enclosure damping with epdm rubber?

[PreSapian]

hi, im building a cabinet with chinese birch ply that seems insufficiently damped. i wanna increase the mass of the enclosure with some epdm rubber sheets that are supposedly for sound damping application. would this make for an acceptable treatment or am i just worsening the problem? any better ideas? thanks.

[picowallspeaker]

Hello ...
Enclosures should separate front emission from backs' . If they are thin , they will vibrate producing sound . Also ,each material has it's own resonance .
Most deaf cabinets are made of sandwich of different materials ,like wood and sand in between . But that's quite heavy . Commonly used are bitumen foils .
Also a thin lead foil I found useful to stop vibrations (and resonances).
This goes together with bracing and sound absorbing (open cells) materials.
I think I saw that epdm rubber sheet in the street (dockyard). I thought it would have been useful somewhere else ,like for the mouth of a big horn .

[Cal Weldon]

Yes the EPDM will work to a point but that may or may not be what you need. What thickness is it and do you have the peel and stick kind?

Bracing is probably what you are after if you have panel vibrations.

[PreSapian]

it's 2mm, no adhesive on the back. just bare rubber sheet that i plan to staple/pvc glue onto the birch ply. the enclosure is from 18mm sheet. double thickness on the baffle and the back. i don't have all the terminology down but i think what i also wanna do is lower the resonance of the cabinet because the chinese birch is just too low density. it's whole lot lighter than mdf and im sure it wouldnt pass the knuckle test without some tweaking. i don't know about bracings since the speaker is already a published design with pre-tuned enclosures. i don't wanna temper with the cabinet volume for i hold the design in a high regard.

[PreSapian]

ttt. sorry, about to install them soon and don't want it turning out to be a failed experiment. any more insight? thanks.

[Top Shelf]

How about not using " chinese" birch, try baltic birch. It works very well for me and many others, with a little bit of properly spaced bracing you should get an enclosure that is relativley "rattle" free. Constrained layer damping is the term, which means you will have to add a third layer of suitable material to the equation which will help diminish/displace panel resonances. I have used a bal/birch ,epoxy, cement board sandwich that was excellent in damping cabinet resonances. Oh and don't staple, glue that EPDM to the internal walls,it will provide a more sound damping characteristic, but do a double layer!

[PreSapian]

well i am in china after all.. believe me this was the best quality i could find after weeks of search and it still is not void free. what i intend to do now is to make series of 1" holes on the enclosure and fill them up with san+wood glue paste. i hope that works.

[Top Shelf]

When you drill into the wall of a speaker enclosure you increase the compliance of that wall, it is better to add a second layer that will aid in the stiffining,mass addition of that wall.

[Loren42]

Originally Posted by picowallspeaker

Most deaf cabinets are made of sandwich of different materials ,like wood and sand in between .

I know of almost no cabinets that use sand as a constrained layer agent or few that employ constrained layer damping (CLD). CLD is an excellent technique to reduce vibration.

Most cabinets deal with this with thick walls of MDF or other materials and heavy bracing.

Vance Dickason's book Loudspeaker Design Cookbook goes into a number of materials that work. Several layers of roofing felt stapled to the inside wall is one inexpensive alternative you may want to try before buying any rubber.

It may also be worthwhile adding more bracing first, then trying roofing felt.

You still need to use fiberglass or some other form of stuffing to dampen internal sound waves.

[Loren42]

Originally Posted by PreSapian

it's 2mm, no adhesive on the back. just bare rubber sheet that i plan to staple/pvc glue onto the birch ply. the enclosure is from 18mm sheet. double thickness on the baffle and the back. i don't have all the terminology down but i think what i also wanna do is lower the resonance of the cabinet because the chinese birch is just too low density. it's whole lot lighter than mdf and im sure it wouldnt pass the knuckle test without some tweaking. i don't know about bracings since the speaker is already a published design with pre-tuned enclosures. i don't wanna temper with the cabinet volume for i hold the design in a high regard.

Actually, you want to raise the resonance points higher. Higher frequencies are easier to dampen and tend to ring with lower power levels than low resonances.

Subdividing panels (asymmetrically) does just that.

Although mass will lower a resonance of a spring, even deep kettle drums use a vey light skinned head for the drum and they go pretty deep.

18 mm is a little light in thickness.

If you don't want to change the internal volume you can layer more wood externally. The best route would be a second layer of 18 mm birch with a layer of Green Glue in between. Only tack nail the outside layer at the edges of each panel and do not nail the center. Follow the application instructions for Green Glue.

Green Glue is a constrained layer damping agent made just for this kind of application and can be purchased online HERE.

Do a search to see if there is a distributer or competing product in your homeland.