I'm not sure about other brands because my recollection don't seem to go back that far, but every Yamaha model I've owned with built-in speakers sounded excellent, and they were all ported with vents beneath both sides of the keybed just for that purpose. The speakers were extremely high quality, well balanced, and situated in such a manner to provide outstanding fidelity--almost as good as headphones.

The only problem I ever encountered was getting my external sound system to sound equally as good. That took quite a bit of tuning, but it can be accomplished.

Cheers,

Gary