[brucew268]

Questions…
In playing around with speaker cabinet damping, I’ve noted that different damping materials seem to have different effects on the frequency balance of the mids and highs. It also seems that how many square inches of the cabinet is covered have effects on the same.

So, would you predict that different thicknesses of the same material would also have different effects on the frequency balance of the mids and highs – and more specifically can you overdamp the cabinet so that the sonic energy is dull by making the damping material too thick?

I’m finally replacing the damaged bitumen panels on one box of a 2-way Proac standmount (don’t ask). The original from the factory was 2 layers adding up to about 6mm and was a bit grainy on the edges. The left channel cabinet still has these. The right channel cabinet had the panels damaged and so has just been fitted with Jantzen 4mm bitumen panels which are a bit more smoothly finished all around.

It still has a bit of ringing and I have some 4mm panels remaining but am wondering what the likelihood is of over-damping the cabinet by using a total of 8mm on the sides rather than ordering some 2mm panels to add on.

Of course, most adhesives are a bit permanent. Remember the other cabinet is unmodified with 6mm bitumen from the factory, albeit 30 years old, and it’s best if the voicing of the two stay pretty close.

[richidoo]

Stock is two layers of 3mm for net thickness of 6mm.
Your new replacement bitumen material is 4mm.
Should you use one or two 2 layers of 4mm?
Is it possible to use too much?

Bitumen is not ideal for damping MDF, or any wood. It is good for damping high Q, high resonant freq materials like metal. It is intended for automotive noise mitigation. The aluminum layer is for reflecting heat to keep the inside of the car cool. I would give this kind of product a C compared to bracing or constrained layer techniques etc for speaker use.  But ProAc knows all this and that's what they chose, they are far smarter than me, and they knew how to stay in business.

It will have diminishing return, so the 2nd layer of 4mm will not double the damping effect of 1 layer.
You can't have too much damping on a box made of MDF. It sounds horrible compared to real wood, so the quieter the better.
Something to be said for stock, and trusting the original designers, but also they were under budget constraints and maybe they really wanted hand fit bracing and two dissimilar woods with viscoelastic rubber between them, but they had to settle for car sound deadening pads. Who knows....

I would use one layer of 4mm in the right speaker and leave the left as stock and get back to listening. 

[brucew268]

Yes, on all that except this is not soft suff with an aluminium layer. It's rigid that doesn't bend without cracking, both the original and the Jantzen stuff.

Some would say that Proac did not go for totally inert cabinets but voiced them to have good synergy with the drive units, both working together rather than the cabinet being a non-factor.

Thank you for the thoughts to chew on.

[FullRangeMan]

In playing around with speaker cabinet damping, I’ve noted that different damping materials seem to have different effects on the frequency balance of the mids and highs. It also seems that how many square inches of the cabinet is covered have effects on the same.
You have deduced correctly. The performance of the cone or its sound is affected by the volume and type of the box and also by the TS pars relative to the moving set (CMS, VAS, FS etc).
So, would you predict that different thicknesses of the same material would also have different effects on the frequency balance of the mids and highs – and more specifically can you overdamp the cabinet so that the sonic energy is dull by making the damping material too thick?
Not or very few with the audiophilic materials sold for resonance control/reduction, these materials do not increase the bass or mid-bass, but yes with the so cal car wood blanket very used in car audio woofer boxes to increase the bass.
I’m finally replacing the damaged bitumen panels on one box
It still has a bit of ringing and I have some 4mm panels remaining but am wondering what the likelihood is of over-damping the cabinet by using a total of 8mm on the sides rather than ordering some 2mm panels to add on.
Its all about your personal taste, try and error.
Please note this topic:
https://www.audiocircle.com/index.php?topic=100689.msg1016047#msg1016047