Damping and bracing?

[jvsb]

Hallo,

I just built a pair of 3/4" Birch plywood enclosures (TL/BR) for a full range driver (Supravox). For different reasons, I decided to make a box with wide baffle 19" and not so deep. The box is 45" high.

Since the front and the back are quite big, I think I need to put some damping on these panels to prevent the vibrations. Can anyone tell me what kind of material should I use? I have heard, that a bitumen foil used for isolation in construction + felt is very good.

Beside damping I guess I have to do some bracing as well. Can anyone tell me some "bracing rules"?

Thank you very much for your help.

Jan

[Vikash]

I think the focus should be on bracing. The enclosure panels should be well, and asymetrically braced. This attenuates the level and raises the frequency, and splits them up so that they do not sum into a narrow peak. If you add damping then it will lower the resonance which is not what you want, unless you can lower it to below the range that is important to you.

Bracing Rules: (or what I've picked up from the forum...)
- Apply bracing (at least) parallel to the longest wall.
- Brace assymetrically. Aim to make each 'sub-panel' of different dimensions/area so that the resonance of each panel is different to the others.
- Do not apply damping, which counteracts the bracing.
- Then apply stuffing to attenuate the raised frequenciy vibrations.

I suggest reading through this thread.

[jewilson]

The side of the cabinet should be coupled by bracing to damping out common mode resonates. The front to back should be coupled to dampen out resonates. The location of the bracing depends on the size of the cabinet. You can normally find these points by rapping on the enclosure, so bracing my be needed every 10" to 16" depending on the size and the type of material and thickness.

You will be able to tell when the cabinet dead by rapping on it.

The brace be as long as the walls of the cabinet. Also the bracing should be a hardwood as it will couple better.