Application of parametric and non-parametric techniques to electroacoustic transfer function analysis

Electroacoustic devices or systems transfer functions are usually described by means of amplitude and phase Bode plots. They are obtained from usually large data series of excitation and response values. Acoustic set-up requirements vary considerably, from normal room to anechoic conditions, from complex instrumentation to simple sweeping ensembles. Filter frequency analysis, cross-spectral estimation by means of the discrete Fourier transform, time-delay spectrometry and the cepstral analysis methods are non-parametric examples. Model based techniques can be classified as identification techniques. They usually employ a limited set of parameters and achieve high information compression ratios and non-redundancy, flexibility and adequacy to convert to other types of models. In the present paper the most important established techniques for electroacoustic transfer function measurement are surveyed in their principles, possibilities, instrumentation and set-up requirements. A comparison is made with an input-output rational model based parametric technique, developed in the F.E.U.P. Practical results are reported, showing the accuracy obtained through this technique when applied to the measurement of a real full-range loudspeaker system. Nevertheless some difficult aspects still persist. In our point of view, a promising new way is ahead for measurement techniques in the electroacoustic field.