Phase Inversion

recently read about a cary slp98 pre amp as well as a few others that are phase inverting. also read that this can be reversed by changing the polarity of the speaker wires. my question, why do manufacturers do this? does it make an audible difference? why reverse it? i also have read about cd's that are recorded phase reversed. what is the point of all this. thanks alot.

aloha keith
They do it because they would have to add another amplifier stage to correct it. Most feel simpler is better and it is definitely cheaper.

Yes, it is audible. Simple example: A whack on a bass drum causes the membrane on the drum to move out intially and then it returns. This causes a compression of air followed by a rarefaction. If your woofer incorrectly reproduces this by first moving in and then out it will sound different.

Some (most?) sudios don't pay any attention to this so some recordings end up being reversed.

FYI, the correct term is inverted polarity, not phase. It is confused by the fact that many manufacturers use the incorrect term.
Consider 'phase inversion' as 'nature of the beast' or 'less is more'. Electricial engineers have always had this quandry when designing audio equipment. Most have added the additional phase to 'bring' the positive and negative 'back' so people are not confused. By doing this another circuit is added, creating another potential undeseriable noise source. Conrad-Johnson equipment is non phase inverting, requiring you to flip plus to minus at your speakers to keep everything in phase. I hope this helps?

thanks for the info, 1 owe you 2 brownie points.

aloha keith
The problem is how many times is the polarity reversed during the entire process starting with the recording?
Most likely a number of times. If that is the case I dont think it makes much difference.
There is an interesting book called "The Wood Effect" (sorry, but I've forgotten the author). This is a rather detailed book that cites many studies and tech papers (with lots of footnotes) regarding 180 degree phase inversion. According to this book, as well as my own observations, by switching phase (reversing BOTH speaker terminal wire connections or using a phase inversion switch, if available, on your preamp), you will get a noticeable change in sound reproduction on most source material! These changes include: wider soundstage, and better soundstage pinpointing of vocals and instruments.

are you saying that inverting phase (polarity) sounds better? i will try this out.

aloha keith
I thought Clark Johnson wrote the Wood Effect.

Most recording engineers are unconcerned with polarity. As a result roughly half of all recordings are incorrect. You will want a switch to do the job- getting up to change the speaker cables can get to be rather a pain :)

If you are listening to multi-tracked recordings it may make no difference, as tracks get inverted going through effects loops and the like, so its one jumble for another. But if it is a pure recording (2 or 3 mic true stereo) the difference can be quite notable.
When you make a plot of the waveform, inversion certainly makes it LOOK different. But the difference is only evident for the first half-cycle of the waveform, a few milliseconds, and I really doubt that the ear can recognize sound that quickly.

I have never worried about "absolute phase" because, as others have mentioned, recorded material is all jumbled up by the mixdown process, making the issue hopeless.

However, this effect is easy to evaluate by listening test, so I guess I will give it a try.