Monitor 7b magnet glueing

bbabb

So, I just picked up some nice original Monitor 7bs and have really enjoyed reading through this forum and all the info out there on these speakers. I’m really new to this vintage audio world but loving it so far. I plan on recapping the crossovers and doing some of the other little upgrades I’ve read about here eventually. Right now I just want to get the magnets glued up before that becomes an issue. Pulled the drivers out and found that the magnets are not perfectly centered compared to the metal plates they are sandwiched between. The speakers sound great and the drivers move freely but I just wanted to check and see if it was normal for them to be slightly off center or if that’s a sign that they have shifted some? I’m sure the magnets are pretty strong but I can’t get them to slide at all so I’m assuming they are still glued tight? See attached photo to see what I mean. I’m talking a couple 32nds of an inch difference. I just don’t want to glue them if there is something off. Anyone else seen them be slightly off center? Thanks!

F1nut

No need for all that crap.

With your finger tips spread evenly around the cone gently push in and let the cone spring back with your finger tips still touching the cone. Do it a few times making sure the finger tip pressure is evenly spread.

No scraping sound, glue the magnets immediately.

bbabb

@F1nut Thank you for your help!!

Gardenstater

Congratulations! If it was me I'd be careful. I really find it hard to believe that they would allow the magnets to be so far off center when building the driver, especially since they glue them up in the unmagnetized state.

If you glue them use something that is not impossible to remove like Gorilla Max Strength Clear. I just mention that one because I was able to successfully remove the glue on mine with that adhesive. I would not use an epoxy like JB Weld in this case.

The voice coil clearances are very tight in MW6500 drivers between the O.D of the coil and the framepiece I.D. but when that starts scraping there isn't much to be done without heroic measures. I just mention that for your information.

Maybe it shifted at some time but somehow ended up reasonably centered which is why I'd glue them after I listened for a few days. A good test is to run some low frequency test tones because that seems to make it more obvious when there is a slight rub.

Oh and also.....don't try pushing the magnets to test any more because if it does move you will lock them up and possibly do damage.

bbabb

Thanks for the quick response! I’ve been listening to them for the last couple weeks and I can’t hear anything weird going on, they sound pretty great to me. I’ve seen the “test tone” thing mentioned before but I’m unclear as to exactly how that works or how to do it…

Gardenstater

bbabb wrote: »

Thanks for the quick response! I’ve been listening to them for the last couple weeks and I can’t hear anything weird going on, they sound pretty great to me. I’ve seen the “test tone” thing mentioned before but I’m unclear as to exactly how that works or how to do it…

In my case I can use the Signal Generator app in my Squeezebox Touch. I can also download test tone files and play them from my hard drive through the SBT.

There are lots of online tone generators.

This site lets you download all sorts of test tones:

https://www.audiocheck.net/audiofrequencysignalgenerator_index.php

If you don't have the ability to play them from your hard drive you could download the wav files and burn them to an audio CD.

bbabb

@F1nut thats what I was doing and they move freely and there is no scraping. I assumed that meant they were probably good to go, but just figured I’d double check to make sure I wasn’t missing something. I’ve read a lot of your comments and you seem to be the Guru. I’m gonna glue them up! I got the Loctite Power Grab because I saw that mentioned in quite a few posts. Is that still good stuff?

Gardenstater

Good luck you are probably fine. Mine were tricky in that they only rubbed when I played music with extreme bass lines and they passed the push test. When I played the 30 Hz test tones they failed that with distorted sound.

bbabb

@Gardenstater I’ve played some pretty bass heavy stuff, rap and hip hop are some of the genres of music I like, and I could never hear anything that seemed off. I think I’m going to go ahead and glue them up. Thanks for your help!!

F1nut

bbabb wrote: »

@F1nut thats what I was doing and they move freely and there is no scraping. I assumed that meant they were probably good to go, but just figured I’d double check to make sure I wasn’t missing something. I’ve read a lot of your comments and you seem to be the Guru. I’m gonna glue them up! I got the Loctite Power Grab because I saw that mentioned in quite a few posts. Is that still good stuff?

I strongly suggest going with JB Weld. Be sure to do around the top and bottom.

Gardenstater

bbabb wrote: »

@Gardenstater I’ve played some pretty bass heavy stuff, rap and hip hop are some of the genres of music I like, and I could never hear anything that seemed off. I think I’m going to go ahead and glue them up. Thanks for your help!!

Cool. Just as further info., mine didn't get *triggered* by all heavy bass music. It had to be something with sustained low bass notes. As I recall, Mike Oldfield Tubular Bells used to be one that they didn't like. That's what first let me know I had a problem. That's why I then used the test tones to confirm.

Good luck.

Gardenstater

^^This was after I had glued them with the Gorilla stuff I mentioned. I was grateful that I did not use the JB Weld because I would have had a he ll of a time to remove that. The Gorilla was hard enough.