Modulation Distortion in Loudspeakers
When comparing a loudspeaker with direct radiator bass system to one with horn loaded bass, the subjective judgment is that the one with the horn loaded bass is -cleaner.- The difference in listening quality appears to be due to modulation distortion. The mathematical analysis of modulation distortion is reviewed and spectrum analyzer measurements are described which have been correlated with listening tests. The spectrum analyses corroborate the mathematical analysis and the listening tests offer a subjective evaluation. It is concluded that frequency modulation in loudspeakers accounts in large measure for the masking of -inner voices.- Reduction of diaphragm excursions at low frequencies reduces FM distortion. Horn loading, properly applied, offers greatest reduction, while simultaneously improving bass power output capability.
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