Mission 781 speaker rattle

[richhutch]

Putting together a retro vinyl playing system for a friend's daughter's 21st in May. Picked up a pair of Mission 781s for next to nothing and checking them out. One of the speakers has a very slight buzz/rattle when very bassy tracks are played (I've been using Kraftwerk vinyl to test them out). It's the kind of noise I've heard before from a damaged drive unit but this one looks immaculate with no flaws or splits. Swapped the speaker leads over and it's still that speaker rather than anything on the track. Had the drive unit out and all looks perfect in behind. Any thoughts out there?
Thanks.

 

[nopiano]

Putting together a retro vinyl playing system for a friend's daughter's 21st in May. Picked up a pair of Mission 781s for next to nothing and checking them out. One of the speakers has a very slight buzz/rattle when very bassy tracks are played (I've been using Kraftwerk vinyl to test them out). It's the kind of noise I've heard before from a damaged drive unit but this one looks immaculate with no flaws or splits. Swapped the speaker leads over and it's still that speaker rather than anything on the track. Had the drive unit out and all looks perfect in behind. Any thoughts out there?
Thanks.

Is the voice coil scraping slightly? You might be able to fudge it by rotating the driver by 180 degrees as gravity can make the difference. But if the voice coil has been cooked by someone overdoing the bass control then it has had it. That won’t be visible from the front.

 

[richhutch]

Thanks for that. What does the voice coil look like? Is it visible?

 

[twinkletoes]

its either the above OR i hand the problem back in the day with Mission on a pair of 701's where the baffle had actually come away ever so slightly and it made a buzzing noise. i had to use Araldite epoxy to seal and stick it back.

It could even be that the driver screws need tightening probable haven't been tighten in the life of the speaker

Edit also if i belive correctly mission had a driver recall on the 780 series line of speakers but i cant remember the models it affected it could be that you have one of speakers that never went back for the drive replacement

 

[twinkletoes]

Thanks for that. What does the voice coil look like? Is it visible?

not visible at all. You would smell it after a speaker has been playing for a while though through the bass port

TBH it could be a number of things, loose wire hitting the back the cone and so on

 

[AEJim]

As nopiano says it's worth checking the coil, when you push the centre of the cone in there should be completely smooth movement with no scraping.

Other things worth looking at; check the glue around the dustcap, if it's dried out and come away a little it can cause a rattle, take a look at the copper braids at the back of the drive unit, if they're a little long they can come into contact with the cone at higher excursion (usually solved by simply bending them out of the way), and also worth checking the rear terminals are screwed down tightly if they're that type - rattles can come from surprising places!



(Copper braids shown).


*Edit - you mentioned some of this while I was typing!

 

[richhutch]

Brilliant tips guys (and girls). I'll try all of the above. Keep the suggestions coming!!

 

[nopiano]

Thanks for that. What does the voice coil look like? Is it visible?

Sorry, I shouldn’t have assumed..

No, it’s inside the speaker. The coil is attached to the rear of the speaker cone, and sits in a circular magnet - signal is passed through the coil - the cone moves! Sound emerges!!

As Jim says, gently pushing the cone inwards and releasing, it shouldn’t scrape.

 

[richhutch]

This just in. Tried what Jim suggested and pushed the cone in gently and there WAS a scraping sound. On further investigation I saw that the paper cone had become detached from the rubber surround (sorry if I'm not using the correct technical terms) over quite a bit of its circumference (photo attached). Surely this must be at least part of the problem!! Any tips on best glue to reattach?

 

[Al ears]

This just in. Tried what Jim suggested and pushed the cone in gently and there WAS a scraping sound. On further investigation I saw that the paper cone had become detached from the rubber surround (sorry if I'm not using the correct technical terms) over quite a bit of its circumference (photo attached). Surely this must be at least part of the problem!! Any tips on best glue to reattach?

might be fixable with Superglue but I would be looking at a replacement unit or two... Check the other one.

 

[richhutch]

The other one has similar issue but to a much less extent. Interestingly, although the paper cone is detached (a little) on that speaker, it does not seem to affect the sound (or my ears are really rubbish!). I suppose the worst case scenario is to try the repair and if it doesn't work replace the units. Dose anyone know if these are still available?

 

[nopiano]

The other one has similar issue but to a much less extent. Interestingly, although the paper cone is detached (a little) on that speaker, it does not seem to affect the sound (or my ears are really rubbish!). I suppose the worst case scenario is to try the repair and if it doesn't work replace the units. Dose anyone know if these are still available?

The best bet might be to look out for some on eBay nearby. Ideally with blown tweeters but perfect bass units. Are yours the Mission Cyrus 781 two-way?

 

[richhutch]

They appear to be, although no mention of Cyrus anywhere. They are described as 2 way reflex on the cabinet label. To be honest I spent so little on these that I am reluctant to spend anything on replacing the drive units and my first choice is to repair/glue the rubber surround back on to the paper cone. I e-mailed Mission for some advice on this but nothing back. I am thinking that a more flexible glue like a contact adhesive might be best because of the movement between the 2, especially at higher volumes. Any thoughts out there?

 

[nopiano]

They appear to be, although no mention of Cyrus anywhere. They are described as 2 way reflex on the cabinet label. To be honest I spent so little on these that I am reluctant to spend anything on replacing the drive units and my first choice is to repair/glue the rubber surround back on to the paper cone. I e-mailed Mission for some advice on this but nothing back. I am thinking that a more flexible glue like a contact adhesive might be best because of the movement between the 2, especially at higher volumes. Any thoughts out there?

Somewhere like Wilmslow Audio, who restore speakers, would be the place to ask about the best type of glue. I’m guessing that it probably depends on the materials the cone and surround are made of. In any event, I don’t believe you want anything other than a firm join, with no flexibility. The voice coil needs to be precisely lined up, so no ‘give’ is wanted beyond that offered by the surround.

 

[richhutch]

Fair point. I was only thinking that superglue type adhesives can be a little brittle and I'm not sure whether that would be the best.