Any idea why I get cancellation at 50 Hz when I turn on both left and right channels?
The measurement was not done at my home. So I cannot take additional measurement at my convenient time.
The mic is one marketed for people doing voice over. I do not know the accuracy for acoustic measurement.
The speakers are Bose 901 VI.
I suspected that the 901 EQ was defective and was sending out-of-phase signals. So I played a 50 Hz sinusoidal tone, and measured the voltage with a multi-meter: L+ and ground 1.121 V; R+ and ground 1.145; L+ and R+ 0.036 V.
P.S.:
I performed the measurement to see how better it is to put PSI AVAA at the corner on the listeners' wall than at the corner of the speakers' wall. However, I found an unexpected 50 Hz cancellation. Even with bare ears, I could feel that the listening position was a null position for 50 Hz.
By the way, PSI AVAA remained at the corner of speakers' wall. The reason was the distance from the window. In winter, they open the windows for some moment everyday for air circulation. If PSI AVAA is at the he corner on the listeners' wall, it will be right below the window, and get temperature shock every day during freezing winter season. PSI AVAA is more expensive than their main speaker system, and they do not want to break it. PSI AVVA's main purpose is to reduce 37 Hz standing wave that is very noticeable at the listening position.
Listening near wall is not desirable, but I understand them because they are not audiophiles. They have a little bit of feeling against hi-end audio market.