Phase angle
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Silver Member Username: James_the_godDoncaster, South Yorkshire England Post Number: 481 Registered: Jan-05 | Simple question here for a subwoofer. Varying 0-180 degrees, is 0 degrees in general faster and more precise where 180 degrees is more 'boomy'. Any phase angle explanation would be nice because theres not much stuff on the internet giving a solid definition of how to use it. I currently use a 0 degrees angle. Thanks |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 10477 Registered: May-04 | . Whose sub has a "phase angle" switch? Phase angle is a product of passing the signal through passive crossover components, i.e. large capacitors and inductors. Most powered subs have active crossovers for the low pass/high pass filter. These sort of active filters generally do not induce severe phase angles and can typically be considered phase neutral, the signal comes out in phase with the signal coming in. If the active crossover or amplifier reverses the phase of the signal, it should be noted by the manufacturer though this would be extremely rare since reversing the connection at the driver during assembly resolves the situation. The "phase" switch on most subs is for relative phase to the main speakers. Which position you choose is relative to the placement within the room of the sub in relation to the low frequency driver of the main speakers and your ears. The switch positions should sound slightly different as you are taking the frequencies shared by both systems through the crossover region in and out of phase with each other. This would be particularly so if the sub's active crossover has a rather shallow filter of no more than 12dB per octave or a second order filter. Steeper, sharper low pass filters (24dB) will roll out the upper frequencies more dramatically and have less effective crossover frequencies shared by both drivers. So, if one position sounds good with the speakers and sub in one location, moving one of either of the two tranducers will place the system further out of phase with the other until eventually the alternate position of the phase switch will sound more correct. Since phase between two drivers spaced widely apart is relative to frequency, the switch only places a narrow band of frequencies "in phase" and one position might sound good with one piece of music while another recording might benefit from the other switch position. If the sub is not placed in the immediate vicinty of the main speakers, the effect of the phase reversal switch will likely be more dramatic, particularly so if the sub has shallow LP/HP filters. . |
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Silver Member Username: James_the_godDoncaster, South Yorkshire England Post Number: 482 Registered: Jan-05 | Erm. Thankyou.  I appreciate that lengthy reply but some of that went right over me. I understood most of it though, although its a lot to take in. The subwoofer is infact my subwoofer with a 'switch/phase pot'. I hardly have the volume up on it at all, it adds enough low end impact to satisfy me, its the fact of wanting the bass to be tight as possible. I learnt a couple of weeks ago that my setting of 95hz crossover was way too high, its now at its lowest setting of 40hz. Bass is much tighter and blends in better. Im sorry I cant relate to your post much its quite confusing, what I can say is my sub is in the vicinity of my speakers, its in between them. I guess I'll keep the phase at 0 degrees because its always been this. I try the other angles and cant notice much a difference, perhaps pyschological mostly. |
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Gold Member Username: NuckPost Number: 7417 Registered: Dec-04 | Hey, JJ, you asked, you got. The 24bd/octave filter, a Linkwitz(4thorder) filter is, in my opinion the most effective, but in many ways the most unforgiving. A First order filer/XO is more direct, but absolutely unforgiving if you need time coherence. In a single driver arrangement(like a sub) you can drive the unit in either manner, but to make sinle driver 'fast' you have to give some things away. As usual. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 10479 Registered: May-04 | . Placement will affect the perception of "tight" bass. If you haven't worked on the best position for the sub relative to the room, you might get better results by doing a Google search for "subwoofer placement" and spending some time moving the enclosure and your listening position around the room. Remember that where you sit will largely affect the degree of tightness, fullness and extension to the low frequencies. Where you sat when you had only the satellites might not now be the best position for low bass response. Any time the low frequency driver is placed in the center plane of the room, the driver excites room problems equally and boom can increase. You are likely better off placing the sub close to one particular speaker rather than between both. Low bass is almost always mixed to mono and your perception of where low frequency instruments are in the soundstage is taken from the higher frequency harmonics of the low bass fundamental. Therefore, this shift in enclosure palcement shouldn't change your perception of where the bass is at in the staging. Each placement decision is a tradeoff between "this" benefit and "that" disadvantage but I've often found tighter bass by getting the sub off the floor to about one third the height of the room. Find the best position for the sub on the floor and then try raising the sub off the floor. I assume the main amplifier doesn't provide for any low frequency roll off of the main speakers. If there is a roll off allowed by the main amplifier, set it to remove the lowest bass frequencies from the satellites. If there is no roll off allowed by the main amplifier, the main speakers are reproducing low frequencies also covered by the subwoofer. Due to the physical distance between the satellite's low frequency driver and the subwoofer's driver, there will be some time smear over the region where both drivers are sharing the same signal. You might find better results by running your mains off the high pass side of the speaker outputs of the subwoofer rather than directly off the amplifier. I would suggest you set the phase switch to 0° and try placement of the sub fore and aft relative to the mains to find the best sound quality. Place the sub at the base of the main speakers and slowly move the subwoofer enclosure forward and backward, only changing its position relative to the main speakers and your ears while listening for the best blend between sub/satellites. I find this sort of proper placement to be more effective at blending subwoofers than using a phase switch/pot to compensate for less than ideal placement. Of course, where the sub sounds best for timing might not be where it works best in the room. This is the purpose of the phase switch/pot, to compensate for the difference in physical distance closer to or farther away from your ears between the main speakers and the subwoofer. After you've heard the sub placed for proper phase/timing with the mains, this is the sound you should try to replicate if you have to move the sub away from the best position for timing of the bass. If you have a variable pot instead of a simple 0° - 180° switch, you will have more control over placement issues. However, whether your sub provides a switch or a variable pot, the two drivers will never be entirely in phase at all frequencies unless they share the same physical space. This is impossible when a separate subwoofer is used (with the lower crossover frequency, as you have found, the less obvious this difference will be) so you should listen to a wide variety of music while making phase adjustments. If you listen to recordings with heavy studio production, the actual phase of all instruments might never be in "absolute" phase from top to bottom. As I said, one recording might sound best with the phase set to 0° while another recording might sound best with the phase control advanced a bit forward. If none of this makes much sense, get some assistance from your dealer. They should be able to provide after the sale service on the subwoofer. Do you know the amount of roll off provided by the subwoofer's low pass/high pass crossover? 6dB? 12dB? Or more? . |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 10480 Registered: May-04 | . Just to clarify, with a second order (12dB) low pass filter on the sub, the roll off of frequencies passing through (the filter and) the sub will only be down 12dB one octave higher than the frequency you set on the sub. 12dB is considered sufficiently down in level to be inconsequential but it is all the frequencies between where you set the crossover and where it finally falls off that you are concerned with. Assuming the crossover actually is set at the frequency you specify (which is rare, it is typically higher than you think), with a 40Hz setting, the sub will be reproducing a signal that would be considered audible at 60Hz. If your main speakers are also reproducing this frequency, the two main speaker's bass drivers will not be in phase with the subwoofer's driver. With a setting of 95Hz, the subwoofer would be reproducing frequencies up to almost 200Hz which is well within the range of the human voice. If your main speakers are ported, their low frequency roll off will be a fourth order filter of 24dB per octave. If they are tuned to have a bass response to approximately 50Hz, they will be reproducing audible bass signals in a typical room down to about 35Hz. If the speakers are a sealed enclosure type, the low frequency roll off is 12dB and a speaker tuned to 50Hz will have audible bass response in a typical room down to approximately 25Hz. If you are trying to get the tightest bass response, you should remove from the satellites the frequencies both the sub and the satellites share and assign those signals to only the subwoofer. . |
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Gold Member Username: John_aLondonU.K. Post Number: 4695 Registered: Dec-03 | Jan;- Jeez, you always know so much. This is an education! JJ and Jan;- From the first post I think your sub, JJ, has a continuously variable phase potentiometer, from 0 to 180º. If so, the the answer to your question is probably "just suck it and see". Which you have. Me, I'd choose "faster and more precise" at 0º. Probably at 180º you are getting constructive interference at low frequencies, which makes the whole sound boomy. If this is the case, then you could then be getting destructuve interference at 0º, and might try 90º which could give more bass will retaining the focussed sound. However, the ideal is to get no duplication of frequencies by the sub and the mains by choosing an appropriate crossover frequency. If you set the crossover so there is overlap, you can probably get some idea of which settings give in-phase and out-of-phase just from how loud the bass sounds. I would guess that the in-phase setting, i.e. 180º might give better results when the two sources are not competing with each other to deliver the same frequencies, i.e. when the crossover is set so that the sub gets what the mains do not or can not reproduce. All the complexities of room reflections and delays, plus the large mass and inertia of say, a 10" electromagnetic driver, mean there is no single solution anyone can predict in advance. I guess the phase angle control is there to let the user tune the sub to the rest of the system, by ear, in the real listening room. Hope that helps. |
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Silver Member Username: James_the_godDoncaster, South Yorkshire England Post Number: 483 Registered: Jan-05 | Nope that all made sense. It took a few re-reads of some parts. I shall say though that I've found I am happy with this new phase angle, of around 35 degrees. (wheres the degrees key on a keyboard?). I cant explain why its better, I can hear the bass more BUT its not a boomy more. Plus it blends in more. It'll be staying as it is now, Im totally happy with the system. Thankyou for the information! I now have just under one month before I move rooms and my bookshelf speakers are infact gonna have to be placed nafftastically  . Either one on a windowshelf and one on a mini stand on top of a cabinet, or wall mount both of them..the walls are hollow :S. If I had it my way, the room would be designed very differently but then I dont own the house! Shame. Things I should know about wall mounting into hollow walls? |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2170 Registered: Sep-04 | In fact, I had been playing with this just a couple of weeks back. My sub only has a 0/180 degree switch. It's not infinitely variable. My room has a huge 40hz bass resonance mode and my main speakers go all the way down to 26hz easily. Therefore they can excite the room very easily indeed. I tried adding the sub for stereo duties and messing about with the switch to see whether it could negate the effect of the main speakers, but the lack of an infinitely variable phase angle meant that it didn't have much effect on the overall result. Eventually, my end result was to use the sub/sat setting and lower the output on the sub in order to get a relatively balanced sound. It's not as pure a sound since the signal's going through the DSP circuits of the processor, but it's a better compromise overall. Regards, Frank. |
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Gold Member Username: John_aLondonU.K. Post Number: 4696 Registered: Dec-03 | Thanks, JJ. Re-reading my post, I'm not sure I understand it, either... Thanks for that post, Frank. |
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Gold Member Username: NuckPost Number: 7430 Registered: Dec-04 | Made sense to me, John. Then again, that hangover... |
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Silver Member Username: James_the_godDoncaster, South Yorkshire England Post Number: 489 Registered: Jan-05 | I have to be curious here Frank. If you're speakers go to 26hz easily, is there a real need for a subwoofer lol? Because if they go down that low I wouldnt think there to be much a frequency db drop. |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2174 Registered: Sep-04 | JJ, Indeed, that's the problem. My speakers are -6db at 26hz. My room has a strong bass resonance between 30hz and 80hz. I say between 30 and 80 because according to measured responses I once did, the in-room response of my speakers is quite high in that region, varying from higher than you'd want at 30hz to even higher with a peak at 40hz and then slowly lowering to about the same level as the rest of the frequency range above 80hz. The higher frequencies in-room response is sensible. I had hoped to negate the bass response by introducing negative phase courtesy of the sub, bringing the response down to something sensible. Since I only have a 0/180 switch on my sub my adjustment was limited. I can oly assume that the phase angle of my speakers is somethign around 90 degrees since flicking the switch made almost no difference whatsoever. Since my wife, who gets the brunt of the blast in her place on the couch, has problems with bass at the best of times, I wanted to effect some kind of solution. I decided to try using the processor's power and set it so all frequencies below 90hz are sent to the sub. I then balanced the sub at a much lower value in order to match neatly with the speakers such that she gets a balanced response. It's a slightly light response for me, but it is far better balanced than the unfiltered version. So in fact, here I am with what I consider to be a really rather expensive solution and expensive set of speakers and yes, I really do need a sub so that the output can be controlled! Crazy? Yup. I have considered an alternative approach such as bass traps and diffusers. This is actually a better approach acoustically since it treats the room and the results should be effective wherever you are in the room. However, my room is just 13'6" by 11' and the short wall behind the main speakers is one big bay window (curtains are allowed and work wonders on the midrange). Bass traps and diffusers are not small things so they would impose significantly on the room. It's still an idea I'm considering, especially if I go back to high end 2-channel stereo (a distinct possibility), but for now the balance works well. I can easily switch on the 'Direct' button when she's not around, but to be honest I don't bother because I prefer a slightly light bass to an overly heavy one. I hope this make sense. Regards, Frank. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 10497 Registered: May-04 | . Frank, you intentionally placed speakers with a strong bass response down to 26Hz in a 13' X 11' room? Why? Were you aware of the room's problems before you did this? "I can oly assume that the phase angle of my speakers is somethign around 90 degrees since flicking the switch made almost no difference whatsoever." That makes no sense to me. At 90° electrical phase angle, whether positive or negative going, you would be driving a purely inductive or capacitive load. And that degree of phase shift would be within a fairly specific frequency range that falls outside of the speaker's passive crossover's affect in almost all speakers. Where would such a phase angle come from in these speakers? What sort of voice coil is on your speakers? Assuming this is the way your speakers manage deep bass, why not try moving the sub to accomodate the out of phase signal? I don't think even a pair of Quads or Apogees ask an amplifier to deliver the amount of current/voltage drive a 90° phase angle would present. How about you heard no difference due to the length of the sinewave you were trying to throw out of phase and the room dimensions that don't allow proper wave propagation. I would think in that room a good pair of monitors would make more sense, which is what you now have with the mains having no low bass ouput beneath a 90Hz high pass filter. I know this sounds harsh, but why did you do this? Did you have these speakers before you had this room? "Since my wife, who gets the brunt of the blast in her place on the couch, has problems with bass at the best of times, I wanted to effect some kind of solution." If you cannot fit passive devices into the room I would think you would choose to go active. http://www.behringer.com/DSP1100P/index.cfm?lang=eng Parametric EQ is the best solution I've found for such room problems. "Purity" of the signal be damned! You're talking about a few octaves of bass response and fixing the rather large problems of the room. I cannot remember ever coming across the concept of "negative phase" being introduced in the manner you've suggested. That is a bit like putting a BandAid on an amputated leg. Everything I've seen that attempts negative phase cancellation is digitally driven, very fast and far more frequency specific than a subwoofer being added to the room. Sorry, Frank, but I'm a bit astounded at this. . |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2180 Registered: Sep-04 | Blimey, I've astounded Jan! The original room I had these speakers in was actually a touch shorter at 11'6". The bass wasn't nearly as prominent there as in the current room, although it was still a bit fat. I agree that it's unlikely to be a 90 degree phase angle (positive or negative) but it's got to be a fairly major angle to make so little effect on the negation which, although not common, is still a valid approach. If you don't want to mess around with DSP, this can be a rather elegant solution. Moving the sub is not an option. It's a relatively small room and there are only two locations where the sub can live as the room's fairly full. That said, I have tried it in various unacceptable locations as well, with similar results in each case. This makes a certain amount of sense since bass frequencies are meant to be omni-directional. As it happens, the two acceptable locations are actually at bass nodes. Going active doesn't necessarily fix the problem. First of all, there are very few active speakers so one is already reducing one's options by choosing to go active. 2nd of all, active operation does a similar job in terms of splitting the frequency responses as passive. You have far lower distortion but adjustment tends to be fairly coarse (bass and treble). This is why DSP is preferable, but DSP is no panacea since it introduces its own digital nastiness to the equation. You thought correctly - I do have a good pair of monitors! I have Totem Mani-2 Signatures. Typical monitors are pretty lifeless. I prefer some life over 'perfect sound' any day. The Mani-2s are really gorgeous speakers. They are a very difficult load (which indicates a high phase angle) and require 200wpc to drive them well in my opinion, so I guess they are in the Apogee ballpark (Quads are easy to drive) when it comes to load. As to the design of the Mani-2s, they're an isobaric ported speaker, a 4 ohm load (dipping to under 2), 85db/w/m, 4khz crossover (not sure what order), the main drive units are 6.5" Dynaudios with 3" voice coils. I searched for over 3 years for speakers I liked more than my Audio Note AN-Es and the Mani-2s were it. I may yet change them (had them for 2 years now) and if so I will obviously choose a speaker which has a more appropriate bass response, but it'll take a lot to beat the Mani-2s, simply because they're such involving speakers. Regards, Frank. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 10514 Registered: May-04 | . I meant active room treatment as in parametric EQ, not active speakers. I'm in favor of simple signal paths but also in favor of clean response by effectively dealing with room problems. Since we are talking about just a few octaves of bass response I think I would have preferred some judicious EQ as the simplest way to fix the problems. "Direct" still could bypass the EQ if you just must have the simple signal path. Granted DSP is sometimes audible in its effects when less expensive approaches are applied but untreated rooms are always audible. I think I will choose to disagree with how "elegant" the solution is. Adding yet another low frequency driver to the mix when the room is already overloaded with too much bass energy seems to me to be stuffing 10 lbs. of potatoes in a 5 lb. bag. Unless the drivers occupy the same physical space, they can never be sufficiently in phase to negate the type of room problems you are hearing over more than a narrow band of frequencies. I just don't believe I've ever heard of anyone succeeding with the approach your took. So, crossing to the sub at 90Hz doesn't present other problems? Does the sub you chose have any parametric EQ functions? . |
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Gold Member Username: Frank_abelaBerkshire UK Post Number: 2181 Registered: Sep-04 | Ah, I see. No, I tried a couple of bass traps (40hz and 80hz) in the room. They not only didn't really do much in the only two places I could put them, but they were awfully big to boot. If they had been successful, they'd have stayed. I have a feeling doing more would be very intrusive in the room. The solution I proposed (and which didn't work after all) should have worked at the frequencies we are talking about. The operating range of my sub (an MX7000SF) is well within the 40 - 90hz range. In theory, since the bass frequencies are omni-directional, the proximity of the sub to speakers is immaterial so long as the sub to listener distance is approximately the same to that of speakers to listener, which is the case. this is why I came to the conslusion that it was the phase angle of the speakers that was far enough out from the 0 or 180 degree point to cause little difference with the sub. Crossing at 90hz allows me to lower the output of the sub enough to arrive at a balanced result. The whole 30hz - 80hz range causes me problems and this is borne out by the measurements I took. I don't need paramteric equalization, though that could improve the situation further. With what I have, all I need do is control that section of the frequency range with the lowered output of the sub. Luckily, the sub is sympathetically timbred to the Totems so it's not an obvious addition. Regards, Frank. |
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Platinum Member Username: Jan_b_vigneDallas, TX Post Number: 10516 Registered: May-04 | . Well, Okey-Dokey then. Happy listening, Frank. |
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Gold Member Username: NuckPost Number: 7470 Registered: Dec-04 | Luckily, the sub is sympathetically timbred to the Totems so it's not an obvious addition. And that, friends, is the best that we could hope for. |
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