Headphone impedanceAlso known as nominal impedance. The impedance is the AC resistance of the coils of loudspeakers and headphones in ohms. Since impedance depends on the frequency, it is always specified at a frequency of one kilohertz.
Polar patternThe polar pattern is the preferred pick-up direction of the microphone. According to the shape of the corresponding measurement plot, there are omni-directional, cardioid, super-cardioid or hyper-cardioid as well as figure-of-eight patterns. for microphone