Relating to Steve Greatrex's problem of loss of bass, I think he is
onto a solution to his problem by installing a solid wall behind the
Polyphon.  A good example of placing acoustic instruments against
a reflective surface can be demonstrated with any upright piano.

Our Christie theatre organ has a moveable upright piano attached.
When the piano is moved in front of the stage curtain, the projection
of sound is very much reduced.  We have a solid brick wall proscenium
which is just wide enough for the piano to sit in front of.  The quality
and volume of sound is very much improved in this configuration.

Another consideration is the 'standing wave' that is produced when an
instrument is placed in a corner of a room, as compared to a flat wall
in the middle of the room.  Organ builders in particular are aware of
wave forms produced by similar pipes cancelling each other out.  It is
possible the placement of the Polyphon may be causing acoustic problems.
Try moving it sideways and rotating it by 100 mm steps in any horizontal
direction.

You can demonstrate cancelling waves by placing two speaker cabinets as
close together as possible and feeding the exact same signal to both.
Particularly at bass frequencies, the result will be that little bass
can be heard.  Slowly drag the cabinets apart and you will hear a big
improvement in volume.

You can also walk around the room (with the speakers separated) and
hear the peaks and troughs caused by interfering (constructive and
destructive) sound waves.

Robert Weismantel
Brisbane, Australia
r.weismantel@griffith.edu.au.geentroep [delete *.geentroep" to reply]