I believe copper plating has some limitations when it comes to thickness. Copper deposition can be thicker, but I am not sure how ideal it would be, and how far one can go with copper. I know some metals can be deposited up to between 0,1 and 1mm, but I am not sure copper is among them. If someone has some reliable information that this can be done with copper, I am interested!
I have run lots of simulations on this. You can clearly see that the AC Flux field is reduced when you increase the thickness of the copper sleeve.
I have run lots of simulations on this. You can clearly see that the AC Flux field is reduced when you increase the thickness of the copper sleeve.
The manufacturer controls this by manufacturing the compensation coil with a different resistance than the voice-coil. I was once interested in a midrange of that type but they are not very easy to obtain. Eighteensound once had an AES paper for download on their webpage. The effect on THD was not very pronounced IMO but IMD was reduced by at least a factor of 2 IIRC.
If I were to use one of these I would drive the compensation coil with a current-source delivering a current proportional to the voice-coil current. This would have to be fine-tuned for lowest possible distortion IMO.
Studer professional once produced an active studio monitor where such a compensation coil was in series with the voice-coil. The compensation coil had less turns than the voice-coil.
Regards
Charles
Could this be the document you are refering to? http://www.eighteensound.com/Portals/0/Img/Img_tech/doc_tech/18_Sound_AIC.pdf
If you do have the two coils in series, the current will be the same in the two coils regardless of signal.
I believe the flux modulation will not be linear, and thus it can not be linearized fully with a compensation coil. First of all, if the two coils set up the same field strength, I believe the field of the correction coil will be far to strong. If the two coils does not set up the same field strength, there should be some kind of remaining flux modulation. This should be both frequency and amplitude dependent. In addition to this, the gap will be relatively wide. The flux distribution does also seem to be a bit uneven in 18sounds implementation. That would not be the best solution for an underhang driver, or for drivers that are overhung, but where the coil end partially enters the gap at high excursions (which is pretty common in pro audio).
If you do have the two coils in series, the current will be the same in the two coils regardless of signal.
I believe the flux modulation will not be linear, and thus it can not be linearized fully with a compensation coil. First of all, if the two coils set up the same field strength, I believe the field of the correction coil will be far to strong. If the two coils does not set up the same field strength, there should be some kind of remaining flux modulation. This should be both frequency and amplitude dependent. In addition to this, the gap will be relatively wide. The flux distribution does also seem to be a bit uneven in 18sounds implementation. That would not be the best solution for an underhang driver, or for drivers that are overhung, but where the coil end partially enters the gap at high excursions (which is pretty common in pro audio).
Yes that is the paper.
And yes, the current is always equal in two series connected coils, like they were used in the Studer example.
I don't know why Eighteensound didn't use something similar. The AIC coil has a higher impedance than the voice-coil. This way they control the current distribution. They do probably use the parallel configuration because it gives a small SPL/voltage advantage as well.
Regards
Charles
And yes, the current is always equal in two series connected coils, like they were used in the Studer example.
I don't know why Eighteensound didn't use something similar. The AIC coil has a higher impedance than the voice-coil. This way they control the current distribution. They do probably use the parallel configuration because it gives a small SPL/voltage advantage as well.
Regards
Charles
You are probably right about that. It looks like the coil in the gap has far thinner wire, which means the current will be lower.
That makes me wonder what happens at Fs. The main coil current goes down, and the relative correction coil current is way to high in comparison. It should affect the Qes significantly.
That makes me wonder what happens at Fs. The main coil current goes down, and the relative correction coil current is way to high in comparison. It should affect the Qes significantly.
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