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

Jea48...Some driver manufacturers (JBL for example) use the oposite polarity definition (cone pulls in).

Some driver manufacturers (JBL for example) use the oposite polarity definition (cone pulls in).

Eldartford,

True..... My point was to verify the polarity was indeed reversed on the driver/s and with the test make sure both speaker box units are in phase with one another. http://recforums.prosoundweb.com/index.php/mv/msg/2661/29039/0#msg_29039

Thanks for the responses so far.

Gregm - Yes, the soundstage does seem a little deeper. But the more obvious improvement is that images are more focused. Your theory that the improvement is attributable to a room interaction was my first thought, but I don't know exactly what acoustical effect would account for it. Any idea?

Dopogue - I don't believe that the improvement is attributable to preserving the absolute phase of the recording, because the improvement is the same across a wide range of recordings.

Jea48 - Thanks for describing that method of checking the drivers. The fact that the tweeters and woofers are wired with opposite polarity is confirmed in Stereophile's measurements of the Focal 1007be, and from what I understand, that is common practice with a Linkwitz-Riley crossover with a 36 dB slope, as described here. Also, I am positive the two speakers are in phase with each other, as I have used a test disc with in-phase/out-of-phase tracks to confirm it.

Almarg - That is a very interesting theory, and certainly would never have occurred to me. In answer to your question, my friend with the same speakers does not have similar electronics. He is using an Ayre dac, a Vincent preamp, and a Parasound Halo amp. How would I know if my system had a DC offset?

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