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AES Journal Forum: Comment by Scott Dorsey on "Providing Foldback with Out-of-Phase Loudspeakers"

Title: Providing Foldback with Out-of-Phase Loudspeakers
JAES Volume 19 Issue 4 pp. 306-309; April 1971
Comment by: Scott Dorsey

The author places two conventional sealed-box loudspeakers back-to-back and drives them with opposite polarity wiring to create a figure-8 pattern with a deep null in the plane on which they sit.  This allows two speakers to be placed directly behind a lectern so that PA monitor audio can be heard by listeners on stage without much leaking into the lectern microphone.

This technique is extremely effective and seldom used today.  Other later variants have come out of this such as putting two floor wedges on opposite polarities so that a lectern microphone can be very carefully placed at the null between them.

These techniques can give more than 20dB improvement in gain before feedback but are no longer taught today.  If you use them in convention jobs they can delight and amaze the house crew, just make sure that the microphone is fixed in place and cannot be moved out of the null.


Posted on August 16, 2021 at 4:38:29 PM EDT



AES Journal Forum: Comment by Eric Wenocur on "Cable Pathways Between Audio Components Can Affect Perceived Sound Quality"

Title: Cable Pathways Between Audio Components Can Affect Perceived Sound Quality
JAES Volume 69 Issue 6 pp. 398-409; June 2021
Comment by: Eric Wenocur

The relative merits of "high-end audio" products have been debated for decades because most of the claims made for outrageously overpriced cables and power cords are indefensible. At the same time, this paper's claim that interconnect differences are audible is hardly news to anyone who works with audio equipment!

So was the point of the paper to show that a cable costing $1000/m is, in fact, better than one costing $25/m? Or simply to find the smallest possible change in "sonic character" that a human can perceive? If the former, one must ask if the purported difference is even due to the cables, since many other factors in the testing setup could cause a subtle difference in perception. The fact of comparing balanced and unbalanced connections is only the most obvious. The circuits comprising those different interfaces would also be somewhat different. The electrical characteristics and condition of the connectors might factor in. Measured differences of hundredths of a millivolt (that's .00001V) could be attributable to all sorts of effects. Even the selection of source material could skew the listening results in both physiological and psychological ways.

If the latter, one could devise much simpler (and less contentious) ways of trying to assess what listeners can or cannot perceive. But even so, attempting to quantify extremely subtle differences in sonic character, which is entirely subjective, prone to human error, and can only be described with adjectives that are also subjective, seems highly fraught.

This paper shows a valiant effort to control every aspect of a test scenario, and must have been an immense headache to perform. I found it painful to contemplate. But in the end I don't see how meaningful results are possible. More importantly, the test cannot answer two critical questions: What is sonic character or "sound quality"? And is it worth spending a boatload of money on any part of a system that *might* result in a miniscule change (compared to what?) in that quality? Unfortunately the consumers taken in by certain types of "audiophile" products are naive to the point of self-deception. But the effects of marketing, ignorance and ego is a subject for a different paper.


Posted on July 7, 2021 at 4:36:57 PM EDT



AES Journal Forum: Comment by Scott Dorsey on "Cable Pathways Between Audio Components Can Affect Perceived Sound Quality"

Title: Cable Pathways Between Audio Components Can Affect Perceived Sound Quality
JAES Volume 69 Issue 6 pp. 398-409; June 2021
Comment by: Scott Dorsey

1 ohm and 4300 ohm would seem to me to minimize differences in cable reactances rather than to exaggerate them.  Much home audio equipment has far higher output and input impedances which one would expect to cause greater frequency response problems with reactive cables.  And of course many commercially-made high end cables are deliberately made to be very very reactive in order to act as  a tone control.  So I would expect typical effects in the real world to be even greater than described in this paper.


Posted on June 23, 2021 at 9:28:44 PM EDT



AES Journal Forum: Comment by Milind N. Kunchur on "Cable Pathways Between Audio Components Can Affect Perceived Sound Quality"

Title: Cable Pathways Between Audio Components Can Affect Perceived Sound Quality
JAES Volume 69 Issue 6 pp. 398-409; June 2021
Comment by: Milind N. Kunchur

The link to the free downloadable preprint in my previous communicatin has not reproduced correctly and does not work. It should read (two simple dashes before Kunchur.pdf): 

http://boson.physics.sc.edu/~kunchur//papers/Stereo-height—Kunchur.pdf

Also only a portion of the URL got hot-linked.

This is for the paper "M. N. Kunchur, Applied Acoustics 175, 107811, 2021".

Thanks for your attention. 


Posted on June 23, 2021 at 9:28:31 PM EDT



AES Journal Forum: Comment by Milind N. Kunchur on "Cable Pathways Between Audio Components Can Affect Perceived Sound Quality"

Title: Cable Pathways Between Audio Components Can Affect Perceived Sound Quality
JAES Volume 69 Issue 6 pp. 398-409; June 2021
Comment by: Milind N. Kunchur

Hello everyone and thanks for your comments and interest. I'll try to answer the various questions to the extent that I have something useful to add. The answers to some comments are embedded somewhere in the long paper (sometimes in the footnotes). I must admit that I don’t check the forum regularly. On a related note, there will be a roundtable discussion of the paper on 10am EDT on June 29th arranged by JAES.

 *  The source and load impedances on the cables used in the REW  frequency-response measurements were 1 Ohm and 4300 Ohms respectively. I have ongoing research in which I am doing an in-depth electrical study of analog interconnects (mainly investigating uncommon time-domain distortions and their possible relationship to auditory neurophysiology). Here I am using various stand-alone signal generators and advanced oscilloscopes. The previous conclusions about frequency response remain unchanged with 100 ohms and 10 k-Ohms source and load impedances. I hope to finish this new work and paper by the end of the year.

* A properly setup 2-channel HEA system (something extremely rare) can produce a shockingly life-like 3-D representation, especially for small acoustic musical ensembles. Please see "3D imaging in two-channel stereo sound: portrayal of elevation", M. N. Kunchur, Applied Acoustics 175, 107811 (2021). A preprint can be downloaded from:
http://boson.physics.sc.edu/~kunchur//papers/Stereo-height—Kunchur.pdf

* The comments on optimizing the durations, gaps, etc. in the blind testing are good observations. We have a long way to go to find the most sensitive way to conduct blind testing. This work represents one step and improvement from past approaches that led to a detectable difference. But the questions about "quick decay of the auditory memory" are deep ones, which are perhaps best discussed at the roundtable (on 10am EDT on June 29th arranged by JAES). The 1 M-Ohm will certainly exacerbate noise pickup, which is why it was chosen — to amplify differences. However, noise was also measured at the amp output, with the cables terminated with the actual impedances in normal use.

* The various comments about balanced versus unbalanced are actually fully addressed in the paper. The wording of the conclusions and title state that "cable pathways" (which includes topology as well as the cables) and not just "cables" or just "topology" (i.e., balanced versus unbalance) produce an audible difference. As stated in the paper, to my knowledge, this may represent the smallest change in an audio system proven to be discernable through IRB approved blind listening tests.

 


Posted on June 13, 2021 at 4:55:08 PM EDT


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