|
Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
|
|
|
Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
|
In Reply to: RE: Early reflections: 5 ms time window for sound source localisation? posted by KlausR. on July 9, 2010 at 22:04:09:
“Ideally yes, but is it really necessary? As it is the case for cabinet edge diffraction, one can always play safe and reduce the level of early reflections to below perception thresholds, which, at -18 to -25 dB re: direct sound, are quite low, so getting there seems to be quite difficult.”
What is necessary, is a cost benefit vs judgment I think and somewhat outside of the acoustic / hearing part of the discussion.
Also, while reflections are mentioned specifically, I would stress that Time is the issue and not the specific source of the late radiation. Those late signals can come from a number of sources, close reflections being just one.
In the time view, if one considers Heyser’s “determination of loudspeaker arrival time” and other work on measuring time / acoustic phase, one finds that even one full range driver can appear to be at different physical positions depending on frequency.
Using Heyser’s Time Delay Spectrometry, one finds that a typical loudspeaker does spread a single impulsive signal out in time even measured anechoically, many have hundreds or thousands of degrees of phase rotation high Frequencies relative to the lows.
Sound travels about 1 foot in .883 ms, so consider a thought experiment.
To say short time delays do not matter, requires comparing two cases, one with and one without.
What kind of loudspeaker could be used for such a test which suppresses secondary radiations out to several or even 5 ms In time? What kind of loudspeaker could be used for this test which by itself appeared to be one source in time and space over a wide frequency range?
“According to Toole reflection treatment may be beneficial if the speakers have odd-looking off axis response.” Floyde did study the preferred spectrum of the reverberant field, the conclusion was listeners prefer the reverberant field to have roughly the same spectrum as the direct field has.
Because the reverberant field is related to the total acoustic power the speaker radiates, there is a built in desirability of having constant directivty. In order to have the largest nearfield possible,
You mention you have Genelec’s. You will notice they take some pains to minimize the re-radiations from the baffle board region, consider what one has if the baffle and treatment were MUCH larger so to accommodate control of mid and lower frequencies and made so the at the high frequency radiation angle was approximately the same for the mid and lower frequencies too. I don’t recall if they publish polar plots but these show the radiation balloon vs frequency in the two planes Vertical and Horizontal. Imagine narrowing the pattern over a broad band down to say 40 to 60 degrees so that there simply aren’t any near reflections.
“I think that the main reason for this is the, compared to loudspeakers, very different radiation patterns of acoustical instruments, in combination with the direcionality of human hearing.”
I should have made a distinction about stereo, capturing a real stereo image is hard to do live, most (by a large degree) of modern recordings have an entirely contrived stereo image. I would agree, except I would add that relative to the electronic end, loudspeakers by comparison appear to be broken, are usually the weakest link and directivity does play a very strong part in what you hear at the listening position.
It would seem you’re a keen listener. I have been working on a different way to capture a stereo image for live sounds, I would be curious to get your reactions to it. If you’re interested in an alternative recording technique (a work in progress) , down load the Harley or other sound files at the bottom of this page. Try these with headphones first, DO NOT convert them to mp-3 files, that kills them as there is no compression in the recording.
http://www.danleysoundlabs.com/technical%20downloads.html
Best,
Tom
This post is made possible by the generous support of people like you and our sponsors:
Follow Ups
- RE: Early reflections: 5 ms time window for sound source localisation? - tomservo 10:26:49 07/10/10 (1)
- RE: Early reflections: 5 ms time window for sound source localisation? - KlausR. 00:30:05 07/12/10 (0)
Top of Page ]
[ Contact Us ]
[ Support/Wish List ]
[ Copyright © 2024, Audio Asylum, all rights reserved ]
