Vaughan Odendaa said:
Because it got me thinking about long wavelengths. Please explain this for me ! Thank you.
--Sincerely,
This is admittedly simplified, but still, it helps to visualize it. Pretend you're a particle of air, being pushed around by sound. You're being yanked forward and back by the frequency of the sound.
If it's a high frequency, and you're near a sheet of, say, OC 703, it's not hard to see what will happen. You'll get pushed into the fibers, collide with some, give up energy in the form of heat, and then the air pressure will switch and you'll be dragged back through the fibers again, giving up more energy, getting more randomized. Repeat. Pretty soon you're just bumbling at random in and near the fibers, getting in the way of other air particles, with little energy of your own and a very diminished relationship to the original frequency. You're just random kinetic noise at a very low energy level. You have been assimilated.
What happens at low frequency is more interesting - and not as effective. You get pushed into the trap, but your buddies behind you just keep pushing. You get forced through the trap and you're still being pushed. If there's air space behind the trap (as should be), the pressure there keeps building.
The pressure wave, after an eternity of a 60th of a second or so, finally falls off. And there are you and your buddies, squeezed behind this trap. It's time to leave - so you all flood out through the fibers.
Except you can't. You're in each other's way and there are fibers to get through again. A bunch of your buddies get knocked sideways in the rush to get out. Eddies form, causing delays. It's like what happened on the way in, but even less organized, because your friends have been bouncing around for a bit and have more randomized orientations. The higher pressure behind the trap (we're not talking much higher) changes the way you interact and tangle, and the result is that you all get back out again, but with varying delay. Basically, what's happening is the phase gets a little smeared. The air behind the trap is averaging out the pressure changes, just a little. In electronics this would be an RC network. In acoustics it's friction and viscosity. Traps with membranes use the mass of the membrane to introduce even more loss (much more, as the membrane rubs against with the fibers) and more smear.
No, it's not extremely effective, which is why traps work better with high frequencies than low ones. Traps using varying density materials can work a little better than uniform ones, but ultimately, no flat trap, even in a corner with a much larger air space behind it, does a perfect job. (I'm still looking for the "Acoustic sponge" that absorbes all and radiates nothing.) So you might end up putting in more traps, or adding helmholtz resonators, and messing with diffusion. Getting a really good solution takes work, practice and thought. Getting an insanely great solution takes all that, plus more space.
In my room I have two extra-large diamater Sonotubes, with holes drilled in the surface, and lined inside with OC 703. They stand floor to ceiling. (This was not fun to build, and they stay hidden behind curtains for a reason.) They help. They definitely qualify for the "insane" part of insanely great, though.
But you get decent results just slinging flat traps in - they are much, MUCH better than nothing, even for bass. I've yet to hear anyone who put in a good number of traps, be anything less than blown away by the improvement. If you can't redesign a room from the ground up, putting in some traps is still very worthwhile.
