Wayne Parham Messages: 18783 Registered: January 2001
Illuminati (33rd Degree)
I should know that answer but I don't, sorry. I kind of lean on my cabinet shop for this stuff. Hopefully one of the regulars here will chime in.
But you're right - Common sizes are 4 x 8 and 5 x 5. Baltic Birch tends to come in 5 x 5 and other stuff usually comes in 4 x 8.
Be careful about your choices though. Definitely do not use any other plywood than Baltic Birch. I tend to prefer MDF if the speakers are going to be semi-permanent (rarely moved) and won't be exposed to lengthy periods of very high humidity. When speakers will be used indoors, at home, MDF is a great material to build with. But if the speakers will be moved a lot or might get wet occasionally, then Baltic Birch is a better bet.