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Re: Time coherence and first reflections

132.239.19.112

Posted by Traddles on May 23, 2001 at 21:17:28

In Reply to: Re: Time coherence and first reflections posted by Tom Brennan on May 21, 2001 at 21:50:52:

The human hearing seems to be quite insensitive to phase differences, including significant group delays, when music is used as the test signal. There have been many "time aligned" speakers available, but generally speaking they have done no better in listening tests than those speakers that were not. The speaker with perhaps the best phase response is the Quad ESL-63, and while it admittedly sounds very good, it has not managed to push speakers with a less perfect phase response out of the market. As Tom points out, if a speaker is used mainly for listening to music there are far more important areas of performance to consider than its phase response.

Single drivers do not necessarily or automatically solve the "combined launch problem". Strictly speaking, they merely solve the non-coaxiality problem, and in rear-loaded horn or TL enclosures they solve it only if the rear radiation takes place in a coaxial manner. Most single-driver speakers use twin cones, and the mechanical crossover plus the displacement in the equivalent acoustic radiating centers of the cones result tend to result in a wild phase response in the crossover region; and even if a single-cone unit is used, it will not be phase linear as the cone will go into various (hopefully controlled) breakup modes over the audible frequency range.

Many people include coaxial drivers (Tannoy, Altec) in the single-driver category. The physical displacement is usually not compensated for in the crossover, although time-aligned versions have been available from UREI among others. But the time-alignment property appears to be often nothing more than a marketing gimmick.

The physical displacement can indeed be "several feet", without its being audible. This is in fact the case in the Klipschorn, and it is fortuitous, as it enables us to enjoy the benefits of two- or three-way horn loading with a speaker enclosure of a reasonable size.

Recommended reading:

[1] John K. Hilliard, "Notes on How Phase and Delay Distortions Affect the Quality of Speech, Music and Sound Effects," IEEE Transactions on Audio, Vol. AU-12, No. 1, pp. 23-25 (January-February 1964).

[2] Paul W. Klipsch, "Delay Effects in Loudspeakers," Journal of the Audio Engineering Society, Vol. 20, No. 8, pp. 634-637 (October 1972).

Trad

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