I typically use the flat polly-fill on all surfaces (sealed chamber) and follow up with the regular poly-fill (loosely packed), leaving a space directly behind the speaker. Does it help? I not sure but I feel if you are taking the time to build an enclosure of this quality you should do everything possible to make it preform to the highest standard. Will the acrylic help? I am not sure but if I was you I would try it just to see if there is a difference. My .02, hope it helps.



HT-EXT