Driving one VC of a dual VC sub (DPL12)

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  • sfdoddsy
    Senior Member
    • Sep 2000
    • 496

    Driving one VC of a dual VC sub (DPL12)

    I've been reading and getting a little confused by some of the info at the Adire site. If I read it right, by driving just one voice coil on the sub, I will increase the Qes and thus the Qts, raising it to 0.8 or so. Does it double?

    And this increase in Qts would result in a peak in the response at around about Fs.

    Can anyone confirm this?

    Thanks

    Steve




    Steve's DIY Dipoles
    Steve's OB Journey
  • Jack Gilvey
    Senior Member
    • Aug 2001
    • 510

    #2
    If I read it right, by driving just one voice coil on the sub, I will increase the Qes and thus the Qts, raising it to 0.8 or so. Does it double?
    Theoretically, I believe so, although I've not tested it. That's how I run mine at the moment, although I've used various resistors to play with different Qes/Qts values.

    And this increase in Qts would result in a peak in the response at around about Fs.
    Not necessarily a peak (unless the in-room response was already flat), but I do get better low-end response, increased output/shallower rolloff approaching Fs. Linkwitz considers this method of counteracting dipole rolloff "crude" and much prefers active eq.

    Here are some further observations on RDO operation from Deon B in answer to my question:

    http://www.hometheaterforum.com/htforum/showthread.php?&postid=1582103#post1582103

    Comment

    • sfdoddsy
      Senior Member
      • Sep 2000
      • 496

      #3
      Thanks Jack.

      Would I also be correct in assuming that to short the unused voice coil I simply run a wire from positive to negative, and that running like this doesn't affect the Qts?

      Cheers

      Steve




      Steve's DIY Dipoles
      Steve's OB Journey

      Comment

      • JonMarsh
        Mad Max Moderator
        • Aug 2000
        • 15282

        #4
        Shorting the unused VC would probably not be a desirable thing to do. It would be akin to shorting unused windings on a transformer, and expecting the other windings to be unaffected. The shorted winding will act as an electromagnetic brake on the driver, EVEN when it is being driven. It will also act like shorted widing on a transformer, and as frequency and drive increase, the effective coupling (and shorting/shunting) will increase also.


        You can do a real simple experiment to investigate the effect of playing with the load on one VC, in either dipole or sealed box, by tapping the woofer cone (say, in the center of dustcap) lightly, with the VC open, then doing the same thing with it shorted.

        The problem with adjusting the "Q" by not using one VC is that you throw away power handling and sensitivity higher in the frequency range, and still need the same net power for a given output lower down- you've just changed the "natrual response" of the system.

        Now, in my other thread, I advocated selection of drivers for a closed box system to optimize the alignment, preferrably to one which could achieve desired results without EQ in this particular system I'm working on. But there were no VC's left unconnected or speakers damaged in this scnenario... :W

        In the case of a dipole system, I think I can see a little more justification for this approach, as electrical power handling is rarely the limit, while cone excursion (which isn't limited by number of VC's) generally is.

        So, while in some regards I agree with Sigfried on this one, I can also offer (for dipole use) a dissenting opinion. But then, I'm the bozo working on an all passive crossover dipole system, so what the heck do I know? :??

        I do know that I don't like scads of opamps in my signal path any more than Charles Hansen does... (well, OK, maybe I'll tolerate one or two carefully selected ones, but not if I can avoid it- I've even designed a non loop feedback LF equalizer to work in this system when it's finished, single ended and balanced inputs and outputs.)

        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

        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

        • sfdoddsy
          Senior Member
          • Sep 2000
          • 496

          #5
          Thanks again for your erudtion Jon. I wasn't thinking of it for my dipoles, but for my sealed 142L monopole sub, the thought being that the change in Qts would act a bit like a Linkwitz transform.

          Checking Unibox, I would get an F3 at 18Hz, which seemed pretty good.

          Steve




          Steve's DIY Dipoles
          Steve's OB Journey

          Comment

          • JonMarsh
            Mad Max Moderator
            • Aug 2000
            • 15282

            #6
            And an F3 at 18 Hz is pretty reasonable, and in that large a box, electrical power handling isn't an issue- you'll be excursion limited at relatively modest powers. Can you say, "IB equivalent"? :W But where do you find the room to have several of them? That's why I was sort of interested in a dual DPL12 design for each side of my line array- with optimum positioning in room, can pick up six dB from back and side wall, and tune for fairly flat to 22 with very slow roll below that.

            But shorting a voice coil would work directly against that; it would be like having an amplifier connected to cone voice coil with no signal. You don't want low impedance sources opposing each other...

            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

            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

            • sfdoddsy
              Senior Member
              • Sep 2000
              • 496

              #7
              It's just an LFE sub, and for rear and center bass. The mains are run full range.

              Steve




              Steve's DIY Dipoles
              Steve's OB Journey

              Comment

              • Jack Gilvey
                Senior Member
                • Aug 2001
                • 510

                #8
                Another option is to leave both voice coils unwired. That results in the ultra-tight, stops-before-it-starts bass so beloved of many an "audiophile".

                Comment

                • Brandon B
                  Super Senior Member
                  • Jun 2001
                  • 2193

                  #9
                  Originally posted by Jack Gilvey
                  Another option is to leave both voice coils unwired. That results in the ultra-tight, stops-before-it-starts bass so beloved of many an "audiophile".
                  I thought the best way to do that was to wire the VCs out of phase? In case of stray wind currents in the room trying to move the driver.

                  BB

                  Comment

                  • JonMarsh
                    Mad Max Moderator
                    • Aug 2000
                    • 15282

                    #10
                    Yeah, Brandon, I think you've figured out that one; then also, if someone by mistake powers up the LFE amp, it remain locked solid... :W

                    just the ticket for totally musical bass, especially if you enjoy the sweet sounds of silence...

                    ~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

                    • sfdoddsy
                      Senior Member
                      • Sep 2000
                      • 496

                      #11
                      So if I reverse the phase on the subs and then turn them to face the other way, will the music stop before it starts?

                      I'm really getting the hang of this wiring stuff.


                      Steve




                      Steve's DIY Dipoles
                      Steve's OB Journey

                      Comment

                      • sfdoddsy
                        Senior Member
                        • Sep 2000
                        • 496

                        #12
                        Jon (or others),

                        Getting back to dipole operation, would I be correct in thinking that even if one raised the Q of the driver, and hence had a shallower roll-off requiring less active EQ, that the overall volume capabilities of the driver are not going to improve?

                        In other words, there is a finite volume limit for a given driver that combination of fiddling with the ratio of Qts and EQ is not going to change?

                        Cheers

                        Steve




                        Steve's DIY Dipoles
                        Steve's OB Journey

                        Comment

                        • Hank
                          Super Senior Member
                          • Jul 2002
                          • 1345

                          #13
                          I've even designed a non loop feedback LF equalizer to work in this system when it's finished, single ended and balanced inputs and outputs
                          Yeah, baby!

                          Comment

                          • JonMarsh
                            Mad Max Moderator
                            • Aug 2000
                            • 15282

                            #14
                            Steve,

                            Yeah, though the Q, roll off slope, and senstivity will change, the basic mechanical properties don't, so volume capability, based on Sd X Xmax, remains the same. Whether for dipole or monopole, for the DPL12, this is the ultimate limitation below 30Hz. Still, I think the DPL12 is a very nicely balanced driver design, especially for the DIY person that doesn't want to get into too much external EQ and whatnot.

                            Hi Hank,

                            Well, the beauty of my silly little balanced differenital gain cell, is that whether you want single ended inputs or outputs, or balanced, the whole circuit is there, working as a unified system (necessary for distortion reduction and basic operation), so one get's the goodies basically for free... The Ayre power amps and preamps are the same way- one fundamental balanced differential amplifier with differential (balanced) outputs. You just hook up what you need, and EQ is done by a RC networks in the transconductance stage, which tailor the output load impedance versus frequency, instead of using just fixed resistors, which would give you a flat, fixed frequency gain. For LF EQ, it's very simple, unless you wanted some peaking high Q gain, and if one does, then there's probably something a bit odd about the LF system anyway...

                            The whole idea is to do minimum damage to the music signal. If ONLY LF was running through it, no problemo- opamps would be fine. But since this is an "EQ Box" for what will otherwise be a full range, passive crossover (contrarian that I am), then I get more concerned. Unfortuanately, this "simple" circuit, once you've put in all the regulation and support to ensure it works open loop really, really cleanly, does have a lot of support stuff, and takes up a moderate size PCB- here'a a scan of the bare PCB, prior to assembly...





                            Yes, we do make more than CAD drawings at "Casa de Juan"; now and then we actually build hardware- this is the same module used in my homemade DAC's, going into a 2nd generation of construction.

                            But as Infineon's director of smart power development in Munich, Dr. Jeno Tihanji says, (and frequently), "Slow work takes time". Sure wish I had one of those sweet retirement deals Siemens was handing out to a lot of folks in their 50's back in the late 80's, early 90's; I coudl get a lot more USEFUL stuff done!

                            ~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

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