This is called the "Frankenstein Amplifier" because I had a couple of amp cabinets with speakers and no working amplifiers, plus some other bits and pieces that were just waiting to be reduced and combined.
I wired a Crate GX15 into 3 separate speakers instead of 1, and turned a pair of old computer speakers into an overdriven 2nd channel.
Step 1: Gluing and Compressing the Plywood Speaker Panel
I had plenty of 3 ply wood lying around, but this wasn't quite up to the task of handling 5 speakers with heavy magnets in them.
So I cut identically sized pieces, spread a thin layer of wood glue between them, and (as you can see in the pic) clamped the hell out of them! Once dry and trimmed to size, the profile was seamless.