Polarity mystery: Can you help me solve it?

Hi Bryon,

Gee, that's a tough one, assuming as you indicate that the effect is repeatable across a wide range of recordings, presumably ruling out the polarity of the recording as being a factor.

The one possibility that occurs to me is that the output of your power amp has some amount of dc offset present, due either to itself or to the preamp or processor that is feeding it, or the source component for that matter (if the entire signal path is dc coupled). Does your friend, who observed the same phenomenon, have similar electronics?

A dc offset would cause your woofers to have a rest position that is either slightly forward or slightly backward relative to their normal zero-signal rest position, the direction depending on the polarity of the offset (and therefore depending on the polarity with which the speakers are connected to the amplifier).

That would tend to bias the contribution of the woofers such that acoustic compressions or rarefactions in the speakers' outputs are slightly emphasized or deemphasized relative to one another, depending on the polarity of your connections but independent of the polarity of the recording. I think :)

That's just a wild guess, of course, but it's the only theory I can think of that seems to fit all the facts.

Best regards,
-- Al

How would I know if my system had a DC offset?

Hi Bryon,

You would need a good multimeter, preferably a digital one that can measure dc voltage with a resolution adequate to read say a few millivolts (mv), or ten's of mv at most.

You would power up the entire system, let it warm up for a few minutes, and set the multimeter to measure dc voltage. With no music playing you would then place the two leads of the multimeter between the red and black speaker terminals of one channel, or between the corresponding terminals on the amplifier. Repeat for the other channel.

I don't particularly have a feel for what the upper limit of acceptability would be for the reading. Perhaps someone else reading this will. But I would feel fairly comfortable with a reading of say 60db below the voltage that, were it ac, would result in the 88db spl that your speakers are rated to produce, at 1 meter, in response to an ac input of 2.83 volts. 60db below 2.83 volts is 2.83 millivolts.

Hope that helps,
-- Al

Hi Bryon,

OK, so much for that theory. Well, I'm left at a total loss in trying to suggest an explanation.

I can't envision how your observations could be related to interaction with room effects, as has been suggested. The effects of inverting the signal polarity into the speakers would be undone by either the polarity inversion or the lack of polarity inversion of some of the recordings you listened to, relative to the effects on other recordings that presumably have the opposite polarities. And add to that the fact that it is meaningless to speak of absolute phase preservation or polarity inversion on many recordings, because they comprise a combination of various sounds and instruments that may be mixed together with random phasing. All of which makes the consistency of your observations across a variety of recordings befuddling.

Best regards,
-- Al

Perhaps it is Folie à deux!

LOL!

I wonder if it has something to do with how the sound from the tweeter and woofer "sums" at a particular listening distance.

Does your room contain many highly reflective surfaces? If so, from looking at the Stereophile measurements, the reversing of the driver polarity could result in a mid-treble suckout which would have many of the sonic effects you descibe.

It seems to me, as I indicated earlier, that while all of these are factors that may be relevant in a general sense to the sonic characteristics of the system, they are inapplicable to the observations Bryon has stated. The reason being that they would not have effects which are simultaneously consistent both with connection polarity and across recordings that maintain absolute phase, that have inverted absolute phase, and that have randomly mixed phases.

It seems to me that that observation, of consistency across many recordings, shoots down all of the theories that have been offered, aside from mine which has been shot down in other ways.

Best regards,
-- Al

Hi Bryon,

I agree completely with everything in your preceding post.

Assuming that the improvement I experienced really is constant across all recordings, regardless of their polarity, then surely we are right to conclude, as you and I both have, that the ABSOLUTE polarity of the recordings is irrelevant to the issue. But does it follow from that, that the RELATIVE polarity of the tweeter/woofer is irrelevant to the issue? I'm getting a little lost in the how that inference works.

BTW, I don't know if it's relevant, but the two drivers are not on the same plane. The woofer is recessed in the speaker cabinet, so that its center is slightly farther from the listener than the tweeter.

While the polarity inversion of the tweeter relative to the woofer is certainly relevant to the sound of the system (and I believe, although I'm not totally certain, that the inversion is necessary to flatten the frequency response of the speaker given the particular crossover design), the bottom line is simply that two inversions in the signal path (prior to the speaker) and/or in the recording = no inversions, regardless of how the tweeter and woofer are phased relative to each other.

Let's say that the speaker connections are reversed, and that a polarity-correct recording is being played, and that imaging is improved for that recording relative to what it was with the speaker connections not reversed. In that situation the tweeter's output will be polarity correct relative to the original event, and the woofer's output will be inverted relative to the original event.

If we now play a recording that has inverted polarity, with the speaker connections still reversed, the tweeter's output will be inverted relative to the original event, while the woofer's output will be polarity correct relative to the original event. Which is the same situation that we had with the previous recording when the speaker connections were not reversed, which resulted in inferior sound on that recording.

So the fact that reversing speaker connections provides improvement that is consistent regardless of the polarity of the recording is what is so baffling.

Another way to look at it is to consider Figure 7 of John Atkinson's measurements, linked to in earlier posts. That depicts the speaker's response to a positive-going pulse or step waveform, which by definition (or, more precisely, by Fourier theory) includes sinusoidal spectral components at both low frequencies and high frequencies. The initial response to the application of that waveform is a negative-going half-sine wave, since the (inverting) tweeter responds to the signal's high frequency content sooner than the woofer can begin to respond to lower frequencies (and also because the path length from listener to tweeter is slightly less than the path length from listener to woofer, as you noted). The response to that high frequency spectral component eventually oscillates to a positive-going half cycle, at which time the output of the woofer starts to predominate, beginning with a low frequency positive-going half-sine wave, and eventually oscillating to be negative-going.

If you were to reverse the speaker connections, that ENTIRE waveform (including the initially negative-going tweeter output and the initially positive-going woofer output) would be inverted. If the polarity of the recording were then inverted, that ENTIRE waveform would then be re-inverted back to what it was for a non-inverted recording with non-inverted speaker connections.

I hope that further clarifies my befuddlement :)

Best regards,
-- Al

I was saying the two drivers housed inside each box speaker are wired out of phase with respect to one another.

Yes, that's correct, Jim. That is done intentionally in some speaker designs, and as I said in my previous post I believe it is necessary in those cases to achieve flat frequency response.

By chance have you listened to the Focal 1007be speakers, wired both ways, with the JL Audio Fathom F113 sub turned off?

Excellent question. Obviously inverting the connection polarity to the main speakers changes the phasing of mains vs. sub by 180 degrees. Presumably that would only affect frequencies for which the sub produces significant output, which presumably don't play a major role in imaging, but considering that we can't come up with any other explanations that hold water the experiment you suggest seems well worth trying.

Best regards,
-- Al

Hi Kirk,

Thanks for your characteristically knowledgeable response.

However, I think you may have misread or misinterpreted some of the earlier posts. As I understand it, Bryon has done nothing internally within the speakers. All he has done is to interchange red and black at the external terminals of each speaker, and also the sub, thereby inverting absolute phase. The result was improved imaging, which mystifyingly seems to occur consistently on a very wide selection of recordings, presumably encompassing some recordings that are absolute phase correct, some recordings that are inverted, and some recordings that are a random mix of phasings for the different instruments and/or voices that are present.

Given that, I'm not sure that the theory you have offered is applicable.

Best regards,
-- Al

This explanation is looking more and more likely. I hope I have not been wasting everyone's time with what is nothing more than a psychological phenomenon!

The thread strikes me as having been a very worthwhile intellectual exercise, with the thoughts that have been presented having potential applicability to other situations in the future. Not a waste of time at all.

Best regards,
-- Al