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Sound Absorption!!!

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Sound Absorption!!!

Postby ramyjackson » Sat Sep 29, 2018 10:54 am

Hello there, been a long-time visitor but never posted. However, I have a question I wouldn’t mind throwing there for either opinion or comment.

Recently, I have been using a large-ish room in my house for band rehearsal and jamming. I previously only used it for post-production edits. I’m now treating the room for acoustics accordingly (i.e. for internal room sound for our benefit and soundproofing so my neighbours don’t hate me). This is being done on quite a budget though.

I have a decent understating of the absorption and diffusion techniques used in studios for acoustic treatment, but I also figure that internal treatment can also play into the overall sound proofing with some good planning.

This question presents as hypothetical, but relates to lower frequencies and the overall path to soundproofing, as I’m trying to limit the noise levels in the most efficient way I can. So if I had a kick drum, for example, and using the same absorption material, would it be better to surround the drum in that material or better to treat the room in that material? (And again, hypothetical, I understand that if on, or very closely over the drum, would cause an affect to room mics, but this question is more related to the physical properties of sound/energy absorption vs distance). So again, would the overall level be more greatly affect by closer interaction (absorbed, then passed through air) or further interaction (passed through air, then absorbed).

Cheers.
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Re: Sound Absorption!!!

Postby blinddrew » Sat Sep 29, 2018 12:16 pm

Firstly I think it's important to stress that any sound treatment is only ever going to have a minimal effect on sound proofing. The latter requires physical isolation, mass, and air sealing. None of this is cheap or easy to do to a shared-use structure.

In terms of treatment at the low end, I find it useful to think in terms of wavelengths. Take a kick drum with a resonant frequency of around 80Hz (just because it makes the maths easy :) ). Your wavelength there is 4.25m.
At the boundary walls you will have peak pressure but zero movement, so your anti-nodes (areas of maximum air movement) are going to be just over a metre from the wall. That's your most effective position for your treatment. The closer to the wall it gets, the less effective at lower frequencies.
I've not thought about this before (perhaps Hugh or one of the other knowledgeable folks can confirm?) but I assume that the source of the sound (our kick drum) represents another anti-node. In which case swaddling the drum would attenuate the sound, but obviously at the expense of the quality of the sound. In order to mic something effectively you'd need to make sure the mic was on the inside of the treatment. But to have any meaningful effect on volume I think you'd need to surround the whole drum, which would make it a) difficult to play, and b) sound like a bag of badgers*.

Basically it all comes down to the same conundrum. Sound treatment (i.e improving the sound in the room) can be done relatively easily and cheaply. Sound proofing is difficult and expensive. 'Ye cannae change the laws of physics.'

* If you're unsure if this is a good or bad thing, try placing several badgers in a bag, hitting it vigourously with a kick drum pedal, and then opening the bag...
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Re: Sound Absorption!!!

Postby Music Wolf » Sat Sep 29, 2018 12:34 pm

blinddrew wrote:
* If you're unsure if this is a good or bad thing, try placing several badgers in a bag, hitting it vigourously with a kick drum pedal, and then opening the bag...

That isn't going to go down well with Dr May
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Re: Sound Absorption!!!

Postby James Perrett » Sat Sep 29, 2018 2:11 pm

ramyjackson wrote:but I also figure that internal treatment can also play into the overall sound proofing with some good planning.

I'm afraid you are going to be in for a bit of a surprise here. Internal treatment and soundproofing are completely different things.
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