concert toms sound 'faster.' there is no bottom drumhead for the moving air to bounce off of; all the air gets pushed out of the drum all at once. the sound decays very quickly.
double-headed toms resonate more because of the bottom head. you also have more tuning options with a double-sided tom that you do with a single-sided, 'concert' tom.
for reference, listen to phil collins's 80's stuff to hear what single-sided toms sound like.
peace, nick soulbelly
www.soulbelly.com www.trueline.com/endorse/amoroso.html 'The music business stinks, and you can quote me.' - Artie Shaw, 1939