Attack transient for combinations of flue pipes
A. W. Nolle · The Journal of the Acoustical Society of America · 2004
The tonal attack due to two or more flue pipes sounded simultaneously is compared to that for a single pipe. Attack duration is measured by the times required to progress from 1% to 50% and 90% of final amplitude. Duration can be reduced by the presence of the pipe(s) of higher pitch, because the number of periods in the sound buildup for pipes of a given design does not change greatly with the pitch. Experimental results are from sound records taken in close proximity to the pipes of a Casavant organ having wind chests of Pittman type. The positive division provides stops intended for use with a closed-end 8-foot rank. The great division provides ranks intended for use with an 8-foot (open) principal. A special situation is found in principal pipes near 200 Hz. Sounding one of these with another stop at unison produces an initial sound suggesting a celeste combination. This is found to be the result of a prolonged burst of second harmonic, locked to the growing fundamental, not of frequency difference. This possibility appears in an analytical mode-locking model by Fletcher [N. H. Fletcher, J. Acoust. Soc. Am. 64, 1566–1569 (1978)].