DIY Beam Blocker / Diffuser For A Guitar Amp

Most guitar players notice that the high frequencies coming from a guitar amp are concentrated in a narrow beam in front. People along the sides of a room have a hard time hearing the high frequencies. If you EQ your amp to sound good off-axis to the side, it will sound harsh on-axis in the front. This can be an issue for bands that play in venues without an in-house PA system.

0:00 Strumming around the room without a diffuser / blocker
0:25 Strumming around the room with 6 inch diffusers with 3/4 inch and 1/2 inch holes
1:11 On Axis comparison - No diffuser vs 3/4 inch hole vs1/2 inch hole
1:30 Explanation of my testing
2:04 Chord comparison, On axis vs extreme Off axis

I did a low budget experimented to see if I could tackle this issue. In the past, I have tried duct tape, a styrofoam ball to mimic a beam blocker, a CD and other methods, but this one is the most pleasing to my ears. It doesn't drastically change the tonal characteristics of the speaker. The type of material, diameter, density and size of the hole in the middle play an important part. A thin and soft material like foam or vinyl sounded best in my testing.

There is 2.5 inches of unblocked speaker around the blocker/ diffuser to minimize the high frequency beaming effect. If your 12 inch speaker reaches 5000 Hertz, a 5 or 5.5 inch circle with a 3/4 inch hole may be enough.
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