Optimization of Band Limited Sine Sweep Measurements

Abstract

This thesis explores methods for low frequency measurements of both linear and non-linear systems, as well as methods for combining individual limited frequency range measurements to calculate the full range impulse response of linear systems. Some of the advantages that a successful development of such methods will cause, are more effective subwoofer measurements and better signal-to-noise ratio properties of building acoustics measurements. It is impossible to terminate the stimulus of sine sweep measurements at frequencies below the Nyquist frequency without introducing damaging errors, like the effects of noise blow-up, to the measurement results. The main focus of the work has been to find ways to avoid or remove these errors. It was found that measuring the impulse response of a system using three frequency bands to cover the total frequency range can be done effectively and with very satisfying results. However, if octave band limited frequency range measurements shall be used, the time variance influence will limit the measurement correctness. Accurate techniques for both linear and non-linear low frequency measurements were found, using a new deconvolution technique that removes the noise blow-up effects caused by terminating the measurement sweep at low frequencies. Finally, great possibilities of controling and adjusting the signal-to-noise ratio properties were obtained by using limited frequency range measurements with individually calculated time durations.