25 bucks buys an 18" Diameter x 6' roll of 6 lb foam carpet underlay.
I've read the same stuff as everybody else regarding using proper room treatment, but I can't seem to shake the thought that the mass/density of this stuff should come in handy somewhere. That and I keep looking at the conglomerate pattern of the foam thinking that should bring some form of diffusion into play as well.
I'm planning on throwing it in the one exposed corner In my room and putting a material drape/cover over it,.. how to they test things like this for effectiveness? Speaker/pink noise/Mic/analyzer (before and after) good place to start?
Thoughts?
Here's the main issue: you're convinced that the density or mass of an object is what gives rise to it's absorptive properties. But this is actually here nor there with absorbent materials. The absorbers resistance to air flow is what really determines the absorption. And carpet underlay will have very high resistance, making it a very poor absorber. All current models of absorption use the resistance parameter as the main parameter for estimation (along with thickness). It is mainly known in the literature as GFR (Gas Flow Resistance) (but sometimes air instead of gas, and sometimes resistivity instead of resistance).
To test efficacy, if you have a microphone, you can use REW which is a free program to measure the sound before and after installation. We've got a video on how to set it up and get going on our site here:
Room EQ Wizard Tutorial - GIK Acoustics
Honestly, any diffusion helps. A bookcase with the books set in and out at different levels will do great diffusion.
Not to be too negative, but this myth is really detrimental so I would like to set the record straight: random books don't diffuse
in the slightest. What they
will do is scatter sound in different directions, and
often this can be better than a flat wall, but it can also cause comb filtering that wasn't present before, so not always worth doing (no harm in trying of course). Often people have the idea that all diffusion does is shoot sound in different direction, but this isn't the case. A proper diffusor
evenly distributes sound in the entire 180 degree span left to right, for sound coming in at any angle, and also does this not just in direction/space but also phase/time and also in amplitude/intensity. This is not a small distinction at all, and makes a huge difference compared to a 'random' scattering device. One is guaranteed to actually reduce problems due to comb filtering, mix the sound field better in the room, etc. The other method has such a small chance of achieving this, it is not really a useful spend of time.
How Diffusion Works - GIK Acoustics