Depends on the speaker quality. Better speakers will give a better sound ofcourse.
Also, a 4x12 gives more volume than a 2x12. and a good cab should resonate, which gives better sound. and speakers have an effect on tone of course.
I've heard that cab must have special architecture - like special chambers for seperate speakers, speaker placement layout. Maybe somoeone could expand this or lead to other thread, where it was told before?
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cab has a large effect. Moving air, speaker breakup, and adding texture to the sound contribute a lot to the overall tone. I've heard great amps sound like crap thru cheap cabs, where just changing the cab made a very noticable difference. It doesn't necessarily have to be expensive, just well built/designed, with good materials, and good speakers. The design features like the baffling system, porting, closed/open back, etc. all make a difference on what it does to the sound being produced.

with certain applications, you want the cab resonating a lot, like chicken picken cleans with an open back solid pine cabinet that really resonates an open airy sound. If you are playing metal for instance, you may not want the cab resonating as much, as you want a very forceful tight punchy lowend. For that, you would normally want something like a high quality multi ply like birch, with a closed back. A 4x12 pine cab would also be damn heavy to even move.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
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