Stupid Question of the day, damping material

[ModMark]

When calculating the internal volume of a cabinet, should you include the damping material attached to the side and back walls ie: if the damping material is 1/2" thick, add 1" to the width and height , 1/2" to the depth?

Second request, does anyone have the link to the thread which discusses the various material I can use?

[cjd]

No and no.

Only partly helpful I know.

I like the multi-layer stuff PE sells if I'm worried about panel resonance and bounce. Rigid fiberglass works really well but I hate working with it.

C

[ModMark]

No and no.

Rigid fiberglass works really well but I hate working with it.

C

fiberglass would stiffen the cabinet but would is prevent a standing wave from forming inside the box (I hope i said that right)?

Damping material attached to the fiberglass seem like a good solution but same as you, i hate working with resins.

thanks for the reply....

[fbov]

Careful... fiberglass can be in the form of mats and resin (structural), or panels of bonded fibers (acoutical). The latter doesn't stiffen the cabinet, the former doesn't absorb sound.

No, you don't subtract the volume of any air-permeable material like open cell foam or rigid fiberglass panels like cjd mentioned (Do a search for "OC703."). You do subtract anything that's not air permeable, like ports, closed cell foam, surface structural treatments (i.e. CLD or damping mats), etc.

Now let's talk separately about DAMPING, as applied to panel vibration, and DAMPING as applied to acoustic vibrations.

An OC 703 panels placed on the inner sides of a speaker cabinet have no structural contribution. The will, however, absorb large amounts of acoustic energy.

A ceramic tile glued to the inner side of a speaker cabinet with a visco-elastic adhesive will greatly affect the resonant behavior of that panel, but it will absorb no acoustic energy inside the box, perhaps increasing internal energy as it's blocked leagage into the box structure.

Any air-permeable material will absorb sound, with effectiveness increasing with density and thickness (OC701 < 703 < 705 for sound absorption, based on density). You can do a search for "acoustic properties" and find a lot of tables of data. I use carpet underlayment foam because I'm cheap and it works. I also found this link, which delves into the physics of absorption - a very interesting read; thanks for asking.

http://www.inceusa.org/nc07/links/Muehleisen_plenary_acoustic_properties_materials.pdf

Have fun,
Frank

[Xander]

I also found this link, which delves into the physics of absorption - a very interesting read; thanks for asking.

http://www.inceusa.org/nc07/links/Muehleisen_plenary_acoustic_properties_materials.pdf

Have fun,
Frank

I haven't been around this forum as much lately, as I have had too many distractions from speaker building. But just today I saw so many of your posts that are extremely helpful with lots of great information. Thanks for the link! :T

[fbov]

Why, thank you! A lot of it's just repeating what I learned here... glad it helped!

HAve fun,
Frank