It's a question very often asked and already well answered here. I'll try to summarise some pros and cons from different perspective.
Open back:
- Sounds bigger and looser which works great for bluesy leads and players who want to dominate the band sound when they play leads. Also great on cleans.
- Disadvantage to that is you really need to control your volume and playing style when you don't want to drown everyone else in your huge open sound. But note almost all bluesy guitar heroes play open cabs.
- Biggest disadvantage to me is they radiate all over the place, which may be a big problem in some clubs etc...at some parts of the club to the side of the stage etc. someone may hear nothing but your guitar then.
- Another downer for me is with an open back the cab sound will vary even greatly according to wall proximity...especially at lower gain the sound can be totally ruined if the cab has to be right next to the wall for instance or, worst case scenario, propped against a sofa back...been there and boy it killed the sound _totally_.
Closed back:
- Sound much tighter and controlled than opens, especially in 4x12" there is no substitute to the sheer onslaught of punch they provide, even at lower volumes. They always stay focused and you can aim the cab sound where ever you want.
- Directivity can be a problem too, for front line listeners - don't point 'em at listener ears!
- Hard to achieve a huge warm and big sound, it will always be snappier. Speaker selection is of course the key here.
- With several guitarists it's easy to keep guitars distinct and not overpower each other. Note not any twin-guitar based rock/heavy band ever uses open cabs.
- They always sound the same no matter where.
I always go closed-back just because it's proven much more convenient in gigging, although if I were the lead player in a blues trio or something, I'd go open-back, and also if I were to record a HUGE bluesy or airy solo I'd try an open back first.
Sonically I think the difference is quite akin to that of semi-hollowbodies and solidbody guitars.
Dee
"When life's a biatch, be a horny dog"
Amps: Marshall JVM 410H w/ Plexi Cap mod, Choke Mod & Negative Feedback Removal mod, 4x12", Behringer GMX110, Amplitube 3/StealthPedal
Half a dozen custom built/bastardized guitars all with EMG's, mostly 85's, Ibanez Artwood acoustic & Yamaha SGR bass, Epiphone Prophecy SG, Vox Wah, Pitchblack tuner plus assorted pedals, rack gear etc. for home studio use.