What kind of foam?

[Snowman3232 10+ year member]

While my sound deadener is on the way, what kind of foam should i get to go behind the door speakers? Regular foam is cheap and I found some pretty cheap eggcrate "acoustic" foam, but is there a difference?

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[CHEMMINS 10+ year member]

Eggcrate foam will absorb water...and rust your doors.

 

[Traks 10+ year member]

Only foam that I know of that does not absorb water is a closed cell foam. Eggcrate is open celled.

 

[GLN305 10+ year member]

You can use eggcrate foam, just make sure and spray it down with scotchguard first. Otherwise a closec cell neoprene foam is your best choice.

Volara Closed Cell Foam, Padding, Sheet Foam Rubber, Poker Table Foam

 

[whitedragon551 5,000+ posts]

Scotchguard doesnt prevent things from holding water.

Closed cell foam is your only option.

 

[Rudy 10+ year member]

More importantly, what are you trying to accomplish by putting foam inside your doors? Foams are too light to block sound. If you're trying to absorb the back wave from door mounted speakers, you'll need something that 1/4 as thick as the wavelength of the target frequency. The space inside a door will only let you absorb frequencies you'd expect to get from a tweeter. If you were trying to get to say 500 Hz, you'd need something at least 6.75 inches thick.

 

[Snowman3232 10+ year member]

Trying to absorb the back wave from door mounted speakers is my goal. But I should want to absorb sounds that should only be coming from the tweeters right?

 

[Rudy 10+ year member]

Trying to absorb the back wave from door mounted speakers is my goal. But I should want to absorb sounds that should only be coming from the tweeters right?

No, what I'm saying is that it is only possible to absorb sound from tweeters - which most people don't have mounted in their doors. Even if they do, the backs are sealed so it isn't an issue. It just isn't possible to absorb the back wave from mids and below. Your best bet is to seal the back wave inside the door and let it do whatever it wants.

 

[Snowman3232 10+ year member]

You're making it sound like putting foam behind the speaker is pointless. Is this the case because I hear that a lot of people do it and it makes their systems "sound better"

 

[Rudy 10+ year member]

You're making it sound like putting foam behind the speaker is pointless. Is this the case because I hear that a lot of people do it and it makes their systems "sound better"

That's exactly it - I should have just said it that clearly to start with //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Here's the thing. Most people who do it open their doors, apply vibration damper and add foam at the same time. They put it back together and it sounds better so they assume that both the vibration damper and foam contributed to the improvement. I've yet to hear anybody say they applied vibration damper, put it back together, listened for a while, pulled the door apart again, applied foam, reassembled and listened and could hear a difference.

Foam in the doors is one of the old wives tales of car audio. Most people advocating adding foam recommend 1/8" or 1/4". 1/8" can only absorb 27 kHz and above, 1/4", 13.5 kHz and above - not where the problems are. To add insult to injury, you really need to use closed cell foam inside a door. Closed cell foam is a TERRIBLE absorber, for the same reasons it won't hold water.

 

[whitedragon551 5,000+ posts]

That's exactly it - I should have just said it that clearly to start with //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif Here's the thing. Most people who do it open their doors, apply vibration damper and add foam at the same time. They put it back together and it sounds better so they assume that both the vibration damper and foam contributed to the improvement. I've yet to hear anybody say they applied vibration damper, put it back together, listened for a while, pulled the door apart again, applied foam, reassembled and listened and could hear a difference.
Foam in the doors is one of the old wives tales of car audio. Most people advocating adding foam recommend 1/8" or 1/4". 1/8" can only absorb 27 kHz and above, 1/4", 13.5 kHz and above - not where the problems are. To add insult to injury, you really need to use closed cell foam inside a door. Closed cell foam is a TERRIBLE absorber, for the same reasons it won't hold water.

I always thought the point of using the CCF was to apply between panels to prevent the rattling. The deadener to add mass to stop vibrations.

 

[Rudy 10+ year member]

I always thought the point of using the CCF was to apply between panels to prevent the rattling. The deadener to add mass to stop vibrations.

That's correct - CCF is a gasketting material - it isolates one thing from another. It's also a pretty good thermal insulator but that's not really relevant in most sound deadening applications.

Vibration damper (deadener) doesn't really work by adding mass - it works by dissipating vibration as heat. Adding mass isn't practical as a strategy for moving a vehicle's panel's resonant frequency below the audible range - you need to quadruple mass for each octave you lower the resonant frequency.

 

[whitedragon551 5,000+ posts]

That's correct - CCF is a gasketting material - it isolates one thing from another. It's also a pretty good thermal insulator but that's not really relevant in most sound deadening applications.
Vibration damper (deadener) doesn't really work by adding mass - it works by dissipating vibration as heat. Adding mass isn't practical as a strategy for moving a vehicle's panel's resonant frequency below the audible range - you need to quadruple mass for each octave you lower the resonant frequency.

Hmm... how does a butyl rubber backing and aluminum convert vibration to heat?

 

[Rudy 10+ year member]

Hmm... how does a butyl rubber backing and aluminum convert vibration to heat?

Butyl compounded for vibration damping is viscoelastic - when it is deformed it returns to stasis more slowly then it was deformed. Vibrations enter the adhesive deforming the butyl. As it returns to stasis strains between the butyl and the constraining layer and substrate create the heat. It's a very small amount of heat so it doesn't cause any issues that need to be considered.

 

[whitedragon551 5,000+ posts]

Butyl compounded for vibration damping is viscoelastic - when it is deformed it returns to stasis more slowly then it was deformed. Vibrations enter the adhesive deforming the butyl. As it returns to stasis strains between the butyl and the constraining layer and substrate create the heat. It's a very small amount of heat so it doesn't cause any issues that need to be considered.

Thats probably why the asphalt based deadeners dont work so well. The asphalt doesnt deform as easily as butyl.