Exactly what does an analog continuously variable phase control do? - Page 2 - AVS Forum
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post #31 of 42 Old 11-07-2005, 12:46 PM
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Originally Posted by Dennis Erskine
However...moving the sub means moving the sub in/out of moderate modal areas.
Sorry, I was a bit vague. I was referring to the common 1' distance increments found in most any of today's pre-processors/receivers. Many now offer incremental adjustments down to 0.1' which would be 2.5 degrees. Indeed, moving a subwoofer around defeats the purpose.

We should differentiate between a polarity switch and a variable phase knob set to 180 deg. The knob will be adjusting an all-pass filter, where the polarity switch will generally just invert the signal (- for +). These two operations will have measurably different results. I wouldn't necessarily say one is all that much better or more useful, but they are different. At the same time, at some specific frequency or frequencies, the resulting magnitude (level) will be the same.

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post #32 of 42 Old 11-07-2005, 12:56 PM
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Quote:
Originally Posted by Dennis Erskine
As well, running your L/R speakers full range in a small room can certainly create some ugly LF problems.

It all depends on your definition of a "small" room!


I have no real problems in the subwoofer frequency area running large mains plus a subwoofer. My particular receiver evidently has an uncommon BM configuration with a L, S, S plus subwoofer setting. LFE as well as redirected bass goes to the mains. Also, R & L main bass is mixed with LFE and redirected bass and is sent to the subwoofer. This is standard Dolby Configuration 2.


Most receivers tend to use the Alternate Configuration 2 for L, S, S plus SW, along with a PLUS option of some sorts.


Anyway, my main speakers (3-way) have use a receiver EQ setting of -3dB @ 125hz setting. This gives the same RTA frequency response in room as compared with a SMALL 50hz crossover setting for my mains speakers. However, the LARGE main settings smooth out room modes more than a S, S, S plus SW setting.


Anyway, my subwoofer and my mains speakers are never in phase at MOST FREQUENCIES with either of my subwoofer amplifier POLARITY setting if I set my speaker distances to AS MEASURED distances. SMALL settings or LARGE settings did not matter. Out of phase is out of phase, but in/out of phase is still a frequency dependent issue. Most people probably use a sort of in/out of phase settings!


Without the use of True RTA, I could never have determined how to PROPERLY integrate the subwoofer with the main speakers as well as possible!
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post #33 of 42 Old 11-07-2005, 01:08 PM
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Originally Posted by Darin
And to the best of my knowledge, that is their primary function. I'm not aware that there is any "universal" phase. In other words, while speaker brand A may move the cone out when a positive voltage is given to the positive lead of the speaker, brand B might move the cone in. The phase switch allows you to easily integrate the sub regardless of which configuration your speakers are. And of course, if you are trying to correct timing differences that are induced by the crossover and equalization circuits, two positions is still better than one. If you are off by 120 degrees, 180 is closer to correct than 0.


The phase switch allows you to EASILY integrate the sub regardless of which configuration your speakers are?????

One should be so lucky!!!



"If you are off by 120 degrees, 180 is closer to correct than 0."

Sort of correct, but it still MAY not sound right. Not to mention the fact that different frequencies will be off by different amounts in MAJOR ways.
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post #34 of 42 Old 11-07-2005, 01:15 PM
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Originally Posted by jamin
Nope, if at the crossover region the phase difference is such that a null is being created, then the bass will be helped tremendously in that region by flipping the polarity.


I don't pay any attention to the EXACT "crossover" region. I look at the entire bass frequency response when I align my subwoofer to my R & L main speakers.

As far as surrounds are concerned, I have limited range surround speakers. I don't have integration problems at 20 and 30hz with "small" surround speakers.

I suppose if you have "small" speakers for your mains, then subwoofer integration MAY NOT BE as critical as it is with "large" main speakers. However, I bet you that it is!!!
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post #35 of 42 Old 11-07-2005, 01:22 PM
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Quote:
Originally Posted by J_Palmer_Cass
The phase switch allows you to EASILY integrate the sub regardless of which configuration your speakers are?????

One should be so lucky!!!
Heh, well, I originally posted that without the word "easily", then went back and added it in to differentiate the relative PITA of going around and swapping the wires on each of your six satellites, to the relative ease of flipping a switch. I didn't mean to insinuate that a simple flip of a switch would cause your system to instantly be completely integrated, just that flipping a switch is an easy way to implement a polarity reversal , which is something you do in an ATTEMPT to integrate your sub to your mains. :)

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"If you are off by 120 degrees, 180 is closer to correct than 0."

Sort of correct, but it still MAY not sound right. Not to mention the fact that different frequencies will be off by different amounts in MAJOR ways.
True, but they shouldn't be off in MAJOR ways until you get relatively far from the point that you are calibrating for. Assuming decent crossover slopes, phase shouldn't be nearly as important, as there would be little overlap between the output of the sub & mains.

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post #36 of 42 Old 11-07-2005, 01:40 PM
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Now I understand what you meant with the word "easily". Internet mis-communications at it's best I guess!


QUOTE=Darin]

True, but they shouldn't be off in MAJOR ways until you get relatively far from the point that you are calibrating for. Assuming decent crossover slopes, phase shouldn't be nearly as important, as there would be little overlap between the output of the sub & mains.[/quote]


The overlap area is a lot bigger than you realize if you have "large" mains regardless of the "typical" SMALL speaker crossover slope. In my case, I found that I had a phase reversal in the 20hz and the 30hz areas as compared with the 40hz though 80hz area with a standard subwoofer distance setting.

One other thing. I have found that if you place your subwoofer on the same front wall as your mains speakers, calibration (time/phase) of the subwoofer and the front main speakers comes out the same for MOST areas of the room. I had to give up something, so perfect time integration to the surrounds is what I gave up. Actually, I gave up very little!
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post #37 of 42 Old 11-07-2005, 04:19 PM
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Getting back to the original question, a continuously variable phase control simply delays the phase at the crossover frequency.
That's assuming the subwoofer 'knows' what the crossover setting is. In any event the continuously variable phase control will affect not one frequency but on the order of 2 octaves.

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post #38 of 42 Old 11-07-2005, 05:08 PM
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Quote:
Originally Posted by Dennis Erskine
That's assuming the subwoofer 'knows' what the crossover setting is. In any event the continuously variable phase control will affect not one frequency but on the order of 2 octaves.
I wrote "there will be different phase delays at other frequencies." You're not suggesting that subwoofer phase adjust circuits are Hilbert transformers, are you Dennis? That's what you need to adjust a range of frequencies by the same phase angle.

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post #39 of 42 Old 11-08-2005, 03:01 AM
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No...I had enough problems with cosines to deal with negative cosines. :)
I missed the guoted phrase; but, was not wanting anyone to lose sight of the fact the analogue phase adjustment does not affect just one frequency (ie, crossover...whatever it may be set to).

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post #40 of 42 Old 11-08-2005, 10:07 AM
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I think that one point was that a POLARITY switch will change all frequencies by 180 degrees, and an analog or digital phase adjustment circuit will affect all frequencies but not by the same amount of degrees!
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post #41 of 42 Old 11-08-2005, 12:44 PM
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Quote:
Originally Posted by J_Palmer_Cass
I think that one point was that a POLARITY switch will change all frequencies by 180 degrees, and an analog or digital phase adjustment circuit will affect all frequencies but not by the same amount of degrees!
Yes. It is remarkable how powerful and capable a polarity switch is! :)

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post #42 of 42 Old 11-15-2005, 09:39 AM
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Quote:
Originally Posted by jamin
Nope, if at the crossover region the phase difference is such that a null is being created, then the bass will be helped tremendously in that region by flipping the polarity.

Sure, but what happens to the other bass frequencies that are not in your specified "region"????
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