Speaker Repair Question

[sweatyk]

I had a Yamaha NS4 recently shipped to me and the seller did not put packing inside the speaker to support the backside of the speakers. As a result both magnets became dislodged and fell off.

A. As a DIY can I put them back in place without having issues with the voice coil?

B. If so what type of adhesive is recommended?

The speaker was free and fully functional before it was shipped so I'm out nothing but a little bit for shipping cost which is no big deal.

[Mick Bailey]

Clean off the mating surfaces and use a good-quality epoxy. Your problem will be aligning the magnet assembly in relation to the voice coil so that it doesn't rub. Use as little adhesive as possible and make sure you keep it well away from the gap. You don't want it to ooze out. Sometimes there are locating dimples or similar - does your speaker have these? May be a good idea to post a pic or two.

[sweatyk]

I have to leave for a while and this is the only pic I have at the moment. I will take a closer shot and post it later if necessary.[IMG][/IMG]

[sweatyk]

Here is a close up of the two. The one with the 3 dimples is the tweeter.[IMG][/IMG][IMG][/IMG][IMG][/IMG]

[Mick Bailey]

The remaining adhesive looks like it will come away fairly easily.

When you try to position the magnet it will want to slam down on the chassis as soon as it touches. Do a dry run first. I would place three spacers about 2mm thick around the face so that the magnet can be more easily positioned, then withdraw each one carefully. You can see how the adhesive was applied away from the gap. You don't need much at all - just a thin smear. If you use regular epoxy (rather than 5-minute) you'll have plenty of working time, so no need to rush.

You will need to check that the coil moves without rubbing by spanning the cone with your hand and moving it through its excursion range without any grating or friction.

If you have a verier it would be useful to measure how concentric the magnet is and to nudge it into final position. The tweeter looks like it could be more challenging to get an accurate alignment, but it looks like aluminium alloy so you won't have the problem of the slamming magnet.

[sweatyk]

Thanks for the advise Mick! I will let you know how it turns out.

[sweatyk]

"If you have a verier it would be useful to measure how concentric the magnet is and to nudge it into final position."



By the way I meant to ask.......what's a verier?




Never mind, just figured out what you meant.............caliper

[Mick Bailey]

It's a typo - should read Vernier.

A cheap digital one is good enough for the job.

[g1]

When you try to position the magnet it will want to slam down on the chassis as soon as it touches.

Be very careful when doing this. If you are not perfectly aligned, the coil will be crushed. As you are bringing the magnet down, the coil must fit into the gap.

[sweatyk]

Yeah I have one of those. I plan to be very very careful with it.

[J M Fahey]

Sorry but you won't be able to.
Definitely impossible with the VC still in the gap.
Big speaker shops do it by first demagnetizing, but with a charged magnet, forget it.
And even them must first disassemble the moving parts (VC, cone, suspension) so they can fit a lathe machined brass or aluminum centering ring.
It can't be done by eye alone.
And then they remagnetize again.

And extra packing would not have solved that, speaker cabinet fell straight on its back from at least 3 ft, probably more.

[Mark Black]

I second Juan's opinion. Although I have been able to pull off several magnet reinstallations without demag/remag they all required me to first remove the cone/voice-coil assembly and fashion a tight-fitting circular plastic shim to hold the magnet & pole-piece centered while the epoxy (I used JB-Weld) became fully set. As soon as you get the magnet/pole-piece assembly anywhere near the plate that forms the outer part of the gap they will suck together with a resounding CLANK, and woe be unto any of your fingers which happen to be in the way! The pole-piece will naturally suck to one side without a shim and you will be left with an off-center non-concentric gap while trying to figure out how to quickly disassemble everything & remove the adhesive. No way I can see it being successfully done in with the cone/voice-coil in place absent of some specialized line-up equipment, or the aforementioned demag/remag process. Even then I would bet the insulation on the voice coils has already been compromised during the separation. Sorry 'bout that...

[eschertron]

... I'm pretty sure I saw James Bond do it in one of his movies...

[sweatyk]

Well while I agree with what Juan says the fact that I have nothing to loose here means I will carefully forge on with the attempt. Notice I said attempt. Obviously not being one of the more sought after models Yamaha does not have any info on it not even a spec sheet to help me find a suitable replacement. I will take all advise in consideration and take my time.