Sam Harris wrote in 031013 MMDigest:

> Would anyone be as kind to explain to me how the bell or glockenspiel
> on a Bruder organ works?

I don't know for what reason, but about percussion systems there is
indeed always a bit of a mystery; most people seem to like to keep
these as bit of a secret.  Having been told quite a bit I am not going
to say too much, but only from my own observations:

The system as Sam Harris originally describes seems fit for something
like a bass drum on an organ: it will be inflated by default against a
spring.  When the hole in the book comes the bellows is shut off from the
wind supply and a exhaust hole opens.  The rest is done by the spring.

Robbie commented:

>[ When the hole in the paper roll or music book occurs on Mortier
>[ organs (and probably many others), the pneumatic slowly pulls the
>[ beater away from the drum.  After the hole passes by the tracker bar
>[ or the keyframe, a large exhaust valve opens and a spring quickly
>[ accelerates the beater.  If the valve opening is sufficient then
>[ this method insures that the beater speed is relatively unaffected
>[ by variations of supply pressure or suction.  I understand that the
>[ beater travel distance is usually adjusted to make the drum strike
>[ coincide with the pipes sounding.  Altering the beater velocity for
>[ greater or lesser volume, if proper timing is to be maintained,
>[ usually means a lot of fiddling with the spring force and valve
>[ opening.

The system Robbie is describing here seems fit for a snare drum or
wood block.  It is by default not inflated; when the hole comes, the
bellows of the beater is inflated against the spring.  The hole-end
the supply is shut off, the exhaust opens, the spring does the rest.
_But,_ these are "offbeat", mind you -- the holes in the book are ahead
of the striking.  They are, by the way, also ahead for the bass drum,
but that's not because it needs to inflate first, but because the
action takes quite long to deflate a big bellows for a big beater.

A direct action is no good; even with high wind pressure the "bang" is
just not gonna be there and in the event that the hole happens to be
too long, the beater will be stuck to the drum, muting it.

So how would a glockenspiel be designed?  I'd suppose it should be
designed more like a bass drum: inflated by default, released by the
hole and, as Robbie said, kept in "close combat" to its target, making
it as fast responding as possible.  For my personal taste I'd extend
that system with some sort of tremolo, making it repeat the beat in
certain steps independent of whether staccato was set in the book or
not.

At least this should go to the extent that, after the beater strikes
the bell, the beater is moved away from the bell, therefor not muting
it, which I find a very disturbing effect in quite a bit of the
Black Forest fair organs.

My 2 cents only...

greetings by(e) InK - Ingmar Krause