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RE: Early reflections: 5 ms time window for sound source localisation?

Posted by KlausR. (A) on July 8, 2010 at 01:30:12

In Reply to: RE: Early reflections: 5 ms time window for sound source localisation? posted by tomservo on July 6, 2010 at 07:22:53:

Hi Tom,

>I don’t have any links handy, but I can say that close reflections are universally accepted as being “bad” sonically in the loudspeaker design end of things.<

Not universally! Floyd Toole doesn’t, and I don’t. I had a look at the relevant scientific literature (and prepared a 23 pages write-up, if interested, drop me a mail) and there is no thorough, systematic research that shows that first reflections are bad as a matter of principle. There are indications that different directivities have an effect on imaging. In some individual cases (strong right-left acoustical asymmetry, bad off-axis behaviour of the speakers) it may be beneficial to treat, but even for that there is no evidence.

I strongly suspect the reason for considering reflections as bad is the simple fact that there are thresholds of perception. In order to perceive a reflection some cue must be present and detected, change in loudness, change in timbre, spatial changes. If you detect a reflection by a change in timbre then yes, the reflections might be considered as having a negative effect. However, all threshold research I know of is using a single speaker as direct sound source and a single reflection. To the best of my knowledge no research exists that examines the 2-channel/multiple reflections case.


>That image is one your brain derives when the ears are presented with two identical signals with no time delays or other aural clues that originate at / near the loudspeakers.<

Summing localisation. Reflections arriving within this very short time window (< 1 ms) may or may not have an effect, but also for this there is no research. One can always play safe and avoid these reflections, i.e. no cabinet edge diffraction etc.


>Set a spell and listen to a couple of your “best” recordings, then, move your stereo outside.<

That’ll be quite an act with my speakers being 70 kg each! But I tried this once with my Genelec desktop monitors, using particularly adapted tracks from EBU SQAM and Chesky JD37. The ceiling of our living room is highly absorptive, so the imaging the speakers produced indoors and outside was the same to me.

I consider the message that there is no principle need for reflection treatment as really good news, since such treatment in domestic living rooms have extremely low WAF and will therefore in most cases inevitably lead to problems.

Klaus

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