Firstly wood congas sound differnt from fiberglass ones, the later is more bright. The inside of a conga is left "crude" mostly because it would take too much work to sand it smooth
. Secondly the sound differs if wood is smooth inside. The sound waves produce a more 'straight' sound, ie. it goes stright down, the more edges on the inside the more the sound bounces around. Its like the difference between a stright drum and a barrell shaped drum, on the barrell the sound waves condesce toward the hole, and some bounce back producing a more lasting sound, while on the straight drum the sound just passes through the hole.
Honestly i wouldnt suggest sanding the inside, both acoustic wise and because the shell thickness would be reduced greatly, and this would also make the sound different, more weak. And it would lessen the life span of the drum. Hope this helps, I'm no real expert in acoustics, but iv made a few drums, some sound better some worse, and this is what i'v come to realise (put very shortly).
Edited By timo on May 28 2002 at 22:53