The good old topic of organ air supply surfaced in the MMD Pipes Forum
in 1999.  At that time I learnt a lot from our experienced community
about what devices you employ to get a stable air supply.

A brief review of these devices and some of their properties, described
in acoustical engineering terms, is presented in a new article at the
MMD Tech site,

  http://mmd.foxtail.com/Tech/
  http://mmd.foxtail.com/Tech/airbounc.htm

Topics include:

 1. Sources
 2. Reservoirs
 3. Transmission trunks
 4. Compensators
 5. Bellows speed
 6. Regulators
 7. Complete feeder systems
 8. References
 9. Unit conversions and air properties

In an organ pipe the tone onset is very important and characteristic,
and there are several factors to determine this onset.  One is the pipe
itself as set up by the voicer.  To keep a predictable pipe tone you
must also have control of how rapidly the playing valve opens and how
well the wind supply stands up to the increase in air demand when the
pipe goes on.  Also any subsequent pressure changes will modulate the
pipe tone, notably when it sounds while other pipes go on or off, in
particular in wide chords.

Special attention is given the problem of regulation of transient loads
and how to keep pressure constant in spite of sudden changes in air
demand.  Richard Vance and Hans van Oost contributed illustrations and
many valuable suggestions and improvements in the process of reviewing
the manuscript.

The paper is not a cookbook on how to make a complete supply system
(a prominent reason is the difficulty to specify what is required)
but, hopefully, one may find some dimensioning guidelines from examples
given.

Johan Liljencrants,
Stockholm

 [ Johan is a professor in the Dept. of speech, music and hearing at
 [ the Royal Institute of Technology of Sweden.  (Pronounce his name
 [ like Lilienkranz.)
 [
 [ Mechanical Music Digest sponsors the MMD Pipes Forum, guided by
 [ Prof. Liljencrants, which is simply a non-moderated email list
 [ server, not a bulletin board or newsgroup.  Discussion topics
 [ include organ theory and engineering design as well as construction
 [ hints; detailed plans and drawings to build a complete organ are
 [ beyond the present scope of the forum.  Write to me if you wish
 [ more information.  -- Robbie Rhodes <editor@foxtail.com>