How to test daming material

[sudhirbhosale]

Verious types of materials are available for damping. Have came across following queries while thinking for TL speakers

1. Among multiple options how to test / measure the damping level/effectiveness.
2. What are pros and cons of various materials
3. Is overdmping a problem?
4. Does only certain frequencies absorbed
5. Damping layer is required for all speaker walls ? as on net I saw some TL designs where only center partition was shown as covered with damping layer not side walls
6. Any other tips on damping

Thanks

 

[Fantastic]

If you are talking about LF damping then you can build a sealed box with a known driver and measure the Qts of the system. Then add a known quantity of damping material to the box and measure Qts again. You'll be able to figure out the effectiveness of the damping material. The damping material makes the box appear to be larger than it really is. Apart from covering surfaces ,the density of the damping material is also important.
Adding too much damping material will reduce system Q and can roll of bass earlier than usual . So it will sound lighter in the bass. Systems with an overall Qts of around 0.6 tend to sound 'tighter' than those with a Q of 0.7 which is closer to the ideal. Higher than that will give you a raised response and could cause havoc depending on it's location in the room. However you can play around with the figures if you know what you are doing. A decent simulator is your best friend !
The damping material isn't a good absorber at all frequencies. You should find the absorption coefficient vs frequency for various materials on the Net.

Best tip for damping I guess is to try out all the different material you can get ! Try to stay away from acoustic grade fiberglass . It's prickly and will penetrate your skin and is a known carcinogen. Besides your hands will itch for a long time. We stopped using it long ago ! You have BAF ( bonded acetate fiber ) and open pore PU foam. Here ,one grade of BAF is used to stuff pillows. So buy some pillows ! You also have felt of different types and wool. You could even try cotton wool ! With loose absorbent material it's better to put them in thin linen bags to prevent fluff from flying all around and lodging itself in the driver and it's moving parts.