Can I get good results with some gaffers tape in a 4inch square attached to the inside grill cloth ?
What size usually works with 12s?
Or do the Weber beamblockers work that much better?
Do a search on the Mitchell Foam Donuts. A different, some say better, approach.
The beam blockers can do funny things to your tone. By reflecting the sound back to the speaker cone it seems to do weird things to the phase.
right; it's a huge thread with lots of science, so let me summarize: beam blockers don't actually work, because treble doesn't come from the center, it comes from the entire cone!
the beam happens when you (or the guitar mic) are centered up in front of the speaker and all the treble from all over the cone hits you in-phase. as you move off-center, the treble from the far side of the cone gets further away from you than the treble on the near side, so some of it cancels from not being perfectly synced up anymore when it hits your ear.