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December 2008
Enjoy the Music.com
Boston Audio Society The BAS Speaker Magazine
More About Absolute Polarity
Article By Dan Shanefield
From BAS Volume 17 Number 3, November 1989

 

  In the Speakers volume 17 number 1, Clark Johnsen defended his book The Wood Effect, which I had reviewed in a negative manner (vol. 16 no. 5). I think there are several important points to be added to the discussion.

The first has to do with a detailed study of the audibility of various phase effects as reported by Stan Lipshitz and co-workers in the Journal of the Audio Engineering Society (vol. 30 no. 9). Johnsen cites a statement on page 583 of this report as evidence for the audibility of absolute polarity. He certainly is correct that absolute polarity has sometimes been (barely) audible in double-blind tests.

But Johnson failed to mention another critical point. The Summary section of the Lipshitz et al report (on page 593) says that the audibility of polarity changes in music played over loudspeakers is only "extremely subtle." This evaluation is confirmed in an exchange of comments between me and Lipshitz et al published in the J.A.E.S. vol. 31 no. 6, in which we all agreed that for music on loudspeakers absolute polarity is (1) not strongly audible to most people, (2) not usually audible above 500Hz (more so below), (3) possibly not as audible over loudspeakers which are comparatively free of asymmetry effects (such as second harmonic distortion). In these letters I said that all kinds of phase effects were "of negligible importance," and Lipshitz et al said at the very end, "We are basically in agreement with Dr. Shanefield."

Further evidence in support of all this is an article in the Stereophile (vol. 4 no. 8), in which there was no audibility of polarity during blind tests done with the use of low-distortion loudspeakers and yet there was good audibility when cheaper, asymmetrical distortion speakers were used. Stereophile's overall conclusion was that absolute phase is of "virtually no significance."

On the other hand, Johnsen has sent me photocopies of several rather glowing letters from readers of his book. And there was a very favorable review in the latest issue of Speaker Builder magazine (4/89), in which the reviewer said that absolute polarity now ranks in his mind among the most important audio considerations he has ever been made aware of [Also a typically weird favorable one in Audio—pub.]

How should we add this up? Is is just a matter of prejudice, pro and con?

There is a principle in science which can be stated, "Once you see evidence of an additional factor which might really be causing the observed results, you should never ignore it in further studies. Instead, it must be carefully eliminated." In this case the "possible additional factor" could be asymmetry in the loudspeaker, or it could be delusion on the part of the investigator. Both have been mentioned in studies of this kind, and both must be eliminated in future experimental procedures or else the results might be mistakenly interpreted. The scientific investigator should report what was done about this when giving conclusions—otherwise we should all doubt the results.

For some strange reason, audio science is particularly prone to delusion. People get turned on to all sorts of new pseudo-scientific effects which become "the most important new thing in audio," but disappear like witches at dawn when subjected to double-blind testing. I have believed in several of these witches myself before doing blind testing, and it doesn't surprise me that Clark Johnsen's book has made many converts. During the 18th century, a group of educated and apparently dependable people once testified that an old lady of the town flew into church through an open window, uttered a blasphemy, and flew out again. Is the importance of absolute polarity a real glitch in present-day audio, or just a witch?

What I suggested in my exchange of letters with Johnsen is that he do some blind tests and tell us about the results. These don't have to be done with DPDT switches just have a disinterested person unhook the wires and hook them up again with reversed polarity. The listening comparisons don't have to be done fast—do them at the leisure of the listener, without a lot of people present who might make for a tense situation, and without a lot of random number generators and digital readouts. Toss a coin about 30 times to generate some test sequences, and also to see how some truly random results would have looked for comparison with the test results. Only the disinterested person changing the wiring knows which polarity is which (and not even he or she, necessarily). Then there can be no excuses about audible switch effects, psychological tensions, etc. (But on the other hand, there can be no excuses from people like me about "witch" effects.)

By the way, people who don't hear the effect do not need to do blind experiments, according to the way I see the logic. Only people who claim to hear something need the blindness, to be sure it's not imagination. (If you don't hear it, how can it be imagination? Of course, you might be somehow suppressing your normal perceptions, but a blind test wouldn't help that.) Also, the burden of proof is only on the people who claim that some new phenomenon is important, not on us doubters. This is because (among other reasons) anew feature such as special wiring will always entail additional costs in dollars, time, and potential reliability problems.

I have done single-blind tests on absolute polarity, a long time ago and once again after reading Johnson's book. I recently tried it on some Japanese LPs, played over Magnepan MG-Il speakers. The MG-Il ought to have considerable second harmonic distortion, since the stator magnets are on only one side of the diaphragm, not symmetrically arranged. I heard a tiny bit of difference here and there when the polarity was changed, but I never could decide which was "more realistic" or "better." Also, I couldn't hear any consistent polarity differences between the alternate bands of Japanese records, which Johnsen says are strongly audible. But whether I can hear such things doesn't count much toward proving the point. I'm just one person with one playback system. What it would take to prove the point either way is a series of foolproof tests, the results of which are essentially repeatable by several independent test groups. Nothing short of this should be believed.

The points that would need to be proven in unequivocal fashion are that absolute polarity is repeatedly audible and that getting it right constitutes a definite improvement.

Actually, I hope several such groups of people will do some foolproof tests and show us that absolute polarity really is important after all. And I hope I'm one of the first people to read about it and adjust my playback system, or practice listening, or whatever I have to do to take advantage of it. Then I can feel superior to the myriad audiophiles who aren't hip.

But until this happens, we should all conclude that the whole business is a tempest in a teapot.

Dan Shanefield. (New Jersey)

 

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