Acoustic Transmission Line Research Articles

An Electrical Method of Measuring the Intonation of Cup-Mouthpiece Instruments

An electrical driving system has been worked out for intonation tests on cup mouthpiece instruments. The system amounts to driving an acoustic transmission line from a closed end and measuring the resonant frequencies. It is shown experimentally that these resonant frequencies correspond quite precisely (within about 10 cents) to the frequencies normally played, except at the lower end of the scale where the player habitually corrects the defective intonation of the usual instrument. The experimental work includes tests on specially designed instruments that could not be played “in tune” with standard fingering.

An Electrical Method for Measuring the Intonation of Cup Mouthpiece Instruments

A method has been devised for driving an acoustic transmission line such that the driving point is a pressure anti-node when the distant end of the line is open and the line is in resonance. The method has been verified by an extensive series of measurements on cylindrical tubes. In this work, the velocity of sound transmission was measured both by conventional complete-series resonance, and by odd-series resonance in which the driving point was at the closed end of the tube. The maximum deviation from the average result was substantially below 1.0 percent. By cutting off the mouthpiece of a trumpet at the throat constriction and driving it electrically at that point, the resonant frequencies are found to be those actually played, provided that the actually played frequency is not unduly influenced by the performer's ear, nor by habitual “lip-set.” Extensive experimental work has been done to eliminate the effects of this personal equation in obtaining a comparison between player performance and electrical measurements. This has included the use of non-harmonic intervals between successive test notes, several bell designs involving small differences in performance, and one special design (conical) that cannot possibly be played in tune for more than a few notes.