ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 2 [All]   Go Down

Author Topic: Field Coil Loudspeakers?  (Read 13505 times)

Jim McKeveny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1454
Field Coil Loudspeakers?
« on: November 28, 2012, 02:26:54 PM »

Field coil loudspeakers use an electromagnet to energize the gap, unlike the (ahem) permanent magnets of varying construction that are currently employed.

With the recent rare-earth price shocks, I wonder which manufacturers are taking a good look at revisiting field-coil technology. TrueExtent, the beryllium diaphragm people, work with a "classic audio" manufacturer that builds some interesting HF devices.

Field coil speakers pre-date microprocessors & DSP, but if they were incorporated into a broader loudspeaker system self-monitoring loop there could be useful merit.

With self-powered speakers taking an increasing share of the pro market there could be some opportunity here. Y/N?
« Last Edit: November 28, 2012, 03:02:54 PM by Jim McKeveny »
Logged

Barry Singleton

  • Full Member
  • ***
  • Offline Offline
  • Posts: 139
Re: Field Coil Loudspeakers?
« Reply #1 on: November 28, 2012, 03:13:24 PM »

FC won't beat ceramic for weight or cost. My bet is nope.
Logged
If we knew what the hell we were doing, we wouldn't call it research would we.

Riley Casey

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 2067
  • Wash DC
Re: Field Coil Loudspeakers?
« Reply #2 on: November 28, 2012, 03:23:55 PM »

A class D power amp running a field coil in a push-pull closely feedback controlled self powered configuration wouldn't be a more effective solution than a lump of mud with some iron fillings mixed in it?  I'm curious as to why not.  Once the the electronics are in the box ( as they increasingly are ) and once the benefits of precision location of magnetic fields as implemented in rare earth magnet loudspeakers ( as they have been for several years now )  it seems like a worthwhile path of research.

FC won't beat ceramic for weight or cost. My bet is nope.

Ivan Beaver

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 9534
  • Atlanta GA
Re: Field Coil Loudspeakers?
« Reply #3 on: November 28, 2012, 06:57:09 PM »

Field coil loudspeakers use an electromagnet to energize the gap, unlike the (ahem) permanent magnets of varying construction that are currently employed.

With the recent rare-earth price shocks, I wonder which manufacturers are taking a good look at revisiting field-coil technology. TrueExtent, the beryllium diaphragm people, work with a "classic audio" manufacturer that builds some interesting HF devices.

Field coil speakers pre-date microprocessors & DSP, but if they were incorporated into a broader loudspeaker system self-monitoring loop there could be useful merit.

With self-powered speakers taking an increasing share of the pro market there could be some opportunity here. Y/N?
For one hting the field coil has to have POWER in order to operate.  So that is a downside.

HOWEVER as a result-it was a double bonus-back in the day.  The field coil was also used as a series choke in the tube power supply.  So it helped to smooth out the DC voltage and provided the magnetic strength for the loudspeaker.
Logged
A complex question is easily answered by a simple-easy to understand WRONG answer!

Ivan Beaver
Danley Sound Labs

PHYSICS- NOT FADS!

paul bell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 609
Re: Field Coil Loudspeakers?
« Reply #4 on: November 28, 2012, 07:14:47 PM »

FC speakers aren't very efficient-and they get hot.

And they are heavy. Although probably not as heavy as this cast iron one, one of the first 18's made.

Logged

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17176
  • Hickory, Mississippi, USA
    • Resotune
Re: Field Coil Loudspeakers?
« Reply #5 on: November 28, 2012, 08:10:06 PM »

Field coil loudspeakers use an electromagnet to energize the gap, unlike the (ahem) permanent magnets of varying construction that are currently employed.

With the recent rare-earth price shocks, I wonder which manufacturers are taking a good look at revisiting field-coil technology. TrueExtent, the beryllium diaphragm people, work with a "classic audio" manufacturer that builds some interesting HF devices.

Field coil speakers pre-date microprocessors & DSP, but if they were incorporated into a broader loudspeaker system self-monitoring loop there could be useful merit.

With self-powered speakers taking an increasing share of the pro market there could be some opportunity here. Y/N?

I actually had an exchange with a guy who shall remain nameless, but knows about such stuff. He almost immediately lost me with the science (i couldn't keep up and didn't want to look as stupid as I am by asking him to explain it more simply). My sense is that yes you could (of course, they did before), but it was not a "great" idea.

From simple observation the coil to make the static field would be another source of heat in a place that doesn't need more. it seems in theory it could add another degree of control, but coils are not cheap. Driving the two coils differentially could have merit, but now we are talking 2x the amplifiers, unless similar coils could be reverse wired, but that sounds like another design can of worms to get them similar.

We are only having this conversation because rare earth magnets have some artificial pricing distortions due to Chinese hoarding and market supply manipulations. The most recent thing I recall reading about RE pricing was that it was softening (but i couldn't find it easily).

In any free market the unnaturally high price will lead to expanded investment in mining and processing to satisfy demand at those high prices. The natural pendulum swing of prices in free markets. Some old mines and facilities in the US closed by cheap chinese RE magnets may reopen. If the Chinese have distorted true supply demand balance, when they release full supply on the market prices could (should) fall.   

JR

PS The reason I asked my speaker expert about this was because i read about a Japanese car company looking at the same thing, more or less, to replace RE magnets in electric cars motors and alternators. This was probably a year ago or more so who knows. I may have the emails laying around but rather not publish private communications. i had no personal interest in this but though he might, since he is smart enough to make it work, and a big consumer of RE... He was not very interested as far as I could tell.

 
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

Sam Feine

  • Full Member
  • ***
  • Offline Offline
  • Posts: 233
    • Personal Website
Re: Field Coil Loudspeakers?
« Reply #6 on: November 28, 2012, 10:51:35 PM »

Not entirely sure how relevant it is but in a discussion I had with a professor who taught a class about power plant technology, (He actually worked at 3 mile island in some of the years prior to its incident), the topic of how the magnetic field used in the generator was produced came up. Apparently in large scale applications such as power plants, a smaller dc generator mounted on the shaft is used to create the magnetic field which is used for the production of power.

Of course this same sort of system could be used for loudspeakers, but as mentioned before, the heating would be an issue.

I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction? In theory this would produce double the heat, but it would allow for a passive speaker design in which the only power needed would be that from the standard amp much like any other speaker.
Logged
Electro-Acoustic Engineer at Community Professional Loudspeakers

paul bell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 609
Re: Field Coil Loudspeakers?
« Reply #7 on: November 29, 2012, 08:15:08 AM »

I was asked who made this thing so I'll share:
Logged

John Roberts {JR}

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 17176
  • Hickory, Mississippi, USA
    • Resotune
Re: Field Coil Loudspeakers?
« Reply #8 on: November 29, 2012, 09:36:50 AM »

ERPI was actually the licensing division of Western Electric for movie and recording products.

Early big dog speakers were developed for movie theater playback.

JR
Logged
Cancel the "cancel culture". Do not participate in mob hatred.

GenePink

  • Jr. Member
  • **
  • Offline Offline
  • Posts: 80
Re: Field Coil Loudspeakers?
« Reply #9 on: December 03, 2012, 07:29:36 AM »


> I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction? In theory this would produce double the heat, but it would allow for a passive speaker design in which the only power needed would be that from the standard amp much like any other speaker.


If you vary both the field strength and the VC voltage, they will multiply. The result would be a cone excursion that would equal the voltage squared, instead of having a linear relationship.

Might be interesting to hear, sort of a downward expander set to ridiculous settings.

Gene
Logged

Frederik Rosenkjær

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 479
Re: Field Coil Loudspeakers?
« Reply #10 on: December 03, 2012, 12:27:33 PM »

> I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction? In theory this would produce double the heat, but it would allow for a passive speaker design in which the only power needed would be that from the standard amp much like any other speaker.


If you vary both the field strength and the VC voltage, they will multiply. The result would be a cone excursion that would equal the voltage squared, instead of having a linear relationship.

Might be interesting to hear, sort of a downward expander set to ridiculous settings.

Gene

This sounds like something that could be dealt with via DSP? Could be interesting - very lightweight speakers...
Logged
Affiliations: Danley Sound Labs, Yamaha (MI)

Don Boomer

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 340
    • RF Venue
Re: Field Coil Loudspeakers?
« Reply #11 on: December 03, 2012, 05:52:48 PM »


I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction?

I'm not sure that you wouldn't get the same thing by just double layering the VC??

There are speakers that use differential VCs currently in production from JBL and Peavey (maybe others) that are along the lines of what you are describing that achieve much lower distortion specs from the differential pair of VCs.
Logged
Don Boomer
Senior applications engineer
RF Venue, Inc.

Sam Feine

  • Full Member
  • ***
  • Offline Offline
  • Posts: 233
    • Personal Website
Re: Field Coil Loudspeakers?
« Reply #12 on: December 03, 2012, 09:22:26 PM »

I'm not sure that you wouldn't get the same thing by just double layering the VC??

There are speakers that use differential VCs currently in production from JBL and Peavey (maybe others) that are along the lines of what you are describing that achieve much lower distortion specs from the differential pair of VCs.

Your right, not exactly the same, but similar concept using traditional permeant magnets.

http://www.jblpro.com/pub/technote/JBL_TN%201-33%20rev3.pdf
Logged
Electro-Acoustic Engineer at Community Professional Loudspeakers

David Morison

  • SR Forums
  • Hero Member
  • *
  • Offline Offline
  • Posts: 821
  • Aberdeen, Scotland
Re: Field Coil Loudspeakers?
« Reply #13 on: December 04, 2012, 08:14:57 AM »

I'm not sure that you wouldn't get the same thing by just double layering the VC??

Surely the Voice coil would have to be able to move relative to the Field coil though, otherwise nothing will happen bar heat?
Unless I'm completely misunderstanding you of course!!!

Edit: un-typo'd
Logged

Ed Walters

  • Full Member
  • ***
  • Offline Offline
  • Posts: 193
  • Holland, MI, USA
Re: Field Coil Loudspeakers?
« Reply #14 on: December 04, 2012, 03:14:16 PM »

Surely the Voice coil would have to be able to move relative to the Field coil though, otherwise nothing will happen bar heat?
Unless I'm completely misunderstanding you of course!!!

Edit: un-typo'd

This would be an interesting experiment with one of the dual coil/differential drive speakers now available. Drive the two coils in series but out of phase; the only audio would be the sum of their nonlinearities...ie distortion.

Back to the field coil speaker, though...a little cocktail napkin calculation shows that to get similar magnetic fields as to that in a modern speaker would require about 150 feet of 12 or 14 gauge wire, coiled up in a four inch coil, two inches high.  Or fewer turns/feet and a LOT more current (and with it heat). Numbers based on typical four inch voice coil, 400 watts drive, approximately 16 Tesla field in a typical woofer.  It won't fit. It's not doable in a practical sense.

/Ed
Logged
The Solution LLC: certified: AMX, Audio Architect, Composer, ControlSpace, CTS, DanteL3/DDM, Tesira, and more.

paul bell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 609
Re: Field Coil Loudspeakers?
« Reply #15 on: December 05, 2012, 12:07:26 AM »

> I wonder however what would happen if there were essentially two coils, the inner voice coil, and an outer field coil that were both wired to the same amplifier power output with their polarities reversed as to provide double the push / pull in either direction?

I actually tried this some years ago. The idea was to have a "magnetless speaker"

A voice coil needs to be immersed in a pretty strong magnetic field with it's flux focused in an oval from top to bottom of the voice coil.

Two voice coils each receiving the same power level would not cause either one to attain any motion.

Even if one of these coils had a higher power level fed to it, it's still substantially too low in power to create a magnetic field to get the other coil to react. Plus the issue of not having an iron pot to focus the field.

The well designed high powered ferrite and neodymium loaded modern speakers we have on the market today are far away better than any field coil speaker could be.
Logged

paul bell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 609
Re: Field Coil Loudspeakers?
« Reply #16 on: December 05, 2012, 12:16:12 AM »

I always felt the best magnets for long excursion woofers was a radial neodymium design, like used in the Aura/Barry woofer and the NeoMax woofer. I wanted to see how that design would be with a dual radial design, neodymium strips outside the voice coil AND inside the voice coil.
Logged

Jim McKeveny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1454
Re: Field Coil Loudspeakers?
« Reply #17 on: December 05, 2012, 06:41:46 AM »

The Aura 1808 was my go-to for custom subwoofers in the 1990's. It modeled and performed like nothing else available. The TC Sounds Pro 5100 is a virtual clone, but some conventionally magneted competitors now match its performance at lower cost.

The radial magnet orientation & extreme excursion seemed to confuse the "offset integrator" on Crown MA5000's, and it needed to be disabled for proper function. Great cone. Loopy Bozeman.
« Last Edit: December 05, 2012, 06:29:41 PM by Jim McKeveny »
Logged

paul bell

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 609
Re: Field Coil Loudspeakers?
« Reply #18 on: December 05, 2012, 07:48:52 AM »

Loopy Bozeman.

Oh yeah!

My testing of these woofers didn't have very good results. The following were the issues found:

-The solder joints on the coil former melted.

-The copper pole sleeve wandered out towards the dust cap.

-Barry Bozeman.
Logged

Jim McKeveny

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 1454
Re: Field Coil Loudspeakers?
« Reply #19 on: December 05, 2012, 10:15:59 AM »

My experiences post-AURA mimic yours.
Logged

ProSoundWeb Community

Re: Field Coil Loudspeakers?
« Reply #19 on: December 05, 2012, 10:15:59 AM »


Pages: 1 2 [All]   Go Up
 



Site Hosted By Ashdown Technologies, Inc.

Page created in 0.04 seconds with 24 queries.