Density of foam? (pcf) - using foam and 703 together?

[666666]

I've read that 703 is 3 pcf in density and 705 is 6 pcf in density...

What is the density of typical good sound foam (like for instance "Auralex" type foam)?

Also, just curious about the following theoretical idea:

Would someone care to predict the general performance of a 4" thick wall trap, first 2" a layer of good acoustic foam, the second layer 2" of 703 or 705?

The idea here would be that the 2" foam layer would face the room to eat up all highs to essentially make the surface "disappear"... zero reflections. But then the inner layer of 703 or 705 would be there to stop the lows (better than foam would) to achieve an absorption response that would hopefully be flatter and thus better than if it was 4" of ALL foam.

Of course many feel that having foam face the room will yield a "lifeless" and unnatural room response and I'd agree. But at the same time, if you're dealing with an ULTRA small room, I think you may have to make some sacrifices... deal with some "lifelessness" as a trade for having NO troublesome close reflections of any type. Because, I know from experinece that in SUPER SMALL rooms that even the smallest amount of close reflections can cause a lot of trouble.

I think my idea might not be so bad if the trap could be thicker, such as say 6" or 8" thick where the top layer is 2" foam and the rest is 703. Perhaps then the absorpton response would be way "flattter". But, in a small room, in most cases, 4" thick would be max due to physical limitations.

So, again, I'd love to hear some opinions on a 4" thick trap made of 2" good foam (outer layer) and 2" 703 or 705 (inner layer).

And if such an idea would make any sense at all, what would be better to use in this case... 703 or 705?

Just thoughts.....

[avare]

703 is better. with the sculpted foam you will get better normal incidence absorption at the price of poorer low end absorption compared to using 4" of 703. The foam method would cost more also.

Andre

[666666]

Originally Posted by avare

703 is better. with the sculpted foam you will get better normal incidence absorption at the price of poorer low end absorption compared to using 4" of 703. The foam method would cost more also.
Andre

Thanks Andre!

Do you happen to know the density of good sound foam? I'm just curious as to how it compares physically.

In the past I have taken two pieces of sculpted "wedge" foam, put them together facing each other so that it becomes a solid panel of foam. If you take two pieces of 2" wedge foam panels and stick them together facing each other, you get a 2.5" thick solid foam panel. This is how I'd use it if I were going to use it.

I understand that 703 is better and less expensive. I happen to be dealing with some people that happen to have a lot of extra foam wedge panels laying around and thinking about how to utilize them in the best way... plus the fact that the rooms are ridiculously small and traps can only be about 4" thick. They are inclined to use just the foam. I am trying to figure out how to increase the performance of the foam, by, for instance, placing 703 behind it... etc.

Thanks Andre

[avare]

There is no solid guideline for foam density. From what you are writing, it would be much easier than going through twenty questions to write exactly what this foam that you already have is.

If you have it, you can stack together like you said. There is no lab testing for that combination that I am aware of. If you have lots of it, do the entire depth with it. Combining the foam and 703 is adding unknowns to unknowns.

If you want more predictable results, use 703 etc completely.

Andre

[666666]

Just wanted to follow up and mention that I took some of the existing Auralex foam panels and carefully measured / weighed them to try to determine the density... I arrived at a figure of about 1.5 - 1.6 pcf density. Sound about right? I measured / weighed several 4" wedge panels and several 3" wedge panels, came up with 1.5 - 1.6 pcf every time.

Again, I realize that density is not the only factor in determining a material's ability to absorb low end, but... it's all interesting.

[Weasel9992]

Originally Posted by 666666

Just wanted to follow up and mention that I took some of the existing Auralex foam panels and carefully measured / weighed them to try to determine the density... I arrived at a figure of about 1.5 - 1.6 pcf density. Sound about right? I measured / weighed several 4" wedge panels and several 3" wedge panels, came up with 1.5 - 1.6 pcf every time.

Again, I realize that density is not the only factor in determining a material's ability to absorb low end, but... it's all interesting.

Andre's right, of course. Rigid fiberglass or mineral wool is what you want for low end. Foam, regardless of density just isn't a stellar performer on the low end for the reason you stated...there's more to it than density.

The point Andre's making about predictability and repeatable results is a very important one. You want your treatment solution to be as dependable as possible.

Frank

[Eatin Weenies]

NEARLY ALL FOAM, is all pretty much useless at low frequencies, and not much better in the low mids and high mids. So it matters not how the various foams test out side by side, as they are all equally useless across the most important areas of the frequency spectrum.

HOWEVER, Foam, even the cheapest foam makes A FANTASTIC FIBER BARRIER, for rigid fiberglass board and or mineral wool, which is what you need for acceptable broadband absorption,.... and as a barrier, it has that "Studio Eye Candy" appeal to boot.

Here is the FREE RECIPE folks for a typical 48"x24" WEENIE TRAP:

3 sheets of 48"x24"x1" thick Rigid Fiberglass (i.e. OC 703 or Rolux 60)
COST = $25 ave.
3 sheets of 48" x 24" x 1" the foam of your choice ( I like the wedge style)
COST = $18
4 little 1" x 1" wood blocks
COST = seriously?
4 screws
COST = .25 cents,.. if that.
1 tube adhesive
COST = Free from most foam houses with order
1 pair of scissors
COST = You already own them

Sandwich the rigid boards together.
Face with the foam of your choice (Front and Back)
Cover all exposed edges with "foam strips" cut from sheet #3
Attach 1" wood spacers
Attach to wall with screws leaving 1" air gap

Total Cost is under $45.00,.... keep $150.00, plus shipping in your pocket each and every time you build a "WEENIE TRAP"

Enjoy!,

Eatin Weenies

[Weasel9992]

So...just gonna cut'n paste that into every thread, no matter how old huh? And you're getting on other people for pushing an agenda? tutt

Frank