Critical subwoofer tip
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. |
@mapman 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. |
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. |
@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. |
"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.... |
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. |
@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). |
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 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? |
Play this demo only with your subwoofer(s) https://youtu.be/kUT6ZhFdLkA 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 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. |
@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 . |
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! |
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. |
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. |
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. |
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. |
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. |
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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. |
