Reversing Polarity -- Voodoo or Easy Tweak?

If ONE speaker has + and - (it's polarity) reversed, then the system will be "out of phase".

Their polarities are reversed, they are not out of phase. However, this description (out of phase) is so deeply ingrained that I should just give up on it. As pointed out, Stereophile uses it as do many manufacturers. I had a Conrad Johnson CD player with a "phase" switch when it was really a polarity switch.

Herman...Agreed that terminology is commonly sloppy. However, "OUT" of phase means a shift of 180 degrees, which is the same thing as a polarity reversal.

No it's not. With a symetrical waveform it is impossible to tell by looking on a scope whether a signal is inverted or 180 degrees out of phase, but musical signals are asymetrical so there is a difference. The usual example is a kick drum that is struck once and then damped. The intial wave that strikes your ear is a compression followed by a rarefaction. If you reverse polarity then it is a rarefaction followed by a compression. This is a big difference. If there was a phase shift then you would still get compression then rarefaction but earlier or later than what it should be.



Waveform A is of equal but opposite polarity to B. They start at the same time but one starts out going positive and the other negative. Waveform C is 1/2 cycle(180 degrees) out of phase with A because it starts 1/2 cycle later. As Eldartford points out, there is no difference between B and C once they get started, but this is because they are symetrical.

Waveform D and E are also equal but opposite polarity while F is phase shifted from D. There is a big difference in E and F whereas B and C appear to be the same. The kick drum (point kd) on waveform D will initially push the speaker cone out while on E it will suck it in.

Some say this all makes no difference in sound, but they are different.

When I said "equal but opposite polarity" I meant equal amplitude but opposite polarity.

If the picture doesn't show up here is the link

[url]http://home.bellsouth.net/p/s/community.dll?ep=334&fileid=1630988&groupid=56202&folderid=203789&curRec=5&folderview=thumbs&ck=[/url]

Herman, your next to last post was great. Back in the early 70s I owned a pair of 3way Wharfedale loud speakers. The woofers were 12". The bass always seemed to be a little light, lacking authority. I had read somewhere to check the polarity of speakers and make sure the drivers were wired correctly, in reference to polarity, was to connect a 1.5V D cell battery, momentarily, across the speaker terminals + to +, - to -. If the speaker polarity was correct the speaker cones moved forward. On the Wharfedale's, the cones pulled back, just the opposite as they should have. I reversed the speaker cable leads on both speakers and the bass was improved.

To be a total stickler for terminology, speakers CANNOT have their polarity reversed, since they are driven by AC, which has no + or - poles! Only DC has a + or - polarity. Speakers can have only an absolute phase inversion [both speakers have the wires reversed on the + and - terminals], out of phase [only ONE speaker wire will have the + and - terminals reversed...very bad indeed!], or have a phase shift. A phase shift occurs when different frequency ranges are shifted [delayed] by milliseconds. This can be due to crossovers, physical driver alignment, speaker wires, or the amplifier powering the speakers. Sort of like a prism splitting white light into the various frequencies of colored light...in effect, a rainbow. Again, not good. But phase shift is pretty much a fact of audiophile life. The amount of phase shifting will determine the coherency [or not] of the sound.

FYI, here's a neat trick to get raw drivers in phase when the terminals are not marked or marked incorrectly [it does happen!], or for car installations where multiple long concealed speaker wire runs can easily be installed out of phase. Take a "D" cell battery, and hold the speaker wires to the battery. Note whether the speaker cone moves out or in. I consider "out" to be the + terminal and "in" to be -, this being a good memory aid.

Herman...You are a bit hasty in saying that the drum sound will be compression followed by rarefaction. It depends on which side of the drum the mic was on. Also, as a disturbance propagates the wave shape changes. Consider, for example a Tsunami, where the initial disturbance is always that the sea recedes, followed by the flood. I have observed a similar effect of a ship bow wave while going through a canal. There must be an explanation, but I don't know it.

Do you have any scope pictures of a mic signal from a drum?