I had this extension speaker cabinet specially built for use with my Two-Rock Opal prototype amplifier head. I paid for the best money could buy, as that amp is so special... and this is what I ended up with, happily. I have both backs, the open version, which is on it now, and the closed version, that is included. I had them match a pair of special Celestion G12 Alnico Blue and install them. You really won't ever find another cabinet of this type of quality for this price. Check out my Two-Rock Opal prototype amplifier HERE. Even though this cabinet was built for my Two-Rock, it would be a great asset to any high-end guitar head.