Quantitative measurement of acoustic whistlers

Abstract

We present an experimental setup capable of quantitative examination of acoustic whistlers in tubes of varying lengths and diameters. It is simple enough to be used as an undergraduate lab or classroom demonstration. The setup can be used to show the transverse modes of a cavity, and the difference between the group and phase velocity of a wave. It can also be used to determine the velocity of sound to an accuracy of 3%. We present the results of several experiments used to determine the acoustic modes present in transient whistlers. Our results differ significantly from a “geometrical acoustics” derivation of the acoustic whistler made in an earlier paper.

Culvert whistlers: Harmonizing the wave and ray models

“…Second, it also seems likely that the upper frequency components involved in both modes were attenuated on each reflection from the wall of the echo tube, and its great length ͑100 ft͒ required many internal reflections before returning to the listener, thus leaving the lower frequencies with greater amplitude. 5 Finally, if Crawford tended to listen analytically rather than synthetically, 25 the 4-Hz beat between his 440-Hz tuning fork and f 0,1,m ͑shown in bold type in Table VI͒ would indeed have been clearly heard. Consequently, the pure sine wave produced by the 440-Hz tuning fork acted as a probe to extract a beat from the 436-Hz component involved in the angular mode whistler.…”

“…͑See Ref. 5.͒ Because their experimental situation was limited to measuring only one or two whistler modes at a time, the persistence of multiple modes throughout the whistler's lifetime could not be observed. They assert ''the temporal duration of the whistler is inversely proportional to the whistler's fundamental frequency.…”

“…Recently Adler et al 5 investigated whistlers in tubes suitable for classroom demonstration. Their experiments, however, used cylinders of such small diameter that only one or two of the lowest normal mode frequencies were observed within the passband of their analysis.…”