Originally Posted by
JeffW
There was a paper here once, I can't find it any more, that went into the thermodynamic properties of different materials for lining speaker enclosures. Fiberglass was much better at converting sound energy to heat than the usual suspects like polyfill. Polyester fibers just didn't have what it takes. Yet polyester fiber fill is cheaper than fiberglass. If cheap was the driving force, seems like polyfill would be in JBL cabinets.
I don't recall if any foam products were tested in the paper, but the type of foam is pertinent in sound absorption. The wrong type of foam, even if it looks good, can act as a reflector.
I didn't find the product sheet on the 66000/67000 series, but pretty sure they have fiberglass lining, too. Did JBL really go all out on these systems only to save a few bucks on the lining of the enclosures, or is fiberglass the correct material after all? :dont-know: