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Thread: Recharging Alnico/Ferrite magnets

  1. #76
    Administrator Mr. Widget's Avatar
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    Quote Originally Posted by spkrman57 View Post
    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.


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  2. #77
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    Quote Originally Posted by toddalin View Post
    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.


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  3. #78
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    Quote Originally Posted by Ron
    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 .

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    RIP 2011 Zilch's Avatar
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    [There are meanies here, apparently.... ]

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    I'm as confused as ever now... not sure what was deleted and who stands for what....

    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`?

  6. #81
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    Quote Originally Posted by tomee View Post
    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

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    Quote Originally Posted by 4313B View Post
    yup that was them!

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    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.

  9. #84
    Senior Member gibber's Avatar
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    Recharging ferrite and/or neo as well?

    Quote Originally Posted by gtimbers View Post
    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

  10. #85
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    De-mag & re-mag Alnico and Alnico oriented grains Italy

    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

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