How to dampen a loudspeaker cabinet
interviewed by Torsten Bätz (7/2004).
Peter, what kind of damping materials do you prefer and how should they be
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.
How should the damping material be attached?
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.