[Stratopastor]

You may have come across reference to this (you may not) but I've just tested it out and it's working for me... a really cheap way to stop a guitar speaker sending out a narrow 'beam' of trebly sound straight out in front. It gives most people in the room a chance of hearing the roughly the same tone and volume.

Here's the relevant article by the originator of the idea...

Speaker Directivity Modifier :: TGP Webzine

I used 18mm foam on my 1x12" combo. Early experience is encouraging. Cost £8 (12 dollars US?) and less than an hour.

[Major Tom]

I've read about that before, but haven't tried it. I'd like to hear your reviews of it after using it for a while. It seems to me like overall, the amount of highs would be lessened, since the majority of them are being absorbed, and "discarded"... but I guess without it, the phase cancellation does that anyway...?

I use a crude beam blocker on one of my 1x12 combos - just a piece of 1/8" plywood cut in a 5.5" circle with a leg on it to slide under the amp logo piece to hold it in place, easily removable when I don't want it. It works pretty well to tame the highs in that narrow field on-axis, when I have it tilted back and pointed at my head.

[Stratopastor]

My experience so far is, it's surprising how many highs DO get through. However, as JM says in the article, the tone controls do have to be played with, and yes, I had to lift the treble a little to get 'my' tone back.

If the only person needing to hear your amp is you (Tom, I take it that's why you've got the amp pointing at your head?) then, as you'll have worked out, the doughnut isn't necessary.

[Stratopastor]

Here's how it can look for one amp... I added a page to my Princeton Reverb II site

Princeton Reverb II; loudspeaker treble-beaming problem; foam donut to reduce high-frequency beaming