...its a long one

/avs-vb/showthread.php?t=255432
fbov's Avatar fbov 04:37 PM 02-23-2009
Quote:
Originally Posted by flashEE View Post

Great find! I was looking for 3" or thicking egg crate foam to put behind my false wall. Thanks.

That would be an "external application" that requires the fireproof version. As used here, "external" is anywhere outside a loudspeaker enclosure. I'd really rather not hear of you and your families demise as the combustion products will kill you if the flames don't.
Frank
flashEE's Avatar flashEE 06:36 PM 02-23-2009
Quote:


False wall, as in HT room wall?

If your are talking about acoustical treatments and sound absorption, it will not do a damn thing...sorry but its a complete waste of money.

Good to know. I have 2x6 exterior walls which has R19 batt insulation in them and thought about using more insulation for sound absorbtion behind the false wall to fill in the empty space. If this is a waste of money then I'll scrap the idea.

When I referred to a false wall, it's a wall that was built about 24" away from the main wall to hang my projector screen and hide the speakers behind it.
russofris's Avatar russofris 07:32 PM 02-23-2009
Quote:
Originally Posted by fbov View Post

That would be an "external application" that requires the fireproof version. As used here, "external" is anywhere outside a loudspeaker enclosure. I'd really rather not hear of you and your families demise as the combustion products will kill you if the flames don't.
Frank

Yup, though I believe that he means that he will use the source link to procure the Class B flame retardant version ($200-ish for 96sq' really isn't that bad).

The other Frank
keynina's Avatar keynina 01:06 AM 02-25-2009
Quote:
Originally Posted by michael hurd View Post

Here's a picture, the club owner installed foam, but cheaped out. He had noise complaints, and bought a foam that was not fire rated. The band used pyro effects that was not mentioned to the club owner. The foam caught on fire, and it spread very quickly. In the ensuing panic, many people were trampled and people were killed, it was a downstairs club.

It is too cheap to be good.
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