Thomas D. Rossing, - Rossing@physics.niu.edu
Judit Angster, and Andrs Miklos
Fraunhofer-Institut Fr Bauphysik
Stuttgart, Germany
Popular version of paper 2pMU6
Presented Tuesday afternoon, October 13, 1998
136th ASA Meeting, Norfolk, VA
The pipe organ has been called the "king of musical instruments." No other instrument can match it in size, in range of tone, in loudness, or in complexity. The large organ in the Convention Hall in Atlantic City, for example, has over 32,000 pipes of various sizes and shapes. No two pipe organs in the world are exactly alike. There are two basic types or organ pipes: flue (labial) pipes and reed (lingual) pipes. Flue pipes produce sound by means of a vibrating air jet, in a manner similar to the flute or recorder, while reed pipes use a vibrating metal reed to modulate the air stream. Although sound production in labial pipes has been fairly extensively studied, very little research has been reported on sound production in lingual pipes. In these pipes, there is a strong and rather complicated interaction between the vibrating reed and the pipe resonator. In most lingual pipes, the reed vibrates against the fixed shallot, and modulates the flow of air passing through the shallot into the resonator. The reed is pressed against the open side of the shallot by a wire ("Stimmkrcke") that can be adjusted up and down to tune the vibrating reed. The pipe voicer generally tunes the resonator to the desired pitch, and then adjusts the tuning wire to produce the best sound.
In these studies, the reed velocity and the sound pressure inside the shallot were recorded in lingual organ pipes as the vibrating reed length was varied by means of the tuning wire . Without the pipe resonator, the reed vibration frequency is a continuous function of the reed vibrating length, but when the resonator is added the frequency jumps abruptly from below to above each resonance frequency of the resonator.
Reed closure may induce an acoustical oscillation in the shallot at a rather high frequency (approximately 1700 Hz in an F3 trompette pipe tuned to 175 Hz), which appears to strengthen a certain range of harmonics in the pipe sound. The oscillation frequency rises as the reed closes, and it is damped by the pipe resonator.
Although design of lingual organ pipes is a well-developed art, it has developed as an empirical art and is very time-consuming. It is believed that a good understanding of the acoustical and mechanical aspects of sound generation in these pipes will allow organ builders and tuners to more easily and more accurately voice them so as to obtain the desired sound.