Meeting Topic: Loudspeaker phase distortion
Moderator Name: Véronique Adam
Speaker Name: Alain Roux and Marc Chablais - Relec SA / Samuel Harsch - Harsch Acoustic / Veronique Adam - AudioNetworks SA (Goldmund)
Meeting Location: Studio des Nouveaux Monstres, Av. du Silo 9, 1020 Renens (VD), Switzerland
26 people gathered on this Thursday afternoon in the "studio des Nouveaux Monstres" in Renens (near Lausanne), in order to attend a meeting about loudspeaker phase distortions.
The three scheduled presentations explained how loudspeaker phase distortions may be significantly heard and put forward different solutions to correct them. After the three presentations, the audience had the opportunity to attend some phase distortion listening tests. The first part was devoted to psychoacoustics and analogue phase corrections. Alain Roux and Marc Chablais began their speech with some theory explaining how phase distortion may be calculated. Then, they summarized the works of J. Blauert & P. Laws about the threshold of perceptibility of group delays. They ended their presentation with a sum up of the past ten years work about the perceptibility of PSI Audio users, giving some technical reminder and explanations on analogue treatments procedure.
The second part was assigned to a digital solution of group delay distortion correction arising from a two-way loudspeaker system crossover. Veronique Adam explained a correction method based on the inversion of a IIR all-pass filter having a group delay response corresponding to that of the system crossover to be corrected. The method was validated under Matlab and implemented in DSP. This method was presented at the AES convention in Vienna (2007).
The third part showed a method for implementing quasi-linear phase loudspeaker using standard IIR crossover. Samuel Harsch talked about different well-known ways of loudspeaker crossover phase correction (FIR, all-pass filters,...) and explained that these methods show the disadvantage of knowing precisely the impulse response of the loudspeaker. To get round this problem, he presented his own method, providing an easy way to create a quasi-linear phase loudspeaker only by using a standard IIR crossover.
After the meeting, the discussions about this interesting topic went on in a friendly Italian restaurant nearby.
The Swiss AES wishes to thank again warmly the "Studio des Nouveaux Monstres" and Antoine Petroff for their kind collaboration, as well as the speakers Alain Roux, Marc Chablais and Samuel Harsch.
