Polk Monitor 4.5: Curse of the Shifted Magnets!
JohnnyK
Posts: 3
Hi all,
So backstory, I'm a broke college student who needs his music, and my roommate hogs the nice Yamaha setup in the living room, so I decided to piece together something for my bedroom. While I wouldn't call myself an "audiophile", a dinky Bluetooth speaker would never cut the mustard for me musically. I grew up with Polk stuff, and my first "real" speakers were a pair of TSi100's that I mowed lawns all summer for in high-school after finding out the little satellite/sub system on my new Onkyo 5.1 were quite the downgrade from Bose 301's. Loved that setup to pieces, until they were stolen while I was moving in to my dorm a couple years ago. Campus police never found the perp, but I doubt they ever bothered looking tbh. Fate, however, was on my side and practically handed me a very clean Yamaha receiver with a pair of wonderful old KLH Model Six speakers (which I've since restored with AR sealant and Dayton crossover caps). Absolutely love those things...and so does my roommate!
Anyway, I lucked into a classic Harman Kardon 430 for $15 at the local goodwill while shopping for furniture, but I couldn't find any decent looking bookshelf speakers to go with it (mostly dinky satellite speakers and a hideous pair of giant Fishers). The local Craigslist turned up a pair of mint-looking Polk Monitor 4.5's for $40, which I jumped on. My dad often reminisced about the Monitor 10's he had in the '70s (paired, incidentally enough, with a Harman 730), and seeing as I have his old Dual 1019 with me (a pet project of mine, currently), I decided to pull the trigger on them instead of some '90s JBL's. Seller was the original owner who purchased them in Germany in the '80s and used them for years in his home theater before buying a Bose system, and rapped their cabinets as he touted their "solid, old-fashioned quality". Everything seemed on the level, so I went home and carefully carried them up to my apartment, quite pleased with my purchase. My stomach dropped when I went to plug them in and noticed that the both woofers were frozen solid. I called the seller back, since he did say I could bring them back if they didn't work, and he hung up once I told him "the drivers are frozen". Damn.
Pulled a driver, and I'm getting a reading of 7.7 Ohms on my meter, so it's obviously not blown out. Read up on the "magnet shift" problem due to old glue coming loose and causing the drivers to lock up if the speakers are dropped or bumped (which I was careful not to do, although there is an unavoidable speed bump in my parking garage). And indeed, I was able to slide a screwdriver between the magnet and move it around, although I couldn't get it to recenter at all.
So here I am, I guess, out $40 and with a pair of locked up speakers and a non-responsive seller. I'd hate to drop some cheapo 6.5" drivers in there willy-nilly, or part out the tweeters, but if I must, I must. Is there anything I can do to save them?
So backstory, I'm a broke college student who needs his music, and my roommate hogs the nice Yamaha setup in the living room, so I decided to piece together something for my bedroom. While I wouldn't call myself an "audiophile", a dinky Bluetooth speaker would never cut the mustard for me musically. I grew up with Polk stuff, and my first "real" speakers were a pair of TSi100's that I mowed lawns all summer for in high-school after finding out the little satellite/sub system on my new Onkyo 5.1 were quite the downgrade from Bose 301's. Loved that setup to pieces, until they were stolen while I was moving in to my dorm a couple years ago. Campus police never found the perp, but I doubt they ever bothered looking tbh. Fate, however, was on my side and practically handed me a very clean Yamaha receiver with a pair of wonderful old KLH Model Six speakers (which I've since restored with AR sealant and Dayton crossover caps). Absolutely love those things...and so does my roommate!
Anyway, I lucked into a classic Harman Kardon 430 for $15 at the local goodwill while shopping for furniture, but I couldn't find any decent looking bookshelf speakers to go with it (mostly dinky satellite speakers and a hideous pair of giant Fishers). The local Craigslist turned up a pair of mint-looking Polk Monitor 4.5's for $40, which I jumped on. My dad often reminisced about the Monitor 10's he had in the '70s (paired, incidentally enough, with a Harman 730), and seeing as I have his old Dual 1019 with me (a pet project of mine, currently), I decided to pull the trigger on them instead of some '90s JBL's. Seller was the original owner who purchased them in Germany in the '80s and used them for years in his home theater before buying a Bose system, and rapped their cabinets as he touted their "solid, old-fashioned quality". Everything seemed on the level, so I went home and carefully carried them up to my apartment, quite pleased with my purchase. My stomach dropped when I went to plug them in and noticed that the both woofers were frozen solid. I called the seller back, since he did say I could bring them back if they didn't work, and he hung up once I told him "the drivers are frozen". Damn.
Pulled a driver, and I'm getting a reading of 7.7 Ohms on my meter, so it's obviously not blown out. Read up on the "magnet shift" problem due to old glue coming loose and causing the drivers to lock up if the speakers are dropped or bumped (which I was careful not to do, although there is an unavoidable speed bump in my parking garage). And indeed, I was able to slide a screwdriver between the magnet and move it around, although I couldn't get it to recenter at all.
So here I am, I guess, out $40 and with a pair of locked up speakers and a non-responsive seller. I'd hate to drop some cheapo 6.5" drivers in there willy-nilly, or part out the tweeters, but if I must, I must. Is there anything I can do to save them?
Comments
-
Hop on the search function, there are 2 or 3 threads that address the situation with varying levels of solution. It takes a bit of patience, but a function generator, amp, a piece of PVC, red loctite and some screws are all you really need to get this done.
-
My only hangup with that is that the only 4" diameter PVC pipes available locally are at least 2' long, and I lack access to a hacksaw to cut it down to the 1.75" that I need. Maybe I might get lucky and the local Lowe's has some spare PVC scraps?
Anyways, I now have one driver fully apart. Guess I’m in the thick of it now. One of my friends, who builds speakers as a hobby and fixed up a pair of SDA’s a while ago, thinks that the voice-coil is flaking enamel and that I should scrap the drivers. I can’t say I know enough to prove him right or wrong, but I certainly hope that he is!
-
If I remember correctly, there is a forum member (Lawdogg) that offers to fix Polk drivers with shifted magnets for no charge. In fact I think he may have a small "inventory" of fixed drivers available and it is basically a swap. Do a search and see what you can find.
-
Yep, I've gotten in contact with him!
-
I don't use pipe, I use a coupler fitting that gets the backing plate perfectly snug. Just a little sanding to get the ring at the right hight.
