A cursory sampling of subwoofer literature shows that the implementation of electronic phase control covers the entire spectrum, from continuously variable to none at all.

So...

Sometimes it is important, sometimes not so much. It depends on the location of the sub relative to the mains as well as certain characteristics of the crossover.

To those of you voting "Critical:" could you please explain your experience, and why you feel a more precision phase adjustment was/is needed?

Everyone's environment is different.

If you don't have it and could us it is a big bummer when you don't. However, this ability is also being intergrated into more and more receivers as .2 option rather than the traditional .1 setup allowing independent phase/distance settings for more than one sub.

Also, products like the AS-EQ1 will allow this as well. I suspect there will be others in the near future.

I, too, would like to see a little bit more discussion. I get what it does. There appears to be very little information on this adjustment. What AVR's are set up with 5.2? I have not heard that before.

I had mine on one phase and it was bottoming out, was told to switch the phase and no more problems.

What AVR's are set up with 5.2? I have not heard that before.

Example: many Yamaha receivers are 7.2, new HKs are on the way with 7.2

When you adjust the distance from your speakers to your listening position via your AVR you are setting the phase. If you have no regard for phase then you will have from very small to very large cancellations and/or summations at certain freqs at your listening position.

If two speakers were exactly out of phase they would cancel each other out.

When you add a second sub at a different distance phase will come in to play. You can choose to not correct and just be happy with the sound. If you take freq sweeps you will see how it affects your particular setup.

Wow, I'd really thought this topic would draw a lot more interest and votes than it has. Is it that phase control really isn't all that important, or is it just a more esoteric subject to reasonably expect much reaction to here?

Over 85% of the 42 voters indicate that phase control is either unimportant, or can be adjusted to be "good enough" by, for all intents and purposes, flipping the wires.

Is that it? Is there anybody else out there that has an opinion on this before it goes quietly into the night? :rolleyes:

I have "large" 3 way sealed main speaker and a pair of corner stacked ported subwoofer(s).

For phase 0 degrees polarity and 90 degrees adjustable phase is the setting that I need to use. In addition, I need to adjust the subwoofer distance control to a distance that is much longer than the as measured distance.

The polarity adjustment of 0 degrees or 180 degrees just does not work properly. I need 90 degrees of phase shift plus a time shift that I make with the subwoofer distance control.

My subwoofer handles 50 Hz and below. The mains are good to 45 Hz.

I used to work at one of the better high-end stereo stores in town. In a set-up we sold, to a client that lived in a town house, an adjacent neighbor was complaining about the amount of bass leaking into his side of the building. :mad: To solve the issue, we basically reset the phase to 90 degrees. As such, the bass notes shifted away from the neighbor, and back into the client's room, and our client only experienced a slight drop in bass level, which he was happy to live with. A sub with a variable phase control probably would have allowed an even better bass match between the two homes... :)

Stimpy

Those that consider it unimportant or not necessary either don't understand what it is or are in an environment where it is not required in their setup.

Personally I very rarely employ a common variable phase control when optimizing a system. Most every time I've used it was when I didn't have preferred options available. In other words, if you have EQ and distance/delay adjustments available, it's mostly fluff and doesn't accomplish much that you can't by other means. There are a few cases where it can be used to your benefit with multiple subwoofers (again if other adjustments aren't available), and when your processor or a 2ch system doesn't afford distance/delay adjustments nor EQ, it can help toward a better result than without.

Those that consider it unimportant or not necessary either don't understand what it is or are in an environment where it is not required in their setup.

I'm in the 'don't understand it' category. I understand what it does but not sure how incorporate it into my calibration. I consider myself to be a tad above average when it comes to audio/ht (though for the life of me I can't get REW to work). There is actually very little written about using the phase control.

If I understand it correctly, it is best used to help blend at your crossover point were being out of phase would probably have the most dramatic effect.

If you have 1 sub, the distance setting (on receiver) for the sub does the same thing.

If you have 2 subs, then you might want phase control on one of them.

There's a science behind frequency response and time it takes for different frequencies to reach your ears. Several speaker manufacturers even position the tweeter farther from the face of the speaker tower than the mid and the woofer (like Wilson, Thiel, and many others).

Assuming the sub is placed up near the front speakers, setting distance mostly fixes the time delay vs your fronts, center, etc to where your sitting position is. The sub could possibly be out of phase with your fronts if the fronts were miswired (i.e. wired out of phase + to - and - to +). Of course, you could simply just rewire, but a phase control switch could help correct the situation also. Based on room resonance, cross over point, and exact positions, a variable phase control could help small variance in the sounds that reach your ears. Also, many receivers or processors only have distance settings in increments of 1ft. If you wanted to be 10.5ft from your speakers, but your sub was 10ft or 11ft, then variable phase control could help because you would not need a 180deg phase shift, only a very small shift. See my crude drawing for a simple explanation. If someone sees something that needs to be corrected based on what I said, let me know, and I will update it.
http://www.magictk.com/phase.jpg

Personally I very rarely employ a common variable phase control when optimizing a system. Most every time I've used it was when I didn't have preferred options available. In other words, if you have EQ and distance/delay adjustments available, it's mostly fluff and doesn't accomplish much that you can't by other means. There are a few cases where it can be used to your benefit with multiple subwoofers (again if other adjustments aren't available), and when your processor or a 2ch system doesn't afford distance/delay adjustments nor EQ, it can help toward a better result than without.

It's usually safe to say you agree with Mark Seaton ;)....but that's just it. Distance and delay settings in a receiver can accomplish very similar results to a phase switch or knob. If you can't adjust these things with your receiver, or as Mark and Jesse S said if you have multiple subs, then a phase switch/knob on a sub is helpful. Otherwise, there are other ways to get the job done. I didn't vote because the answer is totally dependent on your room/subwoofer placement and the capabilities of your other gear. The phase control can be extremely important or a non factor. I'd say it's better to have it and not need it than the other way around.

BTW, great illustrations MagicTK

getting a second subwoofer that's not colocated also ups the need for variable phase control.

Example: many Yamaha receivers are 7.2, new HKs are on the way with 7.2Other than offering a 2nd subwoofer output, do you know what other features this affords? Can the two outputs' levels be adjusted independently? Are you sure? Their distances? Are you sure? Can the receivers apply EQ to each sub output independently? Are you sure?

Time is NOT phase. If you really want to understand phase, it is important to understand this, but to also understand the relationship between phase and time. Adjusting the subwoofer's distance setting affects the timing, and because of this it can affect the phasing.

Also, I think it should be pointed out that the best phase setting is the one that provides for the flattest FR.

Time is NOT phase. If you really want to understand phase, it is important to understand this, but to also understand the relationship between phase and time. Adjusting the subwoofer's distance setting affects the timing, and because of this it can affect the phasing.


This is an important understanding, as a distance/delay adjustment can actually delay the main speakers relative to the subwoofer (when the sub dist > LCR dist). A variable phase control can only add group delay. 98% of the time the former is the desired action. Of course desired/preferred is not the same as being the only solution. Using a variable phase control to correct a significant suck-out in response at the crossover is much preferred to leaving a wide-band suck out that might otherwise rob the system of punch/kick/impact. Once you gain the insight of real measurements, it is easy to blow narrow response notches out of proportion from their actual audibility, but there are certainly cases of more pronounced losses.

A variable phase control is another effective tool you can put to use, although not always the most preferred for the task at hand.

This is an important understanding, as a distance/delay adjustment can actually delay the main speakers relative to the subwoofer (when the sub dist > LCR dist). A variable phase control can only add group delay. 98% of the time the former is the desired action.




I find that I need to use both. Yes, the variable phase control changes group delay. Big deal, a lot of adjustments change group delay. For the last step in the process you still have to adjust the subwoofer distance to match everything anyhow. The variable phase control allows you match phase over a much greater bandwidth than is available with a simple 0 / 180 degree polarity switch.

A few other things that change group delay / phase are crossover frequencies and slopes of the crossovers. Also, if you have mains that play low and you try to blend them with a ported subwoofer, then the subwoofer is 180 degrees out of phase at the port frequency, but sort of in phase at other frequencies.

One other issue here. With my particular receiver when I use the Cinema modes, the speaker distance settings are ignored even though they still shown on the menu. In order of adjustment I have to set subwoofer polarity, then variable phase, and then subwoofer distance to get the best blend between the subwoofer and my mains. If I touch the crossover frequency and/or subwoofer border EQ, then I have to recheck / tweak the distance setting again. I then have to confirm that the Cinema modes work properly.

This is an important understanding, as a distance/delay adjustment can actually delay the main speakers relative to the subwoofer (when the sub dist > LCR dist). A variable phase control can only add group delay. 98% of the time the former is the desired action. Of course desired/preferred is not the same as being the only solution. Using a variable phase control to correct a significant suck-out in response at the crossover is much preferred to leaving a wide-band suck out that might otherwise rob the system of punch/kick/impact. Once you gain the insight of real measurements, it is easy to blow narrow response notches out of proportion from their actual audibility, but there are certainly cases of more pronounced losses.

A variable phase control is another effective tool you can put to use, although not always the most preferred for the task at hand.

I believe this is why a lot of receiver owners equipped with Audyssey notice that the auto setup determines the sub distance to be much further than it really is physically. In this situation I appreciate being able to set the phase to 0 on the sub and let the receiver handle things...though I was unaware of the issues J_Palmer raises above.

Other than offering a 2nd subwoofer output, do you know what other features this affords? Can the two outputs' levels be adjusted independently? Are you sure? Their distances? Are you sure? Can the receivers apply EQ to each sub output independently? Are you sure?

No, I don't manufacture or write the code for them. I am only sure about death (taxes have been taken off the list since apparently Democrats don't have to pay them, so why should I).

No, I don't manufacture or write the code for them. I am only sure about death (taxes have been taken off the list since apparently Democrats don't have to pay them, so why should I).Hey, sorry. You seemed like you knew about these receivers' capabilities. I've always wondered exactly what the 2nd subwoofer output offered in terms of independent settings. Thought you might be able to nail it down for me.

However, this ability is also being intergrated into more and more receivers as .2 option rather than the traditional .1 setup allowing independent phase/distance settings for more than one sub.So, I'm still wondering if the 2nd subwoofer output on these faux .2 receivers really does offer a separate distance adjustment.

No apologies, I was just joking.

I am very confident in the distance control being offered with the .2 receivers. I think if that were not true they would have just added a second sub out or instructed people to add a Y cable to the single one.

Regarding EQ, I doubt that it would EQ the subs seperately. In fact, the built in EQs in the receivers are not the best at EQing below 80Hz anyway. Hence the upcoming EQ1 and SMS-1 and other sub only units.

I am very confident in the distance control being offered with the .2 receivers. I think if that were not true they would have just added a second sub out or instructed people to add a Y cable to the single one.I have always wondered if the distance and level trims could be adjusted separately. Still wondering. I may have to download a manual or two.


Regarding EQ, I doubt that it would EQ the subs seperately. In fact, the built in EQs in the receivers are not the best at EQing below 80Hz anyway. Hence the upcoming EQ1 and SMS-1 and other sub only units.Yeah, I wouldn't expect these receivers to EQ the subs separately as that is not really too useful.

I have always wondered if the distance and level trims could be adjusted separately. Still wondering. I may have to download a manual or two.

please share with us your findings :D im too lazy to read manuals - i dont even read the ones i own :) TIA

What if you had a sub and a mid=bass module (the MBM 12)? I set the phase of the sub at 0 and also on the MBM. My understanding is that if the frequencies don't overlap too much, then there shouldn't really be a problem, eh? They are placed on ether side of the center speaker. I don't run REW, or really care to run moderate calibrations....I like what I hear, but just wanted to know about this combo....

KBMAN,
Not that simple. What if its taking long for your sub to emit a sound than your MBM surrounding the crossover frequency? You've got a dip that could be corrected. You may like it now, but maybe you'll like it better and the only way is to run some test.

General question.

Since phase and distance settings are somewhat related, is there a chart that would provide the equivalent distance adjustment for a given amount of phase adjustment??

Does this vary by frequency and if so, is there a resource you can link to that would detail these amounts?

I had mine on one phase and it was bottoming out, was told to switch the phase and no more problems.


Sorry, but that sounds wrong. You probably should have just turned your sub down and gotten multiple subs if you wanted the volume at a higher level. Are you using an SPL meter or REW?

I used to work at one of the better high-end stereo stores in town. In a set-up we sold, to a client that lived in a town house, an adjacent neighbor was complaining about the amount of bass leaking into his side of the building. :mad: To solve the issue, we basically reset the phase to 90 degrees. As such, the bass notes shifted away from the neighbor, and back into the client's room, and our client only experienced a slight drop in bass level, which he was happy to live with. A sub with a variable phase control probably would have allowed an even better bass match between the two homes... :)

Stimpy

So what does the neighbor on the other say since turning the signal 90 degrees should have boosted his?

Seriously, you are kidding right?

If not, all you accomplished was lowing the subwoofer volume by creating cancellations(speakers and sub out of phase). You could have done the same by keeping in phase and turning the gain down.

I've found phase adjustment VERY useful in the crossover area between mains and sub. I locate sub(s) for flattest overall response and mains for best imaging. Then use phase to minimize any cancellation between mains & sub. Only after this do I employ equalization.

Using a real-time FR display and variable phase adjustment shows a continously and often significantly changing output - proof enough for me that continuously variable phase is important - I can pick the one setting with best overall response.

Multiple subs magnafies the need for variable phase and significantly complicates the process of balancing the overall reinforcement and cancellations.

Sorry, but that sounds wrong. You probably should have just turned your sub down and gotten multiple subs if you wanted the volume at a higher level. Are you using an SPL meter or REW?

Actually if the initial setting produced significant cancellation between the sub and mains, the sub could be driven harder (and fruitlessly) to make up for the cancellation. If this was the case, a 180 phase shift would almost certainly reduce the cancellation allowing the sub to run with less gain and less possibility of bottoming out.

Actually if the initial setting produced significant cancellation between the sub and mains, the sub could be driven harder (and fruitlessly) to make up for the cancellation. If this was the case, a 180 phase shift would almost certainly reduce the cancellation allowing the sub to run with less gain and less possibility of bottoming out.True, but that is not the way mrcoop presented it. He simply said:

I had mine on one phase and it was bottoming out, was told to switch the phase and no more problems.

To those of you voting "Critical:" could you please explain your experience, and why you feel a more precision phase adjustment was/is needed?

I have 4 subs and I have full control over them. tweaking phase changes my FR plots....some are better some are worse, I have been able to control some nulls and peaks with phase so its critical to my setup.

True, but that is not the way mrcoop presented it. He simply said:

I was pointing out the scenario where simply switching phase could have 'fixed' the 'problem'.

With no understanding of what was actually happening, it could just as easily have made the problem worse or had no effect at all...

I suspect Phase comes into play more often for people with a multiple sub system. I can see how one sub is not effected as much, you can move that sub around, tweak crossover and trim settings on it to obtain better FR plots before you play with the phase.

I was pointing out the scenario where simply switching phase could have 'fixed' the 'problem'.

With no understanding of what was actually happening, it could just as easily have made the problem worse or had no effect at all...Yeah, but the way he posted it didn't imply a recalibration. Only that flipping the phase stopped it from bottoming out which, on its own, makes no sense.

Is a Phase Control really all that important?

If someone were kind enough to do the plots you could see how much difference the phase can make. If you plot the FR while incrementally increasing the sub's distance setting (1 ft. increments) you would see some interesting stuff. With no real discernible pattern there, either.

I have no recent comprehensive FR measurements, but here is an old FR chart with my old subwoofer run with both of my mains.

The red FR plot is a base plot of my mains set to small FR with no subwoofer.

The other FR plots include both mains plus the subwoofer with incremental changes of the subwoofer distance in the receiver (1 foot changes).



Now, what do you make out of this mess? Do you see anything that is obvious?




http://i297.photobucket.com/albums/mm232/Red_Foreman/Subwoofer_Distance_Adjustment.jpg

Yeah, but the way he posted it didn't imply a recalibration. Only that flipping the phase stopped it from bottoming out which, on its own, makes no sense.

OK - I see what you're saying.

I was automatically presuming that a level check would be done after any change but that is not spelled out. Simply changing the switch would not stop the bottoming presuming overall volume setting was kept at the same level.

Now, what do you make out of this mess?Not much. Not that it will show anything, but can you just show <100Hz or so and adjust the dB range from -15 to -60? Thanks for posting this, btw.


Do you see anything that is obvious?Your mains do pretty well.

Not much. Not that it will show anything, but can you just show <100Hz or so and adjust the dB range from -15 to -60? Thanks for posting this, btw.






One of the things that combined mess shows is the prime crossover frequency. Look at 48 Hz. No matter how screwed up you set things, my speakers and room have a natural crossover at 48 Hz.

A second potential crossover frequency is near 60 Hz.

The second thing (more important) that can be seen is the polarity of the subwoofer is reversed from the proper setting. Observe the FR sweep above and below the 48 hz point. They sweeps are going in opposite directions above and below that point when you look at how the individual FR sweeps vary foot by foot.






Your mains do pretty well.




That is a blessing and a curse. An 80 Hz crossover just does not work that well. However, I can follow the HSU MBM setup easily since my mains go down to 48 Hz. Locate the subwoofer in the corner, crossover to the mains around 50 Hz, use the right bass management, and performance similar to that of the combination MBM speaker plus a subwoofer is there.

Next I crossed over to the subwoofer at 50 Hz, and then did the same type FR sweeps again with various distance setting (1 foot at a time). I used the True RTA quick sweep function at the time.


I then weeded out the "bad" looking subwoofer distance FR sweeps (AKA phase mismatch), and the following FR chart is what I ended up with. Violet is the FR chart for the main speakers with no subwoofer, and the red is the FR chart for both mains plus the subwoofer. The two sweeps match very well from 80 Hz on up.


Sweeps are 1/24 octave with no smoothing was applied. I used the TrueRTA quick sweep function.


Final touch up of the subwoofer distance setting was via test tones.




http://i297.photobucket.com/albums/mm232/Red_Foreman/Subwoofer_Distance_Adjustment_Selec.jpg

Those that consider it unimportant or not necessary either don't understand what it is or are in an environment where it is not required in their setup.That or we understand how to properly use the distance settings in our AVR's making it a crude and unnecessary adjustment. ;)

Here is my current setup measured at a different seating position. I used pink noise averaged 100 times. The red FR chart is for both main speakers, the orange FR chart is for the subwoofer, and the green FR chart is for both mains plus the subwoofer.


Crossover is at 50Hz, 1/24 octave, no smoothing applied, variable phase adjusted to 90 degrees, polarity in phase, best subwoofer distance setting selected, border EQ set to +3dB.


The mains are the same as in the above charts. The subwoofer(s) are the same as above (passive), but the subwoofer electronics are EQ'd and modified for a 20 Hz tune.


You can see room issues clearly, but they are not easily heard. I could clean up the chart for show with 1/3 octave smoothing, but the raw data shows all the problems.





http://i297.photobucket.com/albums/mm232/Red_Foreman/PinkNoiseSystemTest2009.jpg

That or we understand how to properly use the distance settings in our AVR's making it a crude and unnecessary adjustment.


Again, someone thinking that we have one sub to deal with....I wonder how you set the distance separately on 4 subs? ;)

Phase is important for people that have REAL SUB SYSTEMS!! :D The rest of you are just common folk ;)

Again, someone thinking that we have one sub to deal with....I wonder how you set the distance separately on 4 subs? ;)

Phase is important for people that have REAL SUB SYSTEMS!! :D The rest of you are just common folk ;)Duh... You get an external processor that lets you set delay and EQ separately for each channel. :rolleyes:

You can find some arguments against a phase control here (http://sound.westhost.com/project103.htm). In my set-up, I found that the best response was with the phase control set at 0° anyway, so when I recently re-built my sub I modded the amp to bypass the phase and crossover control.

Again, someone thinking that we have one sub to deal with....I wonder how you set the distance separately on 4 subs? ;)

Phase is important for people that have REAL SUB SYSTEMS!! :D The rest of you are just common folk ;)

You can either treat the multiple subwoofers as one entity and take measurements of the result, or you first examine the combination of the subwoofers at the desired listening area. Get the subs to play nice here, and then deal with the combination as one entity. While I still prefer to use delay or low passing on the subs arriving first, a variable phase control can be of use here. Of course it would be preferred to use this on the early arriving devices. You can then use distance/delay and crossover adjustments to best integrate the subwoofer with the individual main speakers.

It should be reminded that changing the crossover changes the effective delay in the sub vs. main speaker, making this another variable to get everything working together.

Also, I think it should be pointed out that the best phase setting is the one that provides for the flattest FR.

Some would say that the best phase setting is the one that peaks out the range of frequencies on either side of and including the crossover frequency.

Would you mind elaborating why you say that getting the flattest FR would be the correct setting???? I'm having trouble understanding it as it would seem that if you deliberatly delay a signal coming from your sub in order to induce cancellation, the combined duration of that signal from the sub and mains would affect clarity (duration,etc).

Some would say that the best phase setting is the one that peaks out the range of frequencies on either side of and including the crossover frequency.





You have it right. How flat the chart looks has nothing to do with correct settings. Just because a curve is flat does not mean any of the settings are correct. A flat looking curve could be the result of multiple errors in time or phase.

I might add that I learn little from an individual sweep. The simultaneous look at the multiple sweeps will tell you a lot more if you know what to look for. It is more of knowing what looks wrong rather than what is good.

I tend to evaluate subwoofer integration from 10 to 200 Hz (and higher). Then I always confirm settings by the use of my ears and test tones, then music, and then some nice action scenes from a DVD.