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 August 12, 2010 at 16:29:35

In Reply to: RE: Echo threshold posted by KlausR. on August 11, 2010 at 22:35:03:

>>I've noticed three main phenomena as speakers were moved away from room boundaries: changes in the bass and midbass response, clearer sound (correlating to intelligibility), and better (or sometimes just different) imaging (correlating in part to differences in image spread and location).<<

>When moving the speakers away from room boundaries you are changing several parameters simultaneously (i.e. boundary reinforcement, room mode coupling, delay and possibly spectrum of early reflections, probably also the interaural cross-correlation), so you don’t know for sure that it’s the early reflections that are responsible for the perceived effect.<

Not all of the are due to early reflections. The bass changes are a consequence of room modes. The midbass variations are a consequence of the Allison effect. Interaural cross-correlation of the direct sound isn't an issue, since the angle subtended by the speakers is constant. That leaves early and late reflections. By rotating a pair of dipoles, it's possible to tune out the first sidewall reflections. The effect is immediately apparent. Also -- and I'm not sure why you didn't hear this -- the effect of adding diffusion or absorption at the first reflection points. I'm particularly puzzled as to why you didn't hear the presence of the doors, assuming they were at the reflection point from the perspective of your listening position. I've heard the effects of proximate boundaries many times. For example, console bounce is a common problem when setting up mini monitors.

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