Acoustic Isolation (Rockwool cylinder, yay or nay?) - AVS Forum
Audio Theory, Setup, and Chat > Acoustic Isolation (Rockwool cylinder, yay or nay?)
morphemes's Avatar morphemes 02:37 PM 04-01-2014

So, what if I effectively made a cylindrical wall of Rockwool panels? What if the 7 speakers of my 7.1 system were flush with that barrier? It's a small room & reverb is N/A. | need a considerable level of absorption to tame the room modes o This seemed like the path of least resistance.

Any thoughts? Was thinking about safe 'n'Sound

JHAz's Avatar JHAz 03:02 PM 04-01-2014
for isolation purposes, absorption is useless. To reasonably fully absorb a sound, you need (iIRC) half a wavelength of absorption. So if you want to go down to 40 Hz, you need 14 feet of absorption to get entirely rid of everything that happens to impinge on the absorber. Everything that doesn't impinge on the absorber remains uncontrolled. Maybe I'm wrong and you only need a quarter wave to fully absorb. So ONLY 7 feet deep to fully absorb whatever 40 hz energy hits the absorber! unless you want to get the deep bass. Quarter wavelength of 20 Hz is 14 feet, half wavelength is (semiobviously 28 feet) . . . . dagnabbit.

to isolate you need double walls (and floors and ceilings) on offset studs, limp membranes, etc.

a lot of what sounds funky inside a room (assuming you don't mean isolation) is well up in frequency and you can do a ton to clean it up with appropriate absorption of much less thickness appropriately placed. for example when you listen to aregular four string bass guitar, normally tuned, the fundamental frequency of the lowest note (at about 30 Hz) is at least 12 dB below the second harmonic at 80 Hz (usually- this is how it comes off the pickup straight into the mixing board, - a classic bass amp like the Ampeg SVT and 8-10 inch speaker cab will have its own fairly severe roll off below about 50 Hz) . Controlling the much louder 2H at 80 Hz (and higher harmonics) can go a long way to cleaning up bass messes, but in the end, the way to get reasonably flat bass across space in home sized rooms is really multiple subs so that you energize multiple different room nodes and everything kind of more or less evens out. Or tens of feet of absorption covering eat least one entire wall. Your choice.
morphemes's Avatar morphemes 04:03 PM 04-01-2014

Well, much thanks,but.. hrm... Well, I wasn't approaching this from a soundproofing context.   The room has some resonance issues & being a small room, well..  there just isn't much space to flatten out the problematic bass frequencies.

I'm going to construct a number of panels using rockwool, so I'll obviously be able to experiment (I also have a measurement mic). 

From a recording standpoint, sitting in the center of a cylinder of rockwool would probably be a pretty good idea, but what about listening in a very small room? 

Something like one of those foam microphone isolation filters...  Except I'd be the microphone... 

I had the thought, but further information on the matter eludes me.

DonH50's Avatar DonH50 06:27 PM 04-01-2014
Room modes tend to be LF (even in small rooms) and it could take a lot (LOT) of absorption to reduce them. In the end you'll likely have a very dead room unless you add membranes to the front of some or all to reduce HF attenuation, and/or replace some with diffusers (or combination diffusion/absorption panels). My room is fairly small and I have lots of panels. It is very dead but I do not mind; any ambiance comes from the source and not the room.

If you could shove a pair of subs at appropriate locations that would probably help with modes, as would getting the listening position a bit away from walls and yet not in the center of the room.
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