How to Make High Performance Sound Absorption Panels for $5

You're gonna want something that's acoustically transparent. I'd guess those movie posters have been gesso-ed, or have some sort of coating that's likely acoustically reflective. plain burlap, or Guillford of Maine for the "expensive" stuff would be a better way to go, imho.

 

If you can blow through it then it's fine.

 

Has anyone used a very thin plastic membrane, like clingfilm, to cover the insulation material (underneath whatever fabric you chose) and can comment on any loss of effectiveness?

I'm hoping to build a bunch of these after we move, but I'm worried about airborne fibres. My son and I are horribly asthmatic and allergy prone.

 

Quite a few of the multi-purpose commercial bass traps (think, the huge cylinder-style helmholz resonators like ASC tube traps) use plastic sheeting on half of the circumference of the trap so that one side is acoustically reflective, and the other side is absorptive.

like riotvan said, the fabric needs to be air-permeable. the way all this stuff works is by taking a pressure wave and converting it into heat by wiggling teeny tiny fibers of some material. so, if you're blocking air pressure waves from entering whatever fibrous material the panel is made of, you're limiting the efficacy of the panel. Depending on what frequencies can pass through the fabric/plastic face, you can create a pass-band diffusor/absorber.

 

I used burlap for mine. Quite cheap at any gardening store, and very acoustically transparent. You could probably dye it black if that was important. I've also experimented with landscaping cloth - not as transparent as speaker cloth, but much cheaper.