Which Type Foam for Doors

[bluesman]

My studio partner are completing our new studio (the old one was destroyed by a tordado) We are going to buy some type of foam (Foam Rubber) for treating all doors, (control room, drum booth, iso booth). I have been reading about open cell vs closed cell foam......which will work best for cutting down low frequencies ?

[Professor]

Well foam doesn't do much for low frequencies either way because the wavelengths are so long that they just push right through.
Where are you thinking of the foam? On the door surface or around the edges like weather-stripping?

-Jeremy

[bluesman]

On the Door itself....Im thinking 4" covering the entire door....probably both sides. I have to do something! Padding with foam seems the easiest route.

[bluesman]

I had read that open cell foam is better for absorbing _________frequencies & closed cell foam is better for absorbing __________frequencies. I realize that this is not the best thing that could be used.......so........tell me what IS the best choice. What would you use instead of foam?

[Professor]

Open cell foam is used for absroption on surfaces. You also should be looking at real acoustic foam anyway and not something like mattress foam or other foams. Make sure that the stuff you get isn't flammable so you don't end up with a death trap at the doors. (Remember that club in Rhode Island where over 100 people died about 3 years ago?) I like Auralex because they don't even make foam that isn't fire-retardant - everything they sell has the fire-retardant chemicals built-in.

Closed cell weatherstripping like the 1/4" thick, 1/2" wide self-stick stuff from the hardware store is ideal for isolating spaces around the door frame. But if you are in a tornado-prone area, then you need to consider dangers of building air-tight spaces as well.

-Jeremy

[bluesman]

I will be buying the foam from a local upolstry supply...they have some really dense stuff in just about any thickness up to 12". The tornado thing has been taken care of too.....our iso room doubles as a safe room, built to withstand a direct hit......so.....if not foam, what would you use?

[bluesman]

So, What is everybody else using?

[Professor]

Yeah, just make sure that the stuff from the upholstery shop is really flame retardant in open air, alot of times the stuff they use is actually highly flammable where a spark or stray cigarette can set them off pretty quick.

As to the effectiveness of foam in general, well it's really good for treating the acoustics within a room, but not necessarily for containing sound or isolating rooms. Making the door seals air-tight will be more effective. Some foam or rigid fiberglass on the surface will help to absorb some sound before it reaches the door. But for low frequencies, double-doors with a dead air space between them is generally more effective.
You might also look into a product like SheetBlok to lay over the door before placing foam or other acoustic materials over the top.

-Jeremy

[bluesman]

I get the part about flame resistant. Since you seem down on foam, give me some other options to consider. By the way, our control room has double wall & double door construction. Thanks for your thoughts, but I only want to hear about possible door treatments, if my idea doesn't suit, then give me some alternatives. I have several doors to treat. I was not consulted when doors were purchased...I would now like to make them as good as they can get.....within reason.

[miasma]

A great absorber for midrange and high frequencies is rigid fiberglass. Owens-Corning 703 and 705, or equivalents from other manufacturers can be bought from home depot and the likes. It's better at resisting low frequencies than foam. The air-tight double door idea mentioned above would be much better.

[MASSIVE Mastering]

Assuming the door is solid, stud the inside with 2x3's and fill the cavity with rockwool. Esentially fireproof, and better than foam.

No rockwool? Try 1" thick OC703 and angle the pieces a bit inside the cavity.

Either way, cover with thin cloth and tack 1" strips to the studs to finish.

[bluesman]

THANK YOU MASSIVE MASTERING!!!!! This is the kind of informationI have been looking for!!!!