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View Full Version : Shorting Rings - Why do we use them ?



sundownz
01-27-2012, 07:17 PM
Pulling this from my other forums... a good read for those that want to learn more :


People ask me this alot... the short answer is that they make the speaker better. The long answer can be shown on some graphs.

http://www.sundownaudio.com/misc/BL_CURVE/Inductance/Part1.jpg

This graph shows inductance over excursion for a basic motor design. The center is at rest, left is rear stroke, and right is forward stroke.

Why is the graph shaped this way ?

Have you ever looked at inductors for a crossover ? You can get a high value in a small package with an iron core. So... what is a speaker motor ? A partially iron core inductor!

As the coil moves back it gets more iron in the core! So the inductance rises. As it moves forward it gets more air in the core so it drops. Pretty cool, huh ?

Now... the field can be absorbed by a conductive material in or around the coil -- so shorting rings come into play.

One approach, which we use on the SA series, Z v.3 series, and NS v.2 series, is a pole cap shorting ring -- note how it reduces forward inductance and at rest inductance. But not much in the way of rearward...

Well the SA Line, the NS v.2/v.3 and Z v.2/v.3 both have a large magnet ID ring -- notice the huge effect on rearward inductance and at-rest inductance ?

http://www.sundownaudio.com/misc/BL_CURVE/Inductance/Part2.jpg

Now... having BOTH rings like the SA Line, the NS v.2/v.3 and Z v.3 has a huge effect across the board! Not only is the inductance more linear but it is much much lower.

Why is this good ?

1) More power delivery to the coil as inductance causes "rise"
2) Less distortion -- inductive distortion is odd order and unpleasant; although a fairly small part of total distortion.
3) More high-end extension as inductance is a 6dB per octave low-pass crossover.
4) These rings also act as heat-sinks; although this effect is not a large reason to use them in and of itself.

Can a speaker sound good without them ? Sure! Many great sounding speakers don't use them and they are pretty expensive too so don't always represent a good price to performance ratio. I do not plan to use magnet ID rings on lines less expensive than the SA series, for example, as the ring represents such a high % of the total cost of the speaker at that point (large chunk of aluminum, copper, or brass).

But they do have benefits and I figured some of you might like to know what those are.

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http://www.sundownaudio.com/misc/BL_CURVE/Inductance/Part3.jpg

This thin sleeve has a nice effect at rest and on rear-ward -- seems to lose effect combined with the magnet ID ring, though, as that is equal to the magnet ID ring only.

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So now lets do a thick sleeve :

Full 1.0mm thick -- and the effect is MUCH better and also alleviates the issue of being cancelled out by the magnet ID ring.

The only problem is you need to add more motor to compensate for this type of sleeve as it widens the gap a good bit -- for this example the pole had to go down from 35.7mm OD to 33.7mm OD to fit this sleeve.

If the design budget allows for this then no problem -- the issue you end up with is spending more money on the motor by adding magnet to it.

The benefit is that the sleeve is the most linear method simulated -- the Le curve is completely flat in this case.

In most cases price to performance the magnet ID ring would be a better selection unless you are going for ultimate reference level.

http://www.sundownaudio.com/misc/BL_CURVE/Inductance/Part4.jpg

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http://sundownaudio.com/misc/Shorting.JPG
* SA motor -- the top aluminum piece acts as a pole cap ring.
* The brass piece is an example magnet ID ring from a Z v.2 motor. This goes around the inside of the magnets below the top plate / above the back plate.

http://i1131.photobucket.com/albums/m546/bumpinbuick/T-yokes.jpg
* Acoustic Elegance drivers with pole sleeve shorting rings

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We used a pretty small motor for this discussion... 120mm OD magnet utilized.

When I made enough room for the sleeve we dropped off 34% of the motor force factor (BL^2/RE) -- in order to get this back the magnet had to go all the way up to 150mm OD and in turn the back and top plate OD both had to expand as well. So much more steel and much more magnet.

634g magnet to a 1109g magnet -- we had to gain 75% magnet mass.

Total motor went from 1890g to 3112g -- so a 65% gain overall in mass not counting mass added by the sleeve.

So it is fairly significant in terms of cost to get a highly functional sleeve and to "gain back" the desired motor force lost by making room for it. And again, if this pans out for the target cost of the driver these thick sleeves do work great.

05trailblazer
01-27-2012, 07:36 PM
this is very good learned lots from this kinds of test! you shuld quiz me

ciaonzo
01-27-2012, 08:14 PM
Thanks a bunch for the graphs, Jacob.

kramer_212
01-27-2012, 08:33 PM
:yumyum:

RAM_Designs
01-27-2012, 08:43 PM
Nice experiment Jacob.

alfanso
02-10-2012, 08:48 PM
does the z v.3 basket come with a shorting ring at the bottom or separate ?

sundownz
02-13-2012, 11:32 AM
does the z v.3 basket come with a shorting ring at the bottom or separate ?

The Z v.2 is the only sub we've sold that offered a top shorting ring.

The v.3 does not offer that as an option but has two internal rings (pole cap and magnet ID).

T3mpest
06-15-2012, 06:07 PM
Good post Jacob. Also just to add a few things.. The Acoustic elegance woofers with the full sleeve run very tights gaps to gain extra motor force which is another way to make up for the lack of BL.. Also as you mentioned, but it's always an issue, it's inductance vs excursion that matter, not necessarily overall inductance. Even if a woofer has high inductance, if it is low enough to play as high as you need, and that inductance value won't change as the woofer moves much then it can still be a VERY good sounding subwoofer.. However, lower LE values do tend to correlate with less variance in most cases as to get a very low value you need to properly utilize rings or sleeves. However, some might look at your NS line which still has a fairly high inductance value and think it won't sound good, however, if you did a good job keeping it linear it may indeed not be any issues when used within it's usable bandwidth.

Suicide Bobb
06-15-2012, 06:49 PM
And...this is why we love Sundown subs haha

Any other well-known car audio companies utilize this technology in their subs? What are some good examples?

Bettr n' Revrse
06-15-2012, 06:59 PM
And...this is why we love Sundown subs haha

Any other well-known car audio companies utilize this technology in their subs? What are some good examples?

Quite a few Im sure

hispls
06-15-2012, 09:34 PM
Great post, Jacob. Many of us appreciate your contribution to the industry and parrticipation in these forums.

wenn_du_weinst
06-15-2012, 09:36 PM
And...this is why we love Sundown subs haha

Any other well-known car audio companies utilize this technology in their subs? What are some good examples?

this has been around since as long as I can remember. Sundown so far has been the only company to actually explain why they use them. Most are to scared they are giving away secrets.

hispls
06-15-2012, 09:36 PM
And...this is why we love Sundown subs haha

Any other well-known car audio companies utilize this technology in their subs? What are some good examples?

Many of the TC built subs use shorting rings of some sort (including tc9, 3hp, and '05 shocker Sig and neo sig that I know for sure). Not sure about LMS based drivers.

NoLoud4U
06-15-2012, 10:10 PM
DD super charged option

Villeza1
06-15-2012, 10:23 PM
Hmm, you learn something everyday.

sundownz
06-16-2012, 11:18 AM
DD super charged option

The SC option uses a pole cap shorting ring for reference.

sundownz
06-16-2012, 11:27 AM
And...this is why we love Sundown subs haha

Any other well-known car audio companies utilize this technology in their subs? What are some good examples?

There are not all that many dedicated car audio drivers using shorting rings. You can find many that are more home oriented drivers that are used in car that have them (TC Sounds, Acoustic Elegance, Dayton Reference, etc) as typically these customers are a bit less price sensitive. With that being said; a large driving force for the lack of shorting rings is cost as I had mentioned earlier... for example; the SA-10/12/15 shorting rings cost about as much as the entire T-Yolk of the driver (pole / back plate).

DD is using a pole cap ring with the SC option, though -- which is superior to no ring at all but not as effective as a magnet ID ring.

Alpine uses them as well; the Type-R has a unique one-piece basket / magnet ID shorting ring design (magnets are split and the frame comes in to the magnet ID to create a shorting ring / heat-sink assembly). This design helps to drive down the cost per unit a bit as it's just one piece rather than inserting a separate machined piece into the motor. Very cool and I think patented design.

T3mpest
06-18-2012, 12:12 PM
Many of the TC built subs use shorting rings of some sort (including tc9, 3hp, and '05 shocker Sig and neo sig that I know for sure). Not sure about LMS based drivers.

The 5400 does use shorting rings.. The LMS coil is very big and heavy due to the inherent design, so a shorting ring is really a must.

hispls
06-18-2012, 12:19 PM
The SC option uses a pole cap shorting ring for reference.

So "Supercharging" is just a shorting ring? I was kind of curious as to what that actually meant but have found little info on the matter.

sundownz
06-18-2012, 12:25 PM
So "Supercharging" is just a shorting ring? I was kind of curious as to what that actually meant but have found little info on the matter.

It is a pole cap ring AND a small Neo slug on top of the pole... it goes pole / neo slug / aluminum cap on top.

hispls
06-19-2012, 10:35 AM
It is a pole cap ring AND a small Neo slug on top of the pole... it goes pole / neo slug / aluminum cap on top.

That is consistant with the speculation I've seen. Thank you, Jacob, you are a gentleman and a scholar.

Suicide Bobb
06-19-2012, 03:35 PM
That is consistant with the speculation I've seen. Thank you, Jacob, you are a gentleman and a scholor.

scholor

hispls
06-19-2012, 10:50 PM
scholor

fixed