Variable Phase Control -- Important?

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  • 4-iron
    Junior Member
    • Aug 2003
    • 13

    Variable Phase Control -- Important?

    Hello...

    I have a Carver TFM-35 (bridged mono @ 700 W/8 ohms) powering an Aurasound 1808 subwoofer (as previously mentioned in an earlier thread). This amp has plenty of power and is also equipped with variable output controls. But I've noticed that many of the subwoofer plate amps available today also feature a variable phase control (0 - 180 degrees). Since I've gone a different direction in choosing amplifiers, am I missing the boat here? How important is this feature?

    Related equipment:
    Lexicon MC-1 Pre/Pro
    Behringer DSP1124P equalizer

    Thank you,
    Paul
  • JonMarsh
    Mad Max Moderator
    • Aug 2000
    • 15259

    #2
    The variable phase control makes it easier to get good blending and balance in the crossover region, especially if the subs and mains are not placed ideally/correctly in relation to each other- i.e., sub about the same distance from listening position as mains.

    Personally, I've never used a plate amp sub setups, using discrete high power amps as in your case, but I'm sure the extra ease in setup doesn't hurt. But what I've generally found is that more than a phase control is needed if there are problems in integration. Most often it's due to the sub rolling off by itself aournd 70 -80 Hz, (especiallly the high Xmax long VC drivers like HE-15, Bluprint BPD XX03 series, etc), and what's usually really needed is an EQ system on the sub woofer before the crossover.

    Plate amps don't got those, more's the pity.

    Regards,

    Jon




    Earth First!
    _______________________________
    We'll screw up the other planets later....
    the AudioWorx
    Natalie P
    M8ta
    Modula Neo DCC
    Modula MT XE
    Modula Xtreme
    Isiris
    Wavecor Ardent

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    Calliope
    Ardent D

    In Development...
    Isiris Mk II updates- in final test stage!
    Obi-Wan
    Saint-Saëns Symphonique/AKA SMJ-40
    Modula PWB
    Calliope CC Supreme
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    Janus BP1 Sub


    Resistance is not futile, it is Volts divided by Amperes...
    Just ask Mr. Ohm....

    Comment

    • Hank
      Super Senior Member
      • Jul 2002
      • 1345

      #3
      4-iron, since I'm the simple-minded guy here, I'll give you my simple answer. The phase control is intended to allow you to get a sub "in-phase" with your main speakers. Speakers that are out of phase will tend to cancel, actually reduce frequencies that are out of phase. The closer to 180 degress out of phase two speakers are at a specific frequency, the more that specific frequency will be cancelled/reduced. For subs/mains, such a potential problem would be frequencies around the sub/mains crossover region, and would manifest itself as a response dip in that area.
      Personally, I don't think it's too big a problem. In your case, let your ears be the judge - don't worry about fixing a non-problem. Do you hear a void around the sub/mains xover frequency?

      Never mind, while I was typing that, Jon answered you.

      Hey, I have a plate amp on my Tempest sonosub and it sounds great. My novice opinion is that a "high quality" power amp doesn't help the sound of a sub over and above a plate amp, if your plate amp has decently low distortion/transient response and you don't crank it up to clipping. I have more plate amps in the garage awaiting subwoof customers, so don't burst my bubble here.

      Comment

      • ThomasW
        Moderator Emeritus
        • Aug 2000
        • 10934

        #4
        Paul

        I don't think in most situations that it's a major issue. I've been using subs since the mid 1970's and never needed one.

        If you want to play with one, the Paradigm X-30 active XO ~$130 has variable phase, unfortunately the XO slopes are only 18dB/octave




        theAudioWorx
        Klone-Audio

        IB subwoofer FAQ page


        "Complicated equipment and light reflectors and various other items of hardware are enough, to my mind, to prevent the birdie from coming out." ...... Henri Cartier-Bresson

        Comment

        • JonMarsh
          Mad Max Moderator
          • Aug 2000
          • 15259

          #5
          Hey, I have a plate amp on my Tempest sonosub and it sounds great. My novice opinion is that a "high quality" power amp doesn't help the sound of a sub over and above a plate amp, if your plate amp has decently low distortion/transient response and you don't crank it up to clipping. I have more plate amps in the garage awaiting subwoof customers, so don't burst my bubble here.
          Hey Hank, I'm not necessarily up for any buble popping! But you know, it's just like the whole thing of separates versus receivers. Back in the 70's, I found that my highly modified Dyna ST400 with 100,000 uF of supply capacitance in electrolytics, plus 200 uF in polypropylene films, would pretty much clean the clock of any commerical amp we had in our store for comparison- this included Stax 150W/channel class A, Luxman 300W/ch AB amps, etc. It simply had a lot better control, dynamics, and sense of ease, including in the bass and deep bass; I attribute a lot of that to the power supply mods; transformer was stock Dynaco.

          If you look at plate amps, and their construction re power transformers and bypass caps, they are built to a price point, not really a performance point. They work well for what they cost, but if I ramped up the bypass capacitance and doubled the output transistor complement in any of them, they would sound better, not just louder.

          Of course, I have the same feeling about most of the so called pro amps that are used for high power HT subs; same power supply issues usually exist. Now, at medium to lower levels, you may not hear much difference; maybe none. But when you put the petal to the metal, that's when it comes into play. BTW, ThomasW still has some old Innersound SP300's I designed in the late 70's; they still do a pretty credible job, but then they too have ~ 80,000 uf in the power supply.

          OTOH, I get pretty nice sound in my bedroom with just a Sony reciever and a pair of M8 MkII's. I'm sure a plate amp on a DPL 12 box I've built wouldn't be an unwelcome addition. It's all a matter of expectations and the performance level one wants to win up at. Plate amps are great value these days- relatively low cost, and good performance.

          ~Jon




          Earth First!
          _______________________________
          We'll screw up the other planets later....
          the AudioWorx
          Natalie P
          M8ta
          Modula Neo DCC
          Modula MT XE
          Modula Xtreme
          Isiris
          Wavecor Ardent

          SMJ
          Minerva Monitor
          Calliope
          Ardent D

          In Development...
          Isiris Mk II updates- in final test stage!
          Obi-Wan
          Saint-Saëns Symphonique/AKA SMJ-40
          Modula PWB
          Calliope CC Supreme
          Natalie P Ultra
          Natalie P Supreme
          Janus BP1 Sub


          Resistance is not futile, it is Volts divided by Amperes...
          Just ask Mr. Ohm....

          Comment

          • 4-iron
            Junior Member
            • Aug 2003
            • 13

            #6
            Hello...

            I went with the Carver amp for a couple of reasons. The first of which was easy -- I already had it! I've been a fan of Bob Carver's designs right along from the early years. I bought this amp new and after retiring it to the closet shelf, I knew I would use it someday for just this sort of task. Secondly, I also believe in robust power supplies and felt the Carver unit was a major step up compared to a typcial plate amp

            I made a vented sub using a 12" Shiva and plate amp last year for a family member and it turned out pretty nice. Notwithstanding, I felt it ran out of fuel as the pedal started to approach the floor-board. ;(

            So, with your comments in hand, I don't think I'll worry too much about the phase control anytime soon. As you can imagine, I don't have a lot of placement options with a 340 L cabinet, but I can do a little. I'm excited to get the most out of the recently added Behringer EQ too, but I'll need to rely on more than just my ears for that. Now, it's time to start looking at some measuring equipment!

            Thank you again for your comments.
            Paul

            Comment

            • Dennis H
              Ultra Senior Member
              • Aug 2002
              • 3791

              #7
              Variable phase is a bit of a misnomer on those plate amps. They are really allpass delay networks. See Linkwitz' filters page for an explanation of how they work. While they have 0-180 marks on the dial, that's only approximate and they are really delaying the signal X milliseconds. Now that's all well and good if your sub is closer to you than your mains. You can delay the sub signal a little and get it in phase. But if, like most of us, the sub is farther away than the mains, delaying the sub signal more only makes the phase problem worse.

              Comment

              • Hank
                Super Senior Member
                • Jul 2002
                • 1345

                #8
                Jon, I believe in quality power amp circuits. I'm running my two side surrounds with my Hafler 220 that I built from a kit severl years ago. I replaced the stock electrolytics with some Sprague electrolytics that they sent me as samples. I won't tell you how big they are, but I had to re-mount the amp cover to raise it an inch or so. I have another kit that I've started to mod - I replaced the stock bridge rectifier with 4 Harris ultra-fast soft recovery jobs.
                Yep, plate amps are definitely designed to a price point, but I think that below a 60 to 80 Hz crossover region they sound plenty good for 98% of the ears that hear 'em.
                Hmmm...think I'll have a cerveza and make some MDF dust in the garage.

                Comment

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