On the subject of suitable timber for making organ pipes, a few
correspondents mentioned that almost any type of wood will give
a result.  Hans van Oost also points out that Carl Frei was using
inferior materials to make pipework in the 1930's.

Here in England there is an 89-keyless organ built in 1980's by Carl
Frei jr. in the style of a Gavioli, probably one of the last large
instruments built by him.  The violin register comprises of four ranks,
all of which have plywood sides and backs.  The result is a bright
stringy Frei violin sound, all of which goes to prove it's not really
the material but skillful voicing which counts.

Best wishes,

Russell Wattam