Oppo PM-1 Measurements & Analysis
Oppo claims the PM-1 driver is made of a very thin and light diaphragm whose entire surface area is evenly driven exhibiting piston like behavior. The double sided diaphragm provisions for twice as many conductors within the magnetic field allowing for greater efficiency, reduction in inductance related intermodulation distortion also making the headphones a purely resistive impedance.
Oppo PM-1 Impedance & Phase Response
Oppo’s claim of purely resistive load seems very plausible. As you can see the PM-1s essentially measure like a straight line at 32 ohms with no appreciable phase shift in the entire audio band. This should allow the PM-1s to sound consistently good regardless of the headphone amplifier output impedance which is an excellent design goal.
Oppo PM-1 Frequency Response
I constructed a very primitive ear by placing a microphone inside a styrofoam cup and positioned the headphones at the open end. As you can see from the graph, these headphones are extremely linear. In fact this is the best measurement I’ve ever pulled on a headphone system and explains why these headphones sound so tonally neutral and accurate.
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