MERGED: KEF Q15.2 Speakers

[Old Sparky]

The only trouble with that pair ohf Q15s on eBay, mark, is that they're 'Collection Only', from Bradford, and I'm in Oxfordshire!   There are others on there, though, plus a pair of B160s c/w their Tweeters, which would be 'drop-in' replacements for the exsisting drivers, so that may be the way to go.

[Old Sparky]

The tweeters (NT19C) in a pair of the above speakers have failed, presumably due to the fact that the connections to the LF & HF drivers have been wired in parallel externally by connecting the leads from both drivers to one pair of 4mm plugs.  For those not familiar with the Q15.2 series of speakers, these employ the B160 dual drivers in which the aforementioned NT19C tweeters are fitted through the centre of the Bass/Midrange driver's magnet assembly.  AFAIK, there are no crossover components fitted, so either external crossovers should be fitted, or a Bi-amplified system should be used to drive them.  The connection plate on the rear of the cabinet has four terminals, which suggests to me that BiAmping should be used.  Can anyone 'out there', familiar with these speakers, confirm my thoughts as expressed above?  N.B.  I haven't yet looked for technical info on the Q15, but will do so shortly.

[Old Sparky]

I have since downloaded the specifications of the Q15.2, which do not specifically mention BiAmping, but surely if, as in this case, the Bass/Midrange and Tweeter terminals are simply wired in parallel, then LF & MF notes are going to appear at the tweeter's terminals, with possibly, nay probably, disastrous consequences for the tweeter?

[Mark Hennessy]

If the crossover is missing, it's because someone has taken it out.

Some people believe that crossovers can be affected by vibration inside a loudspeaker cabinet, and report incredible subjective advantages to mounting the unit externally. It's fairly common in "hi-fi land".

Alternatively, someone might have designed a low-level crossover that sits between the preamp and a pair of stereo amplifiers. Such an arrangement would be called "active", rather than bi-amping.

Bi-amping retains the existing crossover, but uses a pair of (hopefully!) identical amplifiers, both of which carry the whole audio spectrum in voltage terms, but only deliver current at the frequencies demanded by the drive unit and crossover combination. Really, it should be called "buy-amp", because that's the overall effect. Exactly like "buy-wiring". Manufacturers are incredibly good at finding new ways to sell stuff...

[Mark Hennessy]

BTW, any relation to a previous thread last year?

http://golbornevintageradio.co.uk/forum/...p?tid=4678

EDIT: These 2 threads are now merged.

[Old Sparky]

These are exactly the same speakers, Mark. What happened was that the owner took them away pending a decision on having them repaired or not, and 18 months later has decided that he would like to have them fixed, so yesterday brought them to me minus the NT19 tweeters, but otherwise as they were when I first had them. In the meantime I'd forgotten some of what I'd found out about them, so thanks for the link to my previous post and the replies thereto. These will save me going over old ground twice, but doesn't alter the fact that a new pair of NT19's are almost £84 on eBay, so the repair, assuming no other faults is going to be at least £125.

[Mark Hennessy]

Yes, my long-term memory is sometimes OK I'll merge the two threads in a minute...

Ok - it seems that we have a pair of boxes with (hopefully!) OK woofers, but no tweeters, and perhaps no crossovers?

We assume the woofers are OK, but as I mentioned on that other thread, the voice-coil gap is open to the elements in that design, so foreign debris can find its way in. With the tweeters removed, this risk is much greater. Scraps of wire wool are deadly to most loudspeakers.

Looking at this from my "outsider" perspective, I'd be reluctant to take these on. These were "decent for the price" in their day, but eBay is full of similarly good models for less money that a repair would cost. And if that repair involves tweeters bought second-hand from eBay, I'd be worried. If they work when they turn up, how do you know they've not been thrashed? Most tweeters use ferrofluid for cooling and damping, but in many models, this gradually dries up and changes the way they sound. Without the means to measure the acoustic output, how can you be sure the replacement tweeters are working correctly? And if there's any doubt about their performance, it'll be you that has to deal with the eBay seller, and potentially take a financial risk in the process. And how about these missing crossovers? I see there's one (not a pair) on eBay for £50 BIN.

For perspective, a couple of years back, the person I share my office with bought a mint pair of Q15.2s from a local charity shop for £15. In fact, as it was a charity shop, he gave them £30! He already had a pair of Q35s (still has), and likes them. But, having just asked him, there's no way he's consider spending anything like £125 on a repair. From a quick look on eBay, working pairs of complete speakers only fetch around £50 + postage. I'd advise your customer to pick up another pair that way. Or, buy him another pair and charge him commission.

Anyway, that's my gloomy "worst-case" view. These are pretty ordinary units. It's not like we're discussing the BBC LS3/5A or similar

[Old Sparky]

The tweeters in question are advertised as being New, which, for £85, they ought to be. Having spoken to the owner, he may bid on a pair of Q15 speakers currently on eBay. instead of having new tweeters fitted in the Q15.2's BTW, the Crosovers are still present, and check out OK 'cold'.

[Mark Hennessy]

Yes, that's definitely the sensible way forward.

Thanks for clearing up the crossover question - looking back over the thread, it's been confusing

Oh, and ferrofluid can degrade in storage. IME it affects some models more than others - I can't comment about the KEF ones specifically. Best out of it!

[Old Sparky]

Point taken, Mark. The job is certainly on hold till I next speak to the owner anyway. In theory it's one of those 'simple jobs', though - just pop in a couple of new tweeters and away you go, but these have been stored, presumably at the owner's home for 18 months without tweeters in them.