yes, would be nice, measured them some years ago, but do not have my ATB Pc Software here at hand. If I find all items (dongle, etc) I will search for it
Imepdance measurement of a 38cm loudspaker with and without a single copper ring (approx. 2mm height).
higher impedance is without copper ring
middle impedance is with 60mm copper ring on the pole piece
lower impedance is with 62mm copper ring on the pole piece
the voice coil has 63mm diameter
so you see its important to get as close to the voice coil as possible
The driver is a AD Audio https://www.traumboxen.de/ad-audio/r1524.htm
Thats the F response of the driver with two copper rings (4mm in height)
higher impedance is without copper ring
middle impedance is with 60mm copper ring on the pole piece
lower impedance is with 62mm copper ring on the pole piece
the voice coil has 63mm diameter
so you see its important to get as close to the voice coil as possible
The driver is a AD Audio https://www.traumboxen.de/ad-audio/r1524.htm
Thats the F response of the driver with two copper rings (4mm in height)
Just putting some copper on top of the pole piece with no other shorting rings in the motor will actually make Le(x) distortion worse. It might lower your global inductance a hair, but worse Le(x) will be the drawback from this. When the coil is on its outward stroke, there is naturally less inductance since your core is now turning into air from steel.
This is a typical Le(x) curve for an overhung motor with no shorting rings:
When you put a pole cap on without any complementary shorting ring under the gap, all you are doing is lowering the outward inductance even more than it already is without lowering any inward inductance. It just tilts the curve even more right and lowers the non-linear limit for Le(x).
This is a typical Le(x) curve for an overhung motor with no shorting rings:
When you put a pole cap on without any complementary shorting ring under the gap, all you are doing is lowering the outward inductance even more than it already is without lowering any inward inductance. It just tilts the curve even more right and lowers the non-linear limit for Le(x).
@hurrication
I was also thinking about this effect.
As far as I know there are manufacturers who do not add a "full sleeve" to their drivers but like in my experiment only a cover on the pole piece.
I found the Dongle and my measurement system.
Not difficult to make now THD and IMD measurement - if the software works on win10 like before on win7.
So when opening and modding a driver I could see what distortion looks like with and without.
In my listening tests a copper topping of the pole piece clearly won over leaving it out.
I was also thinking about this effect.
As far as I know there are manufacturers who do not add a "full sleeve" to their drivers but like in my experiment only a cover on the pole piece.
I found the Dongle and my measurement system.
Not difficult to make now THD and IMD measurement - if the software works on win10 like before on win7.
So when opening and modding a driver I could see what distortion looks like with and without.
In my listening tests a copper topping of the pole piece clearly won over leaving it out.
Feyz Pirimoglu wrote on this in his paper (posted in this thread)
In practice, the exact placement, shape and the number of these shorting rings in a
motor assembly vary from design to design. Some of them are on the base of the pole
piece, some cover the pole piece as a sleeve, some are wide and cover the inner surface of
the magnet, some are two rings that sandwich a T shaped pole piece from above and
below, etc. A shorting ring which is a coaxial sleeve with its radius equal to inner radius
of the voice coil and with a length that covers at least the over all excursion range of the
voice coil, has the most effect on the impedance of the voice coil than other ring
configurations that are used. Because of this and since this document is on the effect of
shorting ring on voice coil impedance, the shorting ring investigated here will be of this
kind.
In practice, the exact placement, shape and the number of these shorting rings in a
motor assembly vary from design to design. Some of them are on the base of the pole
piece, some cover the pole piece as a sleeve, some are wide and cover the inner surface of
the magnet, some are two rings that sandwich a T shaped pole piece from above and
below, etc. A shorting ring which is a coaxial sleeve with its radius equal to inner radius
of the voice coil and with a length that covers at least the over all excursion range of the
voice coil, has the most effect on the impedance of the voice coil than other ring
configurations that are used. Because of this and since this document is on the effect of
shorting ring on voice coil impedance, the shorting ring investigated here will be of this
kind.
It really requires simulation software to determine proper shorting ring implementation, otherwise it is just a guess. The only place I have ever seen just a pole cap for a shorting ring is in smaller high frequency drivers that do not have much excursion.
If you have a coil which is averagely (especially for small signals) reduced by a certain amount in impedance there is also less modulation in the gap itself?
I never saw a "full sleeve" in drivers. Only covered pole pieces but omitted making the sleeve reach out outwards to give a "full sleeve".
This is what Pirimoglu writes on efficiency:
In short, the shorting rings are good to have, as long as their shape and position is
well thought out and placed on the motor. The only problem they bring is they generally
reduce the sensitivity of the driver, because either they cause to widen the air gap if they
are placed in there, or they cause the shape of the pole piece to be made such that a it
won’t be able to channel the maximum amount of flux to the air gap.
As the driver gains efficiency in the higher frequencies and does not lose efficiency due to a full sleeve:
I consider a topping of a pole piece already as justified (for fullrange drivers for example).
I never saw a "full sleeve" in drivers. Only covered pole pieces but omitted making the sleeve reach out outwards to give a "full sleeve".
This is what Pirimoglu writes on efficiency:
In short, the shorting rings are good to have, as long as their shape and position is
well thought out and placed on the motor. The only problem they bring is they generally
reduce the sensitivity of the driver, because either they cause to widen the air gap if they
are placed in there, or they cause the shape of the pole piece to be made such that a it
won’t be able to channel the maximum amount of flux to the air gap.
As the driver gains efficiency in the higher frequencies and does not lose efficiency due to a full sleeve:
I consider a topping of a pole piece already as justified (for fullrange drivers for example).
Can't speak for US coins but all Canadian coins are very magnetic. I said all, as we no longer use pennies, just:
5, 10, 25, $1, $2.
From Google:
Most metals aren't magnetic with the exception of iron, nickel, cobalt, gadolinium, neodymium and samarium.
If the air gap is not too tight manufactured I was dreaming about adding a full sleeve to an existing driver:
But the production of a coper sleeve which would fit tightly a given pole piece for just dropping it from above into the motor and being thin enough not to prevent jamming the moving system is practically impossible. (Apart from having no stability on such a fragile construction during handling).
So I was looking for what a DIY faraday ring would look like. For the efficiency the described method works.
Luckily there are some manufacturers using already faraday rings in their designs.
But the production of a coper sleeve which would fit tightly a given pole piece for just dropping it from above into the motor and being thin enough not to prevent jamming the moving system is practically impossible. (Apart from having no stability on such a fragile construction during handling).
So I was looking for what a DIY faraday ring would look like. For the efficiency the described method works.
Luckily there are some manufacturers using already faraday rings in their designs.
I was thinking about conductive silver which could be painted - but such a delicate operation/application with an unacessible and sensitive area is impossible to do, too.
Cal, I was referring to the lack of copper in our coins. Faraday rings use copper because it creates an eddy current that counters the excess coil movements. US coins have less and less copper in them and I don't know if non-magnetic nickel will work as a Faraday ring. Still, US coins are mostly copper. Pennies are a good investment.😉
I stand corrected on Canadian coins most are magnetic. Since they are made from regular steel with a copper, zinc, and/or nickel covering, they won't work as Faraday rings, they will simply extend the pole piece and not create the necessary eddy currents. Maybe the thin layer of copper on the outside of some coins will be enough to create the effect? If it's copper I bet it's enough. Is a few molecules thick enough?
[Not to derail the thread, I deleted my rant on coins and inflation]😡
I have some brass shim stock that is very thin and could be wrapped around the pole piece. The problem is I think you would have to remove the speaker cone and spider to glue on the brass. I think that's an operation that is out of the range of possibilities in the average hobby shop.
I design and build speaker motors with many combinations of shorting rings, including some with full pole sleeves. You truly do need to simulate the effects of them in software as steel and its saturation level also affects inductance. More time than not, just guessing on where to put shorting rings can hurt more than help. The Dayton reference line uses full sleeves, and their subwoofers also use a full sleeve in combination with a magnet ID ring below the gap.
Here is an example of how a pole sleeve does not always help. This is an underhung motor that I developed, and the blue Le(x) curve is what I measured with a full pole sleeve in the motor. The green curve is the same motor with a strategically placed pair of shorting rings and no pole sleeve. The compromise was a slight increase in global inductance, but a much better Le(x) curve.
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@hurrication
the linearity of cone travel is better with the optimized use of copper. Nice to see.
How do the companies decide on putting faraday rings into their loudspeaker motors?
It would be great to learn if they design with care or the marketing department is dominating the result?
I am only working on fullrange drivers. Here very rarely there is investment into cone travel only doing classical optimization for having a lightweight voice coil and low inductance for a linear frequency response giving mostly short cone travel.
I am or better was interested in making a fullrange driver with a long cone travel at the expense of bandwidth using dsp to linearize the construcion (like once Bose or Pfleid). What worked out well if done right.
Therefore I experimented with the use of bigger drivers or bass drivers as fullrange drivers.
I have here on the shelf a 30cm Reference Dayton bass driver which had perfect data but a full metal cone with resonances I could not tame. It looked good on the waterfall but the remaining little ringing is more annoying than it looked like on the paper.
the linearity of cone travel is better with the optimized use of copper. Nice to see.
How do the companies decide on putting faraday rings into their loudspeaker motors?
It would be great to learn if they design with care or the marketing department is dominating the result?
I am only working on fullrange drivers. Here very rarely there is investment into cone travel only doing classical optimization for having a lightweight voice coil and low inductance for a linear frequency response giving mostly short cone travel.
I am or better was interested in making a fullrange driver with a long cone travel at the expense of bandwidth using dsp to linearize the construcion (like once Bose or Pfleid). What worked out well if done right.
Therefore I experimented with the use of bigger drivers or bass drivers as fullrange drivers.
I have here on the shelf a 30cm Reference Dayton bass driver which had perfect data but a full metal cone with resonances I could not tame. It looked good on the waterfall but the remaining little ringing is more annoying than it looked like on the paper.
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Some companies do not believe in shorting rings. Focal is one of these brands for example. Other companies that do use them will usually balance out whether or not it is necessary for the design goal of the speaker. For example in a woofer or midrange with a limited bandwidth. Other times, it's purely a cost issue. Even though the addition of them is just a few dollars, sometimes the bean counters can nix that.