Originally Posted by catapult
The noise measurement is higher because it's looking at all the frequencies other than the harmonics and they all add to the SPL. The noise at 9K may be -75dB but the noise at all the other frequencies added together is higher.
I forgot about that when I wrote the bit about mics. My Dayton has a broadband noise of 39dBA but it might be 10dB lower at any single frequency.
About the distortion, Herb ran a couple of tests and posted them at HTS. His reference mic is a cheaper version of the one JonMarsh uses. Looks like the Behringer is better at HF than at LF. When looking at the numbers you can assume the ACO is measuring the speaker distortion pretty accurately so the difference between the two is distortion the Behringer is adding.
I just ran a quick test comparing the distortion of my one of my reference mics (ACO Pacific 7052, rated to 144 dB) to an ECM8000 at 1 kHz.
At 115 dB, my ref mic gets 0.13% distortion, the ECM8000 reads 0.54%
At 120 dB, my ref mic gets 0.22% distortion, the ECM8000 reads 0.81%
At 125 dB, my ref mic gets 0.46% distortion, the ECM8000 reads 1.37%
Tests at 30 Hz:
At 115 dB, my ref mic gets 1.8% distortion, the ECM8000 reads 3.1%
At 120 dB, my ref mic gets 2.95% distortion, the ECM8000 reads 5.0%
At 125 dB, my ref mic gets 4.2% distortion, the ECM8000 reads 7.4%
FWIW, this is a different ECM8000 than the one used for the 1 kHz test.