ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

5aMU10. Sound spectra from air-driven American organ reeds.

James P. Cottingham

Ben L. Colson

Scott T. Wilson

Phys. Dept., Coe College, Cedar Rapids, IA 52402

Keelyn W. Quigley

Coe College, Cedar Rapids, IA 52402

The ``American'' reed organ is distinguished from the ``European'' harmonium by the use of a partial vacuum to draw air past the free reeds rather than the use of a pressure bellows to drive compressed air through them. A sample of reeds from three instruments has been studied in the laboratory using a specially constructed windchest. Spectral analyses of near field sound produced by air-driven reed vibrations were obtained. Measurements were made of the variation with pressure of the frequency and amplitude of the fundamental as well as the spectral components. Relationships between certain aspects of reed design and the spectrum of the resulting sound can be compared with some ``conventional wisdom'' found in the literature on the instrument. Results are also compared with spectra obtained when these reeds are played in the instruments and with averaged sound spectra from the instruments. It is found that the frequency remains essentially constant over a very wide pressure range, and that the sound spectrum from a given reed, although modified somewhat by its surroundings in the actual instrument, is recognizably the main determinant of the sound spectrum radiated from the instrument.