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Thread: Effects of loss of magnetism?

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    Effects of loss of magnetism?

    We all know the Alnico magnets are prone to loss of magnetism if separated, dropped, over driven, etc. I'm curious what one could expect from a speaker with a lower than original Gauss rating? I was assuming the speaker would be less efficient and have a lower power capacity, but could it have other effects on the sound?
    If you had 2 identical speakers with reduced, but matching Gauss rating, how would they differ in sound from a pair with the factory speced Gauss rating ... all other things being equal.


    Thanks,

    Eric M.

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    Administrator Robh3606's Avatar
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    Thanks, that about sums it up!

    One question. In this sentence from the link, I understand all but the reference the "knee". Would you know what that is? Could it be the bottom of the gap?

    "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."


    Quote Originally Posted by Robh3606 View Post

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    Senior Member edgewound's Avatar
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    Loss of magnetic strength results in lower sensitivity, output, damping/control of the moving assembly, loss of high frequency extension.
    Edgewound...JBL Pro Authorized...since 1988
    Upland Loudspeaker Service, Upland, CA

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    Thankyou.

    Edgewound, could I get you to take a look at the post? Your name came up as a good source for the answer.

    http://www.audioheritage.org/vbullet...561#post428561

    Thanks!

    Quote Originally Posted by edgewound View Post
    Loss of magnetic strength results in lower sensitivity, output, damping/control of the moving assembly, loss of high frequency extension.

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    Administrator Robh3606's Avatar
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    One question. In this sentence from the link, I understand all but the reference the "knee". Would you know what that is? Could it be the bottom of the gap?

    Hello

    I will give it a shot. If you graph the parameters you end up with an sideways L. The knee being the bend on the curve where you see a more rapid change in value. Once you go past that point is when the demag occurs.

    Rob
    "I could be arguing in my spare time"

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    Quote Originally Posted by Robh3606 View Post
    Hello

    I will give it a shot. If you graph the parameters you end up with an sideways L. The knee being the bend on the curve where you see a more rapid change in value. Once you go past that point is when the demag occurs.

    Rob
    Well, sorry I asked! (No, thanks for the response). That was more complicated than I had hoped. WhichThiel parameter is being graphed (or is it all that have the same rapid change at the same point)?

    Thanks,

    Eric

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    Administrator Robh3606's Avatar
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    Hello Eric

    It's not the T/S parameters it is the graph of specific magnets properties. I have attached a graph that shows the demag points. Please don't ask me to explain it Just do a Google search for demag and there is a ton of stuff you can take a look at.

    Rob
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    Senior Member RMC's Avatar
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    Hi Eric,

    If you have access to a local public library I suggest you check with them if they have a copy of John Eargle's Loudspeaker Handbook, which you can look at or maybe even borrow.

    There's a chapter called "Principles of Magnetics" with what you need to know, and more, about speaker magnets: how design engineers conceive them, what they look for or try to avoid, the properties and good/bad of each type, Alnico vs ferrite vs neo, etc.

    Eargle follows and outlines the steps, starting with basics then adding things on the way, as he often does to explain a matter, leading to a more complete design (i.e. progressively putting the elements together).

    There's a somewhat similar graph to the one posted in previous post, as well as others for magnets, and that one is called the Hysteresis curve.

    Can't guarantee you'll understand all that stuff, I haven't, but a good part can be digested and the lessons to remember are pretty clear. Regards,

    Richard

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    Thanks. Yes, library once things settle down around here. Are libraries even open during this Corona Virus lock down?
    I looked up the book on e-Bay and Amazon. It must be a good one, its about $140!

    Thanks. I will check it out.

    Eric




    Quote Originally Posted by RMC View Post
    Hi Eric,

    If you have access to a local public library I suggest you check with them if they have a copy of John Eargle's Loudspeaker Handbook, which you can look at or maybe even borrow.

    There's a chapter called "Principles of Magnetics" with what you need to know, and more, about speaker magnets: how design engineers conceive them, what they look for or try to avoid, the properties and good/bad of each type, Alnico vs ferrite vs neo, etc.

    Eargle follows and outlines the steps, starting with basics then adding things on the way, as he often does to explain a matter, leading to a more complete design (i.e. progressively putting the elements together).

    There's a somewhat similar graph to the one posted in previous post, as well as others for magnets, and that one is called the Hysteresis curve.

    Can't guarantee you'll understand all that stuff, I haven't, but a good part can be digested and the lessons to remember are pretty clear. Regards,

    Richard

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    Senior Member RMC's Avatar
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    Hi Eric,

    Yes its a good book, but unfortunately engineering ones are generally expensive since they're made in limited number.

    Not sure the library would be open during Cov 19. You can check with them. If they have a Web site maybe you can see if they have the book in stock, some may provide a list of available books on their site.

    Another option: if your local library doesn't have Eargle's book, sometimes another public outlet within the same State may have it on their shelves. Then your local outlet may ask the other one which has the book to transfer it or loan the book to them. Such "inter-library loans" thing, if they do it, some actually do, may get you the book with little or no pain... Regards,

    Richard

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    DeMagnetizatin vs Temperature and Mag.Field

    Quote Originally Posted by Eric M. View Post
    We all know the Alnico magnets are prone to loss of magnetism if separated, dropped, over driven, etc. I'm curious what one could expect from a speaker with a lower than original Gauss rating? I was assuming the speaker would be less efficient and have a lower power capacity, but could it have other effects on the sound?
    If you had 2 identical speakers with reduced, but matching Gauss rating, how would they differ in sound from a pair with the factory speced Gauss rating ... all other things being equal.


    Thanks,

    Eric M.
    Hi Eric M.

    Useful info can be find in the:
    https://www.researchgate.net/profile...-Generator.pdf

    2.
    https://www.google.com/url?sa=i&url=...AAAAAdAAAAABA5



    but next figures would be very instructive about demagnetization magnetic field applied, but temperature influence to the demagnetization is important too. So AlNiCo V is sensitive to the strong field demagnetization, but is very sabile vs temperature, while Neodymium magnet is fare less sensitive to the strong field demagnetization, but is sensitive to the higher temperature. Samarium-Cobalt magnet seems the best compromise , but its price is so high that applied in the speakers would be out of interest. So 'Ceramic' magnet is very popular due to the lower price, and temperature stable, but must be used in larger amount (weight) that proper amount of the magnetic field strength in the gap can be reached.

    Regards
    Ivica
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    This may be better in a separate post, but thought I'd start here as most of you are knowledgeable about magnetism. I had a pair of LE85,s I sent in to be remagnetised. They measured below 5000 gauss before and came in a 16,000 gauss after. But, the original specs of an LE85 is 19,000.
    Is the 3,000 loss is gauss due to the age of the magnet, the ability of the re-magnetizer to reach the 19,000 gauss or something else?

    Thanks,

    Eric M.

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    Senior Member Flodstroem's Avatar
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    Quote Originally Posted by Eric M. View Post
    This may be better in a separate post, but thought I'd start here as most of you are knowledgeable about magnetism. I had a pair of LE85,s I sent in to be remagnetised. They measured below 5000 gauss before and came in a 16,000 gauss after. But, the original specs of an LE85 is 19,000.
    Is the 3,000 loss is gauss due to the age of the magnet, the ability of the re-magnetizer to reach the 19,000 gauss or something else?

    Thanks,

    Eric M.
    Whom has measured the 16000 Gauss? The question is 1) the accuracy of the equipment used for the measurement 2) the power of the magnetizer and coil used in this case.
    (AlnicoV needs at least 3000 Oe (Oersted) for to be fully saturated)
    Flodstroem

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    It was Speaker Repair Pros, they have Orange Country's old magnetizer. I have no idea the tool he tested with, he gave me the brand a while back, but I have since forgot.
    If you do not have 3000 Oe, does it only partially recharge (like this, 16K vs 19K) or does it not charge at all?

    Thanks



    Quote Originally Posted by Flodstroem View Post
    Whom has measured the 16000 Gauss? The question is 1) the accuracy of the equipment used for the measurement 2) the power of the magnetizer and coil used in this case.
    (AlnicoV needs at least 3000 Oe (Oersted) for to be fully saturated)

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