Phase and SDA question

Ricardo

Something really weird happened last night; my preamp (AES-AE3 DJH) inverts the phase in the circuit, and it does not invert back as others do; the instructions say that the speakers must be connected out of phase (positive wire to negative post at the speakers).
I've been using the Carver AL-III's connected out of phase, and have confirmed with a test CD that at the speaker things are right.

Last night I connected the SDA's using the out of phase connection....and no SDA was present....inverted the wires and bingo, SDA came back; listened to the phase test CD and confirmed that for the SDA's, following the instructions on the pre will make the speakers be out of phase

Can anyone explain this?

hoosier21

You can not connect amplifiers to SDA speakers any way other than positive of amp to positive on the speakers. The SDA circuitry uses the neg. (ground) side of things to connect left speaker to right speaker (this is while you have to have a common ground amplifier)

If you connect the connect the positives of the amp to the neg. of the speakers, and the SDA circuit is asking the positive side of the amp to tied L to R speaker, either doesn't work or might damage the amp.

Hopefully somebody who can explain it better will chime in here, I know enough to be dangerous.

Ricardo

Thanks; true on the common ground...don't know why it didn't click to me....but I still don't understand why would they sound in phase with the test CD, when the preamp inverts the phase?

unc2701

The test CD probably only tells you if they're out of phase with each other. Not out of phase in general.

hoosier21

What test CD do you have? and how does it test absolute phase?

hoosier21

unc2701 wrote:

The test CD probably only tells you if they're out of phase with each other. Not out of phase in general.

what I am thinking

out of phase left and right in one thing, but absolute phase is a whole different thing.

Ricardo

unc2701 wrote:

The test CD probably only tells you if they're out of phase with each other. Not out of phase in general.

Hmmm...didn't think about that either. Makes sense.

So, this means that with this preamp, listening to SDA's will need to be done "out of phase". I have not listened much, but for the little while I did, the sound was good.....as in not being able to tell that the drivers are going the "wrong way"....

I really like this preamp, but I want to have the capability of listening to both sets of speakers, so here are the two "newbie" questions:

1.-Does running both speakers out of phase actually change the sound that much?

2.-And the most important question...can speakers be damaged?

Thanks.

Ricardo

I'm using the Chesky Gold CD; I think you are probably right that it only tests phase between both speakers...actually now that I think of it, I don't know if it would be possible to test absolute phase with a CD..

hoosier21

HTrookie wrote:

1.-Does running both speakers out of phase actually change the sound that much?

Not to me

HTrookie wrote:

2.-And the most important question...can speakers be damaged?
Thanks.

? does what damage the speakers?

unc2701

Absolute phase is just about up there with cables when it comes to the "can you hear it" debate. To my knowledge, there is not a way to test absolute phase with nothing but a CD and your ears/eyes. With a mic & some computer programs you can tell.

I guess with a very, very, low frequency tone and good eyes you could see which way the driver goes first, but a lot of systems would filter anything that low & you run the risk of damaging your system.

Ricardo

hoosier21 wrote:

? does what damage the speakers?

Running both out of phase....

Ricardo

unc2701 wrote:

Absolute phase is just about up there with cables when it comes to the "can you hear it" debate. To my knowledge, there is not a way to test absolute phase with nothing but a CD and your ears/eyes. With a mic & some computer programs you can tell.

I guess with a very, very, low frequency tone and good eyes you could see which way the driver goes first, but a lot of systems would filter anything that low & you run the risk of damaging your system.

Right...in my case, I "know" they are out of phase because the preamp inverts the phase; I just cannot follow the instructions of connecting red to black because of the SDA, so I'm pretty much limited to:
-go like this if there's no sound impact (which I could not tell while I heard them last night), and if there's no possibility of damaging the speakers.
-change the preamp, which is not something I would like to do, since I find it blending so well with the rest of the system.

hoosier21

Keep the preamp, wire the speakers + to + and - to - and enjoy, period.

unc2701

Yep, go with what Hoosier said. Besides, for all you know the DAC in your CD player could invert phase and you're back where you started.

hoosier21

small bit of text to show why I have little concern if my system is in absolute phase:

To better understand how phase and polarity are related, let us examine the very beginning of the process that brings music into our homes - the recording session. Musical instruments create sound by modulating the air, producing sound "waves." These sound waves are actually compressions and rarefactions of the air molecules. The pressure changes impinge upon our eardrums and are interpreted by our brain into the sounds we hear. A microphone, like our eardrums, senses these same pressure changes, converting them into electrical impulses which are fed to the recording equipment.

When the leading edge of a musical waveform (compression) strikes the microphone diaphragm, a positive voltage is created at the microphone output. Similarly, as the waveform passes, its trailing edge (rarefaction) produces a negative voltage output from the microphone. Simple, right? No, unfortunately. For in between the microphone and your ears lie a vast array of electrical "obstacles," each capable of skewing phase to some degree.

Ideally, after all the mixing, signal processing, mastering and cutting have been completed, that same positive output voltage from the microphone will produce a positive (forward) motion of the loudspeaker diaphragm. Often it does not, and therein lies the rub.

The making of records is a very complex process involving a bewildering quantity of electronic equipment, each possessing the potential to manipulate phase. The microphone, cables, mixing console, tape machines and the myriad of signal processors (delay, echo, reverb, equalizers, limiters etc., etc.) could each be wired out of phase with respect to one another. In addition, smaller phase errors (several degrees here and there) may occur within the electronics of any of these components. Finally, your stereo system may perform tricks of its own to further complicate the issue. Many tube preamps for instance, invert phase. Often this occurs only in the phono section, which puts the turntable out of phase with the line sources. So, after the original signal has traversed its' long and complicated path, it may arrive at your ears out of phase with the original musical event.

Ricardo

Thanks....I'm ready to crank that volume with no concerns now