Digital measurement method for dynamic distortion of loudspeakers

Though many sorts of measuring methods using digital signal processing techniques have been developed, most of them are only for measurements in a linear range. There is still no suitable digital measuring method for nonlinear distortion of acoustical devices. An accurate and convenient nonlinear distortion measurement system should be developed for evaluation of electroacoustical transducers. A new digital distortion measuring method for acoustical devices is presented briefly. This method applies a Pink-TSP signal (time stretched pulse, i.e., quickly swept sinusoidal signal), whose frequency band is partially eliminated, to an acoustical system to be measured. The detected component produced in the rejected band is picked up by a bandpass filter and measured as a distortion. First, two kinds of small size electrodynamic loudspeaker units were measured by using the dynamic distortion measurement system mentioned above. Next, distortion characteristics of mechanical single resonant system models whose component shows amplitude-dependent nature were examined. This paper describes the relationship between distortion characteristics and quality factor, input signal level, and nonlinear parameters. The difference in distortion of two kinds of loudspeakers is detected by this measurement. It is seen that the resonant phenomenon has an influence on distortion characteristics.