Best and cheapest absorber of only high frequencies at 0.75" max thickness?

[666666]

Due to the fact that I have severe allergies to assorted types of dust and chemicals, I'm choosing to use thin plastic wrap around whatever bass trapping materials I use in my bass trap construction. I know it's been proven here that materials commonly used in commercial bass traps are not harmful, but for whatever reason, I'm just overly sensitive to insulation products. I've had bad allergies to regular dust and pollen all my life as it is, don't wish to take any chances inside my limited ventilation tiny tracking room.

So, the question here... since I will be wrapping my main bass trap insulation material with thin plastic sheeting (limp 0.7 or 1 mil, extremely thin), I need to place a relatively thin (and hopefully inexpensive) layer of high frequency absorbing material in front of the plastic sheeting to avoid high frequency reflections off the plastic. Per my trap design so far, I have about 0.75" of space (or less) to work with. I will be covering this final absorbing layer with a burlap type material.

Some have suggested that the burlap type material alone might be enough, leaving 0.75" of air space between the burlap and plastic sheeting, but I think it would be a better bet to add some "fluff" as well in front of that plastic.

Some possible ideas so far...

-carpet underlay, foam or felt

-some type of thin cotton or polyester batting as found at a fabric store, perhaps several layers

-almost considered 1" thick commercial foam absorbers (ala auralex or similar), but way too expensive of course

In a perfect world, whatever material that would be chosen here would come in "sheet" form, such as a cotton batting material or carpet underlay, so that I can "attach" it to the frame to avoid any movement or sagging / settling. I do not wish to "fill" the gap with mere "loose" material.

I've never worked with any of these "thin" materials so I need some guidance here in terms of their effectiveness at eating high frequencies and/or hopefully not reflecting high frequencies.

Of course not much is written about such "thin" absorbing materials since typically 0.75" of any material is too thin to be effective as a stand-alone absorber... in my case though, there will be some heavy mineral wool or 703 or whatever behind all this... just need to merely kill any reflections off the 1 mil plastic.

Thanks.

[Ethan Winer]

Bass traps out of the way of reflections do not need to absorb highs. But for anything else, 1/2 inch thick (or thicker) batting works well. Get the type called "thermal batting."

--Ethan

[666666]

Originally Posted by Ethan Winer

Bass traps out of the way of reflections do not need to absorb highs. But for anything else, 1/2 inch thick (or thicker) batting works well. Get the type called "thermal batting."
--Ethan

Thanks Ethan. As it turns out, these traps WILL be very close to instruments that are being recorded, very well within a close-reflection zone, which is why I'm concerned about it.

The "thermal batting" you speak off... where might I find such material? Is this something found at a fabric store, or a hardware store, or an HVAC supply, or...? Not familiar with it.

Thanks!

[Ethan Winer]

Thermal batting is the same as regular batting, but it's thicker. I've bought it at the local Jo-Ann Fabric store. More than you'll possibly need for less than $20.

--Ethan

[666666]

Originally Posted by Ethan Winer

Thermal batting is the same as regular batting, but it's thicker. I've bought it at the local Jo-Ann Fabric store. More than you'll possibly need for less than $20.
--Ethan

Thanks Ethan,

Anything wrong with polyester batting, or is cotton batting preferred for some reason?

I was just at Joanne, they have a 100% polyester batting that's about an inch thick (uncompressed), exactly the thickness I need for my design. It seems quite fluffy and porous. It's "10oz per yard" weight, the thickest stuff available on a roll, I'd guess this is the "thermal" stuff.... $6.99 per yard, 4' wide roll. (The 4' width will make it easy dealing with 4'X2' traps)

They did have some cotton batting but not in the right size and it was a lot more expensive. Hopefully the polyester stuff will be ok.

[Ethan Winer]

I've never compared cotton, but I know that polyester is okay.

--Ethan

[666666]

Originally Posted by Ethan Winer

I've never compared cotton, but I know that polyester is okay. --Ethan

Thank you!