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Post by cletuschrist on Jan 19, 2023 20:24:57 GMT
Hello! I apologize for bringing up the topic of air gaps because I know this poor horse has been beaten through the space/time continuum and into the next dimension. I've read so much in here over the last couple years but can't seem to find an answer to my question.
When putting an air-gap between your acoustic panel (in my case, 4" thick OC703) and the wall, does the gap have to be for entire assembly, including the frame? Or, does it just need to be the absorber material? For example, do I need to use 4" wood frame mounted off the wall? Or could you use a 6" deep frame mounted flush to the wall, but with 4" thick absorber inside the frame, leaving a 2" gap between the absorber material and the wall inside the frame?
The application is simply getting some control in a big boomy square live tracking room. I appreciate any insight!
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Post by Hexspa on Jan 19, 2023 22:55:26 GMT
It's the absorbing material. The frame is reflective so gapping it does nothing. It seems like you know but a 1x gap for a frictional material is optimal.
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Post by cletuschrist on Jan 20, 2023 18:04:15 GMT
Thanks! I was confused about whether the gap had something to do with waves hitting the wall and bouncing back into the insulation, or if it really only matters when the wave energy goes through the insulation once THEN AGAIN after hitting the wall coming back the other way.
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Post by Hexspa on Jan 21, 2023 7:24:37 GMT
Afaik, it's all about getting the absorber to the 1/4 wavelength of the lowest frequency. Friction works on the velocity aspect of a wave which is 90deg phase shifted from the pressure aspect. The way that manifests in standing waves is the pressure is always against the boundary and, depending on which harmonic of the mode it is will determine how many velocity phases are in the room. The fundamental has one at the center of the room the second harmonic has two and so on. For frictional absorbers, you're looking to absorb that second harmonic and 1/4 wavelength (boundary distance). Naturally, higher frequencies will have shorter 1/4 wavelengths so the absorber works just fine from then on. Luckily, it's not all-or-nothing: the wave still has velocity at all points other than maximal pressure so you'll get some absorption before totally absorbing 1/4 wavelength. Plus, if you use FRK then you add a pressure element but that doesn't really translate directly to depth in the same way. Here's a (somewhat old) blog post of mine that has a good image that I recreated from somewhere: hexspa.com/velocity-vs-pressure/ |
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Post by rock on Feb 1, 2023 13:55:42 GMT
Sorry, I've been away for a while.
Hex is correct! But add on and put it another way:
(cletuschrist wrote:) "Thanks! I was confused about whether the gap had something to do with waves hitting the wall and bouncing back into the insulation, or if it really only matters when the wave energy goes through the insulation once THEN AGAIN after hitting the wall coming back the other way."
I'd answer: It's BOTH!. Sound waves bounce off the wall from both going through the absorber first and then back again... and to a lesser degree from any sound waves reflecting off the wall from other angles.
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Post by Hexspa on Feb 2, 2023 12:09:58 GMT
Sorry, I've been away for a while. Hex is correct! But add on and put it another way: (cletuschrist wrote:) "Thanks! I was confused about whether the gap had something to do with waves hitting the wall and bouncing back into the insulation, or if it really only matters when the wave energy goes through the insulation once THEN AGAIN after hitting the wall coming back the other way." I'd answer: It's BOTH!. Sound waves bounce off the wall from both going through the absorber first and then back again... and to a lesser degree from any sound waves reflecting off the wall from other angles. Good to have you back. Any war stories? |
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Post by cletuschrist on Feb 3, 2023 15:36:26 GMT
I forgot to come back and say thank you! (I was in a hurry to go acquire materials now that I have a solid plan). I appreciate the feedback. Getting this live room under control is going to make it a lot easier to record and create on the fly.
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Post by rock on Feb 6, 2023 14:13:44 GMT
Good to have you back. Any war stories? Thanks but no war stories LOL. Seems I filled up my Bookmarks Bar and Ethan's got pushed off screen and down the list  and since the site has been fairly inactive lately, I have gotten out of the habit of checking in. BTW, I've got a couple yet-to-be-deployed 2'x4'x4" mineral wool batts still in the package. I'm in the process of building thin wood (6mm Baltic Birch) frames. They're a little different in that instead of cutting holes in the sides, it's built out of 1" wide "rails" all the way around. I should take some pix. All the panels I've built so far are frameless and the fabric is not stretched tight and cosmetically they look a little shoddy. These should look better. We'll see... Cheers |
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Post by Hexspa on Feb 6, 2023 17:57:04 GMT
Yeah, I've seen 'pix' (haven't seen that abbreviation in awhile) of frameless panels and they look very middle aged. I'm currently recombining my 2" rigid panels into 6" ones. This metal drywall bead is very sharp but it's much stronger than the vinyl stuff I'm using for my safe n sound 12" panels.
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and since the site has been fairly inactive lately, I have gotten out of the habit of checking in.