Suitable sound deadening material

**Hermit** · 6th April 2013, 09:43 PM

Originally Posted by BobL

Unless you are talking 1 m thick concrete bunker, you cannot rely on one material alone to remove the sound and you cannot think of sound absorption as a one way operation

A soft material will simply not absorb all the sound on a single pass so to stop the sound that gets through the soft material you really need a reflector to send it back through the same soft material.
The sound that passes through that soft material crosses the chamber and then goes through the soft material on the other side and is then reflected back into the chamber by the hard material on the back of that etc
It's this multiple reflection of the sound by a hard heavy material through the soft material that eventually absorbs it.

Reflection is done with a material with as much mass/density as possible - something like lead sheeting works because it is so dense, next best comes concrete, then hardwood, then softwood.

If the dense reflective material is too thin (eg metal sheeting) it may resonate and re-radiate the sound out of the chamber.
Likewise if the sound absorbing material does not absorb the sound the sound levels will build up and escape through the reflector.
To absorb sound something soft with air pockets like foam or carpet, or even layers of cardboard will work.

So - something stiff, hard and heavy surrounding something soft and full of air pockets.

Hardwood is a better reflector of sound (hence the use of hard wood for the back and size of guitar) and softer woods are used on the front because they are not as stiff and resonate better with musical frequencies - so Both help make the sound that comes out of the hole and radiating off the front of the guitar louder.

Thanks for your well thought out reply, Bob. I think I'm beginning to get the idea now. I've been doing a fair bit of reading today.

For anyone interested, a couple of links: -

Soundproofing Walls, Ceilings and Windows

Soundproofing

There are a lot more links to related stuff at the bottom of those pages, too, for the diehards.

**Markw** · 8th April 2013, 04:27 PM

I seem to remember egg cartons, especially the the larger 12 x 12 squares bases (not the boxes with lids) being very effective as the sound passing through would bounce around owing to the angles of the cardboard domes.

**graemet** · 10th April 2013, 03:22 PM

We had to soundproof a room at work and called in the "experts". Without adding huge amounts of insulation, the most effective method involved the use of MASS in the form of lead sheeting, about 3mm thick in the walls and ceiling. It cost a bomb but was very effective.

**smartalex76** · 14th April 2013, 10:16 AM

A friend of mine builds speaker boxes and he is a fanatic when it comes to getting the best out of sound dampening the interior of his speaker boxes.

He uses carpet underlay against the interior walls of his speakers then hangs a layer of lead over the underlay. Lead is the deadest material known.

D

**BobL** · 14th April 2013, 11:06 AM

Originally Posted by smartalex76

A friend of mine builds speaker boxes and he is a fanatic when it comes to getting the best out of sound dampening the interior of his speaker boxes.

He uses carpet underlay against the interior walls of his speakers then hangs a layer of lead over the underlay. Lead is the deadest material known.D

Well, your friend is obviously not serious enough as heavy precious metals like gold and platinum are even deader. A vault full of gold is apparently quite an erie place, a bit like an anechoic chamber.

**Christos** · 18th April 2013, 02:36 PM

Originally Posted by BobL

Well, your friend is obviously not serious enough as heavy precious metals like gold and platinum are even deader. A vault full of gold is apparently quite an erie place, a bit like an anechoic chamber.

Do you have access to the Perth mint and can I tag along to test this theory?

**gpsmith** · 21st April 2013, 10:21 AM

If it is not too late for a suggestion - my son and I have rehearsal rooms - accoustically engineered - and we had to use soundchek or firechek plasterboard, soundbat insulation and a 300mm gap then plaster again. To cut the reflection of the sound in the room we made baffles that were filled with soundbats. They are just a wooden frame with the insulation packed in and covered with material. If they are recording an instrument within the room they arrange the baffles around the instrument to isolate the sound. The baffles can be connected to surround the instrument or compressor.

Regards,

**BobL** · 21st April 2013, 03:31 PM

Originally Posted by gpsmith

If it is not too late for a suggestion - my son and I have rehearsal rooms - accoustically engineered - and we had to use soundchek or firechek plasterboard, soundbat insulation and a 300mm gap then plaster again. . . . ,

This clearly works but most suburban woodworkers can't afford to use 300 mm thick walls around sound enclosures for compressors and dust collectors. About the most wood workers could afford is about 100 mm

**rusel** · 21st April 2013, 04:10 PM

just adding my sound proofing story here.....
I help in a sound reduction of some offices and we used a product that was a couple of layers of hessian that had thousands lead balls stuck to it hung over studs then plaster boarded over. The balls being bigger then 2mm and smaller.The idea was that the sound vibrated the lead ball thus using up the sound energy. Sounds good but i was not there for the testing????
I do remember it was very heavy stuff to hang up.

**gpsmith** · 21st April 2013, 05:31 PM

BobL,
I suppose that I did not make the point clearly - I really meant to stress the baffles around the noise source does really make a big difference within the room.

If you constructed a timber frame around the compressor and filled the frame with csr sound bats I am sure that you would significantly reduce the noise.

Regards,

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