If you do it right, that is. I build all my prosound cabs from 1/2" plywood- or thinner for curved parts- and they don't vibrate because they are properly braced. Panel to panel cross bracing is no less than 4 times as effective pound for pound as sheer panel mass in controlling vibration. For home use where portability is les of a concern 3/4" ply or MDF is fine, but crossbracing is still the key. If you have no unbraced panel wider than 6 inches the box will not vibrate.