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Technical and scientific discussion of amps, cables and other topics.

RE: Echo threshold

>I had a look at all publications Toole refers to w.r.t. early reflections, and some more, and apart from some indications there is no evidence for the deleterious effects of first reflection.<

If you're fond of 40 dB nulls in the midrange. There really is a science here, whether Toole has discovered it or not.

>The requirement of placing speakers at least 1m from reflecting surfaces looks as if it was based on the Allison effect, ensuring that boundary reinforcement occurs for frequencies below 34 Hz, which is sufficient to avoid bass boom for the great majority of loudspeakers.<

Early arrival first reflections impair midrange clarity and imaging. And in general, the further you move loudspeakers from the wall, the greater their ability to reproduce depth.

Why does Toole say that side wall reflections are beneficial in the case of dipoles? One of the main advantages of dipoles is that they minimize side wall reflections without the need for diffusion and absorption at the first reflection points. I've found that orienting a dipole so that the first sidewall reflection is nulled at the listener's position significantly improves midrange clarity. Floor and ceiling reflections, though, are beneficial in the case of a low frequency line source, since they approximate an infinite line source.

>Naqvi’s active listening room looks like very promising approach, but so far no results for 2-channel stereo<

Their description of the results are similar enough to what one observes with two channel stereo. It will be nice to have more information about audibility thresholds, though.


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