| Abstrakt: |
The six major techniques used heretofore for the swept-sinusoid measurement of air column input impedances are first reviewed, after which the basic theory of a new, impedance head design that requires no servo mechanism is outlined. In this simple device, a low-cost piezoelectric disk is used as the primary flow excitation source, and the resulting response pressure is detected by a similarly inexpensive miniature electret microphone. Detailed experimental tests of the device are presented. Analysis of these tests shows that, up to about 5000 Hz, essentially no calibration corrections are needed; furthermore, the driver impedance is so high that its perturbations of the air column are experimentally negligible. A detailed mathematical analysis of the major finite-impedance, displaced-microphone, and higher-mode perturbations associated with the driving disk itself are set forth, and an outline of general procedures for obtaining the absolute calibration of any air column impedance head is given. [ABSTRACT FROM AUTHOR] |
