主题：HI---2 distortion

Hi-2 distortion is the total harmonic distortion with the weighing of harmonics. An 8.0-volt sine sweep from 20 Hz to 1 kHz to the speaker (appropriate maximum output voltage of the intended amplifier). The speaker is mounted in 1/2 space baffle or an equivalent of in-use acoustic condition with the microphone centered above the speakers protective grille. The fundamental is notch filtered and the harmonics are amplified by a 12 dB per octave high-pass slope to simulate annoyance. Weighted harmonics are summed and compared to the mid-range output of the speaker.

Why do we measure HI-2 distortion ? The limited height of voice coil, magnetic field, excursion capability of the mechanical suspension, varying voice coil inductance and nonlinear radiation (Doppler) are the dominant nonlinearities in loudspeaker systems. For loudspeakers without additional defects the amplitude of the harmonic and intermodulation components generated by the dominant nonlinearities decrease rapidly with the order of the distortion. Although, the second and third-order components contribute mostly to the total distortion and these components are perceived as benign distortion. When the voice coil hits the back plate or the loudspeaker has defects such as an axial mis-alignment of coil and gap or buzzing leads this may cause extreme distortion that produce higher-order components. D. Clark defined an intermediate type of distortion (called blat distortion) between the benign and extreme type "Blat is a result of an intermediate stiffness change which produces amplitudes of fourth and tenth harmonic which are too high to be masked by the fundamental and the benign second and third harmonics. Blat results from a design characteristic rather than a rub, buzz or tick type of unit defect. "