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Subwoofer shorting rings really necessary?

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  • Subwoofer shorting rings really necessary?

    As I was reading up on a few things, I found an interesting article about shorting rings and whether or not they are beneficial in subwoofers. I've no idea whether or not the site is a credible builder, but he references Eminence (a credible builder in my book) as his source. The article can be found below, but here is an excerpt from it:

    "I had originally asked Eminence to investigate the possibility of putting a shorting ring into a subwoofer to reduce harmonic distortion... ...Eminence found that they were unable to get significant distortion reduction below 150Hz from a shorting ring. The reason is pretty simple - The shorting ring works like a transformer winding, and it has to inductively couple enough energy to create a magnetic field large enough to offset the difference in force caused by flux modulation. As frequency goes down, this becomes harder and harder to do and the size of the ring becomes prohibitively large. The volume displaced by the ring makes magnet size smaller so more magnet has to be added to compensate and the requirements become a vicious cycle. So there just isn't enough "meat" to make a good flux stabilized subwoofer.

    Now, I think I understand the basic principles involved with a shorting ring and the positive effects it can have on a driver. Most often as a quantifiable result, it reduces inductance in the driver. The ring counteracts the eddy currents and flux modulation induced by the voice coil as it moves through the magnetic field. I'm sure there is much more to it than that, but if I am off point, please correct me.

    Hi-dollar wiz-bang drivers almost always have some sort of shorting ring in them nowadays. For midranges, mid basses, wide ranges, and woofers asked to play above 150 hz, I suspect the rings are effectively utilized. But for subwoofers? Has the industry and implementation of shorting rings evolved in motor structures advanced to the point the they are effective? Or are shorting rings just another feature on a checklist that is expected in a "quality" driver, so MFG's put them on despite the postulation that they don't really do anything in the frequencies that most subwoofers play (100hz and down)?

    What do you think?
    Last edited by Blenton; 03-17-2018, 12:00 AM.

  • #2
    One of the problems of finding some empirical evidence for one's self is how do you find two identical drivers, one with and one without shorting rings?

    One question I have about that finding from Eminence is whether they used aluminum or copper. IINM, copper works better, as the better conductor of electricity will also set-up the stronger magnetic field from the inductive coupling.

    Second question is where they placing the ring. There are 4 possible places, assuming the gap is left alone, you have above the gap, on the ID and/or the OD of the voice coil former, and below the gap, also on the ID and/or OD of the voice coil former. So the part about "The volume displaced by the ring makes magnet size smaller so more magnet has to be added to compensateleaves some questions unanswered.

    Just because Eminence has not found a way to get significant (as per their definition) reduction in distortion <150Hz, doesn't mean another company hasn't made headway. I know B&C, 18 Sound, Faital Pro all use demodulation rings in [some of] their larger bass drivers.

    Here are some articles .

    An alternative approach to minimize Inductance and related Distortions in Loudspeakers.

    The Effect of Faraday Ring (Shorting Ring) Usage on Voice Coil Impedance and It's Benefits

    The new JBL Symmetrical Field Geometry and Flux Stabilized Magnet Structures

    Optimization of demodulation rings in professional loudspeakers

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    • #3
      Originally posted by guitar maestro View Post
      Just because Eminence has not found a way to get significant (as per their definition) reduction in distortion <150Hz, doesn't mean another company hasn't made headway.
      With drivers used full range, which is often the case in pro-sound, shorting rings are going to have a lot more effect than when they're used as subs. The physical size required of a shorting ring to be effective above, say, 500Hz is going to be far smaller than one effective below 150Hz. A key phrase in the 18Sound document is 'distortion affecting mainly the vocal range'. Full range drivers work into the vocal range, subs don't. The other issue with pro-sound subs is that most THD is likely to be sourced from mechanical low frequency compression, the result of driving them at and above xmax. Reducing non-linearity of the voice coil Le won't affect that.
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      • #4
        Originally posted by billfitzmaurice View Post
        With drivers used full range, which is often the case in pro-sound, shorting rings are going to have a lot more effect than when they're used as subs. The physical size required of a shorting ring to be effective above, say, 500Hz is going to be far smaller than one effective below 150Hz. A key phrase in the 18Sound document is 'distortion affecting mainly the vocal range'. Full range drivers work into the vocal range, subs don't. The other issue with pro-sound subs is that most THD is likely to be sourced from mechanical low frequency compression, the result of driving them at and above xmax. Reducing non-linearity of the voice coil Le won't affect that.

        I completely understand your point. Can you offer some insight as to why some top-tier pro audio subs are using shorting rings?

        Examples:

        B&C - sw152-8
        18 Sound - 21nlw9600
        Faital Pro - 18XL1800

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        • #5
          Because some people will run them up to 500hz or even higher.
          Don't listen to me - I have not sold any $150,000 speakers.

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          • #6
            Originally posted by johnnyrichards View Post
            Because some people will run them up to 500hz or even higher.
            Well then that contradicts what Bill had said about "Full range drivers work into the vocal range, subs don't.", now doesn't it.

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            • #7
              There's no hard rule that says you have to use a "subwoofer" as such. It's just a lable. Cross a woofer at 80hz, is it now a subwoofer, no what I mean?
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              • #8
                Originally posted by 6thplanet View Post
                There's no hard rule that says you have to use a "subwoofer" as such. It's just a lable. Cross a woofer at 80hz, is it now a subwoofer, no what I mean?

                Yes I was already fully aware of that.

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                • #9
                  Originally posted by guitar maestro View Post

                  Well then that contradicts what Bill had said about &quot;Full range drivers work into the vocal range, subs don't.&quot;, now doesn't it.
                  Not really.
                  Don't listen to me - I have not sold any $150,000 speakers.

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                  • #10
                    Originally posted by johnnyrichards View Post

                    Not really.
                    It sure does.

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                    • #11
                      A driver marketed as a "sub woofer" is intended to be used below 100Hz. And when used as a "sub woofer" then by definition, it is not being used into the vocal range.

                      However, a "sub woofer" that uses shorting rings might very well be capable of good performance well beyond its intended range. The RSS subs from Dayton are those kinds of transducers. They're designed to be used for lowest octave reproduction. Their TS parameters indicate that design parameter. However, they employ shorting rings and have exemplary performance well beyond 100Hz and can easily be used as woofers too.

                      A subwoofer is not just the transducer. It is the combination of transducer, enclosure and low pass filter that defines it ultimately as a subwoofer.
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                      • #12
                        Originally posted by guitar maestro View Post
                        It sure does.
                        ​You need to understand it in context. Any reduction of distortion is a good thing, regardless of the woofer. But is the shorting ring absolutely necessary in the sub bass region? Certainly doesn't hurt a manufacturers sales pitch proclaiming lower distortion and such. If it matters to you then go for it.

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                        • #13
                          https://www.youtube.com/watch?v=kQFKtI6gn9Y

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                          • #14
                            Originally posted by guitar maestro View Post
                            It sure does.
                            Nope.
                            Don't listen to me - I have not sold any $150,000 speakers.

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                            • #15
                              ​I'm glad at least someone around here (you) has a sense of humor! I watched the entire skit. And this my friend, is post 6500 for me.

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