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Does driver magnet have negative influence on induction coil?

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  • Does driver magnet have negative influence on induction coil?

    Elsewhere I saw a discussion about the positioning of induction coils on crossovers to reduce undesirable influences. Then as I am closing up the ER18DXT project I notice that it is a REALLY tight fit, with the tweeter magnet inserted essentially between the crossovers. What I don't know is the impact of such close proximity because, well, I don't know anything about that. But if a coil on a board can influence another coil on a board I've got to wonder about the magnet and driver coil.

    Are these influences something to be concerned about, or are they nonexistent/negligible.

    Below is the box on its side. Tweeter will go in front of the vent on the left. Very tight. The curved 0.5 box makes it very difficult to place the crossovers in the stuffed area behind the brace.



    Backside of the baffle, with drivers shown. (yes, I noticed the reversed polarity on the woofer before I closed it up. :D)


  • #2
    Re: Does driver magnet have negative influence on induction coil?

    Personally I put crossover boards outside the speaker cabinet to allow for tweaking and minimizing any potential interference from the magnet and iron screws.

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    • #3
      Re: Does driver magnet have negative influence on induction coil?

      i was actually just wondering about this issue too. never got around to posting. in an OS build i'm doing, the back of the woofer magnet winds up being about .5" away from the larger crossover coil. in the case of the OS, the b4n is a shielded woofer though. is it safe to assume that if this is an issue in the first place, it's less of one (or maybe not one at all) with a shielded driver?

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      • #4
        Re: Does driver magnet have negative influence on induction coil?

        .5" will definitely have an effect on the inductor.
        R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
        Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

        95% of Climate Models Agree: The Observations Must be Wrong
        "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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        • #5
          Re: Does driver magnet have negative influence on induction coil?

          .5" will definitely have an effect on the inductor.
          even with the shielded driver? oh well, there's no turning back at this point. and i've listened to them and they still sounded great to me, in spite of it. just one more thing to remember in the future, i guess.

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          • #6
            Re: Does driver magnet have negative influence on induction coil?

            It absolutely has an effect on the inductor. There should always be some space.

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            • #7
              Re: Does driver magnet have negative influence on induction coil?



              The smaller inductors are positioned incorrectly too: http://www.troelsgravesen.dk/coils.htm

              I would also apply a dab of glue or zip tie to those resistors to hold them in place.
              "He who fights with monsters should look to it that he himself does not become a monster. And when you gaze long into an abyss the abyss also gazes into you." Friedrich Nietzsche

              http://www.diy-ny.com/

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              • #8
                Re: Does driver magnet have negative influence on induction coil?

                That is the link I looked at AFTER I constructed the crossover that got me wondering about this. Yet another site suggested simply altering the plane with each additional coil installation, which I did.

                Here is a photo of Mark K's crossover set up, from his site. My coil arrangement seems similar to his. :



                Seems to me those big driver magnets are potentially the bigger issue. It is tight in there. I've got the thing wired so I can easily pull them out and run them externally, but then I have all those wires and an increasingly skeptical spouse. :D

                What kind of 'minimum' distances seem advisable. I expect that varies with the size of the coils and the driver magnets, but perhaps a rule of thumb?

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                • #9
                  Re: Does driver magnet have negative influence on induction coil?

                  Originally posted by absolootbs View Post
                  even with the shielded driver? oh well, there's no turning back at this point. and i've listened to them and they still sounded great to me, in spite of it. just one more thing to remember in the future, i guess.
                  Shielded drivers will have much less impact.
                  R = h/(2*pi*m*c) and don't you forget it! || Periodic Table as redrawn by Marshall Freerks and Ignatius Schumacher || King Crimson Radio
                  Byzantium Project & Build Thread || MiniByzy Build Thread || 3 x Peerless 850439 HDS 3-way || 8" 2-way - RS28A/B&C8BG51

                  95% of Climate Models Agree: The Observations Must be Wrong
                  "Gravitational systems are the ashes of prior electrical systems.". - Hannes Alfven, Nobel Laureate, Plasma physicist.

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                  • #10
                    Re: Does driver magnet have negative influence on induction coil?

                    my vote is for what ligs said, placed on the outside for adjusting but then that can also be something that can be presented well. Nothing like looking at a sweet crossover network all done nicely!

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                    • #11
                      Re: Does driver magnet have negative influence on induction coil?

                      For a while not only I placed the crossovers outside the cabinets, I even separated woofer crossover board from tweeter board per recommendations of Northcreek Music System. They have published a wiring guide for crossovers for $5.00, the only kind I know of.

                      The following is a link to their outboard crossovers for B&W speakers.
                      http://www.northcreekmusic.com/801web.html

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                      • #12
                        Re: Does driver magnet have negative influence on induction coil?

                        I try for outside xovers or active systems.


                        If I go active I use 1 inside protective cap on the tweeter most often 17-20 uf for an 8 ohm tweeter 40uf or so for a 4 ohm tweeter

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                        • #13
                          Re: Does driver magnet have negative influence on induction coil?

                          Here's another one of those "it depends" cases. If you look at the common orientations (ignoring the one that you just wouldn't do, one on top of the other, etc) the difference is less than +/-5% in Troels measurements. Small linear changes would result. In most cases this would be negligible. Depending on the exact orientation, and the place of the inductor in a circuit it might have a small effect on the FR curve.

                          Most components are rated with a 5% tolerance so it would be hard to get excited about this. Remember, depending on the exact orientation, it might have a positive effect on the FR curve.

                          The correct was is to measure the final product. If the FR curve meets the target, then it's fine, right?
                          audioheuristics isn't around right now...

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                          • #14
                            Re: Does driver magnet have negative influence on induction coil?

                            Many times I've found myself sweating a detail, beating it to death, endless research, getting into the increasingly fine points of distinction... Sometimes to the point of loosing sight of the actual/ultimate goal.

                            Then, a simple bit of advise from an experienced designer puts things back into perspective.

                            Thanks Mark

                            PS
                            It is when you find a problem in the final result that these tid-bits of information can be very useful.
                            Jay T
                            http://sites.google.com/site/lhwidgetssite/home

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                            • #15
                              Re: Does driver magnet have negative influence on induction coil?

                              Shielded drivers will have much less impact.
                              awesome, thanks pete. thats what i figured, but it's always good to hear from someone who knows. and i've read enough of this forum to know that, like mark, you're someone who knows.

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