Loudspeaker distortion

Distortion in 3 types of loudspeakers is measured and compared. Horn, vented box, and total enclosure type speakers display increasing amounts of distortion in the given order. The most important type of distortion is modulation. Since this is usually several times the magnitude of harmonic distortion, and consists of frequencies which are not harmonically related to the input frequencies, modulation distortion is much more obnoxious than harmonic distortion. Modulating frequencies in the subsonic range were found to produce high modulation distortion in vented-box speakers. Reviewers of equipment who report 0.01% amplitude modulation distortion in amplifiers and ignore 10% or more amplitude and frequency modulation distortion in loudspeakers might well revise their prejudices.