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Subwoofer shorting rings really necessary?

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  • Blenton
    started a topic Subwoofer shorting rings really necessary?

    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.

  • guitar maestro
    replied
    Originally posted by billfitzmaurice View Post
    It doesn't look to have a positive effect within the driver pass band. The opposite, actually.
    I agree, not in terms of distortion measurement, but the FR graph and listening tests do show extended high frequency response.

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  • billfitzmaurice
    replied
    It doesn't look to have a positive effect within the driver pass band. The opposite, actually.

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  • guitar maestro
    replied
    Originally posted by Blenton View Post
    guitar maestro - interesterting. Would you happen to have the FR plots for the same driver wired with and without the AIC?
    Yes, just look up my thread on the testing of the 10" monster midbasses. I posted it all there.

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  • Blenton
    replied
    guitar maestro - interesterting. Would you happen to have the FR plots for the same driver wired with and without the AIC?

    Leave a comment:


  • guitar maestro
    replied
    So I was thinking about this the other day when I was measuring my 18 Sound 10NDA610. I found it very interesting that with the AIC coil connected in parallel as intended, the low-end distortion byproducts were reduced drastically.



    The difference goes away by the time you get to 100Hz, but now I'm wondering if different coil would provide the distortion-reduction characteristics in the bass-region for woofers/subwoofers, in the same way that shorting rings provide for the upper frequencies in other speakers. Obviously this speaker would never be used at such low frequencies, so it's not like I'm gonna experiment with it. It was just a "Hmm....would you look at that...." kinda moment.

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  • billfitzmaurice
    replied
    I'd say that Le becomes an issue starting around 150Hz, and gets more problematic as you go higher. I wouldn't use it above 100Hz, if that high, that's not what subs are for, especially those with such a long xmax. I suspect that if you took it to 200Hz or more at high excursion that modulation distortion would be more of an issue than non-linear Le.

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  • guitar maestro
    replied
    Originally posted by billfitzmaurice View Post
    Look at the impedance chart for the driver, Le is only what I'd call significant where impedance is at least twice Re.

    Based on this and the chart



    The light gray scale division are 2ohms. Re is 3.09Ω, so impedance goes above 6ohms right around 100Hz. Therefore it's your take that if this speaker is X'over above 100Hz, that the rings would be a benefit, correct?

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  • dlr
    replied
    One thing it does is reduce eddy currents in the metal in the pole-piece gap which is a function of coil displacement. It reduces that portion of non-linear distortion. Lowering the impedance change with frequency is an additional benefit. That impedance change can vary with displacement, so the interaction with the crossover will vary with displacement. That's another form of non-linear distortion.

    dlr

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  • Pete Schumacher
    replied
    Isn't the amount of inductance changing with excursion the cause for distortion?

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  • billfitzmaurice
    replied
    Look at the impedance chart for the driver, Le is only what I'd call significant where impedance is at least twice Re.

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  • guitar maestro
    replied
    Originally posted by billfitzmaurice View Post
    Still, the THD created at 100Hz due to non linearity of Le for the lack of shorting rings isn't going to amount to diddly, as there's not enough inductive reactance present at 100Hz for the shorting rings to make linear.

    Bill would you go as far as to say that the massive aluminum shorting rings in the new Peerless/Tymphany superwoofer won't amount to much if you LPF it at say 200-300Hz? Or would they make a difference at that point?

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  • billfitzmaurice
    replied
    So 1% THD of a 100Hz signal with its midrange components will be more noticeable than 1000Hz with the same level of THD.
    True, because it's the ear is a lot more sensitive at the frequencies of those harmonics that make up the THD than they are at 100Hz, but they're not more sensitive to the harmonics of 1kHz than they are to 1kHz. Still, the THD created at 100Hz due to non linearity of Le for the lack of shorting rings isn't going to amount to diddly, as there's not enough inductive reactance present at 100Hz for the shorting rings to make linear.

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  • Pete Schumacher
    replied
    Harmonic distortion of low frequencies is probably a little easier to hear than harmonic distortion of higher frequencies simply because our ears are attuned to the midrange. So 1% THD of a 100Hz signal with its midrange components will be more noticeable than 1000Hz with the same level of THD.

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  • Blenton
    replied
    Want a second or third opinion about your speaker cabinet design or other audio related problem? Post your question or comment on the Technical Discussion Board. Hundreds of technicians, engineers, and hobbyists, nationwide read and discuss electronics related questions each week. We welcome your participation

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