Usually, people would read some information about the earphones before purchasing, such as looking at the parameters. Then, how to understand these parameters?
Impedance: The obstructing caused by objects on the current is called resistance in DC. While in AC, except for the resistance, capacitor and inductor will also impede the flow of current, which is called reactance. So the impedance is the sum of resistance and reactance.
Sensitivity: This value is a reference value in an engineering test environment, not the results in actual use. So, it's just for reference.
Frequency Response: The range of human hearing is about 20Hz-20000Hz. At present, mature headphone technology has all reached this request. The larger headphone frequency response is the higher quality it is.
Total Harmonic Distortion: Normally, total harmonic distortion in 1000Hz is the least. Thus, lots of earphones use this distortion as its index. So, you may test the total harmonic distortion in a voice of 1000Hz, the smaller the value, the better. Thanks to the headphones small size and rigid, this index is always reasonably good.
The author reviews: The parameters could describe the performance of headphones to some extent, but it may be inaccurate because of the differences in test environment. So, the parameters could only be referenced. Don't treat it as the single index. After all, judge it by listening to it.