I think it was harp tech/harp meister Nicolas "Froggy" Fouquet who told me the Hohner Bb, and lower, used longer reeds and thus had greater sustain, or residual vibration.
This could explain some of Bb's appeal as compared to, e.g., the ubiquitous C, if it has a shorter reed set and thus arguably shorter sustain. I seem to recall Nico tuned a Bb up to C to get a deeper tone due to its ostensibly longer reeds.
I dunno whether the Seydel also uses different length reeds starting with the Bb and down, but the theory "resonates" with me. (And so does my Seydel low Bb which Ben Bouman sold me, it's beeyootiful!)
Dave "ain't no techie" Fertig _______________________________________________ Harp-L is sponsored by SPAH, http://www.spah.org Harp-L@xxxxxxxxxx http://harp-l.org/mailman/listinfo/harp-l