Investigation on the Effect of Loudspeaker Ringing on Perceived Spectral Balance
Examensarbete för masterexamen
Sound and vibration (MPSOV), MSc
The Ringing artefacts of a loudspeaker can have a large impact on the perception of music in home, studio and car audio systems. A large contributing factor to this ringing effect is given by the driver’s natural resonance. In the case of car audio systems, additional mounting components and cavities within a car’s door and body of the driver can enhance the ringing effect. Unfortunately, the ringing effect cannot be eliminated completely, as it is an intrinsic property consequent to any resonating object. Alternatively, its effect can be controlled. A thorough investigation on different methodologies for detection and measurement of the driver’s natural resonances, as well as the perceptual effect of ringing caused and enhanced by the resonances from cavities, mounting enclosures and other components of a car door was implemented. A comparison of different systems, created with synthetic transfer functions was performed, in which artificial low frequency resonances were employed. These artificial low frequency resonances have similar characteristic properties of the driver resonances, in which they are detected and measured by using signal processing techniques involving Cumulative Spectral Decay (CSD) and Continuous Wavelet Transform (CWT) plots, as well as a System Identification Method that uses the Steiglitz - McBride algorithm. These methods rely on the impulse response measurement of a loudspeaker. The methodologies successfully detected the driver’s natural resonance frequency and its strength in terms of Quality (Q) factor, with a minimal degree of variance from each other. From these results, three low frequencies and their corresponding Q factors were chosen, and were set into a listening test platform as second order IIR peak filters. This was implemented by using MATLAB’s GUI and Simulink interface. The test used two music audio of different genres: a recorded jazz ensemble and a synthetic electronic ensemble. To emulate the effect of delayed resonances, three delay time values were given into the resonance settings, and the test was carried out. The test primarily focuses on three case studies: the threshold of audibility of resonances, the threshold at which a non resonant system with a parametric bandpass filter is perceptually similar to a resonant system, and the threshold at which a system’s resonance is inaudible when the same filter is used. The results show a high degree of dependency between the frequency in test and the audio. Very low frequencies are found to have the highest audibility thresholds in the case of recorded audio. The control of ringing is dependent on the type of audio played, as indicated by the high variance in the results with the recorded audio in comparison to the synthetic audio. The effect of delayed resonances has had a minimal impact on the results. This shows a good promise, and further future work is definitely needed in order to create a metric for loudness of a mounted car loudspeaker resonance, as this metric can intuitively suggest a severity threshold to the effect of ringing in the spectral balance of audio. This thesis work serves as a starting point into developing the metric for ringing loudness.
Ringing, Resonance, Quality Factor, Centre Frequency, CSD, Wavelet, System Resonance, Listening Test