frequent questions I have is how to damp speaker cabinets
and it's not easy to give general recommendations. Below
is seen the materials I use:
1. 8-10 mm felt material
2. 30 mm polyester foam, acoustilux
3. Bitumen pads (found in car-fix shops) (Harald Nyborg
in Denmark, the cheapest place to find this excellent
material). Also available from Jantzen Audio in 2 mm thickness (use two
4. Pure sheeps' wool material (not easy to find; found
mine in a shop dealing with knitting stuff). Also available from Jantzen
5. Egg crate foam, can usually be bought from all shops
dealing with speaker parts. Also available from Jantzen Audio.
That's about it.
Download Jantzen Audio catalog on damping materials
Based on numerous mails, it appears a lot people think
bitumen pads will "dampen sound waves", i.e.
absorb sound. Bitumen pads are actually excellent in reflecting sound, thus do not absorb sound at
Bitumen pads adds weight to the cabinet panels and reduce panel vibration - and that's a
Felt and foam will absorb sound and soundwaves travelling through felt/foam will reduce speed and
energy will be converted into heat (- don't worry, not a lot of heat!)
FELT MATERIAL AND POLYESTER
Above my preferred damping materials: 8-10 mm felt and
30 mm polyester damping sheets (acoustilux). Both available from Jantzen
To fix the felt sheets to interior panels I use Superfix, view below.
For the 30 mm polyester I use staples - or nothing depending on actual
Egg crate foam in various qualities. I suggest 30 mm egg crate foam as part of
the damping material for very large bass cabs.
Bitumen pads, 4 mm, available here in Denmark at Harald
Nyborg shops. http://www.harald-nyborg.dk/templ.asp
The pads have the following id:
Audio has an extensive range of 2 mm bitumen pads. Dowload data file here.
Despite being self-adhesive, I strongly urge using glue with any bitumen pads.
I use a thick layer of glue used for vinyle tiles. Check QUATTRO
file to view how.
I've had self-adhesive bitumen pads falling off after a couple of years
due to not being glued.
Example of damping of ~24 L floorstander
Seen from side.
example of a common floorstander cabinet damping strategy.
1. The bitumen pads are optional and if only you want to do a little
better, or you may have used light-weight panels needing additional
2. On top of this I recommend adding 10-13 mm good felt material as
shown above. The front panel doesn't necessarily needs any damping.
Three sides are usually enough.
3. 30 mm acoustilux: Right behind midbass drivers I always add 1-2 layes
of acoustilux to reduce early reflections towards the thin driver
4. Quite often we see problems with minor impedance peaks in the 100-200
Hz region and this usually caused by standing waves between top and
bottom. Having an internal height of e.g. 1 meter we may have a
resonance at 34000/100/2 = ~170 Hz (half wavelength), thus 10-15 cm
acoustilux at top and bottom usually cures the problem.
of 13 L monitor:
Cabinet for ScanSpeak 18W/nnnn driver.
Apply 10-13 mm felt material on all internal panels and
leave space free for the crossover. Felt here attached by SuperFix.
Left: Place MDM3/acoustilux on top (L) panel as shown.
Right: Place MDM3/acoustilux on top of crossover and a
second sheet at bottom of cabinet (R).
I usually do not glue acoustilux to the felt but cut a little wider to have the
material suspended between panels.
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