I have disassembled my speakers; ADS L1590/2, to upgrade the internal wires. I noticed the magnet size of midrange drivers was as close as those on woofers, they’re simply slightly smaller. I wonder is it possible use the magnets of woofers in midranges as the two drivers have the same 2-inch voice coil. What are pros and cons in performing this? Actually, I also have a pair of L1590/2’s damaged woofers in my hand, maybe, I think I could upgrade my midrange drivers with the magnets from these woofers.
Do you have an Industrial size Magnetizer/Demagnetizer?
Big mean machines, not for the faint hearted.
https://en.vatmag.com/products_28/364.html
Big mean machines, not for the faint hearted.
https://en.vatmag.com/products_28/364.html
I think of it a lot more easier. I would remove the magnet from the damaged woofer’s frame, drill the holes on the magnet for mounting screws of midrange faceplate, assemble the magnet and faceplate together, and finish the process. Isn’t that easy? But the question is the magnetic power/ field/ strength will absolutely change, the positive way I think. So what will be the result?
You can not.
Unless you demagnetize it first.
Look again at the machine I show above.
You can not drill a magnet.
It takes a diamond tip tool, it needs to be demagnetized first, not even Factories drill them, holes are created in the shaping die while ferrite is still a paste.
Once it is cooked in an oven, it becomes harder than anything except diamond.
You can not assemble an already magnetized magnet.
As you see, next to impossible.
If you could remove and replace a magnet, all that messing would lose about 40% power. (Field strength)
The proper way is to demagnetize > do whatever work is needed > remagnetize
These are not weak fridge door magnets you can attach and remove with your fingers but some 1000 times stronger, so much so that they are magnetized inside the already assembled magnet structure.
As a side note, besides magnet diameter, I expect both magnetic circuits to be different and incompatible.
Woofers - skawkers - tweeters have absolutely incompatible requirements.
Just as a final comment.
An accident that sometimes happens with speakers is that if you bump them hard in a certain way, (usually cabinet falls on its back), heavy magnet unglues from front plate and by the strong magnetic attraction it shifts sideways.
Polepiece sticks to top plate and pinches voice coil, blocking cone movement.
Speaker "sounds like a tweeter" because it loses all lows and mids ... it can't move!
You hear weak highs only because coil still vibrates in place.
Obviously speaker is useless.
Normal speakers get junked, period, but on certain old very expensive ones it may be worth repairing that.
As said above, they require disassembly (removing cone, voice coil, spider, etc.), demagging, re centering (using centering fixtures), remagged and reassembled.
We are talking a couple hundred $ jobs.
So afaik only two speaker repair shops offer that service in all of USA, go figure.
Great Plains Audio who deal with classic Altec Lansing speakers and Orange County Speakers who deal with James B Lansing ones, both being the Kings of the Jungle in Pro Audio (initially Cinema Theater speakers) from about 1935 on.
https://greatplainsaudio.com/services/
https://www.audioheritage.org/vbulletin/showthread.php?38151-Orange-Co-Speaker-is-gone
which apparently are gone 🙁
Their top Technician continues on his own though.
I bet there are a few top reconers who have needed machinery, count'em with the fingers of one hand.
A Factory such as Eminence (or Celestion) certainly can, but they are into manufacturing, not servicing.
An accident that sometimes happens with speakers is that if you bump them hard in a certain way, (usually cabinet falls on its back), heavy magnet unglues from front plate and by the strong magnetic attraction it shifts sideways.
Polepiece sticks to top plate and pinches voice coil, blocking cone movement.
Speaker "sounds like a tweeter" because it loses all lows and mids ... it can't move!
You hear weak highs only because coil still vibrates in place.
Obviously speaker is useless.
Normal speakers get junked, period, but on certain old very expensive ones it may be worth repairing that.
As said above, they require disassembly (removing cone, voice coil, spider, etc.), demagging, re centering (using centering fixtures), remagged and reassembled.
We are talking a couple hundred $ jobs.
So afaik only two speaker repair shops offer that service in all of USA, go figure.
Great Plains Audio who deal with classic Altec Lansing speakers and Orange County Speakers who deal with James B Lansing ones, both being the Kings of the Jungle in Pro Audio (initially Cinema Theater speakers) from about 1935 on.
https://greatplainsaudio.com/services/
https://www.audioheritage.org/vbulletin/showthread.php?38151-Orange-Co-Speaker-is-gone
which apparently are gone 🙁
Their top Technician continues on his own though.
I bet there are a few top reconers who have needed machinery, count'em with the fingers of one hand.
A Factory such as Eminence (or Celestion) certainly can, but they are into manufacturing, not servicing.
It depends totally on the construction and the size.
I have successfully removed magnets in the past, without to much trouble.
But certain constructions are better suited for this than others.
When it's very heavily glued, there is no way to remove them.
Which is the majority of more modern speakers.
Well you can heat them, but that will cause strength loss in the magnet.
Placing them back is much more difficult.
Unless you can take apart the entire construction, this is close to impossible or totally impossible.
Mostly because of the voice coil that you don't want to damage.
Jigs are needed in all cases.
All that being said, I wouldn't do it with anything that is bigger than simple 8 inch midwoofer.
With like a magnet size of 80mm max.
Definitely not a 15 inch woofer.
Like you said, a lot of force is involved!
Which can be very dangerous.
Ferrite and neodymium magnets don't loose their strength, only alnico (and than it also depends).
Yes, you can, sort of, with a lot of effort and with small magnets.
Back in the day, in an emergency situation (whole borough was flooded so no electricity at all), couldn't drive either, I went with a backpack to a colleague's shop carrying only a dozen 102 mm ferrite rings, magnetized them and then assembled speakers at home.
In that case, they lost about 20% flux density, not too noticeable, speakers were usable.
Now when I remove a larger (130-160 mm) shifted magnet to clean old epoxy residue, reglue and recenter it, loss is greater, think around 40%
If you test speaker on its own, it "works" , no doubt about that, and might seem normal if used alone, but side by side with an unmolested one, difference is obvious.
It loses volume but it's more noticeable in mids and highs, it loses "bite/attack".
Maybe not too noticeable in a woofer.
Problem is that you have a very nonlinear BH curve
First the "normal" case:
Ferrite is bought unmagnetized, so it starts at "0"
Then magnetizer coil applies a huge magnetizing field to it (that's why machines are beasts) reaching point "a"
Old field coil speakers (which were VERY good) just stay there.
Problem being that you must feed magnetizing coil continuously.
With permanent magnets, you remove magnetizing current, magnetic field lowers to point "b" but a lot remains (that's why it's called "remanence")
Notice "b" is lower than "a" but in any case it's usable.
Not needing to feed a field coil all the time is good 🙂
"Molested" magnet (disassembled/reassembled while magnetized):
Magnetic field will again move just because of the "mechanical" movement: being inside the speaker magnetic system and outside (separating ferrite ring from plate, removing polepiece from inside the gap) is not the same as just leaving it there.
It will still move following the same kind of curve but now starting at the "b" level.
After reassembly it will reach a new level, which will be lower than "b", that means it will lose at least some strength.
How much?
It depends on material.
Ferrites are quite "hard" so a certain %
Measurable and even noticeable by ear if tested side by side with another same type.
Alnico is trashed, it is magnetically softer, suffers even under "normal" use in certain circumstances, that's why remagging services are offered.
Never used NEO , they are very hard, not sure how would I even disassemble it, let alone reassemble.
In a nutshell:
Back in the day, in an emergency situation (whole borough was flooded so no electricity at all), couldn't drive either, I went with a backpack to a colleague's shop carrying only a dozen 102 mm ferrite rings, magnetized them and then assembled speakers at home.
In that case, they lost about 20% flux density, not too noticeable, speakers were usable.
Now when I remove a larger (130-160 mm) shifted magnet to clean old epoxy residue, reglue and recenter it, loss is greater, think around 40%
If you test speaker on its own, it "works" , no doubt about that, and might seem normal if used alone, but side by side with an unmolested one, difference is obvious.
It loses volume but it's more noticeable in mids and highs, it loses "bite/attack".
Maybe not too noticeable in a woofer.
Problem is that you have a very nonlinear BH curve
First the "normal" case:
Ferrite is bought unmagnetized, so it starts at "0"
Then magnetizer coil applies a huge magnetizing field to it (that's why machines are beasts) reaching point "a"
Old field coil speakers (which were VERY good) just stay there.
Problem being that you must feed magnetizing coil continuously.
With permanent magnets, you remove magnetizing current, magnetic field lowers to point "b" but a lot remains (that's why it's called "remanence")
Notice "b" is lower than "a" but in any case it's usable.
Not needing to feed a field coil all the time is good 🙂
"Molested" magnet (disassembled/reassembled while magnetized):
Magnetic field will again move just because of the "mechanical" movement: being inside the speaker magnetic system and outside (separating ferrite ring from plate, removing polepiece from inside the gap) is not the same as just leaving it there.
It will still move following the same kind of curve but now starting at the "b" level.
After reassembly it will reach a new level, which will be lower than "b", that means it will lose at least some strength.
How much?
It depends on material.
Ferrites are quite "hard" so a certain %
Measurable and even noticeable by ear if tested side by side with another same type.
Alnico is trashed, it is magnetically softer, suffers even under "normal" use in certain circumstances, that's why remagging services are offered.
Never used NEO , they are very hard, not sure how would I even disassemble it, let alone reassemble.
In a nutshell:
- when you vary magnetic field, it will follow the "S" or "Sigma" shaped curve.
- Unless you remagnetize it with a machine, on each "movement" it will return to a lower value than it had before
- So much so, that demagnetizers work that way: they apply an oscillating field, which is always decreasing.
These days there are those lugs or just cilinders.
Those are very easy to remove.
When it's a ring, there is no change.
I think I understand our miscommunication here btw. (or rather something I forgot maybe)
When a loudspeaker motor is magnetized again, the entire (magnetic) circuit is magnetized.
So how much the losses are, probably depends on the quality of the iron as well.
Besides the quality of the magnet itself.
I am pretty sure @Kravchenko_Audio can tell the exact details about this? 🙂
Your graph is showing you a representation of the point where a magnet will stay magnetized. You already write about heat and loss in magnetic strength. Alnico being the most sensitive to heat. But also having the softest switching from polarity to polarity so an Alnico magnet can have the least distortion motor. Can is the word. It is not guaranteed. Ferrite are much more easily energized than Neodymium. A magnetizer that can successfully charge a Neodymium magnet is very capable of charging a ferrite magnet. But not the other way around.
As for metal. Yes, it should be as low in Carbon as is possible. Carbon is the enemy of an efficient magnetic motor. Silicon Iron is good too. Iron is hard to find and terrible to work with as a machinist. Like hard sticky butter.
Mark
@Kravchenko_Audio What is your experience with the amount of demagnetization losses when a motor is pulled apart again?
Seriously if you can pull apart a motor it is pretty damaged already.
I have never taken a motor that was properly charged and easily pulled it apart. If it is properly glued the only method you have is heat it up above it's curie point and disassemble it.
If you can do this already, you have a magnet that has been cooked to pretty near it's curie temperature already.
Might come as a shock to many but loudspeakers are enormously inefficient. Ones that are 90db/watt use 0.5% of the power in to actually make sound. The rest is converted into heat. Think about it. Cook top elements are generally 1kw or more. People are doing the same in a loudspeaker. Depending on the duty cycle of the music you are listening to, you can be heating up you driver motor with pulses of a couple hundred watts. It adds up quickly. And this is called power compression.
Again, preaching to the choir, copper or aluminium as it heats increases it's resistance. requiring more power to get the same relative SPL.
Mark
@Kravchenko_Audio and hypothetically speaking? 🙂
70s/80s drivers are not so hard to pull apart btw, often there is a little edge you can put something underneath and with a the right force it snaps right off.
Or you can squeeze some kind of spatula in between.
Same goes for cheap woofers, which are still manufactured like it's the 80s.
Anything serious, and forget it, I totally agree 🙂
Yes, efficiency is bugger all.
70s/80s drivers are not so hard to pull apart btw, often there is a little edge you can put something underneath and with a the right force it snaps right off.
Or you can squeeze some kind of spatula in between.
Same goes for cheap woofers, which are still manufactured like it's the 80s.
Anything serious, and forget it, I totally agree 🙂
Yes, efficiency is bugger all.
I once visited a motor (electric) rewinding shop, Everytime a permanent magnet dc motor was taken apart, it had to be remagnetized - something that was new to me, and when they demonstrated the process you were asked if you had a pacemaker, and to leave your phones in a Faraday cage, and there was one hell of a crack as they gave it the juice. I inherited some old Sony speakers, one of the magnets had come unstuck, I did think of regluing it, but it became obvious that it REALY didn't want to stay central.
This will be very low BL high Qts loudspeakers. Big bump around 10 to 150 hertz nothing much below.
I tend to design unobtainium. Easy stuff I send people to the good manufacturers.
Mark
Suppose one buys solid 12,5cm (5") outer dia, 2,5 cm(1") thick ring magnets new, does the need to magnetize still exist after putting/glueing those between the pole pieces? I have seen manufacturers do this standard, but do not know how necessary that actually is.
@mark: do you (re) magnetize your assemblies in prototyping, or do you receive those motors ready from manufacturers?
@mark: do you (re) magnetize your assemblies in prototyping, or do you receive those motors ready from manufacturers?
@Boden
Obviously I can't talk for Mark, but when designing something new from scratch, it's always possible to get sub-assemblies.
So like the iron+magnet in one go.
Later on you can always fit in the cone+coil with some jigs and fittings.
On a similar way I have seen people using triangle shaped jigs (kinda hard to explain) to fit and center a magnetized magnets on the iron parts.
An than fitting the rest of the parts
It's not ideal, can be VERY sketchy, but it works.
This doesn't work when the cone+coil is already mounted like the TS wanted.
Obviously I can't talk for Mark, but when designing something new from scratch, it's always possible to get sub-assemblies.
So like the iron+magnet in one go.
Later on you can always fit in the cone+coil with some jigs and fittings.
On a similar way I have seen people using triangle shaped jigs (kinda hard to explain) to fit and center a magnetized magnets on the iron parts.
An than fitting the rest of the parts
It's not ideal, can be VERY sketchy, but it works.
This doesn't work when the cone+coil is already mounted like the TS wanted.
I receive them ready. One of my old clients assembles with live magnets. It requires a very robust press like jig as the magnetic strength is nearly 400kg. Not for fingers you want to keep!
Genrally I work with Neodymium. Reasoning is brutally simple. You ship according to volume and mass from the factory. You ship again from your distribution point on volume and mass again. Add those two together for a ferrite motor and you end up a little more than the cost of a Neo motor. Playing with reasonably sized Neo magnets as in 100mm diameter with say a 53, to 53mm hole is not something you move with your fingers, or with a screwdriver.
Re-magnetize, I do not a magnetizer here. Quite an expenditure truly. Perhaps one day. If I get one I want to be able to magnetize some truly large motors. Then I can do custom work!
Mark
That is not exactly designing. That is playing with Legos. You are constrained by what another has already done.
You may know [..redacted], but many will not know that the multi-magnet stacked up woofers that you see are rarely if ever actually charged fully.
Also it is not common knowledge that it is surface area of the ferrite magnet that allows for the transmittance of the magnetic flux. not a great thickness. You quickly hit a point where more thickness is doing nothing for you. It is simply there to take up space for a long voice coil. Not good engineering.
Mark
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