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Thread: Recharging Alnico/Ferrite magnets

  1. #46
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    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..

  2. #47
    Senior Member ratitifb's Avatar
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    my 0.02

    take a look on this exhaustive overview
    Attached Files Attached Files

  3. #48
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    Quote Originally Posted by 4313B View Post
    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.

  4. #49
    Senior Member Beowulf57's Avatar
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    Interesting thread! Okay: who can report the real world audible affects of demagnetization that have led a listener to conclude: "I must remagnetize!"?

  5. #50
    Senior Member Ducatista47's Avatar
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    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
    Information is not Knowledge; Knowledge is not Wisdom
    Too many audiophiles listen with their eyes instead of their ears


  6. #51
    Senior Member Beowulf57's Avatar
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    Quote Originally Posted by 4313B View Post
    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.

  7. #52
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    Quote Originally Posted by 4313B View Post
    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.

  8. #53
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    Quote Originally Posted by toddalin
    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.
    - 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

  9. #54
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    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

  10. #55
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    Quote Originally Posted by DonM
    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 .

  11. #56
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    Quote Originally Posted by Earl K View Post
    - 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.

  12. #57
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    [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!

  13. #58
    Senior Member Beowulf57's Avatar
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    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.

  14. #59
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    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!) 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.

  15. #60
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    Quote Originally Posted by 4313B View Post
    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!!!

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