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Subs with reversed polarity (surprise!)
Subs with reversed polarity (surprise!)
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Old 13th June 2019, 09:05 PM   #1
bentoronto is offline bentoronto  Canada
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Subs with reversed polarity (surprise!)
Default Subs with reversed polarity (surprise!)

It is an Article of Faith that polarities must be preserved. And for dipoles, that the phase annihilation diagram for woofer frequencies in the textbook is an Eternal Truth.

On the other side, anybody with experience fooling with phase and even with polarity and certainly with dipoles, knows that the sound hits walls and is in a multiple of ways shaken from its phase locksteps.

So I figured there's a real simple way for a person with a Behringer DCX2496 - the all-singing all-dancing DSP - to explore the notion with about 6 button presses of the DSP box.

The subs are in the front corners of the room. L is a 5-cu ft sealed box and the R a 17-foot labyrinth. Both with some EQ. A mic was placed mid-way between the subs and near my listening chair. The REW sweep is 10-500 Hz (OK, 10 Hz is pushing it a bit with my 1980 JVC receiver amp, but you can see for yourself what the mic picks up).

The first illustration shows the (1) L and (2) R traces when run separately. Many similarities are reflections of the room (literally, of course).

The second illustration shows the (1) R sub trace and the (2) R sub with polarity inverted trace. Many readers will notice a certain overlap.

The third illustration shows results when (1) both subs are running and when the (2) R sub is inverted. Needless to say, the reversed trace is the lower one. But not annihilated. Far from it.

The fourth illustration repeats the inverted trace shown in the third illustration. Funny, it looks so much better than the non-inverted trace. Maybe I'll raise the volume control and keep that. I bet just the thought of somebody doing such a thing would cause indigestion among many members here.

B.
Attached Images
File Type: jpg L plus R.jpg (63.0 KB, 351 views)
File Type: jpg R plus R invert.jpg (57.8 KB, 351 views)
File Type: jpg both plus both w invert.jpg (68.9 KB, 354 views)
File Type: jpg L and R invert.jpg (57.0 KB, 353 views)
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Last edited by bentoronto; 13th June 2019 at 09:44 PM.
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Old 13th June 2019, 09:18 PM   #2
Brian Steele is online now Brian Steele  Grenada
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SO, you're comfortable with giving up 10~20dB in the passband to make it look smoother in a graph?
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Old 13th June 2019, 09:32 PM   #3
bentoronto is offline bentoronto  Canada
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Subs with reversed polarity (surprise!)
Absolutely yes. As would anybody who isn't running a dance establishment. Wouldn't you?

Not that I was 100% serious about doing so in the OP.

B.
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Old 13th June 2019, 09:35 PM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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I once bought a speaker that had the connections marked the wrong way around.
Luckily I checked with a battery first before wiring it up.
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Old 13th June 2019, 10:11 PM   #5
rayma is offline rayma  United States
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Quote:
Originally Posted by bentoronto View Post
Absolutely yes. As would anybody who isn't running a dance establishment.
Are you saying that the right sub response changes that much, from just reversing its polarity? Is the flatter response the one with correct absolute polarity, or reversed?

Last edited by rayma; 13th June 2019 at 10:13 PM.
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Old 13th June 2019, 10:13 PM   #6
nigelwright7557 is offline nigelwright7557  United Kingdom
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An inverse function would suggest the speakers would just cancel each other out.
But in a real room the speakers will be a distance apart and there will be phase shifts etc.
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Old 13th June 2019, 10:21 PM   #7
bentoronto is offline bentoronto  Canada
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Subs with reversed polarity (surprise!)
Quote:
Originally Posted by rayma View Post
Are you saying that the right sub response changes that much, from just reversing its polarity? Is the flatter response the one with correct absolute polarity, or reversed?
+1 nigelwright7557.

As the second illustration shows, there is zero change in the FR of the R sub when its polarity is reversed.

If the orthogonal polarity led to a flatter response, I wouldn't bother posting it, eh. Pretty much accidental, but the reverse connection (which does show some of the expected cancellation) looks flatter. Accidental, I am sure. But I set up my mic stand and took the first runs without moving it. So I didn't fish for a good result.

B.
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Old 13th June 2019, 10:47 PM   #8
ICG is offline ICG  Germany
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Quote:
Originally Posted by nigelwright7557 View Post
An inverse function would suggest the speakers would just cancel each other out.
But in a real room the speakers will be a distance apart and there will be phase shifts etc.
You are right, that will probably fix the phase in one place, in others it will likely get worse. It's much better to find better positions for the subs. Or build a double bass array.
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Old 14th June 2019, 12:14 AM   #9
kgrlee is offline kgrlee
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Quote:
Originally Posted by bentoronto View Post
The third illustration shows results when (1) both subs are running and when the (2) R sub is inverted. Needless to say, the reversed trace is the lower one. But not annihilated. Far from it.

The fourth illustration repeats the inverted trace shown in the third illustration. Funny, it looks so much better than the non-inverted trace. Maybe I'll raise the volume control and keep that.
If you measure the response is your listening area, eg within 3' of your favourite chair, you will find the 'in-phase' subs give MUCH more consistent performance over a larger area than your 'out-of-phase' subs.

You may also like to listen to a central (mono) voice comparing in & out of phase if your 'subs' go up to 100Hz or more.
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Old 14th June 2019, 12:24 AM   #10
bentoronto is offline bentoronto  Canada
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Subs with reversed polarity (surprise!)
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Originally Posted by kgrlee View Post
If you measure the response is your listening area, eg within 3' of your favourite chair, you will find the 'in-phase' subs give MUCH more consistent performance over a larger area than your 'out-of-phase' subs.
Is that a question or an assertion of faith?

Quote:
You may also like to listen to a central (mono) voice comparing in & out of phase if your 'subs' go up to 100Hz or more.
Huh?

Is that a question or an assertion?

First, the measurements show there's only a bit of "correct" phase because there's only a bit of interference. Second, there's no content down there to hear. Third, there's no sense of localization down there. Fourth, any issue would not be better anywhere except up close to one of the subs in which case, the polarity reversal wouldn't be evident either way.

B.
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