Why do transducers use permanent magnets instead of electromagnets?

A typical loudspeaker transducer uses two types of magnets: a permanent magnet whose magnetic field is basically constant and focused in a small gap, and an eleftromagnet called the voice coil whose magnetic field changes with respect to the electrical current running through. The change in the voice coil’s magnetic field causes it to move with the rest of the moving assembly.

Okay, but why is a permenent magnet used to generate a constant magnetic field instead of just another electromagnet? Why can’t it be replaced with another coil wound in opposite polarity as the voice coil? You send an electrical current to the system and it creates magnetic fields in the moving voice coil and fixed electromagnetic assembly and the voice coil should move the same way as it would with the permanent magnet.

Most motor systems work like this and don’t need permanent magnets. So why do we need permanent magnets for loudspeaker transducers?


Well it looks like my idea has been implemented before. I remembered Focal using electromagnets in the marketing for some of their Utopia speakers, so I looked it up and here we have a woofer that uses a huge coil instead of a neodymium or ferrite magnet.

Someone needs to stick one of those on a Klippel and see how it performs. It’s interesting technology.

Here is more information about this driver. It has been measured. The parameters (predictably) change with respect to the DC voltage applied to the electromagnet.

My idea was to send the same AC voltage to the electromagnet as the moving voice coil, but this is a similar concept.

let me start out by saying my very first speaker i built in high school at the turn of the millenium or so was based around a 10" Focal woofer ( it was a 3-way ). it worked well but after using it for a few years i moved on to active studio monitors ( Mackie and JBL ) + active subwoofer ( first JBL then TC Sounds LMS DIY ). instead i put the Focal 3-ways in storage, which meant Grandma’s room since this was NYC and there was no basement or anything. My grandma then put her potted plants on top of my speakers even though i told her not to, and then my sadist father secretly added more water to them so that it leaked and destroyed my speakers. He has been threatening to ruin them for years prior to that. My sadist father never had any other source of joy in his life than causing pain to others especially children and animals and as most sadists are also empaths they sense what you hold dearest to your heart and then they arrange for some “accident” to happen to it. so that was the end of my Focal 3-way. i still have them and i could restore them if necessary but i’m not going to because obviously i can design a better speaker now than i did in High School more than 20 years ago.

now the 10" Focal woofer i used in High School was a 3-layer Kevlar sandwich cone, with two outer layers of Kevlar and glass microsphere damping layer in between. later Focal has moved on to Fiberglass from Kevlar and for a long time i couldn’t understand why since Kevlar is the superior material … eventually i realized that the real reason was style - yellow color of Kevlar was all the rage when i built my speaker but it quickly got “played out” and Focal switched to GREY colored fiberglass cones because they were deemed more stylish.

this is what i didn’t understand about Focal when i built my speaker - is that Focal is a style-first company. the build quality of their products is great. the fit and finish on my Focal woofers was excellent all around, absolutely top notch, from any angle - any surface - everything was perfect. even the SMELL of the driver was perfect. and that’s of course why DIYers love Focal.

if you take a JBL driver on the other hand the experience is quite the opposite … they feel quite cheaply made, because they are. the build quality looks so cheap you wonder if it is even going to work but when you play them they go really loud and sound great doing it.

why ?

because JBL doesn’t target the DIY market. they don’t design their drivers to SMELL GOOD or to have perfect finish on the back side of the motor or to have really pretty looking suspension spider or terminals or basket and so on …

in fact they don’t even design the front of their cones to look special - they’re all just paper - and the best JBL speakers have non-transparent black grill and you can’t even see the driver when installed …

i think you may be getting my drift here. Focal is 90% for show.

Yes Focal is a high-end brand and their products are good and work well.

But they are designed primarily to bedazzle those who don’t know better, such as myself when i was just a kid starting out or the average audiophile even at the sunset of their “career” …

TLDR: that electromagnet driver is 100% BULLSHIT.

but don’t worry i will explain exactly why, but perhaps later. need to rest my eyes …

Let’s go through Focal’s marketing BS …

The drivers performances are directly linked to the magnetic energy transmitted by the magnet.


A subject Focal knows well for having invented original and technically advanced solutions such as the Multiferrite magnet that was and still is one of the technological signatures of the brand.

What a joke. Those Multi-magnet designs are just for decoration. Should be obvious to anybody with half a brain. I have one of those actually but luckily mine is neodymium, not ferrite, so it actually works pretty well. A regular ring magnet would have been better, but it doesn’t make that much difference.

But the permanent magnet is limited in power and in the framework of a reference woofer, it’s a real problem.

more BULLSHIT. they are using small ferrite magnets and claiming they don’t have enough power. well why not use a large neodymium magnet then dummies !

Because a woofer should at least combine two essential performances: high efficiency and ability to go down in the low frequencies.


To go down in frequencies, we can adjust the surround and the spider flexibility, but we should above all increase the cone weight.


what an absolute joke !

have those idiots heard about DSP ?

you don’t even need DSP. you can use simple analog circuits to extend bass like what Linkwitz has been doing even when i was in High School.

this idea that you need large cone mass is one of the biggest lies in audio. cone mass is ALWAYS DETRIMENTAL. less is ALWAYS better.

get your cone as light as possible then extend bass with DSP. that’s how the pros do it.

if we increase the cone weight, the efficiency drops.

yeah well that’s why only idiots increase cone weight !

And to compensate this drop, we have to increase the magnet power.

here is where i need you to understand something about audioPHOOLS. they are always trying to invent nonexistent problems to them triumphantly overcome them. that’s their business model. so they are deliberately causing the problem with the weight in order to then come up with a solution for it. governments work the same way. all frauds are the same.

That’s where the limits of the permanent magnet step in, forcing a compromise between efficiency and resonance frequency.

only if you pretend DSP doesn’t exist. except that every single professional speaker uses DSP, so it does. modern DSP is so good you wouldn’t hear it even through a ribbon tweeter but we’re talking about a subwoofer here. DSP is not only not audible in this application but you would have a better chance of being able to read a newspaper from 10 miles away than hearing good DSP on a subwoofer.

Only solution for Focal, reconsidering the very existence of the permanent magnet. We adopted an Electro-Magnet for the woofers that equip the Grande and the Stella Utopia EM.

it seems our fucking idiot friends at Focal have again conveniently forgotten something. namely that electromagnet based speakers came BEFORE permanent magnet speakers. it was called “field coil” back then, rather than electromagnet. when it became practical to produce permanent magnets field coil speakers went away.

leave it up to Audophiles to bring back technologies from the grave. they brought back vinyl records after they were already obsoleted 30 years ago and now they’re bringing back field coil speakers

field coil speakers are so old i watched a tour of JBL museum on YouTube and they were very proud to show off a JBL Field Coil speaker, which proved that JBL was one of the very first speaker manufacturers - so old that they were already making speakers in the Field Coil era…

here is that video:

Focal aren’t the only clowns trying to bring back Field Coils. here is the first result on Google that comes up for example:

typical audioPHOOL scammery …

Thanks to the simulation software and to the existing materials, this extreme solution goes back to the very origins of the driver and was optimized to supply the expected force (patent pending).

“goes back to the very origins of the driver” is a very clever way of saying “is nothing new” …

you can also patent anything, it means absolutely nothing. very clever use of language. Focal marketing is second to none.

The magnetic field in the air gap reaches 1.75 Tesla (0.9 for the woofer of the previous Grande Utopia Be that was yet equipped with a Multiferrite magnet) to supply a force factor (the real power of the motor) of 34T.m.

1.75T is typical flux density for higher frequency drivers and 34 TM BL is found in several high end Subwoofer drivers. the fact their new motor is better than their multi-ferrite motor only really proves their multi-ferrite motor was a scam to begin with. even so i would still rather have the multi-ferrite older version to avoid he complexity, size, weight, reliability and heat issues of this new system.

The goal is reached: the efficiency for 1W @ 1m reaches 97dB, whereas the resonance frequency drops to less than 24Hz. Here lies the true performance.

Great LOL. The cheapest JBL 15" woofers achieve 97db efficiency. Resonance frequency is completely irrelevant as low end can be extended with DSP.

now let’s dissect your link to PE forum.


these specs are nothing to write home about.

even at the highest voltage of 15V we still only get BL of 10 and QTS of 0.4 … these are MEDIOCRE specs. it’s pretty much the specs i had on my Focal woofer that i used in high school back in the PREVIOUS MILLENIUM over 20 years ago. I think i paid $150 for that woofer, and most of that money was for the fancy Kevlar sandwich cone, not the motor.

27 hz FS nothing to write home about either. Scan Speak produced woofers with 19 hz FS even in those days, not that FS is relevant to anything, just saying Focal seems to be proud of it.

and here is my man Jeff Bagby ( he was around in the DIY scene even when i was a kid ) chiming in:

Use the T/S parameters at your higher voltage and then just plug them into a standard box model. It should give you predictable results on bass tuning and performance.

of course Jeff is a gentleman so i have to translate what he is saying here. he’s basically saying that it works the same as a regular woofer just more expensive, which is the entire essence of companies like Focal. their products work absolutely fine, you just pay more for them.

and here is a quote from the OP:

Based off the trendline in excel it seems the max SPL is at almost 17 volts, but I wonder if this is ideal not only sonically but thermally since the electromagnet seems to generate a fair amount of heat.

“a fair amount of heat” well there you go - there is your answer for why nobody does this.

why would anybody want to pay extra just to have a bonus space heater installed next to their speaker for no real benefit ?

it is an absolutely idiotic product that is at the same time a brilliant scam.

now to address your post directly:

because a permanent magnet is simpler, more compact, more reliable and doesn’t use energy or produce heat.

this isn’t true. early Tesla ( the car maker ) motors were like this ( windings on both stator and rotor ), but later Tesla switched to permanent neodymium magnets in the rotors. all modern Electric Vehicles use a “switched reluctance” type motor with permanent neodymium magnets and NO coil windings in the rotor.

i watched ( on YouTube ) Sandy Munro tear down the motors of most new EVs they are all the same.

as for loudspeakers the most powerful BY FAR subwoofer motor is PowerSoft M-Force which also uses a MOVING NEODYMIUM MAGNET design, just like the electric motors in Tesla cars.

it is an order of magnitude more powerful than what Focal claims and two orders of magnitude more powerful than what the folks at Parts Express measured

and it accomplishes this without any extra coils or heat …

to summarize - stick with permanent magnets.

use moving coil for normal frequencies.

use moving neodymium magnet for infra-bass frequencies.

i’m not aware of anybody other than PowerSoft having a moving magnet transducer though and PowerSoft system costs as much as a small car.

the biggest challenges in motor design are:

1 - producing as little waste heat as possible
2 - efficiently extracting what heat is produced

the Focal design is basically THE WORST POSSIBLE ON BOTH COUNTS

Tesla motors as well as PowerSoft Motor are the best possible on both counts

when it comes to high-end audio though worst can sometimes be best …

because the goal isn’t to solve a problem efficiently but to be as inefficient as possible and to create as many problems as possible so that you can then charge more money to solve them …

this is why prosound amplifiers are class D mosfets but audiophile amplifiers are class A vacuum tubes

( in Andrew Tate voice ) do you understand now ?


of course Audiophiles will claim there is a reason why they do things a certain way - but what did you expect - for them to admit they’re full of shit ?

the reason i allowed myself to be banned from all Audiophile forums is because i literally didn’t see any value in continuing to communicate with those zombies …

i understood the game they were playing and i simply didn’t want to keep playing that game …

now, not all DIY or Audiophile forums play the same exact game - each forum has their own flavor of the game being played. and they all like to poke fun at other forums. this is like Jews and Muslims will make fun of each other’s religions but reality is religion is religion.

the truth in audio is found somewhere between Prosound speakers like JBL, studio monitors like Genelec, and OEM car audio systems like Harman Kardon …

JBL Prosound focuses on high SPL

Genelec Studio focuses on flat frequency response

Harman Car Audio focuses on deep bass

what they all have in common though is they’re selling PERFORMANCE rather than underlying technology …

the problem with DIY / Audiophile market is they sell you TECHNOLOGY rather than performance.

with DIY / Audiophile you pay for silver cables, vacuum tubes, electromagnet / field coil / alnico drivers …

do those things offer performance benefits ? no. they just offer you an opportunity to pay more for same result. i am very much done with that crap.

your goal as an aspiring guru should be to understand how those 3 things i listed above differ from each other and why, as well as how they differ from DIY / Audiophile markets and why.

to be a G_d level guru you must equally understand:

1 - technology and physics
2 - difference between markets ( prosound vs PA vs home Hi-fi vs studio vs Car Audio etc )
3 - marketing ( what people need vs what they think they need vs bragging rights vs style and bling )
4 - having good ears and taste in music

most people don’t understand any of those 4 things.

personally i started out as a teenager with a focus on 1 and 4, then later i learned about 3 and i only recently understood 2 …

i was in the scene for over 20 years before i started understanding the difference between “PA” and
“Prosound” for example …

and MOST IMPORTANTLY if you don’t want to end up like me - forced to retreat to your own website - you will need to learn how to keep what you know to yourself …

it’s kind of like Kanye West isn’t the only one who knows about the Jews, but he’s the only one crazy enough to speak about it out loud …

you must at all times be aware not only of those 4 things i outlined but also of who you’re talking to and WHERE ( what website ) you are talking about it …

when you consider all those factors you then say something that will at the same time sound profound, humorous, educational and not offensive to anybody likely to read it as well as in line with the spirit of the platform you’re on …

do that for 10-20 years plus invest actual time, money and effort into building real products or services or anything really and you will be universally loved and respected …

i couldn’t be bothered to though, i’m just a Troll :slight_smile:

for those not in the know “PA” ( public address ) is mostly low cost plastic speakers like JBL EON that are used at weddings and proms along with some powered subwoofers … the defining feature of “PA” is that they’re usually operated by the DJ himself …

“Prosound” is typically flown arrays controlled by sophisticated DSP but the defining feature is that the system is designed and set up by people who do this for a living and NOT by the DJ or whoever is providing the content that plays on this system.

so in this sense “PA” is somewhere in between home hi-fi and prosound. I actually run PA speakers with my TV to watch movies. many beginners think PA and Prosound is the same, because they look the same - but they don’t cost the same.

PA is basically like toy prosound. It’s designed to be cheap and easy to set up - friendly to beginners and broke ass wannabe DJs.

Prosound is designed to deliver high performance reliably and offer advanced functionality. Cost is generally no object with Prosound as it’s employed by established acts that mint money. Ease of use is also not a consideration because it is set up by pros that do it every day.

at first i thought that it’s simply a continuum from more entry level stuff like Behringer to the high-end stuff like JBL VTX but it seems to be two separate markets …

so outside of car audio it’s really 4 separate markets: home, studio, PA and prosound and one should understand the difference between them before one can claim to understand any one of them individually …

that is a person who only knows home audio actually knows nothing at all …

which describes 90% of audiophiles …

if there is one of those 4 that you can skip it’s probably PA, as it’s pretty much to Prosound what Hi-Fi is to High-End.


to Prosound:

is what Hi-Fi

is to High-End

i feel the need to point this out because in the Audiophile community most don’t understand the difference and argue that Prosound is trash when all they had experience with is PA …

in actual reality Prosound is the pinnacle, higher on the totem pole even than Main Studio Monitors …

everything in Audio trickles down from Prosound …

it takes about 10 years for Prosound tech to trickle down to PA, Studio and high-volume Audio products by companies like JBL and Bose … then another decade for it to reach lower volume companies and DIYers …

and then of course there are audiophools which are a solid HALF A CENTURY behind modern tech … using technology that was obsoleted in Prosound before we were even born !

I didn’t know this was actually old technology that had been used before. I didn’t do a lot of research.

I figured that it would be cheaper to build a huge coil with a cheap material like aluminum or copper, but I don’t even know if that’s the case. Ferrite magnets aren’t all that expensive.

On second thought, yeah it seems like an impractical design. All you get is more heat and no real added benefits except maybe cost savings.

The moving neodymium magnet design is another idea. Why hasn’t this been explored more? A neodymium magnet is lighter than a voice coil with the same magnetic field strength, so wouldn’t it make more sense to use it instead and make the fixed magnet a coil? This would also allow you to use a larger coil with more power handling without having to worry about its mass.

one neat trick you can do with this setup is you can liquid cool the winding, just like the windings of the motor are liquid cooled in a Tesla.

Tesla Plaid motors are about 250 kilowatts each. The most powerful conventional subwoofers are maybe about 5 kilowatts. The reason for this disparity is that in a Tesla Motor ( or any modern EV motor ) you have a pump that is pumping oil over the windings that then goes into a heat exchanger and a radiator to cool the windings in the most efficient way possible. This is possible because the windings are in the external stator, while the internal rotor does not generate much heat due to having no windings.

( i suppose you could pour cooling oil over an internal rotor as well if you really needed to … and also there are some ferrofluid cooled tweeter voice coils as well, but there is simply no need to have windings in the rotor of a motor )

Powersoft M-Force uses same concept ( external windings ) but doesn’t use liquid cooling. Even without liquid cooling the windings are more directly cooled by external air than in a design that shoves the voice coil inside a gap with limited airflow around it …

Remember the chain is as strong a the weakest link. If a voice coil is deep if any single part of it burns out the entire driver fails. So there may be good cooling to let’s say top or bottom or middle of the voice coil but if any part of the VC doesn’t get good cooling the whole driver is toast. That’s one reason why some more advanced drivers from Beyma etc can have much higher power handling is because they really focus on optimizing the cooling of that one part of VC that runs the hottest, by building special air funnels etc.

The reason we don’t see more subwoofer drives like this is because the more powerful a motor the less resistive and more reactive the impedance becomes. even B&C iPal ( Co-developed with Powersoft for use with special PowerSoft amplifier modules ) already has difficult impedance even though it still uses conventional voice coil, just a very powerful one.

This limits the range of amplifiers that can drive such a driver and also potentially requires DSP as mandatory to equalize the very low QES / QTS of such a driver.

Basically look at B&C iPal and realize it has high FS, low Re and low Qts. When people plug that driver into modeling software they realize they can’t make it work. But that’s because it was never meant to work with regular amps or without DSP.

the M-Force is the same but taken even further. It is almost a purely reactive load just like a real electric motor as opposed to mostly resistive like a typical speaker. you wouldn’t plug a Tesla motor into an audio amplifier - would you ? You need special power and control electronics to drive it. Same with the M-Force.

the M-Force was developed by Powersoft primarily to showcase their Amplification and DSP technology - to make the point that Powersoft has the technology today that can drive subwoofers of the future.

as for moving mass i don’t agree that neodymium magnet is lighter than an aluminum voice coil, but it’s besides the point as we’re talking about subwoofers here not tweeters. nobody needs 10 kilowatt tweeters :slight_smile:

the other potential downside is high inductance of large windings, but again, this is not a huge issue for a subwoofer but more importantly it is something that can be handled with DSP provided that the amplifier is a class D type that is optimized for recycling the reactive energy reflected back from the motor, as all PowerSoft amplifiers are.

as i said, PowerSoft was driving home the point that their amplifiers can recycle reactive energy and drive impossible loads. They made M-Force to prove this.

the reason it isn’t very popular is because most people want a driver they can use with ANY amplifier not to mention one they can actually afford.

regardless, the trend with high-end prosound subwoofers is towards more difficult loads … the iPal is right on the edge of what can actually be driven by a conventional amp … even so the only test i have seen of the iPal was done by Ricci of data-bass.com and he used a PowerSoft amp to test it …

so in a sense PowerSoft is a bit like Tesla - they got slightly ahead of themselves just to make a point, but the rest of the market is slowly and begrudgingly moving in the same direction because they have no choice …