Channel 10 is for percussion instruments. The pitch values determine what instrument to play.

So in addition to changing the channel you will need to tell it what instrument to use by issuing a patch_change( $channel, $patch ); command. Where $patch is the MIDI instrument you wish to use (i.e. 8 for Celesta). However, usage of BeatBox in this manner is not recommended since there are easier ways of doing what you want. :)