Home Propeller Head Plaza

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

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

Hi
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. These reflections cause a series of late arrivals, partial duplicates of the actual signal but delayed according to the difference in distances they have traveled.

In the recording studio, since the 80’s it has become normal to make the front half of the room absorptive and the rear scattering reflections.
A real Stereo image depends on the “mono phantom” or image that floats between the two speakers.

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. What one DOESN’T want is anything that wasn’t part of the original signal, everything else acts to make the brains job more difficult by adding “clues” as to the speakers location as well as the reflected sounds arriving from different physical locations.

When one can reduce everything but the original signal, a weird thing also happens. Playing one speaker with a voice signal, one finds that with your eyes closed, it is easy to hear what direction the sound is coming from BUT the more like one source it is, the harder it is to hear how far away it is.
In other words, most speakers, even well away from the walls or floor, still radiate addition delayed sounds, sounds which have other origins and you ears can identify those discontinuities and use that to localize the physical depth of the speaker. The stronger these “extra” signals are, the more easily the depth is audible AND the less able the speaker is to produce a strong mono phantom or stereo image. This is also why the ability to locate depth is stronger in a typical multi-way speaker over a single radiator element, the multi-way system is not coherent, in addition to “where the sound goes” by having separate sources, does not have a single source or acoustic origin.
This all might sound rather odd, that disconnected or reflected sound is “bad” but it is true so far as hearing the original signal. Also, the larger the room dimensions, the worse the problem of reflected sound becomes (because the volume of the room and surface area do not track linearly) and the more important it is to project the sound only where the people are.
It is summer in the northern half, one can demonstrate what I mean pretty easily and have a nice time.
Set a spell and listen to a couple of your “best” recordings, then, move your stereo outside. Set it up at roughly the same distance as it was indoors, with the speakers at the same height BUT no walls behind or to the sides of the speakers. You system will be bass shy because of the lack of LF room gain etc so ignore that. Now play the same recordings, sit back and listen. If your speakers are pretty coherent, you will hear a much stronger stereo image, you are hearing more of the recording and less of the stuff which was arriving after any signal impulse. Fwiw, this is a great excuse to have a BBQ also.
Now, when you move back in your room the difference will be more noticeable. The up side is absorbing close reflections will help a great deal. Keeping the speakers away from the walls is also a strategy which reduces the strength of the reflections BUT makes the image / sweet spot proportionally narrower. If you can put actual sound absorbing foam on the side walls near the speakers, you make a very noticeable improvement / allow a wider speaker position. I had a narrow listening room once where this was a REAL problem and by putting absorbing foam UNDER a couple of my wife’s weavings, I had a very good solution with SAF.
Best,
Tom



This post is made possible by the generous support of people like you and our sponsors:
  Amplified Parts  


Follow Ups Full Thread
Follow Ups

FAQ

Post a Message!

Forgot Password?
Moniker (Username):
Password (Optional):
  Remember my Moniker & Password  (What's this?)    Eat Me
E-Mail (Optional):
Subject:
Message:   (Posts are subject to Content Rules)
Optional Link URL:
Optional Link Title:
Optional Image URL:
Upload Image:
E-mail Replies:  Automagically notify you when someone responds.