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How to dampen a loudspeaker cabinet?

Peter Strassacker Dr. Peter Strassacker
involved in loudspeaker design since 1977
Books on material and field research
speakers like Lagrange 98, Pascal, Sub 10-60

How to dampen a loudspeaker cabinet
Peter Strassacker
interviewed by Torsten Bätz (7/2004).
 
 

Torsten:
Peter, what kind of damping materials do you prefer and how should they be applied?

Peter:
First of all I would like to explain how sound waves radiate within an enclosure. The sound is reflected by the cabinet walls. Right at the wall the sound pressure gets to its maximum, the sound particle velocity is at its minimum. The sound can only be dampened efficiently where something is moving. Therefore, sound dampening cannot take place right at the wall where there are only air pressure fluctuation, but no air movement.

As a result dampening should be done inside the cabinet (not right at the wall). For that purpose damping material like polyester fleece, sheep's wool or any other not too dense material should be placed loosely inside the cabinet. Bass reflex tubes and their ports should be remain clear by a distance of 1 or 2 tube diameters.

Torsten:
How should the damping material be attached?

Peter:
In most cases it doesn't need to be attached. It is sufficient to loosen it up (not torn up). The material attaches itself to the driver. In difficult cases, where a transmission line speaker needs only slight damping, the material may be glued or stapled to the opposing side.

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