jimjimbo Posted February 7, 2017 Share Posted February 7, 2017 This is a spin off thread from the A-55G mid driver thread, where there have been a couple of questions raised relative to potential issues with the age and/or loss of magnet strength of older Heritage drivers. Would love to have some input on this from @Chief bonehead, @BEC, @Chris A, and other folks on their thoughts, experience and/or measurements. 1. Is driver magnet strength loss a concern? If so, would it be more applicable to a tweeter, mid, or woofer? 2. How is a driver magnet measured? Lab measurements? Any way to "ballpark" check this for a more technical consumer? 3. Are there reliable ways to have the magnets refreshed? If so, recommended vendors? Feel free to add other questions, comments, etc. Quote Link to comment Share on other sites More sharing options...
Chris A Posted February 7, 2017 Share Posted February 7, 2017 1) My experiences with loss of magnetic field strength comes from neodymium magnets, which has a relatively low Curie point (about 300 C), which can be experienced in service if a driver's voice coil gets red hot. For audio drivers, this occurs most often in woofers, not midrange compression drivers. Obviously, Klipsch compression drivers usually aren't driven to anywhere near those levels. I wouldn't think that any of the magnets in Klipsch loudspeakers...save those that have been very badly over driven to the point of failure from internal heat generation would have issues with demagnetization in home environments. There are instances where a magnet could be demagnetized from exposure to an opposing external magnetic field (ferrite or Alnico magnets), but that isn't something that happens often with home consumer acoustic drivers, but more related to poor practices shielding drivers from strong external magnetic fields. 2) There are Gauss meters that are available to measure magnetic fields. 3) Once a driver's magnet has been demagnetized, my suggestion is that you buy a new or refurbished driver. The process of re-magnetization depends on magnetic material type, but in general, it isn't something that you'd do at home. Perhaps there are driver rebuild shops that have access to big remagnetizers. Ref: http://www.physlink.com/education/askexperts/ae472.cfm https://en.wikipedia.org/wiki/Curie_temperature Chris 1 Quote Link to comment Share on other sites More sharing options...
Khornukopia Posted February 7, 2017 Share Posted February 7, 2017 Great Plains Audio website says "Our Standard Service includes remagnetizing old Alnico high and low frequency loudspeakers to restore their original magnetic strength at no extra charge." 1 Quote Link to comment Share on other sites More sharing options...
Grizzog Posted February 7, 2017 Share Posted February 7, 2017 For the Alnico magnets, I spoke with Bill at Great Plains. According to him, unless dropped or damaged in some way, the magnet should be fine. Ceramic is even harder to demagnetize. I spoke with him when I had questions on my Altec 19s. Both woofers and tweeters have the Alnico magnets. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
Khornukopia Posted February 8, 2017 Share Posted February 8, 2017 Good to know that our Klipsch magnets are still strong after all these years. 1 Quote Link to comment Share on other sites More sharing options...
John Warren Posted February 9, 2017 Share Posted February 9, 2017 On 2/7/2017 at 10:40 AM, jimjimbo said: This is a spin off thread from the A-55G mid driver thread, where there have been a couple of questions raised relative to potential issues with the age and/or loss of magnet strength of older Heritage drivers. Would love to have some input on this from @Chief bonehead, @BEC, @Chris A, and other folks on their thoughts, experience and/or measurements. 1. Is driver magnet strength loss a concern? If so, would it be more applicable to a tweeter, mid, or woofer? 2. How is a driver magnet measured? Lab measurements? Any way to "ballpark" check this for a more technical consumer? 3. Are there reliable ways to have the magnets refreshed? If so, recommended vendors? Feel free to add other questions, comments, etc. On #2, the strength is measured indirectly by way of the T/S parameters, Z-magnitude, etc. The electrical impedance of a loudspeaker is related to the "motional impedance" of the driver moving mass and suspension parts. The motional impedance is a mechanical analog of the electrical impedance. So when the impedance of a loudspeaker is measured, the motional impedance is what's really being measured (plus, of course, some electrical resistance). The BL-product is responsible for the translation between the two domains. B is the flux density in the voice coil gap and the units are Tesla, L is the voice coil wire length in the gap in meters. So when the impedance is measured and there are big differences in the magnetic strength between otherwise like drivers, the shape of the impedance curve near Fs will differ depending on the differences in B. A very high flux density is 1.8-2.0 T and found on Neo magnet drivers. 1 Quote Link to comment Share on other sites More sharing options...
thebes Posted February 11, 2017 Share Posted February 11, 2017 On 2/9/2017 at 1:34 PM, John Warren said: On #2, the strength is measured indirectly by way of the T/S parameters, Z-magnitude, etc. The electrical impedance of a loudspeaker is related to the "motional impedance" of the driver moving mass and suspension parts. The motional impedance is a mechanical analog of the electrical impedance. So when the impedance of a loudspeaker is measured, the motional impedance is what's really being measured (plus, of course, some electrical resistance). The BL-product is responsible for the translation between the two domains. B is the flux density in the voice coil gap and the units are Tesla, L is the voice coil wire length in the gap in meters. So when the impedance is measured and there are big differences in the magnetic strength between otherwise like drivers, the shape of the impedance curve near Fs will differ depending on the differences in B. A very high flux density is 1.8-2.0 T and found on Neo magnet drivers. Why is it whenever I wander into this part of the Forum, I leave confused and with a headache? Quote Link to comment Share on other sites More sharing options...
jimjimbo Posted February 11, 2017 Author Share Posted February 11, 2017 Glad I could be of service Marty… You should thank me! Quote Link to comment Share on other sites More sharing options...
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