Best thin damping material?

[bcodemz]

I believe the consensus is that wool felt is the best material for absorbing rear waves inside a speaker.

What if the thickness comes into play? If I'm limited to a specific thickness, say 1/4'', would wool felt still be the best material? If not, which material would be?

 

[eriksquires]

Sonic Barrier

But they don't make anything that thin. The multi-layer materials are particularly good. Below that the really think materials are best suited for damping sheet metal, such as PC enclosures.

Gravesen uses a lot of 8mm thick felt, about 1/3" in the kits he designs.

Best,

Erik

 

[cumbb]

Use fabric, t-shirts, throusers, stockings...-)))
Fill up without pressing. Tune the sound by quantity and density.

 

[picowallspeaker]

"rear waves" may exist only when l<λ otherwise it's just "pressure"
i.e a wave exists only if the fluid where it propagates...

 

[cumbb]

Avoid the most waves. My mind.
"Tune the sound by quantity and density"-) Try,-!

 

[Face]

Anything that thin really isn't going to do much.

 

[bcodemz]

1/4'' won't even absorb midrange frequencies well?

 

[planet10]

A felt of natural fibre (wool or cotton) is likely the best. How effective it is is dependent on how thick it is. We use ½" cotton felt. That is going to be effective about a further octave downward.

dave

 

[SKAFAN]

What type of dampening would you recommend for small monitor type BR speaker?

 

[planet10]

We use ½" UltraTouch cotton felt.

dave

 

[bcodemz]

I've been reading that stuffing can increase the apparent enclosure volume to the driver, which result in a lower F3 in a sealed speaker. Does this apply to passive radiator speakers and mean the PRs would be tuned lower than without stuffing?

 

[planet10]

Typically with a reflex enclosure one uses limited damping (ie the ½" cotton felt) so that the damping does not interfere with the reflex action (or increase the apparent volume).

In a sealed box you need to fill the entire speaker volume to get an apparent increase in volume (nominally one can get up to about 20%).

dave

 

[AllenB]

You have to fairly stuff a cabinet to make it appear larger. Thin lining isn't going to do that.

 

[Face]

You have to fairly stuff a cabinet to make it appear larger. Thin lining isn't going to do that.

He's looking to absorb the rear wave.

For sealed enclosures, I line them with Ultratouch and stuff with polyfill.

 

[bcodemz]

So stuffing does not take away apparent enclosure volume right?

I'm making a very small speaker with maybe 2.5L of effective internal volume, so every bit of enclosure volume matters.

If it doesn't, I can line the walls with felt, and the stuff with polyfill or something. I'm reading it is not good to overstuff the enclosure, so I'm not quite sure what the balance should be without some trial and error.

 

[AllenB]

He's looking to absorb the rear wave.

I guess my reply was simplistic and I was implying that stuffing to this level may not be what is wanted here. If the rear wave (primary mode) is absorbed then so is the reflex action.

 

[AllenB]

So stuffing does not take away apparent enclosure volume right?

Not in small quantities. You need a fair amount to make it appear larger and even more makes it smaller again.

Higher air coupled box modes are not difficult to absorb with moderate damping. If you are going to use limited material it can be better to space it away from the walls. Waves build pressure at the walls and the opposite (velocity ie movement) is needed for this kind of damping to work.

 

[planet10]

You do not want to stuff a reflex enclosure. Line the walls to help kill reflections is all.

dave

 

[bcodemz]

You do not want to stuff a reflex enclosure. Line the walls to help kill reflections is all.

dave

I can see why stuffing is bad for a ported enclosure, but why is stuffing bad for a passive radiator enclosure?

 

[jplesset]

Passive radiator is the same as a reflex, the passive radiator is simply a substitute for the port.