The Beam Blocker is a simple device that is installed between the speaker and the baffle on rear-mounted speakers (see drawing for front-mounting.) The dome shaped diffuser prevents point-source high frequencies from beaming directly out of the cabinet to create that ice pick sound. Instead, they are diffused evenly in all directions to blend with the lower frequencies which tend to radiate in a wider pattern.
The Beam Blocker allows you to make use of speakers that have a tendency to be beamy, harsh, or generally unusable due to their extreme high frequency response. The idea of using a diffuser is not new. Many performers including SRV were known to have applied a patch of duct tape on the grill cloth directly inline with the center of the speaker to block the beaminess. The Beam Blocker performs that same function while diffusing the high frequencies evenly in all directions.
Here is a video by Rick Fass, which shows some very helpful information about the Beam Blocker, including how to install it. (Try to ignore the speaker brands in the video. Your setup will sound much better with Weber Speakers.)
Note that the purpose of any gasket, whether it is on a speaker, a door, or a car engine, is to form-fit around any irregularities in the two surfaces being joined. In the case of the beam blocker, the speaker will be sitting on the beam ends when you first install it. Install the speaker (being careful not to overtighten) as you normally would and after a couple of days, the gasket will depress at that location and form-fit around the beam end. Some have suggested compensating at other mounting locations by stacking up washers or going as far as notching out the gasket for the beam end to fit in. I wouldn’t recommend that, it could cause problems. The washers could cause the basket to warp, and the notching could cause the beam to rattle at high volumes.
Suggested For Front-Mounted Speakers: Install the Beam Blocker to your cabinets baffle using slightly longer screws than those already used to mount the speaker. Next, add a nylon rack washer (midlantic) then a steel flat washer for stability and then another nylon rack washer (these dampen any vibrations and also protect the metal mounting plate of the Beam Blocker. Carefully tighten the two screws until the Beam Blocker just touches the speaker gasket, be careful not to over-tighten and compress the gasket.