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How do you know if your preamp has inverted the phase?
How do you know if your preamp has inverted the phase?
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Old 24th July 2021, 02:49 AM   #21
cnpope is offline cnpope  United States
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In most systems, I wonder whether any attention is even paid to the polarity of the connection from the amplifier output terminals to the speakers? (The same for both, obviously, but what about the absolute polarity?)

Is there a universal convention among speaker manufacturers about denoting which terminal needs to go positive for an outward movement of the cone? (Again, obviously, the same for all speakers of a given model made by that manufacturer, but what about different speaker types, and different manufacturers?)

I've never paid attention to this because I'm sure I would not be able to hear the difference of an absolute polarity change anyway. I am doubtful that anyone can genuinely hear a difference (and prove it by means of blind testing), but then I am a natural skeptic. But I am still curious as to whether speaker manufacturers follow a universal convention that indicates the absolute polarity of the speaker terminals.

Anyway, as was said on this thread a few years ago, if one wants to experiment with the effect of an absolute polarity reversal, an easy way is to flip the two wires on each of the speakers.

Last edited by cnpope; 24th July 2021 at 02:53 AM.
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Old 24th July 2021, 03:16 AM   #22
rayma is offline rayma  United States
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Standard polarity is that the woofer cone moves outward when a positive voltage is applied
to the positive (red) speaker terminal.

Last edited by rayma; 24th July 2021 at 03:20 AM.
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Old 25th July 2021, 07:43 PM   #23
cnpope is offline cnpope  United States
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"Standard polarity is that the woofer cone moves outward when a positive voltage is applied to the positive (red) speaker terminal."

Thanks for that. It had never occurred to me before that there might actually be a convention that is followed. I checked with some speakers of mine, and indeed they all follow your rule.
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Old 25th July 2021, 09:18 PM   #24
mdpaudio is offline mdpaudio
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Also there is a difference between in phase and in positive phase. In phase just means both speakers go in or out at the same time. In positive phase means they both go out when a positive signal is applied. The difference is that when a speaker is moving outward it is compressing the air in the room, inward creates a lower pressure. There is no limit to how much the air can be compressed but a vacuum can only go to zero pressure. A system that is in correct absolute phase usually has more impact or slam than one in inverted phase. Pressure waves travel better than vacuum waves. The net lesson is listen to something with sharp impacts on your system then flip both speaker plus and minus connections and listen. The correct way will have more impact. On a solid state system you can use a small 1.5v battery on the input to see which way the woofers move when plus on the battery is connected to plus on the input rca. Tube amps don’t do DC so it doesn’t work with them.
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Old 25th July 2021, 10:23 PM   #25
6A3sUMMER is offline 6A3sUMMER  United States
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All the way from which side of the strike of the bass drum and which side the mic is on . . .
All the way from the microphone connections . . .
All the mic transformers, preamps, on-site recorder, studio editing, recording machine such as CD recorder or LP cutting head . . .

And then all the way through the playback system . . .

What you can say about absolute phase (compression or rarefaction), is that there are too many places that may not have been paid attention to, in order to be sure what the absolute phase is.

Standards are such a wonderful thing, everyone has his own.

1.Look at the bass drum signal at your speaker terminals
2. Then look at the trumpet signal at your speaker terminals
3. Then look at other instruments signals at your speaker terminals
Compare that to your own microphone and scope for which you have tested them for absolute phase.
You may find that in the 'professional' recording, and then that is sent through your playback system, some of number 1, 2, and 3 are in the correct absolute phase, and some of 1, 2, and 3 are not in the correct absolute phase.

A lot of musical instruments have waveforms that are Not symmetrical, which allows you do do the testing and see for yourselves.
I first looked at such waveforms, and absolute phase in high school in the early 60s.
The problem with maintaining absolute phase, with each and every microphone, and including all the way through the recording process, and then your playback system, has never gone away.

YPMV (Your Phase May Vary).

Last edited by 6A3sUMMER; 25th July 2021 at 10:28 PM.
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Old 25th July 2021, 10:40 PM   #26
mdpaudio is offline mdpaudio
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To reproduce the recording faithfully positive must be positive and negative negative. This does not mean the material was recorded properly but to play it back as it was recorded warts and all the system must be in correct absolute phase. This assures you will hear it as the engineer mixed and mastered it. If the engineer did a good job you will hear it as it was meant to be. If he recorded the kick from the wrong side you will hear that too because you are in correct absolute phase.
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Old 25th July 2021, 10:46 PM   #27
cnpope is offline cnpope  United States
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Quote:
Originally Posted by mdpaudio View Post
Also there is a difference between in phase and in positive phase. In phase just means both speakers go in or out at the same time. In positive phase means they both go out when a positive signal is applied.
Yes. I think it was understood in all of the present thread that it was the absolute polarity that was under discussion, and not merely getting the relative phase of the left and right channels correct, which is an easily heard thing, and very simple to get right.

Quote:
Originally Posted by mdpaudio View Post
The difference is that when a speaker is moving outward it is compressing the air in the room, inward creates a lower pressure. There is no limit to how much the air can be compressed but a vacuum can only go to zero pressure.
That is true, but one does need to keep in mind that the change in air pressure in even the loudest soundwaves one is likely to encounter in audio is a tiny fraction of the ambient air pressure. (Of order 0.02% or so at the very most.) So any nonlinearity in the soundwave transmission in air due to rarefaction versus compression asymmetry you mention will probably be negligible.

Much more significant, probably, are asymmetries (distortions) associated with the response of the speaker cone itself, possible distortions in the amplifier (especially if it is a highly distorting one like an SET playing at high volume), and even asymmetries in the response of the ear itself.

Since some musical instruments certainly produce asymmetric waveforms, it would indeed be conceivable that the absolute phasing of some of the aforementioned sources of asymmetric distortion, relative to that of the original sound source, could be noticeable.
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Old 25th July 2021, 10:54 PM   #28
6A3sUMMER is offline 6A3sUMMER  United States
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Let the recording engineer pick where to locate each and every microphone.
After all the recording process is done, and all the playback process is done, then . . .

Any instrument note or percussive transient that starts with a compression of air (from where the microphone was located) . . .
Should start with a compression of air from your loudspeaker to where you are sitting.

and . . .
Any instrument note or percussive transient that starts with a rarefaction of air (from where the microphone was located) . . .
Should start with a rarefaction of air from your loudspeaker to where you are sitting.

Anything other than that is Not Absolute Phase.

This is a total complete system of reproducing "what" the microphone "heard".
Doctor it as much as you want after that for sound effect, and destroy Absolute Phase.

Just my considered opinion.

One more problem:
I had 2 tweeters of one model, and two tweeters of another model.
The first model pair had one of them that was mis-marked for phase, probably the ceramic magnet was installed upside down.
The second model pair had one of them that was mis-marked for phase, probably the ceramic magnet was installed upside down.
Because I was so unlucky, I will not go to Las Vegas.
But I was lucky to find the problem, so maybe I am lucky, I think I will go to Las Vegas.

Last edited by 6A3sUMMER; 25th July 2021 at 11:01 PM.
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Old 25th July 2021, 10:58 PM   #29
mdpaudio is offline mdpaudio
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That is what I’m saying to sound right it must be in the phase it was recorded. To do that the system has to be in correct absolute phase.
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Old 25th July 2021, 11:08 PM   #30
6A3sUMMER is offline 6A3sUMMER  United States
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Some recordings have some instruments recorded in Absolute phase, and some instruments on the same recording might be recorded in the Opposite of Absolute phase.

That is what I am saying.

Two microphones, 2 microphone elements, 2 internal matching transformers;
2 XLR cables, 2 preamp input transformers, and . . .
Poor quality control, and no testing of phase = 10 possible places where one signal is Not in absolute phase.
Then there are all the other places to go wrong all the way to your loudspeakers.

It might sound great to the recording engineer in the initial recording studio, but that does not make it absolute phase.
Unless every part along the way was tested individually, or at least all those parts were tested as a complete system.

That is what I am saying.

And . . .
All the other parts the rest of the way through the recording, playback, amplifiers, and loudspeakers can either preserve, or cancel the absolute phase of the instrument.

Last edited by 6A3sUMMER; 25th July 2021 at 11:16 PM.
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