ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

3pEA7. Measurement of throat impedance and far-field directivity for acoustic horns.

John T. Post

Klipsch Professional, P. O. Box 1320, Hope, AR 71801

Elmer L. Hixson

Univ. of Texas, Austin, TX 78712

Experiments suitable for the measurement of throat impedance and directivity of acoustic horns were designed and implemented using an axisymmetric exponential and tractrix horn. The horns have equal length (55.9 cm), throat radius (2.54 cm), and mouth radius (27.1 cm). A modern implementation of the ``reaction on the source'' method was compared with a two-microphone method for the measurement of acoustic impedance. The indirect reaction on the source method was found to be less accurate but has the capability of in situ-type impedance measurements. The far-field pressure was derived by measuring the near-field pressure and mathematically extrapolating to the far field, a technique which has been used in the area of antennas since the early 1970s.