What are high fidelity headphones？

The main performance of iec581-10 high fidelity earphones of IEC 581-10 standard are as follows: the frequency sound is not less than 50 Hz to 12500 Hz; the allowable error of typical frequency response is ± 3 dB; the slope of frequency response curve is not more than 9 dB without octave, and the difference of average sound pressure level between the left and right units in the same octave bandwidth is not more than 2 dB in the same octave bandwidth, and the harmonic loss occurs when the sound pressure level is 94db in the range of 100hz-5000hz The frequency response of the earphone is allowed to decrease between 2KHz and 5KHz to improve the transparency and spatial sense.