Sound from the front VS side of cab

[lilkuku]

When I'm in front of my closed back 2x10 it's perfect, but off to one side or the other there is a dramatic loss of treble and it's very muffled (which when a mic is used it's not an issue). I'm just curious if it could be as simple as making the cab an open-back, or if anyone has another suggestion. I assume that's just the nature of speakers and cabs in general. Obviously while standing directly in front of the cab you get all of the sound, but if there is a way to get some more treble off to the sides, I'd appreciate the help.

 

Pat