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Acoustic Diffusers?

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Acoustic Diffusers?

Postby Elephone » Wed Nov 28, 2018 2:03 pm

Hello. I'm just wondering about acoustic diffusers, whether they have to be made out of hard materials (wood), do you have to know what frequencies you are trying to affect in advance? Or are broken reflective surfaces simply preferable, generally? I remember seeing a studio on Youtube where a shelf of vinyl records was being used as sound treatment.

Is there no super cheap or abundant material, like glass bottles or spent light bulbs, that can be fixed to a panel to diffuse sound? For instance.

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Re: Acoustic Diffusers?

Postby Martin Walker » Thu Nov 29, 2018 1:14 am

Hi Elephone!

Diffusion can be a good way to 'break up' your reflections so they become less troublesome, but you ideally need to be at least a couple of metres away from them to avoid hearing a set of discrete reflections, rather than a more diffuse soundfield, so they are not often used in small rooms.

Putting shelves at the back of your room and part filling them with books, manuals, CDs and bits of unused gear can work quite effectively, but you do need to make the fill as random as possible (simply filling a bookcase with similarly-sized books won't do anything at all). Your suggestion of a row of vinyl records would only really work if you alternated chunks of albums and singles, which wouldn't provide good long-term storage for them, as there might be a tendency for the albums to warp if pressed against singles.

Stiff cardboard tubes used at the centre of carpet rolls could also be used as diffusers - you'll need some of different diameters, and could cut them in half to make convex gutter-like shapes and then glue these onto a board.

I suspect a range of differently-sized glass bottles might work, but not with the tops open, as they would act as tuned resonators rather than diffusers. However, I'd be concerned about possible glass breakage ;)


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Re: Acoustic Diffusers?

Postby Sam Spoons » Thu Nov 29, 2018 1:23 am

And it is worth considering that they don't remove the high end like absorbers do so if you are getting the room under control but concerned about losing too much top end then a well designed diffuser or two might be worth considering rather than that extra broad band absorber.
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Re: Acoustic Diffusers?

Postby Hugh Robjohns » Thu Nov 29, 2018 1:55 am

Elephone wrote:Hello. I'm just wondering about acoustic diffusers, whether they have to be made out of hard materials (wood)...

No, they don't have to be solid wood. Some are plaster or fibreglass, or even brick/concrete. However, if the underlying material is flexible it will absorb or resonate at LF which might not be very helpful.

...do you have to know what frequencies you are trying to affect in advance?

Ideally, yes. The dimensions of the lumps and bumps on the panel determine the frequency range over which it is effective. Most usual designs affect only the upper mid frequencies.

Or are broken reflective surfaces simply preferable, generally? I remember seeing a studio on Youtube where a shelf of vinyl records was being used as sound treatment.

They might claim it was... But it probably wasn't. Clearly, any irregular surface will tend to scatter sound rather than reflect it in a coherent way, so it will prevent obvious slap echoes, but proper diffusers are carefully designed and calculated to give a very controlled and smooth spread of reflections in a beneficial way.

Is there no super cheap or abundant material, like glass bottles or spent light bulbs, that can be fixed to a panel to diffuse sound? For instance.

Sawn off bits of 2x2 aligned to make a 2D diffusor is pretty cheap... But I've also seen 1D diffusers made with half-logs very effectively. Lightbulbs would be too fragile, and bottles too damaging for your liver... :-)

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Re: Acoustic Diffusers?

Postby Mike Stranks » Thu Nov 29, 2018 10:55 am

As we're here...

Any thoughts on these: https://www.studiospares.com/Studio-Gear/Sound-Diffusers/Universal-Acoustics-Mercury-Diffusor-300x300-x1_466360.htm

I have a set of 8 mounted irregularly on a stiff board, but just propped up against a wall as 'management' put the foot down about ceiling mounting above the mix position... :lol:
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Re: Acoustic Diffusers?

Postby ef37a » Thu Nov 29, 2018 11:07 am

Mike Stranks wrote:As we're here...

Any thoughts on these: https://www.studiospares.com/Studio-Gear/Sound-Diffusers/Universal-Acoustics-Mercury-Diffusor-300x300-x1_466360.htm

I have a set of 8 mounted irregularly on a stiff board, but just propped up against a wall as 'management' put the foot down about ceiling mounting above the mix position... :lol:

They look handy Mike. "Above the mix position"? Would you not want to "lose" any upward radiation from monitors? I would have thought randomly scattered sound coming back 'at yer would mess with stereo imaging?
(And do we all rememeber the BBT episode where Rahj has a whip crack on his phone?!)

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Re: Acoustic Diffusers?

Postby CS70 » Thu Nov 29, 2018 11:19 am

I am setting up some on the back wall of my mixing station these days, and they're 55x55 squares made by solid oak cubes calculated to diffuse properly. The things weight 16Kg (35 pounds) each! I plan to screw them on a plywood base so that I only have to make a few holes in the drywall, and I had to import heavy duty SnapToggles (which aren't readily available in Norway) to ensure they stay up. :)

The things are so heavy that they scare me a little bit. :-D
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Re: Acoustic Diffusers?

Postby ef37a » Thu Nov 29, 2018 12:02 pm

CS70 wrote:I am setting up some on the back wall of my mixing station these days, and they're 55x55 squares made by solid oak cubes calculated to diffuse properly. The things weight 16Kg (35 pounds) each! I plan to screw them on a plywood base so that I only have to make a few holes in the drywall, and I had to import heavy duty SnapToggles (which aren't readily available in Norway) to ensure they stay up. :)

The things are so heavy that they scare me a little bit. :-D

Bit of a "Final Solution" but when I wanted to mount speaker and monitor brackets on my wall I used a "No Nails" type glue, plugs and 50mm #8 screws.

My house is just pre war and plaster over brick walls. The bricks are full of voids and the mortar not good for plugs. Only 1 in 2 holes get a grip! So, a sheet of 19mm MDF was stuck up then holes drilled and where a good fixing found, plugged and screwed which pulled the MDF in tight and I dare say atmospheric pressure counts for a lot of the security!

I never mount anything directly to a wall, always use battens or a piece of ply/mdf but not usually glue!

Of course, getting all that off one day will be a pain! The plaster will come with it but at 73 I am "done" with the room and it will be the kid's problem!

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