Wayne Parham Messages: 18783 Registered: January 2001
Illuminati (33rd Degree)
Honestly, I'd stick with fiberglass unless I had measured the system with the Rockwool product to see how it fared.
If you choose to do that, what you want to look for is response in the 100-400Hz range. Compare the response between a speaker with fiberglass to a speaker with Rockwall. The one with smoothest response wins, of course. If it's a tie, that's cool too.
Measurement at this frequency range should be measured outdoors. Best to do it with the speaker on its back in a pit, so the baffle is flush with the ground. Instead of a pit, you can also make a "false ground" with sheets of wood sitting flush with the baffle on the side nearest the speaker and touching the ground on the side furthest away.
Indoor measurements aren't good at this frequency because of reflections. You're measuring the room more than you are the speakers.
While we're on the subject of damping material, be sure to include the sheet that sits on the cross-brace, spanning the cross-section of the cabinet. Some people forget that but it is vitally important.