Vandersteen Audio 3A loudspeaker Sidebar 3: Measurements page 2

The general trend of the midrange and tweeter response is quite linear, though some clearly visible response ripples—particularly from 1kHz to just above 2kHz—would appear to be due to reflections from the cabinet top and its support rods (footnote 2). The sharp peak at about 26kHz is the ultrasonic tweeter resonance.

Fig.3 shows the overall response of the Model 3A averaged across a 30 degree horizontal window (again, measured at 39" from the bottom of the cabinet, 50" away). The bass is down by 6dB at 23Hz, and very flat up to about 500Hz—both excellent results. There is a mild suckout on this axis just below 1kHz, presumably due to less-than-perfect integration between the woofer and the midrange units at this microphone distance. The slight roughness just above 1kHz may be the cause of the slight midrange coloration I noted prior to backing off a notch on the midrange level control, but I wouldn't run too far with this supposition. The general response trend of the 3A is admirably flat.

Fig.3 Vandersteen 3A, anechoic response on optimal axis at 50" averaged across 30 degrees horizontal window and corrected for microphone response, with complex sum of nearfield woofer and bass-coupler responses below 300Hz.

The effects of the midrange- and tweeter-level controls set to their maximum and minimum positions, after subtracting out the actual response of the loudspeaker, are shown in figs.4 and 5. Both controls have a small effect on the range below their primary-response region—and opposite in direction to the primary-response change. But the limited effect of the controls results in a usable range of operation, and no setting of the controls is likely to seriously degrade the 3A's performance.

Fig.4 Vandersteen 3A, effect of midrange control set to maximum and minimum settings ref. the "0dB" setting (5dB/vertical div.).

Fig.5 Vandersteen 3A, effect of HF control set to maximum and minimum settings ref. the "0dB" setting (5dB/vertical div.).

Footnote 2: To minimize reflections from the test setup, the measuring microphone is flush-mounted inside the end of a long tube. Reflections of the speaker's sound from the mike stand and its hardware will be sufficiently delayed not to affect the measurement.—John Atkinson
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