The Acoustical Meaning of Harmonic Distortion
The availability of extremely wide-band amplifiers with distortions approaching the infinitesimal and the gradual engineering of a limited number of loudspeakers with distortions just under 1% at usable levels (90 dB SPL–100 dB SPL at 10–12 ft) brings up an interesting question: “How low a distortion is really needed?”
Calculating the Maximum Allowable Total Harmonic Distortion in an Arena Sound System
The most difficult parameter to achieve in the typical arena sound system is a sufficient signal-to-noise ratio (SNR) to ensure acceptable articulation losses for consonants in speech. It must be at least 25 dB. In that case, the total harmonic distortion should be at least 10 dB below the 25-dB SNR to avoid the addition of the two signals. If both signals were at the same level, a 3-dB increase in level would occur. Therefore (-25 dB) + (-10 dB) means that the total harmonic distortion (THD) should not exceed -35 dB.
