So, new here, and with zero knowledge of speaker design, but I know what I like to listen to, and have a reasonably good ear - I can hear when something’s astray, even if I can’t describe what it is.
I recently inherited a pair of KEF 104s (not ab’s) from my Dad, which he bought new when I was a kid, in about 1975. I’ve always loved the sound of these speakers, and almost from the day he bought them my Dad promised they’d be mine eventually.
He had the speakers serviced about 10 years ago, I think mainly the passive radiators which had perished, and the grilles which were foam but are now cloth.
When I got them home though, I found the bass driver in one speaker wasn’t working. I thought it might be the crossover, but swapping the driver to the other speaker proved that wasn’t the case.
The driver is “bottoming out” in its rest position, with what sounds like a metal on metal click.
I can’t afford to have the driver repaired if that’s even possible, so I thought I’d try an experiment;
My previous speakers were KEF Q15s. So I initially took the coaxial driver and crossover out of one of those and tried it in place of the dead driver in the 104 with an mdf “adaptor plate” to make it fit, so basically a Q15 in a 104 cabinet, with the 104 crossover and tweeter disconnected, but with no reflex port.
The result was awful - very harsh, with no bass to speak of - less than in the correct enclosure in fact. The passive radiator hardly moved even at high volumes.
So next I tried the Q15 driver in the 104 cabinet, but with the LF connected to the 104 crossover, and the original 104 tweeter connected as well (so the Q15 tweeter disconnected).
Comparing the modified speaker with the working original, I could honestly hear no difference, so I went ahead and applied the same mod to the “good” speaker. The result, as far as I can tell, is a sound every bit as good as the original 104s, and with a very similar characteristic.
So, to the experts here, is this sacrilege? Should I hang my head in shame and leave via the back door? Or have I been extremely lucky and happened to have drivers available that maybe on paper shouldn’t work, but do?
Have I created any issues for the future, in particular with the crossovers maybe?
The mods are completely reversible, so is there something simple (and low cost), that I can do to get the original driver working?
I recently inherited a pair of KEF 104s (not ab’s) from my Dad, which he bought new when I was a kid, in about 1975. I’ve always loved the sound of these speakers, and almost from the day he bought them my Dad promised they’d be mine eventually.
He had the speakers serviced about 10 years ago, I think mainly the passive radiators which had perished, and the grilles which were foam but are now cloth.
When I got them home though, I found the bass driver in one speaker wasn’t working. I thought it might be the crossover, but swapping the driver to the other speaker proved that wasn’t the case.
The driver is “bottoming out” in its rest position, with what sounds like a metal on metal click.
I can’t afford to have the driver repaired if that’s even possible, so I thought I’d try an experiment;
My previous speakers were KEF Q15s. So I initially took the coaxial driver and crossover out of one of those and tried it in place of the dead driver in the 104 with an mdf “adaptor plate” to make it fit, so basically a Q15 in a 104 cabinet, with the 104 crossover and tweeter disconnected, but with no reflex port.
The result was awful - very harsh, with no bass to speak of - less than in the correct enclosure in fact. The passive radiator hardly moved even at high volumes.
So next I tried the Q15 driver in the 104 cabinet, but with the LF connected to the 104 crossover, and the original 104 tweeter connected as well (so the Q15 tweeter disconnected).
Comparing the modified speaker with the working original, I could honestly hear no difference, so I went ahead and applied the same mod to the “good” speaker. The result, as far as I can tell, is a sound every bit as good as the original 104s, and with a very similar characteristic.
So, to the experts here, is this sacrilege? Should I hang my head in shame and leave via the back door? Or have I been extremely lucky and happened to have drivers available that maybe on paper shouldn’t work, but do?
Have I created any issues for the future, in particular with the crossovers maybe?
The mods are completely reversible, so is there something simple (and low cost), that I can do to get the original driver working?
Last edited by a moderator:
If the front surround looks alright, then examine the corrugated rear suspension (the spider) which can become unglued from the speaker basket or from the voice coil former.
Attachments
Thanks 🙂
Galu, I’ve had a look at both drivers based on what you said, and they look intact externally, but whereas the good one can be pushed both ways from its resting position (in and out), the bad one will only go out - it feels like the cone or voice coil is hitting the pole piece, just before it reaches the mid point of the travel it should have.
Galu, I’ve had a look at both drivers based on what you said, and they look intact externally, but whereas the good one can be pushed both ways from its resting position (in and out), the bad one will only go out - it feels like the cone or voice coil is hitting the pole piece, just before it reaches the mid point of the travel it should have.
If you are sure the rear suspension has not failed, the voice coil former may have become deformed, in which case there is no easy fix.
Thanks Galu. I’ve had a look at those yes, they may be an option.
I’ve also seen these recommended; any thoughts between the two, as there’s quite a price difference?
https://willys-hifi.com/products/monacor-spm-205-bass-mid-speaker?variant=42205576787
I’ve also seen these recommended; any thoughts between the two, as there’s quite a price difference?
https://willys-hifi.com/products/monacor-spm-205-bass-mid-speaker?variant=42205576787
I withdrew my post in order to make further checks on KEF B200 replacements.
I had mentioned Wilmslow Audio, who recommended the Monacor SPH-210.
However, the Monacor SPM-205 you've discovered at Willys Hifi look good value at around £74 the pair - and you would have to replace both originals to maintain sound balance.
EDIT: I can't comment on which would be the better replacement regarding emulating the original sound of the B200, but the Willys would be the better physical fit.
Repairing a bad driver is a dice throw. Speaker manufacturers have no incentive to give you the T/S values or even the sensitivity, since they make more money selling you an "exact" replacment. At least for the few years the company is still alive.
You have one surviving good OEM driver. There are ways to measure the T/S values, then you can shop with the information to find a matching driver. I haven't done it, but requires an omni microphone, an interface, and software like REW or ARTA or others. Look up the software on that forum, or there are bits of advice on this forum. I use condensor microphone into a used PA mixer (PV8) with phantom power, out the 1/4 phone plug main jack into the 1/8" stereo line level jack of my PC.
You would disconnect the surviving driver from the crossover to do the test. Moving to a flat surface at least a meter by 1 meter would approximate the way they test them at the factory (6 m x 6 m more likely).
You have one surviving good OEM driver. There are ways to measure the T/S values, then you can shop with the information to find a matching driver. I haven't done it, but requires an omni microphone, an interface, and software like REW or ARTA or others. Look up the software on that forum, or there are bits of advice on this forum. I use condensor microphone into a used PA mixer (PV8) with phantom power, out the 1/4 phone plug main jack into the 1/8" stereo line level jack of my PC.
You would disconnect the surviving driver from the crossover to do the test. Moving to a flat surface at least a meter by 1 meter would approximate the way they test them at the factory (6 m x 6 m more likely).
Last edited:
The Thiele/Small parameters of both potential replacements are quite different from each other, and unlikely to match those of the B200 SP1039 of which I have no knowledge.
It seems that using either of these as possible replacements would be a rather hit or miss affair.
All I can offer is that the bass resonance frequency of the original KEF B200 SP1039 (large magnet) is stated as 25 Hz, the Willys as 37 Hz and the Wilmslow as a more compatible 28 Hz.
If you are happy to sacrifice your Q15s, then perhaps you should stick to what has been found to work for you.
... as far the B110 Bextrene medium range driver and the T27 tweeter are ok, you should keep the good voicing of this loudspeaker 🙂
The B200 being paper cone it is more easy to swap but as say members : if the specs of the drivers are close enough. Ideal if not a close brandnew swap exhist is to look at cheap second hand that pop ups sometimes.
I would also ask to the guys from Falcon Acoustics, as by the way the lythic caps may need remplacement. They know very well the Kefs and should be full of good advices about a good enough swap. Up to you after if it is worthing the cost.
But if it sounds good with the drivers you swapped : then it is ok, again the important parts are the mid and tweeter !
Also they are not made for home cinema or rock party... more for casual listening level where it sings 🙂
The B200 being paper cone it is more easy to swap but as say members : if the specs of the drivers are close enough. Ideal if not a close brandnew swap exhist is to look at cheap second hand that pop ups sometimes.
I would also ask to the guys from Falcon Acoustics, as by the way the lythic caps may need remplacement. They know very well the Kefs and should be full of good advices about a good enough swap. Up to you after if it is worthing the cost.
But if it sounds good with the drivers you swapped : then it is ok, again the important parts are the mid and tweeter !
Also they are not made for home cinema or rock party... more for casual listening level where it sings 🙂
Check out the drivers in the KEF 104, iggy.
It has no B110, and the B200 SP1039 has a Bextrene cone.
P.S. To my knowledge, Falcon Acoustics are unable to recommend a suitable replacement for the B200 and would suggest searching for a second hand original.
It has no B110, and the B200 SP1039 has a Bextrene cone.
P.S. To my knowledge, Falcon Acoustics are unable to recommend a suitable replacement for the B200 and would suggest searching for a second hand original.
The B200 is betrene like the B110.
The B200 in the 104 is one of the bigger magnet ones, never available to diyers. https://www.t-linespeakers.org/drivers/b200.html
dave
Nice link!
Yes, as stated earlier, the KEF 104 employed the large magnet, SP1039, version of the B200.
Thanks so much everyone. I wish I had a clue what the various technical terms mean, but for now I’m going to stick with the Q15 drivers, and then get hold of some good used SP1039s when I can.
I think I’ll replace both drivers when I can - even the working one I have doesn’t look 100% to me, with the surround beginning to come unstuck from the cone in places.
I think I’ll replace both drivers when I can - even the working one I have doesn’t look 100% to me, with the surround beginning to come unstuck from the cone in places.