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** Originally posted 6/3/11 on our other forums **
People ask me this alot... the short answer is that they make the speaker better. The long answer can be shown on some graphs.
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 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 NS v.2 and Z v.2 both have a large magnet ID ring -- notice the huge effect on rearward inductance and at-rest inductance ? As a note... the SA will also have this ring shortly too.
Now... having BOTH rings like the NS v.2 has now and the SA will have soon... 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.
People ask me this alot... the short answer is that they make the speaker better. The long answer can be shown on some graphs.
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 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 NS v.2 and Z v.2 both have a large magnet ID ring -- notice the huge effect on rearward inductance and at-rest inductance ? As a note... the SA will also have this ring shortly too.
Now... having BOTH rings like the NS v.2 has now and the SA will have soon... 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.
