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How important in phase control on a subwoofer?

warthor

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I have been watching some of Erin's Audio Corner reviews and his recent interview with Audioholics. He is one of the premier subwoofer review guys. In a number of his pieces he mentions the importance of having phase control on the subwoofer (he has gone further to say 0 degree and 180 degree is not quite enough, but ratio scale phase control is critical). I have not heard many other people emphasize this point.

So my question is why is this the case?

The practical implication is that there are a number of brands that don't have this that would be ruled out in terms of purchases (PSA, Klipsch [just has 0, 180]).

EDIT: I was wrong about PSA. They include phase control as a delay in milliseconds. Thanks to @MZKM
 
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Doodski

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Subwoofer phase is important because if the subwoofer driver and the speaker woofer are not moving in and out at the same time they algebraically cancel each other out and that's a bad thing for bass response. Imagine if one is 180 degrees out of phase and that would result in cancelation of the energy each driver is producing and so if they are slightly out of phase then slight cancellation is occurring. I have not seen many subs with ratio scale phase control but they are out there.
 

sigbergaudio

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It's not quite as simple, as the subwoofer is not either in phase or out of phase, the phase changes with frequency. So a phase control like what is present on many subwoofers is not something one can use to get the subwoofer perfectly in or out of phase. But it can be "less" out of phase, or more in phase at a given frequency (the crossover is the area that is typically problematic).

Whether this is important or not depends both on your setup and the subwoofer.
 

KSTR

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Matching a generic subwoofer to generic main speakers opens a whole can of worms ;-)
It puts the customer in a situation only speaker designer is normally faced with, the perfect integration of two ways in a multi-way speaker.

But the main speaker is unknown to the subwoofer and vice versa (unless it's a dedicated extension model for certain speaker).
Thus, the more possibilites a generic subwoofer has for adjustment, the better... but the more tedious to find the best settings...
 

KSTR

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It's not quite as simple, as the subwoofer is not either in phase or out of phase, the phase changes with frequency. So a phase control like what is present on many subwoofers is not something one can use to get the subwoofer perfectly in or out of phase. But it can be "less" out of phase, or more in phase at a given frequency (the crossover is the area that is typically problematic).

Whether this is important or not depends both on your setup and the subwoofer.
Adding to this, an adjustable phase control (not to be confused with a polarity switch) always introduces extra (superfluous) group delay so you often can end up in a situation where a steady state sine nicely cancels but it is delayed one full cycle, spoiling time response. This not easily spotted by its associated FR ripple as that is often drowned in room modes etc.
 

GGroch

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Matching a generic subwoofer to generic main speakers opens a whole can of worms ;-)
.......

I always assumed that the worm can is just as much about the location of the sub in the room as it is the relative phase of the drivers. Even if the speakers and sub are known by the designer, they would still not know the relative position and distance from the primary listening location in a home.
 

HighImpactAV

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A phase control is nothing more than a delay knob. If you have an 80 Hz crossover, then 180 degrees of phase shift equates to 6.25 ms of delay at 80 Hz. So, in this case the phase knob adds delay from 0 to 6.25 ms to the entire signal.

This is rarely beneficial. The mains need to be delayed in relation to the subwoofers unless the subwoofers are much closer to the main listening position than the mains. The reason the mains need to be delayed is that the low pass filter on the subwoofer adds a cycle of delay to the signal, the DSP being used on the subwoofer adds delay to the signal, the internal amp on the subwoofer may also have DSP which adds latency, and the subs are often positioned further from the main listening position than the main speakers.

It can be helpful if the delay in the receiver is not granular enough. For example, if you can only adjust the distance setting by 1 ft and need to set 7.5 ft, then you can set 7 ft in the receiver and add in the extra delay with the phase control. However, I haven't seen a receiver with not enough granularity in years.
 

Mnyb

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Yes if you have an AVR or pre pro , you adjust the delays between mains center and sub , no need for the phase knob.
 

sigbergaudio

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Depending on the design of both the sub and the speakers, this can be more or less of an issue. If both the speakers and subwoofer(s) are sealed, that will help. Also the types of crossover slopes choosen will affect phase issues. It's perfectly possible to get a good result, especially if you can experiment a bit with placement. The best approach is of course to have an amplifier/receiver/processor with somewhat advanced DSP capabilities so these things can be configured automatically and/or manually there.

Even if you do end up with phase issues, some are more sensitive to this and others, and resulting nulls in frequency response may be very narrow, and thus not necessarily very audible.
 
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warthor

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Thank you all for your insight! This seems like an issue that is above my head! I don't think I could use adjustable phase control really well (except the usual 0 and 180 degree options). But any more than that I think I would be lost. Once you get to 97 degrees this stuff doesn't make sense to me any more :).

The SVS app, for example, gives you advanced phase control. Monolith subwoofers have a knob that does advanced phase control as well. I was trying to determine if that is something I would need to consider when buying a subwoofer. Thanks again!
 

MZKM

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A phase control is nothing more than a delay knob. If you have an 80 Hz crossover, then 180 degrees of phase shift equates to 6.25 ms of delay at 80 Hz. So, in this case the phase knob adds delay from 0 to 6.25 ms to the entire signal.

This is rarely beneficial. The mains need to be delayed in relation to the subwoofers unless the subwoofers are much closer to the main listening position than the mains. The reason the mains need to be delayed is that the low pass filter on the subwoofer adds a cycle of delay to the signal, the DSP being used on the subwoofer adds delay to the signal, the internal amp on the subwoofer may also have DSP which adds latency, and the subs are often positioned further from the main listening position than the main speakers.

It can be helpful if the delay in the receiver is not granular enough. For example, if you can only adjust the distance setting by 1 ft and need to set 7.5 ft, then you can set 7 ft in the receiver and add in the extra delay with the phase control. However, I haven't seen a receiver with not enough granularity in years.
Some subs actually do not have it as a delay, they implement it as a filter which only affects the crossover region (how wide I do not know). JL Audio subs state this.

But yes, the vast majority has it as a simple time delay. PowerSoundAudio subs even use milliseconds instead of degrees for the knob, as it’s technically more correct.
 
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warthor

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Some subs actually do not have it as a delay, they implement it as a filter which only affects the crossover region (how wide I do not know). JL Audio subs state this.

But yes, the vast majority has it as a simple time delay. PowerSoundAudio subs even use milliseconds instead of degrees for the knob, as it’s technically more correct.

That makes sense! I was wondering how the highly regarded PSA didn't have such an important control option. But they do have it. Thanks for pointing that out.
 

MZKM

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highly regarded PSA
Now imagine my disbelief that even in their $7500 flagship model, REL does not have any phase control, only 0/180 polarity. They even have a controller so you can adjust settings from your couch (a physical controller, not an app like with SVS), and even that is just for polarity:
25_Remote_CF_3_4_Hero-600x581-1.png



It does offer 2-band EQ, but in a weird way. You have to move the switch to A and use the left knob for frequency (20Hz-90Hz) and right knob for level (+/-6dB in 1/3dB intervals), then switch to B and do the same.
 
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Ron Texas

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I have measured the frequency response of my system with the phase knob at 10 positions from 0 to 180 and finds it measures flattest at 0. Note my subs (L12's) are near the mains, do not have a built in DSP, are very slightly closer to the listening position, and the mains are on a Crown XLS 1502 which has a 1.25 ms delay from it's built in DSP.
 

Mnyb

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I have measured the frequency response of my system with the phase knob at 10 positions from 0 to 180 and finds it measures flattest at 0. Note my subs (L12's) are near the mains, do not have a built in DSP, are very slightly closer to the listening position, and the mains are on a Crown XLS 1502 which has a 1.25 ms delay from it's built in DSP.

Yes measure for sure it would be darn impossible to dial in by ear only especially with music . I used the built in DRC in my pre pro and dialed in the distances etc , but still i was left with some options to decide between .
The aforementioned increments in distances for example my actual distance is between two notches so which to choose ? REW and umik to the rescue
 

Chromatischism

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I have been watching some of Erin's Audio Corner reviews and his recent interview with Audioholics. He is one of the premier subwoofer review guys. In a number of his pieces he mentions the importance of having phase control on the subwoofer (he has gone further to say 0 degree and 180 degree is not quite enough, but ratio scale phase control is critical). I have not heard many other people emphasize this point.

So my question is why is this the case?

The practical implication is that there are a number of brands that don't have this that would be ruled out in terms of purchases (PSA, Klipsch [just has 0, 180]).

EDIT: I was wrong about PSA. They include phase control as a delay in milliseconds. Thanks to @MZKM
If you are using the sub in a system with Room EQ a phase adjustment is not used and therefore not needed.

If you use it in a system without DSP, then it is essential.
 

Chromatischism

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Some subs actually do not have it as a delay, they implement it as a filter which only affects the crossover region (how wide I do not know). JL Audio subs state this.

But yes, the vast majority has it as a simple time delay. PowerSoundAudio subs even use milliseconds instead of degrees for the knob, as it’s technically more correct.
Right, most subs actually use phase and not a linear delay, PSA and Rythmik being exceptions. A true delay control is better for integration.
 

sigbergaudio

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Thank you all for your insight! This seems like an issue that is above my head! I don't think I could use adjustable phase control really well (except the usual 0 and 180 degree options). But any more than that I think I would be lost. Once you get to 97 degrees this stuff doesn't make sense to me any more :).

The SVS app, for example, gives you advanced phase control. Monolith subwoofers have a knob that does advanced phase control as well. I was trying to determine if that is something I would need to consider when buying a subwoofer. Thanks again!

I think you are nailing it pretty well here. Most people haven't got the slightest idea how to use a phase control, so to most people it will be useless at best. Even if you did know, it wouldn't necessarily help you. The reason many people don't get it, is that with their setup in their room, they can't really tell the difference if they flip the switch or move the dial, because they don't have a phase issue, or it is inaudible, or can't be helped by phase control alone.

I'm not saying a phase control is useless all the time for all people in all rooms regardless of the type of subwoofer or speakers. But if someone says that unless you purchase a subwoofer with a variable phase switch, a puppy will die, it's probably somewhat of an exaggeration. :)

Full disclosure: We sell subwoofers without any phase control whatsoever. :eek::p
 
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