Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics.

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RE: Echo threshold

Posted by josh358 (P) on July 28, 2010 at 10:30:09

In Reply to: RE: Echo threshold posted by KlausR. on July 28, 2010 at 06:35:26:

>>Early arrival first reflections impair midrange clarity and imaging.<<

>The simple experiments I made to test this didn’t show any such effects. There is no scientific evidence to support that statement.<

First reflections are typically within the fusion range and their amplitudes are within the range that has been shown to affect tonal character and alter imaging. Besides which, referring to the figure:

http://www.avguide.com/forums/first-reflections

The remarkable thing is that the brain can so effectively minimize combing of that sort (more effectively with both ears than one, as the Salomons paper points out). I'm not sure why your experiments didn't produce an audible result.

>Minimize yes, but to levels below perception threshold?

I have no way of knowing, but I don't see why not, if precisely on the dipole null and for wavelengths that are small with respect to the side wall. In practice, other considerations make it unlikely that the dipole null will be at exactly the right angle, so acoustical treatment could potentially produce an audible improvement. The general rule of thumb seems to be "maybe, but not as necessary as with omnidirectional speakers." I doubt that science could add much here, since rooms and speaker placement vary so widely.

[Naqvi]

This is a good illustration of the disjunction between basic research and practical engineering. It's frequently unclear as to how and to what degree idealized tests of perceptual thresholds apply in real-world circumstances. Had Naqvi attempted for example to emulate the acoustic impedance of various common construction materials, the experiment would have grown unwieldly, and it would still have been of questionable utility, since the acoustic impedance of materials varies -- sheetrock, plaster, brick, glass, concrete, wood, not to mention the furnishings and objects that are found in the typical listening room (and which are sometimes used as a rough-and-ready form of acoustical treatment).

Thus, to a large extent, our scientific understanding of these phenomena lags behind our practical understanding and there's still a fair amount of practical art involved. Which, however, didn't prevent Stradivari from making a better violin than we can today, or, arguably, the designers of 18th- and 19th-century concert halls from making acoustically superior halls.

Avery Fischer notwithstanding, what usually happens I think is that our scientific understanding gradually advances and supplants practical art as it becomes available, with usually superior results. But as far as I can tell, we're still very far from having sufficient understanding of these phenomena to rely entirely on theory here. In fact, some pretty important phenomena still don't have a solid explanation, such as the superior depth rendition of dipoles. There are theories, yes, but to the best of my knowledge, little by way of solid research.

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