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Phase Response of Loudspeakers-Measured with Phase Meter and Digital Delay Line

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The impulse resonance of a loudspeaker system can often be improved simply by repositioning the speakers. How much axial movement is required will be indicated by studying the phase response of the system. The phase response together with the amplitude response gives the complete transfer function which, according to Heyser, describes the steady state and transient responses of the system. Traditionally, one has concentrated only on the amplitude response and ignored the phase response. Obviously, the reason being the practical problems of making loudspeaker phase response measurements. Techniques using tone bursts or Fast Fourier Transforms have provided the only possibilities until now, before Brüel & Kjaer produces a phasemeter with a delay line. The traditional, sinusoidal amplitude response curve measured in an anechoic room tells us only about the speaker itself, whereas the amplitude response using 1/3 octave pink noise measured in the listening room tells us something about how this combination, in fact, performs. This method illustrates the considerable room dependence which correlates reasonably well with the results of listening tests. Primarily, we shall look closely at the phase response, but remembering that noise and amplitude ought, in general, be seen as interrelated and not as isolated phenomena. In addition, we shall look at the relation between transient response, time distortion and phase response. We shall look at minimum and non-minimum phase, at amplitude curves, phase response curves, measuring set-ups and, finally, at how phase response curves are interpreted, and how an improved phase response indicates an improved impulse response.

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