I second the melamine suggestion. Easy to source in various thicknesses, and probably consistent behavior from different manufacturers.
I'd also predict a waveguide will reduce this effect. Less energy to illuminate the baffle means less reflection energy to interfere. It won't be zero interference, but I bet it will look quite a bit better.
Regarding the 3-6khz ripples, have you taped the edge of the tweeter? Tweeter response can be very sensitive to how perfectly flush it is with the baffle. Some tweeters are more sensitive than others. For example the Vifa NE19 must be nearly perfect flush with no gap. The Peerless 810921 is less sensitive to gap, but if it is a bit proud of the baffle it creates a problem.
If you ever design both a TM and MTM, you'll see this is much worse with the MTM.
I'd also predict a waveguide will reduce this effect. Less energy to illuminate the baffle means less reflection energy to interfere. It won't be zero interference, but I bet it will look quite a bit better.
Regarding the 3-6khz ripples, have you taped the edge of the tweeter? Tweeter response can be very sensitive to how perfectly flush it is with the baffle. Some tweeters are more sensitive than others. For example the Vifa NE19 must be nearly perfect flush with no gap. The Peerless 810921 is less sensitive to gap, but if it is a bit proud of the baffle it creates a problem.
If you ever design both a TM and MTM, you'll see this is much worse with the MTM.
I've actually compared 3mm layers stacking them. Does a little for 6-10khz. Lots for 10khz and above.
On some level, I am changing the shape of the baffle so when I eq flat w/ the felt and remove it the response goes to crap.
This has a ton of diff felt shapes and shows the changes.
https://journals.sagepub.com/doi/full/10.1177/1461348417744307A paper comparing felt to felt + MPP.. It shows the limit of felt.
I'd expect the wool curve to be similar to the black line.
edit: one last set. I thin these show how much felt cleans up the decay.
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