Re-charging Alnico Magnets

[InventiveAudio.com]

I have a pair of K-horns from 65. I was told that Alnico magnets lose about 1% of their power per year and should be re magnetized every 20 years. Mine are long overdue, if this is true. Is there any truth to this? The speaker shop only charges 10.00 to bring them back up to speck.

Also, is it possible to remove the phase plug on a K-55 with spring connectors?

Thanks

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This message has been edited by trader on 08-02-2002 at 08:16 PM

[kenratboy]

How in the *.*. would your replace a magnet?

$10 is good, what does than include?

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Turntable: Technics SL-J3 with Audio-Technica TR485U

Speakers: JBL HLS-610

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Sub amp: Parts Express 180 watt

Center/surrounds: Teac 3-way bookshelfs

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[TBrennan]

Alnico magnets can de-magnetize from hard knocks or strong currents, some strength may be lost just over time but as to if always and how much I've heard contradictory things. Some of the guys at the Lansing Heritage forum at www.audioheritage.org are pretty knowledgable on this stuff, also some of the guys at the Altec message board. Pose this question at those forums and you'll probably start an intersting thread. Link to the Altec board on my site.

www.chicagohornspeakerclub.org

[Malcolm]

Do your 1965 K-horns work? If so, the bit about 10% loss per year is pure B.S. By now, the magnetic field would be down to about 2% of what it started out as if it were true. Your speakers would be pretty useless.

How close are the magnets to their original strength? Hard to tell without a gauss meter and the figures from the manufacturer. Probably pretty close.

Magnets can be partially demagnetized if the speakers are abused. Alnico magnets are more susceptible than ceramic magnets. The magnetic field produced by the voice coil essentially tries to demagnetize the magnet. Normally, when the voice coil's field is reduced or removed, the magnet recovers. If the voice coil's field is too strong, the magnet is not able to recover and permanently loses some of its magnetic field. If you don't abuse your speakers, you should not have a problem. If you fry voice coils, you may have one.

If I had speakers in for a recone, I would expect to have the magnets discharged before the gap was cleaned and recharged after. This is the only way to get out any magnetic particles, if there are any, in the gap. Short of a recone, I would not bother recharging the magnets.

[InventiveAudio.com]

Interesting stuff. I actually meant to type 1% a year which would make my speakers magnets almost 50% gone. My friend is an electrical engineer and he said that Alnico magents are less stable then materials used today for speaker magents. For 10.00 a driver the price seems right since I'm going to have two new diaphragms put in my tweeters. I was also contemplating sending them my mid drivers and woofers. Kenratboy-10.00 includes re-charging the magnets to changing them.

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[HDBRbuilder]

Do the speakers work? Do they sound great? Then leave em alone for Crissakes!!...and just LISTEN TO EM!!!

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[Malcolm]

At 1% per year, they would be down to about 70% of what they started with. My guess is if they were actually that discharged you would be dissatisified with the sound.

I don't think less stable is the correct description. Left alone, they are not going to change much. It takes an external influence to demagnetize them, like a magnetic field or a big physical impact. Inside the speaker cabinet, the magnets are pretty well protected from these influences. The difference with the newer, cheaper materials is that they are more difficult to magnetize, and correspondingly more difficult to demagnetize.

At $10 a piece, price is not much of an issue. If you send the mid drivers, you might want to replace the diaphragms while you are at it. Keep in mind that when shipping woofers, there is always a possibility of damage. Even a minor frame tweak can have consequences.

[InventiveAudio.com]

HDR,

They sound good but when you buy something that is almost 50 years old components start to go bad and degrade. Who knows if they sound right. My Cornwalls are definetely more lively but harsher at higher volume levels. My Heresy seem to be more articulate in the mids. I knew something wasn't right and found a blown tweeter in one of my K-horns( I believe I bought them like that). I think they can sound better but I also think that to do mae them sound better I need to change the crossovers and do some tweaks like getting rid of oxidized wiring and if the magnets are worn they need to be re-generized. If what the repair guy said is true and Alnico magents do lose power, after time, wouldn't it be a good tweak to re-magnetize the magnets. I like things to work right and I can't be sure that my K-horns are sounding right until I do some maintenace. Some people will settle because they don't want to be bothered, are too cheap or can't be bothered to learn. I'm not sure why you care if I want to tweak my speakers or not? I find this BB kinda slow. I'm sorry if I am posting too much. I'll back off but please don't tell me not to enjoy myself or to bring my speakers up to spec because you think it's a waste of time or bandwidth. I've contributed some good information to this board and I think your post is a bit out of line.

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[HDBRbuilder]

Trader,

I can certainly understand replacing a blown tweeter diaphragm, but the other drivers in your k-horns are very likely just fine and will give you no problem whatsoever. The wiring, if corroded needs to be addressed, too(but that may just necessitate stripping the wire back to get a better connection)...but if something isn't OBVIOUSLY WRONG with the components, then why go through all the bother of messing with them just because some "tech" or "engineer buddy" is feding you a bunch of THEORY?

Those woofers have less likelihood of having any noticeable de-gaussing than they have a likelihood of having a voice coil dust-cover separation!! And the mid-drivers are probably just fine, unless they have a bunch of crap built-up in their"screen" area.

Once again...the Alnico magnets take a serious beating to de-gauss(something like being rapped with a hammer a number of times)...OR...like any other magnet, they have to be extremely close to another magnetic field for a good length of time.

Keep in mind that the cobalt used in them became EXTREMELY EXPENSIVE in the 1970's due to our federal government's "apartheid" stance against South Africa (where the cobalt was generally processed) and Zaire's warring and genocide(formerly the Belgian Congo, where most of our cobalt was sourced)...and this reason led to the demise of the alnico magnetted drivers...COST!!!

When the changeover to ferrite mud slurry magnets from the previous alnico occurred in the industry, alot of hype concerning the "superiority" of ferrite mud over alnico came about in an attempt to hide the truth about the situation...COST!! And, at first, it was ONLY hype...it took awhile for the mud magnets to get to the reliability of the Alnico...but it soon did!!

Even at Klipsch, we had alot of problems with the mud-magneted drivers we changed over to early on...the magnets were more easily broken or cracked in shipping, and our sources had to re-vamp their packing methods, etc. It was also found that the square mud magnets tended to have equal performance to the round mud magnets, and it cost less to produce them square than round for our suppliers. Other problems cropped up, but the industry set about solving them. Whenever the industry has been using a particular type of material for many years due to its superiority and is left without this material, but has other options, it takes awhile to "work out the bugs" in the new material.

In other words, between the theory and hype about the mud vs alnico magnets, and without "chalking up" the real reason for the changeover(COST!!), much of what was said at that time has somehow become "gospel" over the years. Oft-times the most miniscule of differences can be blown WAY out of proportion!!

If you feel a need to improve the woofer performance of your k-horns, it will likely not have anything to do with the magnets in them having de-gaussed...but a much more viable option would be to take some compressed air and direct it into the woofer motorboard throat and watch all the crap that comes flying out of the back of the bass bin that has "somehow managed to accumulate in it over the years!!", IMHO...add to that any replacement of corrosion problems and you SHOULD BE ALL SET to enjoy your purchase!!

My advice is to follow the "if it ain't broke, don't fix it" axiom.

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[TBrennan]

Trader---I see Don McRitchie addressed this with you, he's very astute and his advice is reliable.

[HDBRbuilder]

Hey Trader,

those k-horns are YOUR toys, so play with them anyway you want...I was just trying to point out that all this re-magnetizing and such will likely be a waste of money(no matter how miniscule) and you outta give the speakers a chance to perform for awhile(once you get those tweeter diaphragms into them and solid connections) before you decide to clean house with the rest of the components in them! I hate to see anybody waste money unnecessarily...I wasn't raised up that way!

If you want to degauss those magnets just to re-gauss them, go for it...but what I said about crap building up inside the folded horn still holds true...there is absolutely NOTHING to keep those little cobweb spiders from getting into those bass bins and then the dust gathers up on those webs and then....well, I hope you see my point...there other things that can get up in there too!!!...just open the door to the bass bin, unscrew the bolts securing the woofer, un hook its wires, remove it, then give a good blowing out to the bass bin from the FIRING END, IOW the motorboard throat opening...and watch the crap come out of em!! It is also a good sign that crap is built up deep into the bass bin if you see an inordinate amount of dust gathered up on the face of the woofer cone when you remove it...after 37 years, there SHOULD be at least SOME!!

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[InventiveAudio.com]

Check this link out. Lots of great information about Alnico magnets: http://www.audioheritage.org/cgi-bin/gforum.cgi?post=759;sb=post_latest_reply;so=ASC;forum_view=forum_view_expandable;guest=6021

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[HDBRbuilder]

Trader,

I read the posts on that site...and am quite happy that (for once) somebody "in the know" has confirmed what I was told when I asked these same questions while working at Klipsch when the changeover to ferrite slurry magnets from the previous alnico occurred...BUT...COST definitely WAS the reason for the changeover...here is why:

Agreed...the NORMAL source for cobalt dried up due to trade embargoes with Zaire(over the genocide in its civil war of that time)which was the major source point for cobalt for the WESTERN WORLD, NOT the ENTIRE WORLD, AND the major processing center for this cobalt also had trade embargo sanctions put against it at about the same time due to its "apartheid" stance(South Africa).

This action left only three major sources of cobalt available to the WESTERN WORLD:

1. Canada...BUT its cobalt was in its far northern territories and was nowhere near cost-effective to produce!!

2. The U.S.S.R., BUT, even though at that particular time, there was a "detente" phase in effect where trade with them was actually going on for SOME things, there was NO GUARANTEE that, once we started importing it, their government wouldn't change its atttitude toward "detente"(or our government, for that matter) and reduce or completely cut-off supplies...BESIDES, they were asking TOO HIGH a price for it, anyway!!

3. Mainland China, same reasons as in U.S.S.R., but at least they had a lower asking price!!

So, the real reason is not only UNAVAILABILITY, but also COST...and there has ALWAYS BEEN a trickle of cobalt from these other sources, but it was VERY EXPENSIVE...which, again leans more towards the COST reason...BUT...

There ARE other sources for cobalt today...sources that are just now being realized due to the vast mineral exploration that has occurred over the past quarter century...and it appears that the cost will be fairly low, once these sources are being exploited...Brazil is one of these sources...as a matter of fact, Brazil, with its vast quantities of (pretty much as yet unexploited) various mineral wealth...COULD be, along with Mainland China...one of the TWO MOST LIKELY CANDIDATES for world economic power in the future!! Both of these countries have vast mineral resources that have been relatively un-tapped until just recently!! Watch em grow into MAJOR mineral giants over the next few decades!!!

As for the alnicos losing their gaussing over time, like I said...it would take severe blows to severely de-magnetize them...such as numerous raps with a hammer...or, like the moderator said...severe peaks run through them...which will likely blow the woofer, anyway...long before the magnet is de-gaussed...in a k-horn...besides, most k-horns never see abuse anywhere NEAR the abuse of power that "PRO" speakers see...again as that moderator said...and as for blows to the woofer...in a k-horn...the blow has alot of wood to get through BEFORE it can reach the woofer magnet!!

Here are some of the questions I remember asking when Klipsch started getting the mud-magneted drivers in while I worked there:

1. Why are the magnets on these new drivers different from the ones we have been using? Answer: These are ferrite mud magnets, all that stuff going on in Africa and our trade embargos have kept the driver companies from getting the mineral they need to keep producing the old style of magnet.

2. Are these magnets as good as the old ones? Answer: Well, that has yet to be seen, but they are SUPPOSED TO BE....right now, our worries are about the damage these new drivers are getting in shipment though...have you seen all the broken woofer magnets over in shipping? It appears that they are not as hard as the old alnico ones and they are getting a good knocking about when being shipped...we have also had way too many rejects after testing of them...hopefully the supplier will solve this soon...our production is sufferring from this!!

3. If you had a choice, which ones would you prefer in YOUR OWN speakers? Answer: The old Alnicos, because it is hard to argue with success...and they have been successful over the years in holding up to ungodly numbers of hours of usage in our tests...24 hours a day for a year or more ...you've seen what we put em through!! Have you noticed that we have kept back a number of the Alnicos? There is a reason...some of us are gonna put em in our speakers we are planning to have built soon!!

4. How long before the suppliers solve this magnet problem? Answer: Hopefully they will solve it pretty damned soon!! We are hurting here!! Everything points to the new magnets being every bit as good as the Alnicos, but we are beginning to have our doubts with all these problems the suppliers are currently having producing them and shipping them!! At least the price on these new ones is a bit lower than the price for the old ones...that helps out some!!

5. Why are the new magnets square instead of round? Answer: Well, at first they were making them round, but they sent some to us to test that had the square magnets and we found no difference in performance, and they said it was cheaper to make em square, so that is how they are making them for us now.

Note: These are just some of the questions I asked...and the answers given are from a compilation of answers(all pretty much the same) from the different engineers who were there at the time!! They all said that the performance was about the same, and one said that he preferred the square mud over the alnicos because they were easier to use in some applications and were a bit less expensive.

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[Don McR]

Hi HDBRbuilder

In describing the events behind the switch to ferrite magnets from Alnico, I think we are down to discussing semantics. There is no question that availability is a function of cost. As with everything, you can purchase the "unavailable" if cost is no object.

However, for practical purposes, Alnico magnets were unavailable to loudspeaker manufacturers for a short period beginning in 1978. To my knowledge, all speaker manufacturers outsource thier magnet supply from third parties. In JBL's case, their supplier was Arnold Engineering. In 1978, Arnold informed JBL that they would not be able to supply Alnico magnets in production quantities for the reasons you cited. JBL had no choice but to begin a panic program of re-engineering their bass drivers to use ferrite magnets.

This change was not inconsequential. The first prototype ferrite conversions sounded significantly different from the Alnico drivers they were intended to replace. It took a fair amount of investigation to determine why. The main problem was due to higher flux modulation in the ferrite drivers.

For those who are not aware, flux modulation refers to dynamic changes in the strength of the permanent magnetic field. It is caused by the electromagnetic field generated from currents in the voice coil interacting with the permanent field generated by the fixed magnet. Even at low power levels, this modulation results in distortion. At high levels, it can permanently demagnetize an Alnico driver.

Alnico magnets are conductive and act as a shorted turn to stabilize the permanent field. Thus, this issue is largely mitigated in Alnico designs. Ferrite magnets are not conductive. Therefore, a copper shorting ring was added to the pole piece of ferrite designs to address this issue.

A second problem was the unsymetric fringe flux field generated by the external magnet topology of ferrite designs. The internal magnet Alnicos generally had magnets that were smaller than the pole piece so that they were inherently undercut. This meant that the fringe fields above and below the gap were symmetrical. The initial ferrite prototypes had the gap adjacent to the massive iron pole piece. The permeable pole piece generatied a much higher fringe field below the gap in comparison to above it and this resulted in a nonlinear response. JBL addressed this with an undercut pole piece in their SFG drivers.

JBL had an uphill battle to convince their customers that their final production ferrite drivers were as good, if not better, than the Alnicos they replaced. Part of this was due to their own advertizing. For years JBL had touted the advantages of their Alnico speakers over the "cheaper" ferrite designs of their competitors. The greatest skepticism of the change was in Japan where JBL had a cult-like following for their Alnico drivers.

One of JBL's engineers related to me an interesting anecdote about this issue. He was sent to Japan to introduce their 136H 15" bass driver that was a ferrite conversion of the Alnico 136A driver that was the primary LF transducer in all of JBL's studio monitors and large home systems. He replaced the 136A drivers in a Japanese reviewer's reference JBL speaker. Unexpectedly, the system sounded different.

The reason for the differnce goes back to the subject of this thread - Alnico demagnetization. The 136A's were found to be partially demagnetized. In a ported system, this resulted in around a 3db drop in output in the 200-500hz range. The ultimate low end was not affected since this is governed more by the enclosure tuning and not the direct output from the driver. By equalizing the ferrite driver to have the same response dip as the partially demagnetized Alnico, the overall sonic character of the system was restored.

What is interesting about this anecdote is what it has to say about the prevelance of Alnico demagnetization. You have to understand that speakers in Japan are seldom driven to high levels. The small rooms and lack of soundproof construction in a home environment prevent this. Nonetheless, the reviewer's reference system was definitely demagnetized. The reason was likely a momentary, unintentional power spike sent though the system.

In my twenty years as an audiophile, there have been more occasions than I care to admit where I have done something idiotic and found myself leaping for the volume control. Some of my more stellar moments include yanking out the headphone plug with the volume up, swapping cables with the amp turned on and dropping a tone arm onto a record with the volume set high. With an Alnico speaker, it only takes one idiot moment to partially demagnetize the motor without damaging the coil, cone or suspension. With a vintage speaker, you will never know unless you actually measure the gauss levels in the gap. The sonic difference can be subtle, and unless you have a reference to compare to, you likely won't realize that it has been affected.

I have to admit that with a Khorn, your chances of permanently demagnetizing and Alnico driver are less than with just about any other speaker. That is because its extrordinary efficieny means it is likely coupled to a lower powered amp. Nonetheless, it is not completely immune, and if I were having a driver repaired, I would have it checked for demagentization at the same time.

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Regards

Don McRitchie

Webmaster

Lansing Heritage Website

[HDBRbuilder]

Hi Don,

I just wonder...did JBL have the same problems with an inordinate amount of fractures in the ferrite magnets it received from its supplier during the shipping of them early on in the changeover from alnico to ferrite mud slurry? We had lots of them...but then again, ours were already on produced drivers...not just the magnets themselves. Either way, long before I left there, those problems had been resolved...but I am still curious about it.

And, yes...most folks don't tend to throw a kazillion watts into a k-horn...especially after they pay for them and know how much they cost and how to utilize them....unless the parents are gone and the kids are home alone and one of their buddies calls up and says..."Hey, man...I got this new SuperDynaWattMonster amp that puts out like ten billion watts...and, since your parents are gone...how about I bring it over and we hook it up to your Dad's K-horns, and invite everybody over and do some serious hip-hop bass jamming to them bad boys? I bet they can REALLY vibrate the house with all them watts going into em when we crank that amp way up!!"

Nawwww, kids would NEVER do something like THAT...would they?

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This message has been edited by HDBRbuilder on 08-04-2002 at 01:28 PM

[Don McR]

Hi HDBRbuilder

I don't know whether JBL had a problem with the raw magnets shipped from their supplier. However, protecting the magnets on their finished drivers remains an issue to this day. Because of the fragility of the ferrite magnets, JBL fits a protective rubber "tire" around the magnets of all of ferrite drivers sold to OEM's.

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Regards

Don McRitchie

Webmaster

Lansing Heritage Website

This message has been edited by Don McR on 08-04-2002 at 01:54 PM

[lynnm]

Hello Dere Don McR!!s>c>

Welcome to the Klipsch Forum Don!!

I sniff around the Lansing site from time to time and always enjoy the foray into enemy territory - (Joking)

I hope you will become a regular here and I encourage my forum mates to visit your site frequently as:

1.) The site is very nicely done.

-and-s>c>

2.)You have some fascinating historical information there not only about James B. Lansing and the JBL company but also about the early days of High Fidelity.

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It is meet to recall that the Great Green Heron rarely flies upside down in the moonlight - (Foo Ling ca.1900)Andf>

This message has been edited by lynnm on 08-04-2002 at 02:33 PM

[InventiveAudio.com]

Oops!

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This message has been edited by trader on 08-04-2002 at 06:33 PM

[kenratboy]

Hi Don!!!

I see your couldn't resist the force! Welcome!!!

This forum has a MUCH higher volume, but it is a little less serious that Audio Heritage, which is both a good and bad thing!

I hope you can get some more JBL lovers on this site to come over to your site!

I flow between both of the sites, so I don't think people will abandon one for the other.

Political, moral, social, and economic issues are welconed (by most) in the General Section...

Enjoy!

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Receiver: Sony STR-DE675

CD player: Sony CDP-CX300

Turntable: Technics SL-J3 with Audio-Technica TR485U

Speakers: JBL HLS-610

Subwoofer: JBL 4648A-8

Sub amp: Parts Express 180 watt

Center/surrounds: Teac 3-way bookshelfs

Yes, it sucks, but better to come. KLIPSCH soon! My computer is better than my stereo!

[djk]

Some comments on Alnico drivers. Unless you can afford to rebuild them, don't buy used pro sound drivers. The woofer magnets are often de-poled from long hours of hot, high power use with huge, high current transients. YOU CANNOT RE-CHARGE THE MAGNET WITHOUT RE-CONING !!! An exception to this would be a Tannoy, the reason here being the cone can be removed and re-installed with only a screwdriver. The cone has to come out before it can be re-charged. Alnico drivers used in home use only are not likely to have a problem, unless they are rusty. Alnico requires a keeper, or top plate, in order to not self-discharge. Ever play with a big Alnico horse-shoe magnet? You take off the keeper and they go dead. Rust pushes the magnet away from the magnetic return casting and/or top plate away from the magnet. In the case of woofers the midrange response suffers, compression drivers loose their top end. Compression drivers are frequently dropped and the top plate either hopps or shifts. A trip to 1)the machine shop to re-face the rusty parts, 2)the guy with the magnetizer, and 3)the re-coner, and lots of $$$$ will have it like new again. The last time I talked to JBL about this they begged off, saying the adapters for magnetizing the Alnico compression drivers were destroyed in the Northridge 'Quake. If rusty drivers are re-faced the magnetic return casting must be trimmed until the top plate is flush again. IMO the only JBL parts worth this much effort are the 150-4C and 375, both collectors items.