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magger
04-10-2006, 03:34 PM
Hello forum,

Question ... I know it is possible to recharge alnico magnets back to their respectable gauss values. Is it possible as well to recharge ferrite magnets? I own various JBL items (alnico drivers, ferrite based basses etc.) I have experienced that alnico JBL items have lost their gauss levels due improper storage/transport/load etc.

That's the reason I post this question. Is there a difference between alnico vs. ferrite magnetic structure losing it's gauss due to mishandling, or (improper)load etc?

MISC: I am from Europe, anyone aware of a place inside Europe that regausses magnets? The case here is varioius JBL items.

Thank you,
Magger

Hofmannhp
04-11-2006, 12:31 PM
Hello forum,
MISC: I am from Europe, anyone aware of a place inside Europe that regausses magnets? The case here is varioius JBL items.

Thank you,
Magger

Hi Magger,

the only company I know is "D. Lange u. Partner" in Berlin a well known Isophon specialist which regausses others too.

HP

Steve Gonzales
04-11-2006, 01:00 PM
You may find this interesting:
http://audioheritage.org/vbulletin/showthread.php?t=4031

There is a search function here that is helpful. It is located in that thin black bar located above. I've never heard of recharging a ferrite magnet as part of routine maintenance. It is strongly recommended to recharge AlNiCo drivers here though.

magger
04-11-2006, 01:29 PM
Steve and Hoffmann,

I was wondering if you have any idea about how much it costs to regauss alnico magnets, and if it's possible to regauss the magnets without removing the diaphragm?

Thank you for your inputs.

toddalin
04-11-2006, 01:33 PM
OCS quotes $45 just to regauss or $25 if you are having the speaker redone. Thus, it seems logical to assume that they can do a working speaker. I think JBL quotes (quoted) $27.


Steve and Hoffmann,

I was wondering if you have any idea about how much it costs to regauss alnico magnets, and if it's possible to regauss the magnets without removing the diaphragm?

Thank you for your inputs.

Mr. Widget
04-11-2006, 03:11 PM
... and if it's possible to regauss the magnets without removing the diaphragm?Yes.


Widget

Hofmannhp
04-11-2006, 03:42 PM
..... to regauss .......

Hi All,

a man to remember, ...certainly as important like James B. Lansing.
Carl Friedrich Gauss 1777 - 1855,... born in Braunschweig / Germany.
HP

BTW: he looks a little ugly hearing some want to recharge Ferrites

Guido
04-11-2006, 03:49 PM
Yes. Widget

Also the Alnicos? I don't think so.

Mr. Widget
04-11-2006, 04:21 PM
Fear not Guido... It may depend on the equipment that a specific shop has, but OCS does them as complete speakers.


Widget

edgewound
04-11-2006, 04:54 PM
OCS does recharge assembled, coned-up speakers...and without cones or diaphragms installed.

The problem with recharging assembled speakers is there is no way to check the flux density in the gap...just hope it's fully charged. It's really the only thing to do if you don't want to recone a vintage speaker...like an Altec 417 for guitar...or a D120/130/140F that still has OEM parts

tom1356
04-11-2006, 05:17 PM
Is there someone in the Boston area who recharges alnico magnets with the cone in?

Zilch
04-11-2006, 05:38 PM
To the best of my knowledge, I've never run into a driver that required recharging.

From the discussions here, there's only three places in the U.S. that do it, and one known in Europe, so it isn't "routine."

Yeah, I read the article about alnicos losing strength over time. Might be worthwhile if somebody relinked to it in this thread.

I don't believe it's even a consideration with ferrites, tho, including if the magnet is disassembled from its "keeper."

What's JBL's direction to its authorized reconers on this subject?

Then again, the question is, "How would I know?"

Gaussmeter if it's a compression driver with diaphragm removed or a coneless basket?

Like, which, and how much to acquire one? Are we talking hobbiest gear here?

With intact woofers, we can measure the BL product with WT2, perhaps?

Steve Gonzales
04-11-2006, 05:54 PM
I've read that an alnico driver should be recharged here so many times that I figured it was routine to do so. I've never run into one that needed it either. Can't IMAGINE what hell I would have caught if I were to advise otherwise Zilch:blink:

Here are some suggestions by people whose opinion you might respect
http://audioheritage.org/vbulletin/showthread.php?t=8555&highlight=recharging+alnico

Robh3606
04-11-2006, 06:13 PM
To the best of my knowledge, I've never run into a driver that required recharging.




I've never run into one that needed it either.


Well I have not either so we 3 with this experience. That does not mean however that they should not be. I think it all depends on how hard the drivers are used. All my Alnico drivers are from home systems and that could make all the difference. I don't think you see this in home system drivers as often as Pro Drivers. I also think any reduction in flux would be much less for the same reason. How would you know if a driver had lost 10% of it gap strength?? What do you have to compare it to?? Not like we all have a NOS bin to pull from for comparisons. Home system drivers just don't take the kind of abuse a Pro Driver does on one tour. Some of these drivers have been in systems for decades under god knows what conditions. With Pro drivers I think it would be a foolish gamble to recone without checking the gap strength.

Rob:)

Steve Gonzales
04-11-2006, 06:17 PM
That doesn't mean I recommend the contrary. So, given that, unless you know where and how a driver has been used, every minute of it's work cycle, I suggest you recharge it if you can.

Robh3606
04-11-2006, 06:46 PM
Hey Steve

That's the problem with EBay and 20+ year old drivers. Who knows where they have been with the Pro Drivers. At least the domestic stuff you may actually get a decent working driver set if you ignore the fact they should probably be reconned on the age factor alone. I am not gonna lie on that one I am prime offender of ignoring that simply because I couldn't afford to recone the drivers I have. Most of the drivers I have are ferrites for that reason. If you need to recone down the line it's one less thing to complicate matters trying to find a place to recharge the magnet. The main exception are my LE-14A's which have been refoamed. I plan on starting to building up a pair of L250Ti's is a month or so and want to get Le-14H-3 too use for this very reason. They work great as subs but I have no idea what to expect from them above that range. I certainly would not use them the way they are in an application like the L250ti without a recone and recharge which is frankly out of the question cost wise.

Rob:)

Ducatista47
04-11-2006, 07:49 PM
I have searched the posts and read what I could find, and hope I have not missed anything. What I need to ask, and I hope I'm not being too thick here:

I have aquired two 2245H baskets that have been through many years of ignorant disco torture in French Canada. They had 2245's instead of 2242's, so they used them...and used them...and used them. They appear to have been blown up and burned out, reconed with waffle surrounds and blown up again; perhaps several times, I suppose. The last fried parts are still in place. VC's read open and rub a lot, cones & domes are abused, surrounds are torn, only the spiders seem to have survived.

My question is: are you saying the motor is going to be in good working condition after all this? No demag issues or heat damage of any kind? If there ever will be a case for ferrite remag, is this it? Inquiring ignorant Peoria mind wants to know.

Clark in Peoria

QwertyAccess
04-11-2006, 11:41 PM
Only my opinion and theory in any case, but i believe after that kind of abuse the ferrite magnet could definately use a recharge, alcino is supposed to be really easily demaginitized "permanetly" compared to ferrite magnets under high power, but if enough abuse is given to a ferrite magnet over a longer period of time i would imagine it would have lost some power atleast, i cannot imagine it to be at the same levels as it was new in that case.

franz
04-12-2006, 01:11 AM
Hi there!

Although I am for sure not among the most knowlegebale members here, I guess its time to "de-mystify" the subject a bit.
Every single loudspeaker manufacturer has to have a magnetizer to get their ferrites charged! I donīt think they are assembled in charged condition for obvious reasons.
So itīs nonsense :bs: to say that there are only 3 or 4 places in the US and Europe together that can handle it.

I once had a K 130 recharged at a Magnet manufacturer in Dortmund/Germany and I know there are at least some other places in Germany alone that can do it. Some (of the better) recone shops have their own devices or know a place where to do it. BTW the process was succesfull in almost restoring the original Q values.
The question is if their charging coils are big enough to accomodate a large magnet and the joules they can give it are sufficient. Even more a problem might be to find the right guys who are willing to do it and handle the shipping, billing, etc. involved. Charging itself only takes a few seconds and seems to be far from complicated.

IMHO the simplest way to detect a low gauss magnet is to take a close look at the free air impedance curve. If a woofer with a decent magnet and normal B values of around 1 T / 10000 Gauss indicates a max impedance of only 10 -20 Ohms thatīs a clear sign that either the coil has shorted windings or the magnet is low. "Normal Q" woofers I encountered had Z max values of 60 - 200 Ohms depending on field strength and Q es of course. The best way detecting a problem obviously would be to compare a speaker in question to a good sample impedance-wise. Also spl in midband is usually some dB lower for a decharged magnet.

Bill Hanuschak (GPA) once told me that the only way to effectively demagnetize a ferrite magnet is to put in the oven and heat it beyond the curie-point which is > 250 °C AFAIK. So its unlikely to find a weak ferrite magnet while alnicos definitely are prone to it when pushed hard.

Hope that helps.

greetz

Franz;)

QwertyAccess
04-12-2006, 01:42 AM
mmm baked Ferite magnets, sounds good...

jbl_man_uk
04-12-2006, 01:42 AM
Hi All,

a man to remember, ...certainly as important like James B. Lansing.
Carl Friedrich Gauss 1777 - 1855,... born in Braunschweig / Germany.
HP

BTW: he looks a little ugly hearing some want to recharge Ferrites

Yes,someone even named a speaker manufacturer after him in Hollywood...shame they are no longer around!

Rolf
04-12-2006, 04:30 AM
Fear not Guido... It may depend on the equipment that a specific shop has, but OCS does them as complete speakers.


Widget

So does Seas in Norway.

4313B
04-12-2006, 04:36 AM
How would you know if a driver had lost 10% of it gap strength?? What do you have to compare it to??You measure it. It's a transducer. If you have no way to measure it then have your reconer measure it for you and recharge it if needed. For me personally, it is SOP to recharge alnico magnets. $15 at Great Plains. We've discussed this before. It isn't anything to devote an entire thread to. Just do it.

Robh3606
04-12-2006, 05:07 AM
You measure it. It's a transducer.

Hello Giskard

Well that makes sense. What would you look for in the measurements?? How much reduction in gap flux density is acceptable?? I just grabbed 10% off the top of my head. When a beat up old warhorse comes in how much are they discharged?? With say 15%-20% give you clearly measurable/audible differences??

Rob:)

4313B
04-12-2006, 06:17 AM
What would you look for in the measurements?Reasonable consistency between driver pairs.

As for the rest of your questions one can work through the formulas to determine the effects of motor strength. (A quick source of some formulas - http://www.birotechnology.com/articles/mass.html)

For those less inclined towards math I think one may be able to do simulations using BB6P.

Ian Mackenzie
04-12-2006, 07:24 AM
My recollection is that loss of flux will at least effect compressions drivers in the extreme Hf area with loss of output. Another reason why devices like alnico 2405's vary from one that another in hf output unless new as new.


Kinda down grade Ebays collector prices on vintage drivers been advertised as mint! :barf:

Mr. Widget
04-12-2006, 10:24 AM
Kinda down grade Ebays collector prices on vintage drivers been advertised as mint! :barf:Unfortunately true... there are those coveted "red wax seals intact" drivers that actually are good, but it isn't worth the gamble. It is better to buy a rust free beater, remag it and pop in a new diaphragm. Barring physical damage, you should be as good as new.

...and well yeah that isn't cheap, but neither is a new driver!


Widget

magger
04-17-2006, 02:53 PM
Thank you all very much for your inputs regarding this specific topic. It is greatly appreciated! Now I have a better idea of how I am going to move on with my vintage JBL gear :)

:applaud:

gtimbers
05-04-2006, 03:18 PM
Ferrite magnets do not demagnitize with time or drive. They are affected by temperature but that is reversible. They will return to normal when they return to room temperature. Ferrite is basically a lousy magnet material for speakers but it is cheap and readily available. JBL has done a ton of things within the magnetic circuit to make the material behave in a more stable manner. At 100 degrees F, a Ferrite motor will be down about 1.5 dB in level which means the midband of the woofer will be lower by that much and there will be increased output around the system resonance. The TS parameters will be completely different - as though the BL was reduced by about 18%.

Alnico magnets, by their nature are easy to demagnitize with drive. They will not change with time and their dependence on temperature is really small - maybe 1% at 100 deg.F. Alnico stability and resistance to back EMF is really good. This is why they make the best sounding magnetic structures. Unfortunatelly, given a big enough pulse of magnetic energy, they will demagnitize by up to 3 dB. The sensitivity to demagging is dependent on the specifics of the magnetic circuit and the length of the coil providing the field. Underhung woofers (LE15 and such) midranges, tweeters and compression drivers do not have sufficient back EMF fields to push the operating point of the structure below the knee. They are essentially stable regardless of input signal. The short gap-long coil speakers are the ones that have a problem. A 2235 can take a hit of up to 3 dB if a big enough hit of current takes place. 1.5 dB to 2 dB is more common. The effect does not get better or worse with time, it solely depends on how much current is driven through the coil. The more current, the more field. Once the field is bigger than a certain number, some amount of demagnitizing occurs. It is perminent (until externally recharged) and will only increase if a larger sustained current hit occurs.

Therefore, if you have a qualifying alnico woofer and you have played it loudly you have some damagging. You can have the unit recharged and it will be fine until you play it again. Exceed the critical level and it will start happening. If you never do, it won't ever demag. Most of these designs trace back to the 50's and 60's where 15 - 30 watt tube amps were the rule. They didn't have the current capability to hurt anything. With the advent of big solid state amps, the current levels went up and the problems started to surface.

Most of the qualifying 4" motors will loose 1 - 1.5 dB unless they are pummeled. Some of the older 3" with really short magnets, like the 2213A and 123A will typically be around 3 dB down. They go really easily. The old decade woofers (116A and 127A) only had to see an amplifier in the room and they got really nervous. FYI, the new 1500Al used in the S9800 can take continued pulses of 5000 watts and loose no more than 1%. The test can only be done a few times before the coil is destroyed, but the magnetic assembly is totally stable.

4313B
05-04-2006, 03:23 PM
Sweet! :)
Thanks Greg.

edgewound
05-04-2006, 03:25 PM
Wow, Greg...Thanks for the education.

It is extremely generous of you to take the time to post here with "from the Designer's Desk" info.

It's very much appreciated.

Mr. Widget
05-04-2006, 03:27 PM
Very interesting....:bouncy:



Widget

hapy._.face
05-04-2006, 03:42 PM
Holy crap!

GT- you have a unique way of saying it all. We BS each other for months on end to no real avail on certain subjects. You make a single post and "POOF"- issue is swept under the rug and we now work with facts- not opinions. If you only knew how beneficial it is to us....all I can say is "THANK YOU, SIR !!!". However, don't let this cut into making more kick-butt speakers! ;)

Travis.

moderator: Can we put a copy of Greg's post here (http://www.audioheritage.org/vbulletin/showthread.php?t=4031&highlight=alnico+ferrite+debate) ??

4313B
05-04-2006, 03:48 PM
GT- you have a unique way of saying it all. We BS each other for months on end to no real avail on certain subjects. You make a single post and "POOF"- issue is swept under the rug and we now work with facts- not opinions.You nailed it dude! A little of his time can clear up a whole lot of other time...

I suspect we are starting to see where that "Moderation Frustration" was coming from with respect to the endless threads, arguments, speculations, etc... :hmm:

Question? Answer. Slam dunk! He scores!!! Game over man! Game over...:applaud:

moderator: Can we put a copy of Greg's post here (http://www.audioheritage.org/vbulletin/showthread.php?t=4031&highlight=alnico+ferrite+debate) ??Techbot must be online right now. Looks like it's been handled already.

mech986
05-04-2006, 05:52 PM
Most of the qualifying 4" motors will loose 1 - 1.5 dB unless they are pummeled. Some of the older 3" with really short magnets, like the 2213A and 123A will typically be around 3 dB down. They go really easily. The old decade woofers (116A and 127A) only had to see an amplifier in the room and they got really nervous.

reminded me that the 116A was also in the L19 and the 125A from the L40 was similar to the 127A so these speakers should probably have a recharge if they were overdriven hard in prior use?



FYI, the new 1500Al used in the S9800 can take continued pulses of 5000 watts and loose no more than 1%. The test can only be done a few times before the coil is destroyed, but the magnetic assembly is totally stable.

That's what I call destructive testing. Necessary I'm sure, like crash testing. Do you ever have any photos of what any of these big woofers look like after a test session like that? I don't get out to enough big concerts to see drivers fail like that.

Thanks Greg, Giskard, and Techbot for helping us understand the physics behind all this.

Regards,

Bart
an 'ol biochemistry major, UCLA '77

scott fitlin
05-04-2006, 06:21 PM
Alnico magnets, by their nature are easy to demagnitize with drive. They will not change with time and their dependence on temperature is really small - maybe 1% at 100 deg.F. Alnico stability and resistance to back EMF is really good. This is why they make the best sounding magnetic structures.

Thank you Greg, for the great info! I have been using JBL 2441 comp drivers since 1979-80, and they always did and still do sound phenomenal. Matter of fact, its my fav comp driver, to me, better than anything else.

Nice to have serious info on the Alnico subject straight from source!

:thmbsup:

hapy._.face
05-04-2006, 06:30 PM
Nice to have serious info on the Alnico subject straight from source!




:yes: ...changes my whole perspective on AlniCo. I'd read numerous articles- yet Greg puts the cigar out in a few choice paragraphs. still so cool.

Mr. Widget
05-04-2006, 06:35 PM
I don't know if Mr. Timbers will revisit this thread, but if he does I am really curious about how neodymium fits into the discussion.

I'd guess that it is harder to demagnetize, but how does it behave with regards to dealing with back EMF and do it's inherent properties have any sonic consequences?


Widget

Ducatista47
05-04-2006, 08:30 PM
Gosh, I work late and look what I miss!

Time to thank Mr. Timbers again, not only for posting here but for answering my specific question (post #17) in the first sentence. Nine words and my ignorance is put to rest. Spooky, but is this man good or what?;)

All the rest of the post did for me was enlighten, entertain and demystify all the issues I ever and never pondered about the subject.

I am beginning to look at the world in a different, simpler way. He is Greg Timbers, and I am not!:D

Again Grateful, Clark in Peoria

scott fitlin
05-04-2006, 08:36 PM
:yes: ...changes my whole perspective on AlniCo. I'd read numerous articles- yet Greg puts the cigar out in a few choice paragraphs. still so cool.Ive always said Alnico sounds best, and you can hear a difference from Alnico to ferrite to neodymium!

scott fitlin
05-04-2006, 08:38 PM
I don't know if Mr. Timbers will revisit this thread, but if he does I am really curious about how neodymium fits into the discussion.

I'd guess that it is harder to demagnetize, but how does it react with regards to dealing with back EMF and do it's inherent properties have any sonic consequences?


WidgetI`d like to hear what Mr. Timbers has to say about this also!

I find neo has quite a different tonal sound from either Alnico or ferrite. I`m still using my favorite JBL 2441,s so I guess thats says what my preferences are.

And I had the TAD 4002,s on the horns again this winter, still didnt like em, not sweet like the JBL, not at all.

JBLnsince1959
05-05-2006, 07:10 AM
Gosh, I work late and look what I miss!

Time to thank Mr. Timbers again, not only for posting here but for answering my specific question (post #17) in the first sentence. Nine words and my ignorance is put to rest. Spooky, but is this man good or what?;)

All the rest of the post did for me was enlighten, entertain and demystify all the issues I ever and never pondered about the subject.

I am beginning to look at the world in a different, simpler way. He is Greg Timbers, and I am not!:D



I couldn't say it better and it's what I would want to say ( I'm not much of a word person so my posts can be choppy)

robertbartsch
06-04-2009, 04:57 PM
I spoke to Bill from GPA about this recently. He says a ferrite remag is not necessary and an alnico recharge is recommended only if overdriven.

All the alnicos I've acquired on Fleabay are recharged since it is not possible to know their history.

Anyway, I recenlty read that since HF comprssion drivers are not driven with big power, that a recharge for these alnicos is very rarely necessary.

I suppose this is logical.

Any thoughts on this?

ratitifb
06-04-2009, 11:22 PM
totally agree with that due to coercitive force ratio alnico vs ferrite and magnet circuit design :)

toddalin
06-05-2009, 10:31 AM
Alnico stability and resistance to back EMF is really good. This is why they make the best sounding magnetic structures.


So do we now have it on good authority that AlNiCo sounds better? Did the value of my all AlNiCo L200/300s just go up? :D Is this perhaps part of the difference I hear between these and my 4430s? (I've always thought that the L200/300s sound more natural. (All of the AlNiCo components were recently recharged and never played "loud" since that time.)

robertbartsch
06-05-2009, 11:39 AM
If the assumption is that alnicos sound better is this based on the fact that during high/low temperature periods the mags loose strength but the strength is returned to spec. when the temperature returns to normal?

I'm not sure about the permanent loss of power on alnicos. Is this related to high power situations that are strong enough to blow the voice coils?

If the power needed to blow a VC is much lower in a compression driver than a woofer, for example, does this mean that it is unlikely that a compression driver would experience enough power surge to damage/reduce the alnico motor strength?

What other conditions destroy motor strength - dropping the driver or placing two driver motors back-to-back? I read on the Net that back-to-back placement can cause magnets to loose strength.

Thx..

ratitifb
06-05-2009, 02:18 PM
take a look on this exhaustive overview ;)

toddalin
06-05-2009, 03:42 PM
Only when "done right" as per the 1500AL, 1500AL-1 and 1501AL. We've gone over how Jerry accomplished it in detail several times and I've posted the Engineering Design Specification as well.Are they loaded with 1500AL's, 1500AL-1's, or 1501AL's? If so then yes. If not then no.

old school AlNiCo < SFG Ferrite < new century AlNiCo



Well, then I guess you disagree with Greg because he was simply referring to an AlNiCo structure versus a ferrite structure.

From what I've read in the library, the 1500AL and similar use the copper and steel rings, etc. to reduce demagnization due to excessiver heat.

The magnetic circuit is a speaker's most fundamental component, the very engine of sound. Alnico magnets, prized for their lively, high-energy sound, were once widely used in the magnetic circuits of high-end speaker systems. But, because Alnico magnets tend to demagnetize at high power levels, they've all but disappeared since the 1970s, when amplifier power outputs increased dramatically.

Having successfully overcome the demagnetization problem, JBL's engineers are pleased to reintroduce the deep, energetic Alnico sound.

But Greg noted that the loss of magnetic strength amounts to no more than 3 dB assuming that the speakers are overpowered. If I never overpower my AlNiCo magnets after recently having them recharged (hardly likely in my living room), any losses should be insignificant and they should contine to have their lively, high-energy sound.

I don't need to put active stabilization set to come on at 150 mph on a car that can do 170 mph if I never exceed 130 mph.

Beowulf57
06-06-2009, 05:52 AM
Interesting thread! Okay: who can report the real world audible affects of demagnetization that have led a listener to conclude: "I must remagnetize!"?

Ducatista47
06-06-2009, 08:40 AM
That is all entirely true, 4313B. A more basic issue here, if I may risk being undiplomatic, is why in the world most of these posts are occurring after Mr. Timbers has so clearly set things straight. God speaks and we still argue the points laid out by the ultimate source. The kindest interpretation would be failure to read and understand his post. Lacking that, I guess some would rather continue to speculate in the face of absolute certainty as a form of entertainment.

In either case, a waste of time. Which being on the internet can be sometimes when compared to actually dealing with what is at hand in the real world. The internet is like a telephone. It can enable things impossible any other way, but it is no substitute for really being there. Try sitting on the patio and sharing a few beers with a friend over the telephone. Or looking at images of a forest instead of walking in the woods. :( Or, dare I say, listening to audio equipment instead of the music it is playing. A little of that goes a long way and life is short.

Clark

Beowulf57
06-06-2009, 01:57 PM
Greg used to change the Q of AlNiCo drivers at will simply by dumping a ton of current into them. When you change the Q of a driver it can have a significant effect on performance. Those who are aware of the situation do what is necessary to rectify it and go on with their lives. If you can't tell that something is wrong then nothing is wrong and you're good to go. Ignorance is bliss.

Many professionals remag their older AlNiCo cores simply because they need a remag. It's a known issue and people deal with it. No one cares what some guy sitting in his living room listening to his little stereo thinks about remags. Remags cost fifteen bucks and are usually done on high performance loudspeaker transducers, e.g. JBL's, which anyone who has to ask "Should I remag?" probably shouldn't have in his or her possession anyway.

Let me rephrase my question: What are the audible effects? I am interested to know if one can assess the presence of this issue through listening.

toddalin
06-06-2009, 02:44 PM
Then plug them directly into the wall and give them a good zap. That should put them back to the way you like them.


Why would I have gone to the trouble and expense to have three woofers and six drivers remagnetized (at $25 each not $15 as you stated) if I liked them "zapped?"

Sounds like a personal attack to me. :hmm:

Earl K
06-06-2009, 04:38 PM
Why would I have gone to the trouble and expense to have three woofers and six drivers remagnetized (at $25 each not $15 as you stated) if I liked them "zapped?"

Sounds like a personal attack to me. :hmm:

- It's entirely reasonable to assume that you might like to "zap" the typical JBL HIFi woofer ( based on your oft stated advocacy of using their car subwoofers within the home environment ) .
- Ignoring the issue of the unavoidable loss of midrange output from this approach .

>< cheers :)

DonM
06-06-2009, 05:17 PM
Earl,

Is there a JBL service centre in the Toronto region that could safely recharge an Altec alnico such as the 806A or 416A?

I'm reluctant to ship them down to the USA.

Thanks,

Don

Mississauga, On

Earl K
06-06-2009, 05:29 PM
Is there a JBL service centre in the Toronto region that could safely recharge an Altec alnico such as the 806A or 416A?

Try Santon Audio in Markham .

Bob ( Santon ) sent out some 802s & 2440s for me some years back ( 6 -9 maybe ) .

He may still have the connection that actually does the ( offsite ) work .

If Santon is a no-go / take your stuff to Belisle Acoustics in Montreal ( they'll definately do it / since they manufacture their own line of woofers for their "Transparance Line" of SR Speakers )

>< cheers :)

ps; Google is your best friend / but, if your are google-challenged, let me know & I'll look up the phone numbers for you . ;)

toddalin
06-06-2009, 05:46 PM
- It's entirely reasonable to assume that you might like to "zap" the typical JBL HIFi woofer ( based on your oft stated advocacy of using their car subwoofers within the home environment ) .
- Ignoring the issue of the unavoidable loss of midrange output from this approach .

>< cheers :)


Get real! ~1,500 watts at 60 Hz. :bs:

DonM
06-06-2009, 05:47 PM
[quote=Earl K;254552]Try Santon Audio in Markham .

Bob ( Santon ) sent out some 802s & 2440s for me some years back ( 6 -9 maybe ) .

He may still have the connection that actually does the ( offsite ) work .

If Santon is a no-go / take your stuff to Belisle Acoustics in Montreal ( they'll definately do it / since they manufacture their own line of woofers for their "Transparance Line" of SR Speakers )

>< cheers :)

I do have the contact information for Santon and if they can't do it I'll take them down to Montreal.

Thanks for responding back so quickly!

Beowulf57
06-06-2009, 08:07 PM
Thanks for the modeling 4313B. I don't dispute the existence of an effect; I am simply asking if anyone can provide actual reports of audible effects. This is not a challenge, it is a sincere request for some basis to judge changes/deterioration from listening rather than from measurements/modeling. I am not sure that I can judge the effects of a couple of dB variation in sensitivity over a particular frequency range. If someone can, I'd like to "hear" about it. Pun intended. :)

m8o
06-06-2009, 08:43 PM
To shift the discussion a bit. Timely that I see this thread as the most recently posted-to today realizing I've been stricken by this ailment this afternoon.

Today, I unpacked a whole bunch of eBay purchased deliveries. Among other things, I found I had a lot more 2404's that I knew about... (and I just bought another tonight; I have a problem!) :p But this isn't about them, well not directly. I proceeded downstairs.

With the top of the La Scala cabinets acting as a workbench, I put the brand new 2407H's onto the old and slightly beat-up 2342 lenses, and played a juggling game moving around 2404s and 2402 drivers with the mini smith horn on them.

I noticed something interesting. The 2404s I had sitting on the top of the cabinet I haven't used for over a year, was magnetically sticking to everything; and the 2407 wouldn't stop sticking to it. But the old 2402 driver I'd been using with the mini wood Smith horn as a tweeter on my La Scala for a few years wouldn't stick to anything! Same deal with left and right tweeter. It's like they've lost a majority of their magnetism. And when I switched to the 2407+2342 lens , wow, suddenly there was a whole spectrum of sound I didn't realize I wasn't getting.

Anyway, never thought I'd run into this. But good thing I've got all those 2404's sitting in the wing. :applaud:

m8o
06-06-2009, 08:46 PM
I went ahead and deleted the measurements/modeling post since it was pointless. I have nothing further to add to this thread. having come to this thread only after this action, I'm intrigued to see the measurements!!! :D

Ralph856
06-06-2009, 08:59 PM
Epic fail!

You just summed up my life in two words.

MikeBrewster77
06-06-2009, 09:01 PM
I am not sure that I can judge the effects of a couple of dB variation in sensitivity over a particular frequency range. If someone can, I'd like to "hear" about it. :)

I think I can ;). In fact, I just posted only a few days ago about a quick and dirty tweeter swap I did and how the results were disastrous. It was apparently only a few dB variation that clearly made one combination work extremely well, and another sound completely unbalanced, bright, harsh, etc. If a few dB's of sensitivity is enough to make that much of a difference through design, I don't see any reason one wouldn't encounter similar results as a result of natural deterioration and time. Then again, maybe I'm just naive, that's not an analogous comparison, and I'm completely missing something here?



I went ahead and deleted the measurements/modeling post since it was pointless.

Disagree that it was pointless - in fact, aren't measurements taken and modeling performed to replicate and/or validate what one will actually hear? I for one find it reassuring to know there's some quantifiable science behind the manufacturer's recommendations on how to maintain my gear. But maybe that's just me...

MikeBrewster77
06-06-2009, 09:06 PM
You just summed up my life in two words.

Dude - stay away from sharp objects... ;)

Ralph856
06-06-2009, 09:07 PM
You just summed up my life in two words.

Lol, only joking.

Mr. Widget
06-06-2009, 11:22 PM
It's too bad.


Widget

Mr. Widget
06-06-2009, 11:32 PM
I noticed something interesting. The 2404s I had sitting on the top of the cabinet I haven't used for over a year, was magnetically sticking to everything; and the 2407 wouldn't stop sticking to it. But the old 2402 driver I'd been using with the mini wood Smith horn as a tweeter on my La Scala for a few years wouldn't stick to anything!Simple answer really. The old 2402 is an alnico motor and the other two are ferrite. The old JBL alnico motors are inherently magnetically shielded... none of their magnetic energy is wasted, it is all focused upon the VC gap.


Widget

m8o
06-07-2009, 01:28 AM
Simple answer really. The old 2402 is an alnico motor and the other two are ferrite. The old JBL alnico motors are inherently magnetically shielded... none of their magnetic energy is wasted, it is all focused upon the VC gap. I'm such an amateur... :slink:
Lol... Much thanx. It's very good to know there's nothing wrong with the drivers in that case. :coolness:

Beowulf57
06-07-2009, 09:07 AM
I think I can ;). In fact, I just posted only a few days ago about a quick and dirty tweeter swap I did and how the results were disastrous. It was apparently only a few dB variation that clearly made one combination work extremely well, and another sound completely unbalanced, bright, harsh, etc. If a few dB's of sensitivity is enough to make that much of a difference through design, I don't see any reason one wouldn't encounter similar results as a result of natural deterioration and time. Then again, maybe I'm just naive, that's not an analogous comparison, and I'm completely missing something here?

Thanks Mike...this is interesting. I realized that yes, I can hear small differences in the regions where the ear is most sensitive (midrange particularly). I'm curious as to why greg timbers' post seems to imply that the demagging effect is largely restricted to certain types of woofers? I can also imagine that two similar drivers could have a dB or two of difference in sensitivity without it being a demagging problem unless one matched them for this parameter.


Disagree that it was pointless - in fact, aren't measurements taken and modeling performed to replicate and/or validate what one will actually hear? I for one find it reassuring to know there's some quantifiable science behind the manufacturer's recommendations on how to maintain my gear. But maybe that's just me...
I also do not think it was pointless...and still wonder about the degree of sensitivity loss in a woofer that is audible...i.e., JND (just noticeable difference)?

spkrman57
06-07-2009, 09:34 AM
It was not pointless, and I'm sure the group of us who did read and follow that post did not think it was wasted!;)

I kind of understand where you are coming from with regards to how some folks interpet some postings here.:(

But there are some of us who look forward to the info!!:applaud:

Thanks,

Ron sends.......

Mr. Widget
06-07-2009, 09:51 AM
...and still wonder about the degree of sensitivity loss in a woofer that is audible...i.e., JND (just noticeable difference)?"Noticeable difference." That is a your mileage may vary situation... for some people, a speaker with a blown tweeter is acceptable, for others they can hear a significant change when swapping a cable... significant enough to drop big bucks.

I don't think anyone can answer that question for you. That said, a dB or more change over a fairly broad frequency range is quite audible. How significant that is will be determined by the listener.


Widget

speakerdave
06-07-2009, 10:01 AM
On the LSR32 there are two settings for the treble. The difference is 1 dB.

Beowulf57
06-07-2009, 10:10 AM
I am asking about the audibility in the low end...but okay, if no one has experience to report: that's all folks:).

Mr. Widget
06-07-2009, 10:15 AM
I am asking about the audibility in the low end...but okay, if no one has experience to report: that's all folks:).
To me it is extremely audible. For someone else it may be too subtle to care about... The graph that 4313B posted showed it quite clearly... thinner sounding and rather lacking of taughtness.


Widget

spkrman57
06-07-2009, 10:29 AM
I had a pair of JBL 2205B's (alnico) that were very shy in the midrange and a bit boomy in the LF band.

I bought these from a individual who ran them in a high powered PA rig, I'm sure they suffered some magnet strength loss.

I measured the drivers on woofertester (the original one that ran on DOS) and it showed the Q factors were much higher than factory spec.

Just one example......

Regards, Ron

toddalin
06-07-2009, 10:33 AM
I can also imagine that two similar drivers could have a dB or two of difference in sensitivity without it being a demagging problem unless one matched them for this parameter.


Very true. I have an original unmolested 075 that that is about 2.5-3 dB louder than my recently remagnetized and thouroughly inspected 2402s. Does this mean that any of them are defective? Hardly.

Just look at the variation in dcr values to recognize that drivers are bound to have differing dB levels.

As for the experience of having AlNiCo woofers and drivers remaged, yes, I have first hand experience (with WT-2 testing data) that I could relate..., but won't.

Mr. Widget
06-07-2009, 10:34 AM
I had a pair of JBL 2205B's (alnico) that were very shy in the midrange and a bit boomy in the LF band.Good point... if you will be using a woofer with a fairly high crossover frequency, I imagine the higher end would be rolled off. I haven't experienced this, but it makes sense.

As for the boomy response, that loss of control is classic.


Widget

Mr. Widget
06-07-2009, 10:40 AM
Very true. I have an original unmolested 075 that that is about 2.5-3 dB louder than my recently remagnetized and thouroughly inspected 2402s. Does this mean that any of them are defective? Hardly.

Just look at the variation in dcr values to recognize that drivers are bound to have differing dB levels.Tweeters are a slightly different case... slight variations in position of the diaphragm relative to the horn and phase plug will radically affect sensitivity and response... magnetic power can have an effect too.

DCR value will tell you how many turns of wire a particular tweeter got... ideally they are all the same, in reality it doesn't always work that way. I suppose if a given tweeter has more winds in the gap it could be more sensitive, but in general I wouldn't use DCR as a guide for sensitivity.


Widget

Earl K
06-07-2009, 11:55 AM
I had a pair of JBL 2205B's (alnico) that were very shy in the midrange and a bit boomy in the LF band.

I bought these from a individual who ran them in a high powered PA rig, I'm sure they suffered some magnet strength loss.

I measured the drivers on woofertester (the original one that ran on DOS) and it showed the Q factors were much higher than factory spec.

Just one example......

Good One Ron !

- Building on your experience ;

- I still have my original pair of 2205a(s) from 1977 / long since reconed with C8R2225 kits . They had a pretty hard life until @ 1990 .

- They have never been remagged ( & obviously need it ) .
- As a consequence ( & the fact that they are used in enclosures with no paper trail ) / when-ever they happen to meet up for usage in a cluster of 4 ( a rare occasion ) / there's a very noticable increase in LF output from the afflicted cluster / requiring this quad to have it's own "special" EQ applied .
- It's not a subtle situation when panning back & forth between clusters.

- If I ever track these puppies down / I'll pull them / & measure the TS parameters / & then post the results within this thread .

- I've grown to hate alnico woofers for this sort of reason.

>< cheers :)

ps;
- FWIW, they are my only two alnico 15s still in service, therefore ( for sentimental reasons ) I just allow them to express their opinion about how things should sound down there / knowing they'll be separated soon enough .

Zilch
06-07-2009, 12:29 PM
[There are meanies here, apparently.... ;) ]

tomee
06-08-2009, 05:37 AM
I'm as confused as ever now... not sure what was deleted and who stands for what....:blink:

my measly experience...
LE14As refoamed and measured with WT2 have specs pretty much dead on for a new driver - BL of 21, Qts about 0.3 etc.

124A woofers from L26 that ended up with a Qts of about 0.9 (stock is 0.45 or so..)....the owner liked how they sounded!

isn`t the saying `your mileage may vary`?

4313B
06-08-2009, 06:23 AM
124A woofers from L26 that ended up with a Qts of about 0.9 (stock is 0.45 or so..)125A

JBL Consumer Systems Reference Chart (http://audioheritage.org/vbulletin/showthread.php?t=25025)

tomee
06-08-2009, 06:45 AM
125A

JBL Consumer Systems Reference Chart (http://audioheritage.org/vbulletin/showthread.php?t=25025)

yup that was them!

robertbartsch
06-08-2009, 06:48 AM
Tweeters are a slightly different case... slight variations in position of the diaphragm relative to the horn and phase plug will radically affect sensitivity and response... magnetic power can have an effect too.

DCR value will tell you how many turns of wire a particular tweeter got... ideally they are all the same, in reality it doesn't always work that way. I suppose if a given tweeter has more winds in the gap it could be more sensitive, but in general I wouldn't use DCR as a guide for sensitivity.



I recently bought a pair of 2405 slots and when I pulled the horns the frams had two pins to center the fram in the voice coil gap. So for drivers with alignment pins, there should not be any variation in sensativity or responce; right?

Do the 2402s bullet noise drivers have alignment pins; my recolloction is no.

gibber
09-26-2012, 02:24 PM
Ferrite magnets do not demagnitize with time or drive. They are affected by temperature but that is reversible

The quoted post is an interesting one. How would NdFeB behave compared to Ferrite? At the time the post was made, rare earth wasn't used in bass drivers often, but things have changed so i wonder if there are inputs to be shared. I have looked in other parts on this site, but not found anything as "inside" as the quoted post.

An issue raised in the quote above and answered for ferrite (but not alnico) is behaviour over time. And how would neo fare in this respect.

Finally, for most stuff i find listed it's virtually impossible to say how much was it subjected to mechanical shock. Even samples without bumps, scratches and missng chips of paint may have been thrown around mounted in a cab or flightcase and still have suffered the shocks. Some inputs i saw in other threads seem to suggest that alnicos demagnetize if knocked unduly. Anyone to share (touring company experience, maybe) on how ferrite and neo compare in this respect?

Ralph

Spaulv
07-03-2015, 02:19 AM
Hi to all, new member and big fan of Altec Lansing Vott speakers .
In reference to companies / services for recharging Alnico magnets I personally us a superb contact in Italy, see link:

http://www.hiend.ch/index.htm

The cost of a full de-mag - re-mg with unit inspection and service with cleaning of components re cantering coil ecc is approx. 60 to 80 Euro's.

Personally have used Hiend for this service on my 416a-803b-808-8a-807-604D & 605A Duplex plus JBL 075-175-375-LE15A , I am very happy with the work done , all units now work has they would when new and the efficiency is back to spec, I have to say that the difference before and after is quite noticeable.

Regards
Steve