KEF coaxial SP1596 tweeter teardown and fix, need 39mm diaphragm!

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Sorry for the long thread title but hopefully gets to the point.

I've wanted to try a Kef coax for a while, especially the later 'tangerine' waveguide versions just because they look so nice!

Bought these recently. They are the 8". I really wanted the 5 but these will probably be used naked and not knowing the FS or qts, maybe the 8 will be a better bet for reaching low enough without box loading.

Anyway the chap I bought the (bare) 8" from gave me the tweeters as they were not functioning. This was great as I really like the look of these things and so I've made a start taking them to bits to see what has happened to them and if they can be mended.

So they measure open circuit unsurprisingly. I tried to unscrew the second black piece on the back to no avail so I started at the tangerine end. Cut through some glue and finally it prised off.
IMG20230716104942.jpg

Then it was obvious where in the VC the failure was. The dome would hang from the one remaining wire! Looks like it has burned through .
IMG20230716105046.jpg

Then I picked away at the black piece around the diaphragm and now have a blank sheet for repairing . Been looking for 39mm aluminium domes but not found anything suitable yet. Found these on AliExpress I might take a punt on. Obviously I will have to measure everything but I was planning on a custom XO anyway.

https://a.aliexpress.com/_Ew7pKpp

https://a.aliexpress.com/_EwfbyKF

The wires that run all the way through to connect to the back of the main driver are not part of the VC but extensions of thicker guage enamelled wire that the VC soldered to. It was here that the failure occurred.

IMG20230716120019.jpg

Shall keep the thread updated with progress.

Anyone know of any 39mm aluminium domes?
 
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You do know that KEF supply parts for their old hardware at reasonable prices? The tweeter and midrange for my 5" coaxials have different part numbers and this is likely to be the case for yours. If you can't find the part number and prices on the web then KEF or any shop selling KEF speakers will be able to supply the part number, price and likely get the tweeter if it isn't decades old and no longer being stocked. This is one of the advantages of a company like KEF that builds drivers themselves and has the option to keep the tooling around to support old drivers.
 
Who is they given KEF don't sell entire coax packages for DIY only replacement hardware to support their current and past speakers? I would suggest taking your broken hardware to a high street shop selling KEF speakers and asking them if a cone and coil assembly is available (unlikely but possible) otherwise what is the price for a new tweeter. When I bought my coaxials from a KEF shop there were 3 part numbers involved: midrange, tweeter and plastic surround. I opted for the first two but not the last. This is likely to be the case for your driver.

Tweeters failing is fairly common and so all companies serious about support (reducing in numbers these days) will stock replacement tweeters. The interesting test is whether they charge for them when it is the result of abuse.

If you have the parts in hand and a receipt from whoever you bought them from what other proof of ownership could reasonably be asked? I wasn't asked for proof of anything when I bought mine but I believe it can happen particularly in the US where at least one commercial speaker company was buying replacement KEF drivers to use in their new products.
 
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I don't think I'm going to get any help with replacement from a dealer having pulled the tweeter to pieces.!

By proof of ownership I mean an entire pair of loudspeakers. Not some drivers bought from a bloke on eBay.!

Thanks for all the input. I guess I put this up here just for interest to those with broken tweeters and not wanting to have to replace the entire coax unit....if that is indeed the case!
 
I don't think I'm going to get any help with replacement from a dealer having pulled the tweeter to pieces.!

Why not? A shop will want the profit from the sale of a tweeter plus the chance to build a relationship for future sales. The shop I dealt with had KEF drivers in drawers to help support sales to customers, performed custom home installations using KEF parts as well as retailing hi-fi and home theatre, were happy to sell me parts from returned failed speakers (budget class D PS and amp modules are not that reliable unlike the drivers and cabinets), etc... We would seem to have rather different ideas about how shops operate which is curious. Perhaps I am missing something?
 
I'm all ears if I can find tweeters for these at a reasonable price. Otherwise I'll DIY something together....measure and implement an XO

The tweeter+mid for my 5" coaxial was £150 a few years back. It is for the range above yours but not top of the range. Given a bit of inflation I would expect your tweeter to be £50-75 which to me looks reasonable compared to £30-40 standard range tweeters without the waveguide.
 
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That looks like a response from KEF customer support? You may get a different response from a shop that is trusted by KEF to install a tweeter but then that would include a charge for fitting unless the shop is prepared to give you the tweeter without. Can you confirm the tweeter in the Q series is straightforward to replace as a unit? Tweeters are normally designed to be replaceable because it is common thing to do over the life of a speaker. Perhaps they have gone the way of batteries in mobile phones?

I would expect the geometry of the dome would need to match the geometry of the waveguide fairly closely. Would be interesting to see the measured response with a non-KEF dome to see the degree to which this true.
 
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It is indeed Andy. The whole tweeter assembly removes very easily. Unscrew the big black locking ring on the assembly comes away once you've unsoldered the two wires. I realise Kef never intend anyone to disassemble the tweeter assembly itself as I have done but knowing these were toast I wanted to see if I could fix them.

You're comments on the dome radius is a valid one and the Kef dome appears to be quite a deep section. The ones I've ordered look much shallower. But I'll hopefully get something working and then measure them. I've saved the Kef domes and unwound the VC, maybe I could graft onto the new VC but I bet the glue would weigh more than the dome!
 
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Got the diaphragms today. The aluminium one has the perfect profile but at 39mm is too large for the gap. The bakelite looking woven thing is 38.5mm and fits the gap nicely but is too tall in profile and the waveguide won't fit over it . I've found the ally one in 38.5mm after some searching so have ordered a pair of those.
 

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I emailed KEF about replacing the tweeters in my older generation R series coaxials myself or at a local dealer (my original dealer has closed down) but they were reluctant stating that the tweeter is centred at the factory. Don't know enough about the construction to comment on this but my old dealer would have known. Despite being the range above yours the price quoted was substantially less. Not sure I fully understand the situation (or why they would sell a MF unit without a tweeter?) and would like to talk to a KEF dealer if there is one locally that has been one for a while and does installations as well as shifting boxes.

It does seem KEF (now?) want to supply the two units together which was not my understanding from earlier dealings. This obviously makes fitting easier and possibly managing the stocks easier but (probably) isn't ideal for a customer (or dealer?) familiar with handling drivers and soldering wires. Nonetheless this should be seen in the context of a driver that is one or two generations old being in stock locally and being supplied for a modest price. KEF are a good company in terms of support.
 
Got the diaphragms today. The aluminium one has the perfect profile but at 39mm is too large for the gap. The bakelite looking woven thing is 38.5mm and fits the gap nicely but is too tall in profile and the waveguide won't fit over it . I've found the ally one in 38.5mm after some searching so have ordered a pair of those.
Jim, did you ever find a diaphragm that fit? Can you provide a link?
 
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Yes, I did and sorry for not updating. I lost a bit of direction with these for the time being. They are quite a faff to fit. I think I need to order a fresh pair and have another go as I think my gluing wasn't up to scratch and I tried double sided tape on the second attempt. I don't think both will measure the same.!

https://a.aliexpress.com/_EuVJmpz

I didn't like the look of these with that weird surround. I guess a cheap production method. But they are the only ones I found with the correct VC diameter and dome profile .
 
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Hi John. How successful this was I'm not sure. I never got round to measuring the frequency response. This was/is one of my many DIY projects. They aren't destined for a factory Kef speaker, and so the relative response of the tweeter to the 8" midrange is quite possibly very different to the factory Kef. Meaning you would probably need to tweak the Kef crossover. Maybe just an alteration to the resistor (s) if lucky. I would be developing a new crossover so none of that mattered.
But they ' work' they make music.! Depending on how discerning an ear you have they may be fine. If it means getting your Q900s working again I'd definitely give it a shot.
It seems a massive shame that we are going to have all these lovely Kef speakers sat about doing nothing as they won't sell the tweeter. Which is obviously a weak link.
If I had some that worked I would re do the XO to a steeper slope to protect them better. I think they are first order. Atleast some of the other Kef coax are.