• 10-27-2004, 03:09 PM
    vr6ofpain
    Phase switch on subwoofers...
    I have always wondered what the purpose of the phase switches that are on most powered subwoofers.

    They usually have two positions, 0 degrees and 180 degrees. Am I correct in assuming the 180 degree switch simply is setting it up out of phase(like swapping the positive and negative leads to the speaker)?

    What would be the purpose of this? Does it actually allow it to blend better with some systems?

    I have always listened to a sub I have setup in both positions, but have always found the change is sound very minimal if any, so I have always set them to 0. Let me know if I am totally off track with my perception.
  • 10-27-2004, 07:09 PM
    spacedeckman
    That's about it
    sometimes it's noticable, sometimes it isn't.
  • 10-27-2004, 09:29 PM
    Lensman
    Quote:

    Originally Posted by vr6ofpain
    I have always wondered what the purpose of the phase switches that are on most powered subwoofers.

    They usually have two positions, 0 degrees and 180 degrees. Am I correct in assuming the 180 degree switch simply is setting it up out of phase(like swapping the positive and negative leads to the speaker)?

    What would be the purpose of this? Does it actually allow it to blend better with some systems?

    I have always listened to a sub I have setup in both positions, but have always found the change is sound very minimal if any, so I have always set them to 0. Let me know if I am totally off track with my perception.

    Here's how I understand it:

    The idea of the switch is to get the sub and your satellites in phase with each other at the crossover point. The phase control reverses the movement of the speaker cone for any given signal. This means is that when the cones on your satellites move out, then the cone on your sub should also move out. So in fact, reversing the phase is rather like reversing your speaker cables, except there's no clear right and wrong way to wire the sub (hence the do-it-yourself switch).

    If the sub and satellites are in phase, you should hear a little bit better, fuller bass. If they're out of phase your satellites will be pushing air out, while your sub is sucking it in, thus they would tend to cancel each other out around the crossover point. Hitting your phase switch puts them back in line, so both push air out at the same time, thus reinforcing the bass. Because it's just around the crossover point where your satellites are cutting out and your sub is kicking in that both are producing the same frequencies, the difference between the in and out of phase sound can appear slight.

    There's probably some decent test disk out there for adjusting phase. But alternately, you can play an audio source and turn the bass control all the way up and the treble control all the way down. Listen to the system with the phase switch in one position and then the other. One should provide you with more bass. Leave the switch in that position.
  • 10-28-2004, 04:12 AM
    kexodusc
    Yeah, it gets even more fun when subs have variable phase adjustment dials...I think this feature is far more valuable in systems that require the sub be connected directly to the amp's left and right speaker outputs (with speakers connected to the sub) rather than the LFE output...with a crossover point at handled by a receiver, the impact phase switches have seems to be quite diminished.

    And correct me if I'm wrong, but speaker and sub signal delay settings can impact phase alignment heavily too...so you could be inadvertently undermining the receivers job at calibrating your system if you play with it too much.

    As you can see, properly integrating a subwoofer into a system isn't easy by any stretch...IMO, this is why so many systems with subwoofers sound bad...it's not that the sub is crappy, it's the cut-rate installation job - human error.
  • 10-28-2004, 10:52 AM
    Lensman
    You had to go there...
    Quote:

    Originally Posted by kexodusc
    Yeah, it gets even more fun when subs have variable phase adjustment dials...I think this feature is far more valuable in systems that require the sub be connected directly to the amp's left and right speaker outputs (with speakers connected to the sub) rather than the LFE output...with a crossover point at handled by a receiver, the impact phase switches have seems to be quite diminished.

    And correct me if I'm wrong, but speaker and sub signal delay settings can impact phase alignment heavily too...so you could be inadvertently undermining the receivers job at calibrating your system if you play with it too much.

    As you can see, properly integrating a subwoofer into a system isn't easy by any stretch...IMO, this is why so many systems with subwoofers sound bad...it's not that the sub is crappy, it's the cut-rate installation job - human error.

    Yeah, the variable phase switch is there because the sub may not be uniformly in or out of phase with the satellites (for a variety of reasons including delays) at or near the crossover point. It can even be out of phase with the satellite closest to it, but in phase with the one on the other side of the room.

    The center and surround channels further complicate things because they may not actually be in phase with the left and right mains above the bass range. Since there’s no phase control on them, you just have to hope they’re already in phase with the mains. A lot of people talk about the importance of timber matching, but having a good phase matchup between the all the surrounds is another point in favor of having matching speakers all around. Of course, if you’re using dipoles for your surrounds, they’ll always have at least one set of drivers in each unit out of phase with something else, somewhere.

    It’s enough to make anybody’s head spin, so it's easy to understand the human error. It’s just fortunate that when the phase is wrong, the dip you get at or near the crossover frequency is usually pretty hard to hear. :rolleyes:
  • 10-28-2004, 11:12 AM
    kexodusc
    Now I'm no expert
    Quote:

    Originally Posted by Lensman
    The center and surround channels further complicate things because they may not actually be in phase with the left and right mains above the bass range. Since there’s no phase control on them, you just have to hope they’re already in phase with the mains. A lot of people talk about the importance of timber matching, but having a good phase matchup between the all the surrounds is another point in favor of having matching speakers all around.

    ...but I don't think phase is really an issue between satellites...assuming the signal is emitted from each channel at the right time, the distance between speakers is more than a few inches, and the drivers are connected properly (ie: in phase), I think the only way to have something out of phase would be to have two speakers facing back to back?

    My limited understanding is that above 80 Hz or so, as the wavelengths decrease substantially and each sound becomes even more directional, the phase impact becomes negligible, hence the integration with the sub being the only real challenge.

    Eventually doesn't it just get to be more of a delay/spl effect rather than cancelling out frequencies effect?

    Lord knows if it was that big an issue, there'd be a zillion products on the market offered at every electronic store.
  • 10-28-2004, 06:31 PM
    Lensman
    Quote:

    Originally Posted by kexodusc
    ...but I don't think phase is really an issue between satellites...assuming the signal is emitted from each channel at the right time, the distance between speakers is more than a few inches, and the drivers are connected properly (ie: in phase), I think the only way to have something out of phase would be to have two speakers facing back to back?

    My limited understanding is that above 80 Hz or so, as the wavelengths decrease substantially and each sound becomes even more directional, the phase impact becomes negligible, hence the integration with the sub being the only real challenge.

    Eventually doesn't it just get to be more of a delay/spl effect rather than cancelling out frequencies effect?

    Lord knows if it was that big an issue, there'd be a zillion products on the market offered at every electronic store.

    Let me start by saying I'm no expert on it either. Too much interest in audio and a lack of gobs of money to buy really nice gear just has me reading a lot. Very sad really...

    Again, here's my understanding of it, and by all means, anyone who understands this better and sees errors, please correct me. Delay and varying SPLs do indeed have a significant effect on sound. But phase is also important and not just on the low end. Just reverse the wiring on one of your mains. Obviously, out of phase bass can sound weaker and less powerful. But out of phase midrange can suffer as well. When the speakers are in phase the sounds that are equal in both speakers will appear to come from somewhere in between the speakers. Out of phase, the voices and sounds that are the same will sound like they are coming from two separate points near the speakers. It does make less of a difference as the frequency gets higher because the wavelengths get so short the phase can actually change when you move your head as little as an inch.

    In an ideal universe, correctly wired speakers playing the same sound will always move in and out together. But there are numerous ways speakers can get out of phase. (For example, take two drivers producing the same sound with different cone excursions. The cones will start by moving in and out at in unison. But over time will get more and more out of phase. Then they'll work back into sync.) For these reasons, most higher end subs have variable phase dials selectable to seemingly random points between 0 and 180 even though logic would indicate a cone that moves in or out should only be in phase or out of phase, and not some strange point in between.

    Though some amplifiers also have phase controls, there's really no single fix for all the ways phasing can get out of whack. And it really isn't a big thing as long as the speakers are generally in phase. But it is possible for combinations of different types/makes of speakers to be out of phase enough of the time to become noticeable and negatively impact the sound. This is one reason folks recommend matched systems. A JMLabs dealer I visited just a few weeks ago even goes so far as to recommend buying identical center channels to use as the center and left and right mains for best results.

    As you point out though, phasing isn't something that bothers a lot of people. Some people go for years without noticing their setup has phasing issues. I've heard of a rare few who even prefer the sound and intentionally wire things out of phase.
  • 10-29-2004, 04:01 AM
    kexodusc
    interesting....
    With the subs, I understand the variable phase dials...it's not as simple as being in or out of phase, there's varying degrees...take two sign waves for example, and superimpose them...then move one to the side ever so sligthly...the phase dial allows you to bring it back to the ideal point. A phase switch might not accomplish this.
  • 10-29-2004, 09:01 AM
    s dog
    2 subs
    Quote:

    Originally Posted by kexodusc
    With the subs, I understand the variable phase dials...it's not as simple as being in or out of phase, there's varying degrees...take two sign waves for example, and superimpose them...then move one to the side ever so sligthly...the phase dial allows you to bring it back to the ideal point. A phase switch might not accomplish this.

    A saleman told me that the phase dial really comes in to play when running to subs is this ture. I have alway wanted to run two subs just never got around two it
  • 10-29-2004, 09:15 AM
    kexodusc
    Slow down...
    Quote:

    Originally Posted by s dog
    A saleman told me that the phase dial really comes in to play when running to subs is this ture. I have alway wanted to run two subs just never got around two it

    First, I'll answer this question...Yes phase dial COULD be handy when running two subs, depending on their relative positioning...

    But from someone who has used 2 subs in a system, I would strongly recommend you invest in a Parametric Equalizer, attempt to correct any room acoustic difficulties you may have, or buy a better sub than buying 2 subs in most cases. Unless your room is absolutely huge, or you can buy 2 subs at a lower price than 1 sub while acheiving the same sound quality.

    I just found 2 subs added SPL (volume), but really, it made more obvious any peaks or drops in frequency response. There wasn't any "stereo" image effect added. Usually, for less than double the money, you can get double (or more) the power, and a more competent woofer with lower resonse and better accuracy. This would be the best way to go in most circumstances.

    ...although it was pretty cool at a few parties to have the bass booming like a 17 year old kid's Honda Civic. :)
  • 11-03-2004, 09:20 AM
    Richard Greene
    Phase control not much more useful than polarity switch
    When listening to full-range music, a continuous phase control produces an effect about the same as a (0 - 180 degree) polarity switch (often mistakenly called a phase switch).

    Assuming you can hear the effect of a phase control at all, you're unlikely to hear anything other than the extreme settings (0 and 180 degrees) while listening to music.

    You might hear the effect of a continuous phase control when playing a sine wave frequency at or near the turnover frequency ... but that's only relevant if you frequently listen to sine waves.

    The correct setting of a polarity switch or phase control is the setting that results in the flattest bass frequency response measured at your seating position with a slow sinewave frequency sweep or seperate sinewave tones spaced no more than 1/6 octave apart.

    If the only choice you have is between too much bass SPL or too little bass SPL at and near the turnover frequency, your ears will probably prefer too little bass (easily overlooked while listening to music ... while too much bass is easily heard)
  • 11-10-2004, 07:48 PM
    mjon99
    Lensman what is a test disk? I'm not familiar with them.
  • 11-10-2004, 11:49 PM
    Lensman
    Quote:

    Originally Posted by mjon99
    Lensman what is a test disk? I'm not familiar with them.

    If you've ever played around with the THX Optimizer on a lot of DVD movie disks, you already have a basic idea what test disks do. Basically they provide calibrated audio test tones and video patterns you can use to adjust your TV and sound system for optimal performance. Though similar to the THX Optimizer, test disks are much more detailed and provide more (and more accurate) calibration options. You can make detailed adjustments for things like black and white levels, saturation and color on your TV, as well as phasing and volume on your sub and satellites. Test disks can be quite useful for determining not only the best settings on your A/V equipment, but also help with environment issues such as lighting, speaker placement and room acoustics.

    Crutchfield provides some more details on what the Avia test disk does:

    http://www.crutchfield.com/S-Am6o82r...info&i=555AVIA

    Here's what Amazon carries - and they have customer reviews:

    http://www.amazon.com/exec/obidos/tg...&s=electronics
    http://www.amazon.com/exec/obidos/AS...746591-5593453
    http://www.amazon.com/exec/obidos/tg...v=glance&s=dvd

    There are about half a dozen different test disks available, but the Avia and Video Essentials disks are generally considered to be the two heavy hitters.

    Stereophile Magazine also sells a number of test disks for audio systems.

    To calibrate your speakers, you'll also want to employ the use of a sound pressure level (SPL) meter. The most commonly used one is available from Radio Shack:

    http://www.radioshack.com/product.as...t%5Fid=33-4050

    Here's a couple of links about this widget:

    http://www.audiophilia.com/hardware/spl.htm
    http://www.hometheaterforum.com/htfo...211#post231211

    Using a test disk and SPL meter can consume a lot of time, and individual adjustments can seem pretty minor. But taken all together, the before and after performance difference in your A/V setup can be quite substantial.
  • 11-11-2004, 05:09 AM
    mjon99
    Thanks for the info Lens. I'm definitely going to look into both of them.
  • 11-12-2004, 04:00 PM
    Quagmire
    I think the issue with subwoofers and phase is that often, subwoofers use a dual voice coil driver which makes it possible for the sub to be out of phase with regard to the rest of the speaker system. That is why most subwoofers have only two settings -- 0 or 180 degrees. One or the other position should correct the phase problem because it is electrically created due to the wiring of the dual coil driver. I suppose subs which offer continuously variable phase switches may be attempting to correct for other conditions which could conceivably effect phase.

    As far as the rest of the speakers... so long as they have been correctly wired "In Phase", the electrical phase problems associated with dual voice coil drivers will not apply. The only other conditions which could cause them to be out of phase would be if speakers were placed at such dramatically different lengths from the listener and one another that it could not be corrected for with delay settings, or... that the lengths of electrical wiring used to the some of the speakers (the surrounds for example) were so much longer than the wiring to the rest of the speakers, once again creating a condition for being electrically out of phase. This is very unlikely.

    Q
  • 11-20-2004, 09:05 PM
    Lerxst
    Phase
    Phase is a complicated issue. Having been involved in a dialog with the designers of my speakers, which are multi-driver monstrosities, I can confidently say I don't understand it a bit better. And I got an A in physics. However it is a function of not only polarity, but also crossover design (Legacy Audio tells me my mids are out of phase with the tweets, and two of the woofers are out of phase with the other one... by design... all in one cabinet) not to mention length of speaker cable, distance from the speaker to the listener, and cosmic karma coefficient. Some amps also invert phase in the output stage. You will give yourself a headache trying to cogitate it. Bottom line: have someone flip the phase switch (or knob) while you're sitting in the listening position, and set it by ear. No brain cell death involved.