Scott Grammer Posted July 19, 2023 Share Posted July 19, 2023 Hi, all. I'm Scott Grammer, a new member and old audio nut. I work on vintage audio for a living, and have done so for years, but I need advice on this subject. Specifically, I have a pair of Cornwall 1's made in 1968, and I can't help but wonder if the magnets on the (original) woofers may have begun to lose their charge. Does anyone have knowledge to share about this? Thanks! (Dear Moderator: If I have posted in error, please accept my apologies, and tell me how to fix it. Thanks.) 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted July 19, 2023 Share Posted July 19, 2023 Welcome @Scott GrammerGrammer... some one will be along... Quote Link to comment Share on other sites More sharing options...
OO1 Posted July 19, 2023 Share Posted July 19, 2023 Alnico V magnets can get demagnerized , yes , it can happen , but they can be re-magnetized by a speaker shop with the right equipment , but the cost may be as high as a new pair of Cornwall woofers the K-33-E is around 140$ / each from klipsch , a drop-in replacement . Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 20, 2023 Author Share Posted July 20, 2023 (edited) 2 hours ago, OO1 said: Alnico V magnets can get demagnerized , yes , it can happen... That's where my uncertainty comes in. I knew that Alnico lost its charge slowly over time, but these are ceramic magnets. K-33-P's. Edited July 20, 2023 by Scott Grammer Quote Link to comment Share on other sites More sharing options...
OO1 Posted July 20, 2023 Share Posted July 20, 2023 1 hour ago, Scott Grammer said: these are ceramic magnets. K-33-P's. Ferrite magnets can also be re magnetized , if that's effectively the case here , a new K-33-E 4 Ohms woofer would resolve the issue + allow for more power handling without having to foot labor costs to repair 55 years old woofers Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 20, 2023 Author Share Posted July 20, 2023 Any suggestions as to how to test to see if the magnets are weaker than normal, short of disassembling them to put a gauss meter probe in the gap? I don't cherish the thought of spending $300 to find out there was no appreciable change. I don't need the power handling, as I drive them with a 7WPC SE tube amp.... Thanks for all input on this. Maybe I can return the favor someday on a topic I know more about. Quote Link to comment Share on other sites More sharing options...
OO1 Posted July 20, 2023 Share Posted July 20, 2023 start with taking a DCR reading the K-33-,P woofers , tweeters and midrange drivers Quote Link to comment Share on other sites More sharing options...
Peter P. Posted July 20, 2023 Share Posted July 20, 2023 Google "how long does it take for a magnet to lose its power" and you'll learn it's a non-issue. We'd love to see more pictures of those Cornwalls! Quote Link to comment Share on other sites More sharing options...
Toz Posted July 21, 2023 Share Posted July 21, 2023 It's my understanding that what will cause the magnets to lose gauss is a sharp impact such as would happen if dropped or smacked. I've also read that the natural decay is insignificantly small. I have plenty of old alnico that still performs as I would expect it to. Just be careful not to knock the old drivers around. If they've lived in their original cabinets, and output sound, they are probably fine. Quote Link to comment Share on other sites More sharing options...
KT88 Posted July 21, 2023 Share Posted July 21, 2023 On 7/20/2023 at 12:45 AM, Scott Grammer said: Hi, all. I'm Scott Grammer, a new member and old audio nut. I work on vintage audio for a living, and have done so for years, but I need advice on this subject. Specifically, I have a pair of Cornwall 1's made in 1968, and I can't help but wonder if the magnets on the (original) woofers may have begun to lose their charge. Does anyone have knowledge to share about this? Thanks! (Dear Moderator: If I have posted in error, please accept my apologies, and tell me how to fix it. Thanks.) I had K77 Alnico from 1977 remagnetised in Germany two years ago. The result was 1.5 dB louder and up to 15Khz frequency band, before only about 11 to 12 Khz. Regarding ferrites, I have not heard that they get weaker, whereas Alnicos can get weaker gradually by playing loudly all the time over years when the magnetic field of the voice coil is erased against the permanent magnet. Another idea, could it be that for some reason the midrange driver has become too loud? Something that affects the old parts of the crossover, capacitors? Are the autoformer taps chosen the right original ones? That's why you could also have the impression that the bass is too weak. Quote Link to comment Share on other sites More sharing options...
OO1 Posted July 21, 2023 Share Posted July 21, 2023 4 hours ago, KT88 said: I had K77 Alnico from 1977 remagnetised in Germany two years ago. Heinz , the shop had to remove the soldered diaphragms of the K-77 before re-magnetizing the Alnico V magnets , were they able to re-use the original diaphragms , Quote Link to comment Share on other sites More sharing options...
KT88 Posted July 21, 2023 Share Posted July 21, 2023 33 minutes ago, OO1 said: Heinz , the shop had to remove the soldered diaphragms of the K-77 before re-magnetizing the Alnico V magnets , were they able to re-use the original diaphragms , Yes, that is correct, Randy. The magnets were without diaphragms when remagnetised. Not only that. They had first installed new diaphragms that I had bought on the internet and given to them from a Dutch dealer. It turned out at the workshop that, despite other promises, they were these cheap Chinese ones. The workshop said that it sounded awful. So they finally put my original diaphragms back in which were also judged to still have a very good sound. And this workshop has experience with other K77s for comparison. 1 Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 21, 2023 Author Share Posted July 21, 2023 8 hours ago, KT88 said: Regarding ferrites, I have not heard that they get weaker, whereas Alnicos can get weaker gradually by playing loudly all the time over years when the magnetic field of the voice coil is erased against the permanent magnet. Another idea, could it be that for some reason the midrange driver has become too loud? Something that affects the old parts of the crossover, capacitors? Are the autoformer taps chosen the right original ones? That's why you could also have the impression that the bass is too weak. The midrange is indeed too loud. I have not re-opened the cabinets to check the connections to the autoformer. They may well be wrong. I do know that when I put the speakers back in service recently after having stored them for a very long time, I had to tighten the screws on the terminal strips of the crossovers, as several of the connections there were loose. I plan to actually remove the crossovers this weekend, check the connections to the autoformer taps, and check the capacitors for value, leakage, esr, etc. I'll also check the connections to the drivers for correct polarity, and the mids and tweeters for DCR. All this, I hope, will give me a clue as to what's going on. The speakers definitely sound different to my memory of them (a LOT different), but then I stored them 20 years ago, and my ears are now 59 years old, so.... Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 21, 2023 Author Share Posted July 21, 2023 On 7/20/2023 at 5:41 AM, Peter P. said: Google "how long does it take for a magnet to lose its power" and you'll learn it's a non-issue. We'd love to see more pictures of those Cornwalls! 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted July 21, 2023 Share Posted July 21, 2023 Yes so,the woofers. How do they sound? Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 22, 2023 Author Share Posted July 22, 2023 1 hour ago, billybob said: Yes so,the woofers. How do they sound? The deep bass is not what I remember it being, and not comparable to the JBL L80t's the Cornwalls replaced. A little overbearing around 400Hz or so. Possibly a panel resonance. Very clean, though, and even on limited power they can play quite loudly, as you would expect. Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 22, 2023 Author Share Posted July 22, 2023 On 7/19/2023 at 11:37 PM, OO1 said: start with taking a DCR reading the K-33-,P woofers , tweeters and midrange drivers I checked the woofers a few days ago, at the cabinet speaker terminals, which f course means that the reading includes the DCR of the woofer chokes. I remember both of them being right at four ohms DCR, but I don't remember the exact figures. Quote Link to comment Share on other sites More sharing options...
billybob Posted July 22, 2023 Share Posted July 22, 2023 27 minutes ago, Scott Grammer said: The deep bass is not what I remember it being, and not comparable to the JBL L80t's the Cornwalls replaced. A little overbearing around 400Hz or so. Possibly a panel resonance. Very clean, though, and even on limited power they can play quite loudly, as you would expect. Cool enough ... thanks. Possible the mid out of spec. You have old but decent caps. Original.. Quote Link to comment Share on other sites More sharing options...
Scott Grammer Posted July 22, 2023 Author Share Posted July 22, 2023 7 minutes ago, billybob said: Cool enough ... thanks. Possible the mid out of spec. You have old but decent caps. Original.. This weekend (for me, the weekend = Sunday and Monday), I plan to pull the crossovers and check connections, and I may pull the mid drivers to measure DCR and take some pictures and make sure they're original. So far, the tweeters are the only parts I'm not worried about. They're playing, they're undistorted, and sound pretty much the same in both cabinets. Of course, I can only hear to about 12.5 or 13 kHz now, unfortunately. 1 Quote Link to comment Share on other sites More sharing options...
billybob Posted July 22, 2023 Share Posted July 22, 2023 Yes guess may as well check. Think you will find all is well with mid drivers. While guessing then, wish you had Klipsch mid caps for both. Don't mind me as, I try trouble shooting... @Scott Grammer 1 Quote Link to comment Share on other sites More sharing options...
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