This instructable is a direct implementation of the "Mitchell Doughnut" guitar speaker directivity modifier proposed by Jay Mitchell
from The Gear Page
discussion forum. The most relevant discussion can be found in the Speaker Directivity thread
A typical guitar amplifier with a 12" speaker will seem to have accentuated higher frequencies when listening directly on-axis with the speaker cone. Listening to the speaker "off-axis" will have the converse effect. This phenomenon is commonly referred to as "speaker beaming". The directivity modifier is an attempt to mitigate this on-axis beaming effect without affecting the off-axis tone. Refer to the above gear page thread for background on the principles involved.
A 3/4" foam "doughnut" that will be affixed behind the grill cloth in front of the speaker cone. See pics.
-Guitar Amplifier (this projects specifies a 12" speaker)
-12"x12" polyurethane foam sheet
-Large sharp razor blade
-3M Super 77 contact adhesive spray from Lowes (optional)
-Black Clothing Dye (optional)