Damping sheets (CFD) for loudspeaker panels

:dontknow:Apologies if this has already been covered in other discussions. I did a search for related terms and couldn't find anything in the results - so here goes.:sweat:

I am wondering if anyone has tried using any of the damping sheets (Dynamat, Megamat etc etc) on in their speaker projects and if so, has anyone attempted to quantify the "before and after" panel vibrations once their enclosure has been treated?
I am putting together a 3 way design at the moment using damping sheets from an Australian manufacturer that is a heavy polymer with a sound absorbing internally facing material. These guys supply to heavy industry and are involved in fixing issues with heavy transport vehicles so they test their products extensively. The sheet adds mass to the panel and of course reduces reflections in the enclosure though of course I doubt this effect will extend in any way to lower frequencies.

There are a lot of car-sound oriented suppliers of damping material out their that offer little quantitative figures on the performance of their products and perhaps rely on empirical data to design their product - though I am by no means stating that they don't work! The great majority of these products seem to rely on constrained layer damping (CLD) which consists of a dense polymer (some use bitumen but this best avoided) and a sheet of "damp" aluminium. I am interested in working out how effective the CLD products stack up against the D10 damping sheet. In fact I am interested in finding out whether the implementation of CLD in these sheets is really effective as their intended use is on metal panels. How do they stack up when placed on a thicker substrate such as MDF or Plywood for example which has different mechanical properties?

Some high end speaker manufacturers have used CLD but their implementation was quite different in that the layer of dense polymer or bitumen is sandwiched between layers of MDF or plywood. I would instinctively think that this would be a massively more effective way to affect damping the panels as the "stiff" layer is much more substantial that the very thin aluminium layer used in the above mentioned sheeting products. I don't have the necessary motivation to embark on a project like that at the moment so I'm looking at a sheet based solution.

I was thinking about getting a piezo instrument pickup then running it into my Behringer UMC204 and using REW to get an idea of the waterfall plots of a panel before and after the damping material has been applied. I know the pickup with inherently have an uneven sensitivity over the frequency range but I am probably going to use a subtractive process i.e. measure a reference panel with no damping, then remeasure with damping applied and subtract the 2nd measurement to see what dB attenuation has occurred and at what frequency.
In the time domain, REW allows you to overlay 2 waterfall plots to see the difference at a given time from the original signal.
So does anyone have any experience with this? I'm sure someone out there has used one of the CLD type products and if so, have you tried to quantify the before and after? Did you try different manufacturer's products to compare them? Or is it all just marketing hogwash! :dontknow: