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A simple method for measuring the peak linear excursion capability (Xmax) of loudspeaker drive units is presented. The method measures the acoustic amplitude modulation of a small high-frequency signal by a very low-frequency signal. The low-frequency signal is increased to produce a target peak-to-peak modulation. A physical measurement of the peak-to-peak diaphragm excursion is made and defined to be twice Xmax.

Unacceptable distortion, sounding like a “blat” on bass notes was reported for some models of 4 X 6-inch loudspeakers in certain 1992 prototype vehicles. A study was initiated to find the cause of this distortion and to develop a specification to limit it to acceptable values. The cause of the distortion was determined to be a rapid increase in suspension stiffness at large cone excursion. The specification is based on the sum of the weighted acoustic amplitudes of the 4th through 10th harmonics of a sine wave input at 8.0 volts.

Delayed arrivals of a stereo source are manipulated to suppress undesirable vehicle cabin acoustics and replace them with optimum acoustics for reproduction of commercial recordings. These optimum playback acoustics are derived from concert hall and listening room measurements. An experimental vehicle sound system implementing these concepts is described.

Vehicle operation noise, even in the quietest cars, produces high sound pressure levels (SPL) at very low frequencies. This noise masks desired signals in and above this frequency range. A blind subjective test, using ten listeners, was undertaken to determine a frequency response equalization curve that would compensate for this noise under specific but realistic conditions. Starting with a 4 dB full-band level increase, an average of 40 listener responses showed a gentle rise in bass reaching an additional 4 dB at 50 Hz.

A body of listening test techniques which produces consistant rankings of sound systems is presented. Sufficient detail is generated in the course of the prescribed listening evaluation to direct engineering changes to the system. A two dimensional weighting system (performance and usage) is used to determine a single-number rating.