Speaker - amp attenuator topologies.

[Reader]

... Notes on the smaller value inductor are important because you can't get within eight or nine feet from the thing with single coil pickups otherwise...

That's interesting Chuck. I'm wondering why the .5mH inductor would radiate so much interference and why the 12mH inductor apparently does not cause a problem. Anyone know? I also wonder why a copper plate is needed between the two sections of the .5mH instead of just an insulating layer.

[Chuck H]

That's interesting Chuck. I'm wondering why the .5mH inductor would radiate so much interference and why the 12mH inductor apparently does not cause a problem. Anyone know? I also wonder why a copper plate is needed between the two sections of the .5mH instead of just an insulating layer.

The humbucking inductor was my own creation. Air core inductors radiate like crazy. The original 500uH inductor worked fine with humbuckung pickups, but single coils would whistle if you were too close to the unit. The 12m inductor has an iron core and that minimizes it's radiant field. It's also, I'm pretty sure, a resonant frequency dependent phenomenon relative to value. At any rate...

Since everything was hunky dory with humbucking pickups it occurred to me to make the offending inductor self humbucking. That is, radiate two equal, but opposite fields so that they would cancel each other. The copper plate in between reduced mutual inductance that would defeat that inductors performance. I read somewhere that even an ungrounded copper shield could do this pretty well. So that's what I came up with. The copper plate is barely larger in diameter than the inductors. So the inductors perform as in series but their inverse phase has more cancellation effect on the radiant field than on the in circuit inductance. I can't say how much of the actual component operation is being defeated by mutual inductance because I don't have test gear for that. But I know it worked a treat to stop the whistling and the attenuator sounds great.

[nosaj]

The humbucking inductor was my own creation. Air core inductors radiate like crazy. The original 500uH inductor worked fine with humbuckung pickups, but single coils would whistle if you were too close to the unit. The 12m inductor has an iron core and that minimizes it's radiant field. It's also, I'm pretty sure, a resonant frequency dependent phenomenon relative to value. At any rate...

Since everything was hunky dory with humbucking pickups it occurred to me to make the offending inductor self humbucking. That is, radiate two equal, but opposite fields so that they would cancel each other. The copper plate in between reduced mutual inductance that would defeat that inductors performance. I read somewhere that even an ungrounded copper shield could do this pretty well. So that's what I came up with. The copper plate is barely larger in diameter than the inductors. So the inductors perform as in series but their inverse phase has more cancellation effect on the radiant field than on the in circuit inductance. I can't say how much of the actual component operation is being defeated by mutual inductance because I don't have test gear for that. But I know it worked a treat to stop the whistling and the attenuator sounds great.

Does it deserve a trip to the patent office?
nosaj

[Chuck H]

Does it deserve a trip to the patent office?
nosaj

I don't think so. Surely something similar has been done to stabilize modern communications equipment or some such. At the very least there's noise cancelling systems that duplicate sound and emit an inverse phase copy to reduce dB. That's pretty much the exact same principal. Then there's humbucking pickups that also do the same thing, but in reverse. And anyway, I don't have the bench gear to properly test and refine the results. Any patent I put together would be too flimsy to enforce or too expensive to be worth it.

[olddawg]

I don't think so. Surely something similar has been done to stabilize modern communications equipment or some such. At the very least there's noise cancelling systems that duplicate sound and emit an inverse phase copy to reduce dB. That's pretty much the exact same principal. Then there's humbucking pickups that also do the same thing, but in reverse. And anyway, I don't have the bench gear to properly test and refine the results. Any patent I put together would be too flimsy to enforce or too expensive to be worth it.

I wonder if Weber would be interested? Got to be cheaper than those speaker motor assemblies. Although the company has been a little odd since Ted died. Didn’t he used to post here occasionally?

[Enzo]

Even cheaper to just mount the coils side by side instead of stacking.

[Chuck H]

Even cheaper to just mount the coils side by side instead of stacking.

That's something I'm pretty sure I've seen too. Two coils side by side on a board. I never looked to see if they were in series, but they probably were. In which case there would be some mutual inductance that could be compensated for by just bumping the components values. But since this thing is passing comparably higher current with substantially higher coil size than what I've seen (and I didn't build this on a board) I thought the shield was a good idea.

Something I thought of later... I could use my signal generator and scope to determine the lowest mutual inductance with the two inductors side by side or in line or .?. Then adjust mutual component value for a near match of the intended value. Then build a small board to mount them as tested. But this might require purchasing several somewhat expensive inductors and since I don't sell these attenuators I haven't prioritized it.