What exactly is a speaker box sound?

Cabinet resonance and buzzing of course let one know the speaker is in a box but I'm not sure that's what we're talking about here. More like the 'closed-in' box sound some may or may not exhibit. I think modern boxes are far better and money seems to buy a more open sound regardless.

I've heard Magnepans for over forty years and owned Martin Logan electrostats as mains. If you enjoy 'large' singers and images, great. I sure don't feel they are more accurate.

I went to a good pair of ported boxes and will never, ever go back as they reproduce music far more accurately IMO. And that's after a lifetime of listening and attending shows, so...to each his own opinion.

Listen to some Magnepans or Martin Logan electrostats playing music you know well. Your music, not someone else's. Take a CD or thumb drive with you. Listen carefully. If you don't hear a better version of you music, stick to what you have and be happy you saved a bunch of money.

@boomerbillone 

"If you don't hear a better version of you music, stick to what you have and be happy you saved a bunch of money."

That is by no means necessarily true as many "box" speakers cost far more than Maggies or most Martin Logans.

I am with Roxy54 in that all speakers color the sound relative to what was produced within the recording chain from the source.