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Opposing coil speakers? Answered

Today's speakers have large heavy magnets, but what would be the result of setting up two coils which create opposing fields, one being the typical voice coil, the other being a replacement for the magnet.  Why isn't this in use today, is the power needed to create the required field just too great? This method could be used to increase volume while not overloading the voice coil right?


I was thinking the same. I am a musician and I hate to break my back on all that heavy weight stuff, especially subwoofers (30 - 40 kg's) I think the magnets in the speakers are the blame, so what if you could replace them with coils? The voltage needed to run the magnet-replacing-coil couldn't be a problem because you always have 230V (in Europe) and lots of current.

To provide the magnet of a speaker by a mains PS would be so much heavier then your present day permanent magnets you would not want to consider the exchange.

Sixty or fifty cycle ripple takes an inordinately heavy and expensive Power Supply to hide mains hum.

Be the musician not the engineer and ask your own question rather then jump into a year old thread..


3 years ago

I think it has to do with the strength of those large, heavy magnets. They produce hugely strong magnetic fields, that would take a LOT of power to reproduce using electromagnets. (I assume you mean a voice coil with another stationary coil with the opposite polarity to create the opposing field...)

The issue that I would see is the resistive losses in the coil would be really high unless some form of liquid cooling was implemented, like in MRI machines. They generally use liquid helium cooling!

I do Not agree, technology of speakers since before you were born never needed anywhere your supposed cooling.

Then they must not have ever needed the current that I would have imagined they needed to work. So are you saying that the answer to the original question is true? IDK.

IDK what you are talking about, 'they' ? and which answer ? yours ??

'they' as in the speakers.

I have made my fare share of small electromagnets, there is a balance between guage, length and voltage needed to get them working. Too small guage wire and it gets too hot, too short big wire lets too much current flow and gets hot as well. The resistance, which limits current and heat is mostly a factor of length. Coil too hot increase the wire length.

Same. Although it has been a long time since I have messed with solenoids and electromagnets with constant DC through them to generate magnetic fields like that. I learned when I was young that there was a diminishing returns with each additional turn of wire, and now I know why. (to some degree, anyway.)

The power dissipated in the coil would be a function of the resistance of the windings, (which is related to the guage wire and the length of it.) and therefore the current and voltage across it The V and I simply multiply to get power dissipated. With few turns of thick wire, there is lots of current needed to achieve meaningful amounts of magnetic field strength, and the few turns mean little magnetic flux for the given flux. and as you add more turns, of course the field strength goes up, but resistance starts to become more and more of a factor, and voltage has to also go up too. In a fixed volume of space, adding more turns will mean that the AWG of the wire has to decrease to fit the same # of turns in a space, Eventually leading to diminishing returns and more power dissipation. (more voltage drop.)

How much power then would an electromagnet small and powerful enough to recreate the magnetic field presented by the standard magnet's they use in 'normal' speakers?

I get it ... you want to push your cooling premise.

Who but you knows ... what you call .... a 'normal' speaker.

.. -.-. . -. --.

The magnetic field that matters is the flux density in the air-gap of the machine which today's speakers provide by means of a permanent magnet at no extra energy cost and together with the voice coil has been optimized over decades of audio enginneering time.

I'm no sound expert but I believe in economics, that is ; if anyone had ever come up with a better speaker, it would be available in the audio market !

There are many flux / magnet configurations to provide the reaction "air-gap" for a voice coil to move a speaker cone which has the mechanical limitations of an electric machine.

There may be something New coming from dreamers like you just around the time corner so to speak. You in fact are working on a modulated plasma arc speaker instructable


that is awaiting your a final design since last year.

Plasma (that singing arc) a concept that by-passes magnetic and mechanical limitations of speakers by placing a DC modulated audio amplifier in series with a high voltage supply capable of maintaining a continuous arc that produces air pressure variations in a 360' circle.


"I get it ... you want to push your cooling premise."

No, you're wrong. I am not trying to push anything. In fact, my original comment simply mentioned the cooling system in MRI machines, and I thought that to generate strong enough fields in a small space, some form of similar cooling would be necessary. Every attempt I have made as a child winding wire around a bolt to make an electromagnet, the wires gets very hot. Since it is DC powered, and there is resistance in the wire.


"that is awaiting your a final design since last year."

Thank you for reminding me to finish that long forgotten instructable. I will add this video sooner or later to it:

"my original comment simply mentioned the cooling system in MRI machines"

OK ... But that comment is Off Topic making it hard to see your contribution to this thread.

That is why I said

"I get it ... you want to push your cooling premise."

So? I do not care it is off topic, and besides, it is not even that far off topic anyway. I figured that to achieve strong enough magnetic fields practically to replace a strong permanent magnet would need active cooling. That was my point, & why I mentioned MRI machines. I ain't no expert, I couldn't be bothered to waste my time calculating what current, voltage, and power would be necessary to achieve similar magnetic fields, and continue to figure out the power dissipation, thermal resistance, and the amount of cooling that would be necessary to do a feasibility check. My gut feeling is that there will be some need for some form of cooling because power dissipation.

But if you are so smart, and plan to get involved, can you do said calculations and teach us a thing or two? I certainly do not mind learning new material! Thats why I participate here. Anyway, I never heard back from you about your final answer to "So are you saying that the answer to the original question is true?" I honestly do not know. I think it will work, but not very well.

They don't use the helium to keep it cooled in the normal sense, those are superconducting magnets, and by using the liquid helium, they are able to bring the coils down to a temperature were the coils have zero resistance. This allows them to induce a massive current once, and so long as the temperature stays low enough the magnets are essentially permanent magnets, you don't need electricity to operate the main coils. Other magnets which fine tune the fields and measurements are not super conducting as it is desirable to be able to shut them on and off without quenching the system.

Anyway, back on subject, most speakers don't use neodymium magnets, they use large iron magnets, and a decent electromagnet easily out powers those, that is why they are used in many motors and generators. Although there are other benefits of using an electromagnet in a motor and generator that aren't the topic here. Anyway, speakers move a decent amount of air to begin with, and there is no reason one would need to cool the coils if they were made with the correct wire and operated at the proper currents.

The VERY highest fields created on earth are created using something called Florida-Bitter coils, where cooling water, at prodigous flow rates is pumped THROUGH the coil.

Addition power requirements, cost and the reduced performance from such speakers when compared to today's speakers using permanent magnets has rendered them obsolete.

No they will not help to increase volume without overloading the voice coil. The problem with too much volume is 2 fold. 1 is overloading the coil but the other is forcing that coil to move further than the speaker can handle causing the coil to jump out of the magnet and ripping the cone from it's housing. This is why you hear a good bit of distortion in speakers when pushing them to their max. It's not because the coil is handling too much current but because the cone is being pushed in an out towards it's limits where it may rip from the frame.

You have good points, and thanks for the response! What I was really aiming for was having reduced input requirements (you can buy a smaller amp) to get the same levels, assuming you can drive a stronger magnetic field than the pre-existing one. I'm curious if any large speakers use neyodimium magnets, or if magnets that large are just too expensive.

They call them rare earth magnets for a reason. Yes larger neodymium magnets get pricey. What are your requirements here for the audio system? What kind of power window are you wanting to work within and how load do the speakers have to be?

Equipment and building-structure shaker tables are huge mega power speakers without the fragile speaker cone used to determine structural failure modes.


3 years ago

I had that kind of old old speaker when I was your age. The as you call "opposing_coil" needed 90VDC and was quite large and heavy.

Today the NIB magnets outperform my old speaker by a sonic mile.

Interesting, I've never seen externally powered speaker magnets.

Back in the selenium age, I made a carbon-rod, maybe zinc or tin metal
in a salt solution jar leaky chemical diode. At night listening to music in the glow of a
full wave bridge of four glass jar diodes is a grand memory even with the 120 cps hum :-)