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Recommendations on MG 15 Rebuild

Pics would help.
In edition to the tweeter installation advice have you checked the 4 spider clamp ring nuts are done up fully? When you resoldered the driver leads to the socket on the basket are you sure you haven't got them the wrong way around ie hf wired to the bass driver etc?
 
Now I'm really confused.

Just got home and double checked that it wasn't rubbing, but it was :(

I moved the cone around a little bit as I was going up and down and now it doesn't rub again. There's obviously something going on with the voice coil.

I'm wondering if something fell in there, or if its actually just bad. Possibly it's just very dirty?

I'll try and pull the foam off the without destroying it but its probably not possible. The voice coil and woofer just lift right out correct? After disconnecting the wires of course.

I'll start looking for a replacement cone either way just in case. Hopefully it's just a matter of cleaning it since the cones look to be very expensive.
 
Where are you located? You say you used shims to refoam so I take it your drivers don’t have dustcaps? Did you glue the foam to the frame or clamp them as you are supposed to do? if you need replacement foams I can supply you with some.
 
If it's an alignment issue (rather than any damage or crud wedged down there) then before anything more drastic you could try loosening the nuts that hold the spider in place and and see if you can find a position in which there's no rubbing.
 
I'll loosen up the spider nuts and try to reposition it. Maybe that will be enough.

If that doesn't work , I'll see how much glue I applied to the outer edge and try and pull it off. Hopefully it didnt stick very well to the metal.
 
Its definitely not an alignment issue.

I was able to get the cone off without ripping the foam.I pulled the whole cone out and used my air compressor to clean out the speaker. I carefully re-aligned it and used shims again . It goes up and down smoothly.

Sadly it's still not ok. It's much more muted than the other speaker.

When I get a couple free hours, I'm going to try switching cones/voice coils to rule that out before I just start buying random parts
 
Have you measured the impedance of the voice coils to make sure they are in the same ballpark/close to what they are meant to be (which I don’t know for HPDs, but I’d guess at about 6-7 Ohms, Frank will know!)?
 
Shawnnnn said:
Its definitely not an alignment issue.

I was able to get the cone off without ripping the foam.I pulled the whole cone out and used my air compressor to clean out the speaker. I carefully re-aligned it and used shims again . It goes up and down smoothly.

Sadly it's still not ok. It's much more muted than the other speaker.

When I get a couple free hours, I'm going to try switching cones/voice coils to rule that out before I just start buying random parts
Click to expand...
Be sure to take plenty of photos to document your investigations. Impedance should be around 5.6 ohms.
 
Is measuring at the speaker terminals ok, or should I pull the drivers out to measure them?

The reason I'm asking is they both jump around a lot. Using my Fluke 115, the bad
one goes from 4 to 8 and every number in between without stopping. The other one is a slightly more solid 5 or 6 but still jumps around quite a bit.

This seems bad, just tested a different pair of speakers and my meter barely moves at all.
 
Shawnnnn said:
Is measuring at the speaker terminals ok, or should I pull the drivers out to measure them?
Click to expand...

Measure at the driver terminals, i.e. at the 4 pin plug where the bass cone is connected. You want to measure the specific driver, not the crossover.
 
When you cleaned the gap with compressed air did you also clean it with double sided masking tape?
Old rotted foam is like glue and compressed air wont shift it if its stuck to the pole piece/gap. Did you also inspect the coil/former for any debris that may be stuck to it? When you first posted your question you described the problem as a tweeter with dull highs but we are now investigating the bass driver because its isnt as clear as the other bass driver so is the tweeter now performing fine and the dull highs have now gone? I'm finding it hard to offer any worthwhile advice as I've no real idea what the problem is other than perhaps a seriously demagged magnet.
 
I haven't figured it out yet, but you've been very helpful and I appreciate your time trying to help me.

I suspected the tweeters because I read a few posts where that was someone else problem, and so much detail was missing from mine.

These were stored for a very long time. When I got them the only thing I did was put new foam on without dissembling anything other than the woofer clamps.

This is the order I've done things in.

Swapped crossovers.

Swapped amps.

Cleaned out the tweeter voice coil gap and tweeter cap.

Swapped tweeters .

Cleaned out the woofer voice coil gap and realigned the woofers. I did not use any tape in the gap, it looked pretty clean. I very gently blew air on the coil.

I'll pull it out again tonight and check the resistance. I can't remember what it was, but I did check it the first time I pulled them out. I think it was ok, but when I checked it last night again the crazy numbers made me think I missed something.

I'll swap the voice coil next and if that doesn't work , I'll look at finding a replacement speaker. Seems weird a magnet would die, but other than the wires there is nothing else to check.
 
You don't need to remove the cone to measure the coil you just test across the LF driver solder tags above the chassis plug socket or the socket itself.
 
I switched woofers and the bad speaker stayed bad.

I used wire leads to make it sure it wasnt a bad connection.

It really only leaves the magnet.

I found one really old post where somebody had the same problem as me. He dissembled his magnet, but it was undetermined if the problem was already there.

https://www.diyaudio.com/forums/multi-way/47234-alnico-magnet-question.html

I asked Lockwood if they had any spare speakers or magnets, and they recommended recharging it. I'm going to send them both off today to a place in the states that can re-magnetize / regauss them. This has to fix it!

https://greatplainsaudio.com/great-...ico-magnets-degaussing-losing-magnetic-field/
 
louisjames said:
The magnet in the speaker that exhibited the lower volume is over 1000 gauss below the other one. He is going to try and recharge the magnet and see what that does.
Click to expand...

Any news on this?
I recently picked up a pair of old Tannoy Eatons with 295/8 drivers.
Built some new closed cabinets and crossovers for them.
One of the HF units sounds significantly rolled-off, just like other posters have reported here.
I note Tony's suggestion that it might just be that the units are inherently badly matched*, but wonder how effective the attempted recharging was?

*May be we could swap individual drivers between us according to which are best-matches...? ;)
 
Do not take a Tannoy magnet apart.
The LF and HF in an AlNiCo DC share the same magnet, the compression driver diaphragm in the Tannoy DC has a short coil and it is incapable of demagnetising the magnet, if the bass driver is ok with no low mids roll off then its reasonable to assume the magnet is ok. You can significantly alter the HF output by poor installation/mis-alignment.
 
There's a guy in Cornwall with an MC6 magnetiser, does Altecs/JBL's mostly but he's informed me he can de-mag(you have to first) then fully charge Tannoy DC's.

Sven Olsen, pm me if you need his contact.
 
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