# Purpose of a copper shorting ring?



## rimshot (May 17, 2005)

Just curious as to what aspect of the speakers frequency response a copper shorting ring improves. Is this another way to keep the frequency response more linear (like xbl2 lmt) or is it for something completely different? Just want to learn, thanks!


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## npdang (Jul 29, 2005)

Simply put, it can be used to lower distortion and/or inductance... when used properly. There's all kinds of implementations, including bad ones which actually worsen the driver's performance. The most popular one seems to be a ring on top of the pole piece, or in the case of the Seas Excel and Scan-Speak there's a ring both on top of the pole, as well as below. The most extreme cases use a full length copper sleeve over the pole piece, such as Lambda acoustics or the Adire Extremis.


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## npdang (Jul 29, 2005)

A good link on motor topologies:

One interesting thing to note is that the Scan-speak SD-1 motor with dual faraday rings is actually somewhat common in alot of high end drivers today... for example the much cheaper Dayton reference line.

http://ldsg.snippets.org/motors.php3
http://www.peerlessaudio.com/technology/html/newdesigndrivers/CCFRing.html


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## rimshot (May 17, 2005)

Much appreciated! 8)


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## oabeieo (Feb 22, 2015)

Morel has a copper ring on the former above the winding. Pretty cool because its shiny!&#55357;&#56859;


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## oabeieo (Feb 22, 2015)

Think of the stray energy field that builds up when power is put throughout a conductor that's inside a magnetic field. A shoring ring typically shorts that stray energy to the basket or motor metal.
Sorta a lightning rod for a speaker miniaturized. But It would be a pretty big amp if it could actually arc , I have never heard of such a thing, but electromagnetic energy is present.


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## SHAGGS (Apr 24, 2011)

10 year anniversary bump! Hells yeah!:laugh:

Seriously though, your input is appreciated, but you probably could have left this one on page 138.


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## oabeieo (Feb 22, 2015)

SHAGGS said:


> 10 year anniversary bump! Hells yeah!:laugh:
> 
> Seriously though, your input is appreciated, but you probably could have left this one on page 138.


Sorry I read allot , I read way more than I post ,


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## SHAGGS (Apr 24, 2011)

oabeieo said:


> Sorry I read allot , I read way more than I post ,


Nothing wrong with that. People who do the opposite are the real trouble makers.  
Just bustin your balls. All in good fun.


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## SkizeR (Apr 19, 2011)

how the hell did you even find this thread lol


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## Patrick Bateman (Sep 11, 2006)

oabeieo said:


> Morel has a copper ring on the former above the winding. Pretty cool because its shiny!��


JBL has used silver instead of copper.

Pretty wild to put that much bling in a motor


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## hurrication (Dec 19, 2011)

The rings or shorted windings on the voice coil formers are for braking to prevent overexcursion.


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## oabeieo (Feb 22, 2015)

hurrication said:


> The rings or shorted windings on the voice coil formers are for braking to prevent overexcursion.


According to morel website that wasn't mentioned. Take a look 

INNOVATIVE TECHNOLOGY - Morel


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## 14642 (May 19, 2008)

Wow. None of this is really correct. The morel link is, but there's no explanation.

When a conductor is immersed in an alternating magnetic field, that alternation causes a current to flow in the conductor. A current flowing in a conductor generates a magnetic field at a right angle to the direction of current flow. The voice coil moving up and down around the shorting ring causes a current to flow in the ring which generates a magnetic field that opposes the change in the coil's magnetic field due to the changing coil inductance as the coil moves in and out over the polepiece. That change in inductance is caused by the coil changing from iron core to air core as it moves upward and downward over the polepiece. At high frequency, where the coil doesn't move very far, the shorting ring simply counteracts the coils inductance. AT lower frequencies where the coil DOES move a lot, the ring reduces distortion caused by changing inductance.

It isn't a shield. It's basically a magnetic self-regulating inductance countermeasure. It doesn't increase sensitivity and depending on how it's designed, opening the gap to accommodate its placement REDUCES sensitivity.


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## oabeieo (Feb 22, 2015)

Andy Wehmeyer said:


> Wow. None of this is really correct. The morel link is, but there's no explanation.
> 
> When a conductor is immersed in an alternating magnetic field, that alternation causes a current to flow in the conductor. A current flowing in a conductor generates a magnetic field at a right angle to the direction of current flow. The voice coil moving up and down around the shorting ring causes a current to flow in the ring which generates a magnetic field that opposes the change in the coil's magnetic field due to the changing coil inductance as the coil moves in and out over the polepiece. That change in inductance is caused by the coil changing from iron core to air core as it moves upward and downward over the polepiece. At high frequency, where the coil doesn't move very far, the shorting ring simply counteracts the coils inductance. AT lower frequencies where the coil DOES move a lot, the ring reduces distortion caused by changing inductance.
> 
> It isn't a shield. It's basically a magnetic self-regulating inductance countermeasure. It doesn't increase sensitivity and depending on how it's designed, opening the gap to accommodate its placement REDUCES sensitivity.



Thank you for the articulate explanation! 
I couldn't put that into words being I read it on parts express forum at 3am and couldn't exactly remember, 

I was just posting the morel link to say that that guy said the ring on morel speakers is for brakes , ( I couldn't resist smiling at that one) but than I talked about a shiny copper ring on morel speakers I wasn't referring to the shorting ring tho I was referring to the top of the bobbin, I needlessly caused confusion to be silly. But anyway , 

Dosent inductive reactance ( reactance from the pole not just plain reactance) in the coil increase exponentially as amplitude is increased? Or is it a linear measurement ? I always wondered about this and coil size ? I also hear term copper cap? That's typically a ring ? Or is it a cap on the pole that does the same thing and just have a band of copper around it ? Pics are great here but you seem to explain things very nicely


Also is it safe to assume based on coil size , and low inductance on any specific driver that it most likely has a ring? I've often compared speakers and look at the TS and notice two speakers that have diffrent inductance ratings but same size coils and they don't state ring or no ring but similar parameters otherwise ?


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## hurrication (Dec 19, 2011)

oabeieo said:


> I was just posting the morel link to say that that guy said the ring on morel speakers is for brakes , ( I couldn't resist smiling at that one) but than I talked about a shiny copper ring on morel speakers I wasn't referring to the shorting ring tho I was referring to the top of the bobbin, I needlessly caused confusion to be silly. But anyway ,


What else is its purpose, then? 


Here's a patent from JBL about how they use this in their differential drive GTI subs. Andy should know all about this. Many speaker companies have been using this for decades.
Patent EP0903961A2 - Inductive braking in a dual coil speaker driver unit - Google Patents


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## oabeieo (Feb 22, 2015)

hurrication said:


> What else is its purpose, then?
> 
> 
> Here's a patent from JBL about how they use this in their differential drive GTI subs. Andy should know all about this. Many speaker companies have been using this for decades.
> Patent EP0903961A2 - Inductive braking in a dual coil speaker driver unit - Google Patents


Not trying to be in a argument here , I strongly think forum fighting its distasteful! I am very fun outgoing happy person and for one you won't ruin my day for trying to say something that made me smile, smile is a good thing friend, I didn't say laugh. 

When you said brakes on a speaker I smiled cause it sounded unusual. I have morel speakers and they don't have any braking system on them I assure you I can pop them bitches quite easily if I drop the crossover just a weebit, the copper ring above the former , I honestly couldn't tell you it looks like part of the titanium bobbin actually and maybe the ring is a clamp to hold the bobbin to the cone, I haven't put that much thought into it , I was being a jokester that morel has to be all bling about there **** , and put useless shiny parts on there speakers , I love these speakers btw they do sound great , but I do strongly believe brakes is quite the opposite of what I want as a feature, or any device that would limit excursion , if the speaker is stopped from trying to move in or out before not past the mechanical limits the voice coil would not be able to turn the energy into movement of the diaphram and would cause that energy to have to go somewhere and would turn to heat , so if I am over excurting a speaker I want it to pop at me and let me know so I don't burn a coil. Anything that would restrict that before the limit would do so imo.


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## oabeieo (Feb 22, 2015)

hurrication said:


> What else is its purpose, then?
> 
> 
> Here's a patent from JBL about how they use this in their differential drive GTI subs. Andy should know all about this. Many speaker companies have been using this for decades.
> Patent EP0903961A2 - Inductive braking in a dual coil speaker driver unit - Google Patents


That link talks about inductive braking , I . E . Lowering inductance , just what a shorting ring does . Not excursion limiter that I can tell . But I didn't read more than 5 second of it


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## 14642 (May 19, 2008)

The braking coil in the JBL patent isn't the same.


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## Patrick Bateman (Sep 11, 2006)

Andy Wehmeyer said:


> Wow. None of this is really correct. The morel link is, but there's no explanation.
> 
> When a conductor is immersed in an alternating magnetic field, that alternation causes a current to flow in the conductor. A current flowing in a conductor generates a magnetic field at a right angle to the direction of current flow. The voice coil moving up and down around the shorting ring causes a current to flow in the ring which generates a magnetic field that opposes the change in the coil's magnetic field due to the changing coil inductance as the coil moves in and out over the polepiece. That change in inductance is caused by the coil changing from iron core to air core as it moves upward and downward over the polepiece. At high frequency, where the coil doesn't move very far, the shorting ring simply counteracts the coils inductance. AT lower frequencies where the coil DOES move a lot, the ring reduces distortion caused by changing inductance.
> 
> It isn't a shield. It's basically a magnetic self-regulating inductance countermeasure. It doesn't increase sensitivity and depending on how it's designed, opening the gap to accommodate its placement REDUCES sensitivity.


If I understand this correctly, the net effect would be:

1) a driver with wider bandwidth (due to the reduction in inductance)
2) a driver with lower distortion (due to the reduction in inductance related distortion at low frequency.)

One question -

Would it flatten the BL curve?

The reason that I ask is that I've noticed that some Peerless woofers exhibit a flat BL curve in their Klippel measurements. But Peerless does not advertise any type of split gap motor, a la "XBL" or Alpine Type S and Type R.


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## 14642 (May 19, 2008)

Patrick Bateman said:


> If I understand this correctly, the net effect would be:
> 
> 1) a driver with wider bandwidth (due to the reduction in inductance)
> 2) a driver with lower distortion (due to the reduction in inductance related distortion at low frequency.)
> ...


Correct on 1 and 2. The ring on top of the pole often provides better distortion performance and inductance minimization at high frequencies than a shorting ring at the base of the pole. The ring at the base helps a bit with distortion at higher excursion (and thus at low frequencies). We use both in the GB60 and only the copper ring on the mids and tweeters. The subs have a cap but no shorting ring--distortion at really low frequencies is much harder to hear.

The BL curve is determined by symmetry of the field over a long travel. Basically, the BL falls as the coil moves away from the gap or as the number of voice coil turns in the gap is decreased. The cap doesn't have anything to do with that. Many of the copper ring implementations install it as a kind of a shield over the polepiece. Any widening of the gap to accommodate the ring reduces B.


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