Critical subwoofer tip

I assume that everyone already knows the importance of phase matching a sub to the main speakers but it’s a little more complicated than simple 90 degrees or 180. The B&W sub that I have has four choices. In every case there has been a definite correct position that can be non standard. My current setup shined at 270 degrees vs the std positions. It’s completely obvious and the other choices would not have been satisfying. 
From my lengthy experience I would want a subwoofer with several phase choices. I personally don’t see how one could seamlessly integrate the mains and the sub without this flexibility. No one asked but i thought this info might be useful to anyone purchasing a subwoofer. YMMV
My subs have "infinite"-ish variable phase controls. Very glad to have this feature.
I assume that everyone already knows the importance of phase matching a sub to the main speakers 

Um, no. Not at all. Physical impossibility. Neural impossibility too. Absolutely positively zero chance this is important at all. None. 

Flies in the face of physics. Sound travels at a rate of about one foot per millisecond. The wavelength of sound varies tremendously by frequency, from as short as an inch at very high frequencies to 50 feet or more for low bass. Sound travels in waves. Waves are reflected, refracted (bent, diffused), or absorbed according to their wavelength and the size, shape and composition of whatever they encounter.  

Got it? Okay, so we play music all these waves start bouncing around the room. Forgot to mention, when waves meet they either cancel out or reinforce each other. Very important. Sounds silly basic but crucially important you understand these points.  

So a sub, it puts out 80Hz and below. Waves 20ft, 30 feet and longer. Most of these waves are longer than the biggest dimension of your room. What this means in practice is a low bass wave emanates from the sub, encounters a wall, and is reflected right back to the sub, all of which happens before even one wave is complete! The sub is canceling- or reinforcing!-  its own output!

This never happens with midrange and treble frequencies by the way. Unless your room is really tiny, like closet size, then you have other problems but not the cancellation/reinforcement problem.  

So you see it cannot possibly matter where a sub goes, at least not in terms of what you think, phase matching. No such thing. Impossible. You can see that now, right?

Next problem, neural or psycho-acoustics. Very low frequencies do not register as sound at all at anything less than a full wave. At 20 Hz that means 1/20th of a second to hear that frequency at all. We know a 20Hz wave is more than 40 feet long. You can look it up, I'm getting a little bored explaining all this for the umpteenth time. Point is, it cannot possibly matter where the sub goes for the simple reason your ears cannot even register its output fast enough to locate where it came from.

Even if you don't buy the science, which a lot don't. Most people talk about how they respect science, when really they go with whatever the most people are saying. In other words not thinking at all but following. This information will do you no good whatsoever if you are a herd animal, it is only useful for thinking beings.  

All thinking beings know from experience you cannot tell where the sub is located. If you somehow screwed this up come on over, happy to demonstrate. Everyone is shocked to look around and see FIVE subs randomly spread around the room, all pointing away from the center, all within inches of the wall. No idea whatsoever that any bass at all is coming from them.  

If phase matching mattered at all the bass in my system would be horribly chaotic. When in fact it is gloriously clean, articulate, and absolutely beautifully integrated with the midrange and treble.  

But only because I, unlike "everyone", understand the unimportance of phase matching subs.  

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Good points MC. I have always asked how you phase match a 64 foot wavelength with a one inch wavelength. Can't be done, except at one point at one frequency but you may not necessarily be matched on the leading wave if I'm visualizing this right.. Most will say it's ideal to be in phase at the crossover point but many speakers are not and it wasn't by mistake. 
i certainly don’t know the technical issues involved in matching a single pair of loudspeakers to one subwoofer. I do know this though. If you can adjust the phase setting on your sub there will be a best choice. That’s my experience. 
REW disagrees with what millercarbon is saying.

In fact, phase, crossover, loudness, and room position all have an effect on getting the best distributed bass out of the room.
Crossover and loudness don’t necessarily all have to be the same on any of the subs to achieve best performance. It takes several hours of testing and tweaking to make this happen (within the parameters - not too high or low for best integration with mains). This is without the aid of DSP.
The idea that reflections negate the need for sub phase matching is erroneous. However, it may be less important for those using DBAs, which (at least from what I’ve read) often run the subs somewhat out of phase with one another.

I have done measurements, and despite reflections, having a sub out of phase with the corresponding main speaker can give a broad and deep (and quite audible) null near the crossover frequency. This isn’t theory or possibility, it’s reality. It’s why expensive subs tend to have continuous phase (delay) controls on them.

phase cohesion is of course important. you want to make sure that the sound from the subs arrives at your ears at the same time as the rest of the music. You will need to adjust the phase to within less than a degree if you want perfect time coherence.

You dont need 5 subs in a small room. One is enough. More subs will take up more space and use more energy. Most of the bass will end up  cancelling the other subs. 

Smaller subs are faster as they have less mass. So they can accelerate more quickly. 

Cheaper subs are made of mdf but if you want the best, concrete cabinets are a must.

The best subs will start and stop instantly. The worst ones will ring like a bell long after the signal stops. 

perfect subs will give you clean bass everywhere not just in the sweet spot. 
Clearly in my 1 sub system phase matters not. Drove myself nuts trying to find the right phase, realized that it didn't matter. One man's opinion. 
The OP reminds me why I have completely given up trying to help people get good bass in a room.  Subs are hard to configure.  Get a preamp or receiver with ARC if you get a sub.


OP is specifically commenting about setting up Phase.

With the subs I have, this was the easiest part of the whole process.

Reverse cables on main speakers.
Play sine wave file with same frequency as subwoofer crossover (ie 50Hz). Turn volume up until SPL is 0db with SPL meter set to something like 80db.
Turn sub phase from 0 to 180 degrees one step at a time and the lowest db on SPL meter is the correct phase. I assume if there is a switch 0-180 you would just flip the switch and see which one has the lowest db.
Reverse main speaker cables back to correct position.
Just to be clear, you adjust the sub phase for your seating position, not the same phase as your loudspeaker but I'm guessing it's near the same thing. Unless you are sitting at a null point. Then the sub phase will be different than your loudspeaker. Agree?  
I spent over a month getting my pair of t7i's to even sound like they managed any semblance to bass response. I can assure you if they are completely out of phase with your mains it does make a difference! You want those subs pushing out and contracting at the same time your mains are. I know there's better terminology but I'm listening to Clapton while responding. It was a pain to get it right by ear but you'll be rewarded when you do. If phase wasn't important why would we have the ability to set them? why would there be mfgs designing then with servo auto driven phase adjustments? When I did what REL said and heard when it was audibly louder it was in phase and when you listen again from LP you'll know it. Still fine tuning but getting there and loving the ride!
@golfnutz, great way for adjusting the phase . I learnt it from Barry Oder .
I totally believe in adjusting the phase/timing  to the listening position for the sub and the mains . You can do the same with an av receiver by adjusting the subwoofer distance setting .
I use 2 subs jl audio 113v2 integrated with my magico m3. The rt sub is phase adjusted  to the rt speaker and lt to lt main ,  at the listening position. Changing the phase, the difference is very obvious  as the subs are placed in the optimal position using the crawl method .so the primary listening position is not a null.
I totally agree with the OP .
Don’t see how????
No imagination. Change the vertical and/or horizontal direction of the wave eminence. Avoid down firing configurations.
A phase switch is mostly a decorator option.
I am simply blown away by Millercarbon's knowledge.  He should be teaching at a university.  Fascinating conversation.  Can't believe people have more than two subwoofers.  

I did a lot of research before I purchased my subwoofers.  I was torn between a Rythmik and REL.  However, how can you buy speakers without being able to hear them.  What made sense to me was the high level connection design REL uses.  This allows the subwoofers to act more like large woofers to extend the bass of the two main tower speakers.  I think the trick is to make sure you do not play subwoofers too loud.  If you can detect them, they are too loud.  I read where subwoofers can take some of the load of the main speakers and allow them to play clearer.  Can't think of the correct terminology.  I went with two REL S2' SHO's rather than one think a pair would level out the room and create a more even sound stage.  

I have seen systems with 6 REL G1 Mark II's stacked 3 high on both sides.  To me this would mean there has got to be too much bass.  However, there must be a reason why some use 6 of these with moderate size tower speakers.  I would be curious to be able to hear what they sound like.  They must have the volume set really low.  I think in my case I think my tower speakers sound a little brighter, but I do not know why.  Someone told me adding subs help to take some of the work load off the main speakers so they can work more efficiently.  I know bass speakers draw most of the power.  Having active powered subs certainly are very efficient.  Wonder how all of this works.  Be curious to learn from Millercarbon how this works and why adding subwoofers really helps to even out the sound.  I think it must increase the size of the sound stage.  I would imagine Millercarbon must be a dealer.  He sounds extremely knowledgeable that's for sure.  So many people in this group are so knowledgeable.  However, at times some can respond rudely.  I think if they avoided the put downs it would allow people like myself to know how to ask the right questions without being criticized.

Hopes this makes sense.  It would be nice for this group to meet over a few glasses of wine and not only discuss, but be able to hear their sound systems so we could learn more in person.

Play this demo only with your subwoofer(s)

If you hear no difference when the phase is switched, the people who think phase does not affect LF sound are correct.

Alternatively, if you sense/hear/feel a difference, phase matters in LF too.

(Play this video full-range and phase change obviously affects spacial cues.)
I would imagine there must be a phase adjustment on my REL's.  However, I would not know where to start.  It would be nice if someone could teach us more about phase and how to set up subwoofers.  Now I wonder if I have mine set up correctly.  All I did was to make sure the volume on my subs were not too high.  When I began to be able to detect them I lowered the volume.  Mine are set at about 40% volume.  

Where can I read about this?  Even phase is a bit complicated.  I am sure it must be related to sound wavelengths and to be able to detect when the sound waves cancel each other out.  When do you know sound waves are canceling each other out in the first.

I am new to this hobby for about 2 years and am anxious to learn.  I have a feeling my system might not be set up at its peak performance.  How do you know when sound waves are cancelling each other out in the first place?

A dealer in town specializes in master setting.  Wonder why people in this group are not discussing this?  Perhaps they don't believe in master set?
The phase difference matters ONLY when it is compared to ANOTHER driver in the acoustic vicinity. It does not matter if the speaker is on its own, or it closely matches the OTHER speakers. In the absence of those, or when the sound from anything else is not significant enough with respect to the subwoofer, the phase angle does not matter.

It is all relative basically :-)

i agree that setup flexibility with a subwoofer is of utmost importance the level and phase can be a big factor in proper sound and mesh with the rest of the system as well as placement.
@larry5729, you really should start with level matching your speakers to your subs instead of just turning down the volume where you can barely hear your subs. At least this will give you a much better starting point for where the volume should be. You've spent all this money on subs, and you don't really know if you have them set up correctly. It's a simple process, and you only need a SPL meter and sine wave signal (free on internet).
Ugh, again...stop complicating things, and ditch any and all subs and buy speakers that do bass....subs belong in HT, and that is where they will stay in "my world". Its 2 channel audio, not 2.1.....
I have an advantage in that b&w’s simple set up software allows you to perform all parameters from your listening position. via laptop you can set phase, crossover and gain very quickly by ear. once dialed in it sounds like the main speakers have great bass as you truly can’t locate the sub’s position. without the laptop set up i’ve had as much trouble as everyone else. 

"However, at times some can respond rudely. I think if they avoided the put downs it would allow people like myself to know how to ask the right questions without being criticized."

You would have better odds at getting Pelosi, Schumer, McConnell, Trump, and AOC to choose between water or Ice Tea for a lunch meeting....

@newtoncr - you are correct, measurements should be from listening position, thanks for mentioning this. Also, I should have mentioned, the subs and main speakers should be level matched first.

@audioguy85 - I get it, there's some guy's that don't think subs belong in an audio system. I can respect that. However, adding subs isn't just about hearing sub bass, with multiple subs, and careful setup, you can get a much better distributed frequency response in the bass region without using an equalizer, or DSP. 
My sub has continuous level crossover and phase adjustments. It is right next to my listening position so very easy to adjust properly. Phase matters the least of the three but still matters and makes a subtle difference on the sound. Granted it is not easy to get tuned in in many cases especially where sub cannot be adjusted from listening position.
The more subs the more randomized the wave patterns are in the room which is a good thing and playing with phase an exercise in diminishing returns.
Funny to me how everything is a black or white issue. Phase either matters always or not at all.   Even fuses:  same deal. Yardda yadda yadda. I know. I know. Thinking is hard. Sometimes I try to think but nothing happens.

Level matching and setting the Phase are the simplest, providing your subs have the functionality. It's everything else that makes it more difficult in my experience. Room placement, selecting the correct crossover(s), and loudness (within the parameters of level matching) become much more harder when you start taking measurements. I tried adding a third sub the other day, and after spending 4 hours of trying to improve my frequency response, I was only able to match, never improve it (most times it was worse). So, I disagree, adding multiple subs and selecting what ever crossover sounds good doesn't mean it's better, you'll only know that if you take measurements. So not so black in white.
Agree about the measurements needed to do it right and get full value from a sub. I use a simple sound meter app and white noise for level and crossover but not enough alone for phase. Have to tune that by ear and only after the other two are dialed in. YMMV.
Good thread on a tough, often debated topic.  MC correct about ability to sense phase of say 20hz and 40ft wavelength using his numbers but two points.  First, thats the extreme case. For most folks xo is up say at 60hz.  So that means a wavelength of 13 ft  for room length.  At 80hz then 10ft is the length. That's real world and pertinent at the top of the sub's range.  Run in phase then, if overlapping some with mains, will produce a peak or boom (best not to use node here)  that will be corrected if the phase is rotated.  At 180 degrees it's a notch and we aren't bothered as much by missing freq.  So yeah, while MC seems theoretically correct at the lowest frequencies, in a modest room at a typical xo point, it could matter.  The OP didn't mention his room size.  The bigger, perhaps the more phase indeed matters.

Second, and this is a question that pertains to rotating the phase, but if a first harmonic is above the sub xo, say 120hz and is therefore played by the mains' low drivers, does our perception treat it as inferior to an in-phase harmonic?  This has prob been addresses ad nauseum in the speaker builder's threads for mid to tweeter crossover design.

Prob over my head now so I'll just sit back, spin some music and see what the group thinks.
Unlike millercarbon, I can switch the phasing of my sub and HEAR! the difference. If there was even an ounce of truth in his erroneous, chaotic statement, I could never hear a difference when I switch the phasing! 

Just an incredibly asinine statement that is SO easily proven incorrect!
Phase match is critically important for me when it comes to my Dual SVS SB16 ultra is like day and night 
The effects of adjusting phase can be easily measured from the listening position.
The effects of adjusting phase can be easily measured from the listening position.
I have a question for people who have phase controls for their subs. How do these work? 0 and 180 seems simple enough. Same thing as swapping the speaker leads. How is continuously variable phase control being accomplished though? Is this just a delay circuit? Is it an adjustable all-pass circuit? This is something I have struggled to understand and implement with my DSP module. 
That response from MC was absolute nonsense. For someone who perpetually lectures on the need to simply listen and let ones ears be the judge on whether a difference in sound can be heard from making changes, I find it incredibly ironic that he would claim phase adjustment does nothing in any setup. Sorry MC but you’re wrong. Perhaps in a DBA setup like his the phase adjustment provides a negligible benefit. That point I won’t dispute because I’ve never personally utilized a DBA in my own room. However, when using a single sub the phase adjustment absolutely does make an audible difference at the listening position. I have a JL E110 with continuously variable phase control and it’s a helpful tool for getting the sub to perform at its best. One just needs to shut their mouth and listen to hear the truth. 
An appropriate topic for me!

I just added the Martin Logan 1600X to my Classic 9 eStats. This subwoofer has all the adjustments you can think of via phone and tablets remotely.

I read the manual front to back. ML suggests (when pairing with their electrostats) to (through remote app.) INVERT the signal, and then dial the phase control to 90 degrees. I set all parameters to ’0’ otherwise and crossed it over with the 3rd order filter at 35Hz. I am really impressed so far.

Today, I await for the ’Bass Kit’ software to arrive. This sub connects to the laptop via USB and runs Anthem Room Control software. I will be eager to see what it comes up with. From the features, it can sample up to TEN positions at your LISTENING AREA. ...and then, once that is set, you can adjust the settings to your liking after the fact. (to taste, lol)

Can’t wait. Oh, and for the nay sayers on subs in 2 channel systems, I like the lowest octave of the symphonic bass drum when tuned low in orchestral music, and being a pipeorgan tech for the same company for 32 years, l sure want to experience those frequencies below 25 Hz. Now, how many PASSIVE stand alone speakers can really reach 16 Hz?

Right, therefore, a subwoofer is a great way to ’augment’ your 2 channel system when done properly.

Why else would Parasound put a point one on their P6 2.1 preamp with a built in LPF via balanced line?

Have a productive one my friends, and enjoy the music (O:
The effect of phase adjustment (or delay if you will) is clearly measurable if you do frequency sweeps around the crossover point. Setting the correct phase is much more important with a single sub, and less important to not important at all as you add additional subs.
Here’s some REW measurements I did today showing how changing the phase on the subwoofers effects frequency response.
This isn’t about how good/bad the subs/mains/room are.
No changes for volume or crossovers on the subs, phase only.
Descriptions in the images should be self explanatory.
The first image are the speakers, and basically my best attempt to get the frequency as flat as possible without using and EQ or DSP. The results are a combination of crossover/loudness settings and room position.
I tried adding a third sub yesterday, and couldn’t improve on what I have with two subs. Mind you, it’s only an 8"/150 watt sub, compared to 15" and 900 watts.

Setting the correct phase is much more important with a single sub, and less important to not important at all as you add additional subs.
Does it also become less important the lower you set your sub's roll-off point?  For example, I have two subs set to roll off at a pretty low 40Hz because of the low frequency extension of my main speakers.

If you're subs are hitting any frequency same as the mains, then it matters. It's either in-phase or out-of-phase, that is, the sub drivers are moving in the same direction as your mains. When they are out of phase, you run the risk of having frequencies cancel because the drivers are moving in opposite directions. There's lots of illustrations on the internet showing this.
Is there another way to figure out the optimum phase except to listen?  Maybe use an SPL meter at the overlap frequency, play the same program material at the same volume setting, and then set the phase at whichever setting achieves the highest SPLs?
Your suggestion is how lots of people try to figure out where to set the phase.

TAS suggests doing what you’re saying, but reverse your speaker cables so your mains are out of phase first. Using an SPL meter takes any guessing out of the equation, it's that obvious.

Here’s the reasoning sent by Rythmik in their setup sheet:

"Here’s what’s happening when you follow this procedure. By reversing the polarity of the main speakers, you’re putting them out of phase with the subwoofer. When you play a test signal whose frequency is the same as the subwoofer’s crossover point, both the sub and the main speakers will be reproducing that frequency. You’ll hear minimum bass when the waves from the main speakers and subwoofers are maximally out of phase. That is, when the main speaker’s cone is moving in, the subwoofer’s cone is moving out. The two out-of-phase waves cancel each other, producing very little bass. Now, when you return your loudspeakers to their proper connection (putting them back in-phase with the subwoofer), they will be maximally in-phase with the subwoofer. (It’s much easier to hear the point of maximum cancellation.) This is the most accurate method of setting a subwoofer’s phase control. Unless you move the subwoofer or main speakers, you need to perform this exercise only once"
New to this forum. Hello All. I would add this:  ybe happy if you can hear the difference cause tweaking the placement or the phase makes audible differences. No argument against science except this is empirical. There are those that can’t hear the difference and those that can. End of story. 
I have a question for people who have phase controls for their subs. How do these work?
see ieLogical SubterraneanHomesickBlues

Most Phase controls are All Pass filters. They don't affect all frequencies equally. see

To properly integrate a 'generic' sub controls for Level, Phase, Polarity, Crossover Hz & Order are required. Delay is icing on the cake. Bespoke subs mating to a specific set of mains may get by with fewer controls.

MC's response is nonsense. But I repeat myself.
Thanks @golfnutz I get it and their reason to listen for minimum bass makes sense.  I suppose with two subs, the method would be to measure and adjust each sub separately, one at a time.
Miller Carbon and all of you that are "amazed by his knowledge" need to come to my house. My Velodyne subs, like the OP’s, also have four selectable amounts of phase delay. If you can’t hear the differences in 0, 90, 180 and 270 degrees with your ears and see them on an spl meter, then you are deaf and blind.  This is a system with two subs rolling off above 40Hz and the loudspeaker pair running full-range.
While it would seem that getting the phase to match the mains is ideal, theoretically this isn't necessarily going to result in no peak or notch at the crossover point.  Not unless the slope of the cutoffs for both are the same.  For a mains woofer, in a cabinet, this isn't actively controlled and is prob more gradual than a sub.  Perhaps this is why best sound and SPL may be something other than zero.  It mitigates that complex interaction, peak or notch.  One of the advantages to wiring speakers to a (some) sub's speaker output and using its high-pass.   Also, distance from sub to listener vs mains to listener further makes this issue more complex.   Adjustable phase is an aid for both issues.  Good stuff on this (in discussions of tweeter to woofer xo designing) at Linkwitz Lab site.