William R. Savage

Air and structural modes of a harpsichord

The acoustical behavior of a harpsichord modeled after 17th‐century Flemish prototypes was studied using both experimental and analytical techniques. The vibrational modes of its enclosed air volume were measured and found to correspond closely to those predicted by the J0 and J9 solutions to the Bessel equation for a wedge shaped space. A modal analysis of the complete harpsichord revealed that the soundboard has 36 vibrational modes over a frequency range of 0 to 600 Hz, and that there are numerous modes where the instrument’s case has a significant amplitude of motion. Additional information is reported showing that the acoustic output of the harpsichord is reasonably flat over a frequency range of 50–2000 Hz. It is concluded that the resonance behavior of both the soundboard and the enclosed air are important to the tone quality of the harpsichord, and that its generally uniform acoustic output results from the excitation of a large number of wood and air modes by the string partials.

Vibrational characteristics of Saron Barong metallophones in the 1893 Field Museum Gamelan

The gongs used in Asiatic music frequently exhibit noticeable glides in pitch comprising a significant fraction of a semitone. Bar‐form metallophones of the 1893 Gamelan also show a glide in pitch. This contrasts with western bar‐form metallophones which are generally pitch stable. Measurements of the keys of two Saron Barong show that they have different lengths, widths, and cross sections but do not “scale” since they have nearly similar masses. The keys of lower pitch are longer and wider than those of higher pitch within a given seven note Saron. The upper surface of the keys is convex for both length and width aspects. The lower surface of the lower pitch keys is concave becoming convex for the upper keys. They are mounted with nails through holes at a distance one quarter the length from the end on resilient pads above individual air cavities. The holes are not symmetrically located and the bars are not straight. They were cast of bell metal in sand molds and roughly finished. The central part of th...

Harpsichord modal behavior

The modal behavior of the harpsichord in the acoustics laboratory at the University of Iowa was determined by percussing approximately 600 points on the external surfaces of the instrument with an instrumented hammer. Both the input from the hammer and the response of the harpsichord were recorded. The data were digitized and the response of each tapped point was converted to a numerical value. These data have been processed into a computer‐generated, three‐dimensional video tape showing the harpsichords vibrating modes from 0–500 Hz. Of particular interest is the way in which all the external structural elements of the harpsichord can be shown to vibrate at some point. The results of this work agree closely with the published [E. L. Kottick, Galpin Soc. J. 48, 55–77 (1985)] and unpublished data developed by the authors of this paper.

Transmission lines and acoustical filters studied by G. W. Stewart

In the years from 1922 to 1936, G. W. Stewart and his students investigated the properties of transmission lines and acoustic filters. Recently a box that contained most of these filters was discovered in one of the attic rooms of the physics building he designed. The filters are formed from a central small diameter tube with side branches of various types. Some transmission lines have a single side branch and others have a small number of identical side branches. The experiments of the expected transmission by the filters were done by Stewart and his students with sufficient accuracy for a comparison with theory. Electric transmission lines formed the model of construction and analysis of the filter response. The general method of analysis is that used for chains of identical lumped parameter networks. Stewart used telephone receivers for sound sources and his hearing or Rayleigh disks for detectors. Transmission lines and filters based on the Stewart filters could be used with modern sources and detecto...

Instructional uses of linear filters and transmission lines

G. W. Stewart was a pioneer in the use of the analogy between lumped parameter electrical circuit theory and acoustical transmission lines and filters. He published a series of papers based on the work of his students and his own studies. Recently about half of these filters were discovered in a storage room at The University of Iowa. The filters were fabricated from standard size brass and copper tubing. Some of the filters will be displayed and demonstrated with modern drivers and detectors. Similar devices could be constructed and used for lecture demonstration, laboratories, and student research.

The acoustics of the harpsichord: A preliminary report

During the spring of 1980 the first author recorded response curves and modes of vibration of over forty harpsichords. About half of these instruments were newly built, while the others were antiques in museums. Sinusoidal forces of appropriate frequency were transmitted to each bridge pin in turn. Sound pressure levels were measured, and a driving point response curve was plotted for each harpsichord. Chladni patterns were detected by vibrating the glitter‐covered soundboard; at certain frequencies of vibration the glitter formed stable patterns which were then photographed. It was found that newer harpsichords tended to respond at higher frequencies than the antique instruments.

Pedagogical aspects of teaching acoustics to a general student group

At a number of colleges and universities courses in introductory acoustics and related areas are being offered. Often these courses are taught in the physics or physical science departments as a science subject. This is not a universal rule since similar courses are found in departments such as speech science, architecture, etc. The teacher may have a deep interest in acoustical phenomena without being a professional acoustician. The courses may serve as a required course for students in the speech sciences or music. These courses can have a large enrollment when they are open to general interest students. Many of the teaching methods relate to the task of explaining a phenomenon that is described perhaps best, at least compactly, by mathematical methods with visual or audible teaching aids.