The ultimate mic preamplifier low noise test?

Caution: At your risk, this must not be attemped unless there is a limiting protection on the headphone circuit otherwise irreparable ear damage may result. When the microphone preamplifier is very low noise such as the Pleiades V6 1H4 open grid...When the mic is connected out of phase and the mic is aproached: to the Sennheiser HD580 headphones, ambient noise cancels out and at the partucular ear it sounds as if silence is sucked out. Caution: if mic is in phase, ambient noise increases and there is possibility of positive feedback which may damage hearing unless a limiter is in circuit.