Rotary Woofer Distortion Measurements
The following distortion test were measured on the rotary woofer. The microphone was three meters from the woofer. The system was calibrated with a Bruel and Kjaer 4145 microphone, pistonphone and 2204 sound level meter. The spectrum analyzer was calibrated to be flat to below 1 Hz using a signal generator and voltmeter. In this test configuration the rotary woofer was able to maintain greater than 110dB sound levels down to 1Hz. Typical maximum sound levels in the 2800 cubic foot test room are around 115-119dB with 350 watts total input power (motor plus audio amplifier power) between 1 and 30Hz.
For comparison most conventional subwoofers will not achieve 110dB output at any frequency 20Hz or lower with 10% distortion or less.
Because these distortion measurements include the room they are likely higher than actual anechoic readings. The room walls experienced resonance modes between 10 and 15 Hz. Below 5Hz there is significant volume velocity at 110dB such that a door will swing back and forth. At 1Hz you don't hear anything other than the rattling of doors, walls and the air moving through the transducer and the room. The THD number includes all harmonics and room noise up to 2Khz.
1 Hz measurement, 110dB 7.24%THD:
5 Hz measurement, 110dB 7.91%THD:
10 Hz measurement, 110dB 9.31%THD:
20 Hz measurement, 110dB 9.38%THD:
25 Hz measurement, 110dB 5.56%THD:
30 Hz measurement, 110dB 2.12%THD:
2Hz square wave mesurement, mic in room 7 meters from the transducer, 95dB: