Leslie Free-Field Horn Measurements

The free-field radiation pattern of a Model 600 Leslie rotating horn was measured using the experimental set-up shown in Fig.4. A matched pair of Panasonic microphone elements (Crystal River Snapshot system) were used to measure the horn response both in the plane of rotation and along the axis of rotation (where no Doppler shift or radiation pattern variation is expected). The microphones were mounted on separate boom microphone stands, as shown in the figure. A close-up of the plane-of-rotation mic is shown in Fig.5.

Figure: Rotating horn recording set up. -- [FIXME: Cannot do both rotation and scaling in latex2html graphicx support]

Figure 5: Microphone close-up.

The horn was set manually to fixed angles from -180 to 180 degrees in increments of 15 degrees, and at each angle the impulse response was measured using 2048-long Golay-code pairs [6].

Figure 6 shows the measured impulses responses and Fig.7 shows the corresponding amplitude responses at the various angles. Note that the beginning of each impulse response contains a fixed portion which does not depend significantly on the angle. This is thought to be due to ``leakage'' from the base of the horn. It arrives first since the straight-line path from the enclosed speaker to the microphone is shorter than that traveling through the horn assembly.

Figure 6: Measured impulse-responses of the Leslie 600 rotating-horn at multiples of 15 degrees. The middle trace is recorded with the microphone along the axis of the horn.

Figure 7: Measured amplitude-responses of the Leslie 600 rotating-horn at multiples of 15 degrees.