Hi,  Many years ago I saw and heard a Wurlitzer 153 band organ in
the shop of the famous J. R. Schott of Fort Worth, Texas.  It was one
of the finest sounds I have ever heard.  I asked Mr. Schott how it
was that it sounded so good and he replied, "It's all in the pressure,
my boy, all in the pressure!"

I do not know what this pressure was but it was perfect.  I will be
glad to have this question answered in future.

Cheers,
Jerry F Bacon