Kef 104/2 one of the woofer is not working? Any help please.

[real08]

Hi, i am new here, i would like to ask if anyone can give me some suggest about my kef's problem, i have kef 104/2 and i found out that one of my speaker's woofer (the low one) is not working but the upper working just fine. The question is that, do they have any way to check if the lf driver is broke? I open the bottom, all connections is ok. Noting disconnect or loose. Thanks for your reply.

 

[bandphan]

You can use a 9v battery and some speaker wire to see if it is blown.

 

[Seth=L]

I doubt it's the woofer, unless there's an obvious sign that it's damaged (rubbing voice coil, locked or some such thing). The most common failure on KEF speakers of that era is the in crossover. KEF used electrolytic capacitors in their crossovers. The problem, the originals work best and finding originals is a pain in the rear. One can't simply replace the bad capacitors with equal value Mylar capacitors and expect the speakers to sound exactly the same. It may not affect the sound a lot though.

The crossovers in these speakers are very complex. I wish you good luck on repairing them, but you may find it was a little more involved than you were expecting. Then again, if the speakers are invaluable to you, just have them serviced. They are very excellent speakers and I would say if you like them they are well worth repairing.

 

[real08]

Kef 104/2 woofer not work

Thank you all of you for reply, it happened on one woofer, but the upper still working. I listen on each speaker to compare the difference. Hard to say, the sound very identical...i think because the lf wave is undirectional. All i heard just the sound from mf and hf. If both upper and lower lf stop working then i believe that i can tell the difference because it is totally miss the lf wave. My system use separate subwoofer anyway so it should full fill the lf. I decide may be it is too risky to do everything by myself and because i value this pair a lot, i don't want to ask someone to fix for me if i don't know them well. Better leave my speaker alone.

 

[TLS Guy]

Thank you all of you for reply, it happened on one woofer, but the upper still working. I listen on each speaker to compare the difference. Hard to say, the sound very identical...i think because the lf wave is undirectional. All i heard just the sound from mf and hf. If both upper and lower lf stop working then i believe that i can tell the difference because it is totally miss the lf wave. My system use separate subwoofer anyway so it should full fill the lf. I decide may be it is too risky to do everything by myself and because i value this pair a lot, i don't want to ask someone to fix for me if i don't know them well. Better leave my speaker alone.

You need to fix this speaker. It is the lower mid that is blown. There are six drive units in each speaker. There are two 8" woofers you can't see in a second order coupled cavity bass system inside the speaker.

First of all by having one blown speaker you will have a bad lobing issue, however the bigger issue is that the power will go to the upper driver and stress it, so you stand a good chance of blowing that.

The other issue is that with a one non working mid the impedance has doubled and so the crossover frequency to that driver has doubled which is very bad.

The driver in question is a B 110. It has a Bextrene cone. There is no longer any Bextrene made in the world, so if the driver is blown, it is not repairable. However there were a huge number of KEF B 110s produced, so the chance of finding a replacement on eBay is excellent.

The first thing you need to do is find out if the driver is blown, which it almost certainly is, as both drivers are connected to the same filter.

Take out the driver and connect wires to the terminals. Then connect one lead to the -ve of the battery and keep taking the other wire on and off the +ve terminal. The cone should move in and out.

The other way you can test the driver is to use the ohm meter of a multimeter. You should get a reading of just under 8 ohms. I suspect you will find an indication the speaker is open circuit.

If you don't have a multimeter, I would get one. You can check that all connection from that driver to the crossover are good. It is all very straightforward.

Do this and post back.

Unless there is a dry joint or spade terminal not making contact, I suspect you will be looking for a used B110.

 

[real08]

it is not B110 Mid speaker!

the speaker problem is B200 8" woofer, the lower one, you can see inside the port.

 

[TLS Guy]

the speaker problem is B200 8" woofer, the lower one, you can see inside the port.

They are not so plentiful, but it is your lucky day. There is a pair of B 200s for sale on eBay now.

The price is well worth it to fix those speakers, and you will have a spare.

I should have guessed it was the B 200, as they are not a highly robust driver.

 

[Mika75]

TLS, I think u have miss-read his post. The driver not working is the lower of the coupled cavity bass section.

 

[TLS Guy]

TLS, I think u have miss-read his post. The driver not working is the lower of the coupled cavity bass section.

I did not understand that it was one of the coupled cavity drivers giving trouble the first time, but I did the second.

The drivers are modified B200s. So he could use the B200s for sale. He would not have the linking bar, but I think that would be a small loss and he would be far further ahead than he is now.

 

[Seth=L]

There's still the possibility of a crossover problem. I had a pair of KEF C80s, which are from the same time period, and they are reported to have one of the most complex and ridiculous crossovers because not only is the crossover complicated, but the parts are odd values for a speaker crossover. The C80s, while in my posession, had crossover problems. The C80 was supposed to be the poor man's 104/2, so I could imagine the crossover being very similar.

 

[TLS Guy]

There's still the possibility of a crossover problem. I had a pair of KEF C80s, which are from the same time period, and they are reported to have one of the most complex and ridiculous crossovers because not only is the crossover complicated, but the parts are odd values for a speaker crossover. The C80s, while in my posession, had crossover problems. The C80 was supposed to be the poor man's 104/2, so I could imagine the crossover being very similar.

Seth, it can't be the crossover if the upper driver of the pair is working. The drivers are in parallel. Twin coupled cavity drivers have to receive the same signal.

Yes, KEF crossovers of that period are complicated. Raymond Cooke, liked total impedance compensation so the load looks almost totally resistive.

I did that on my downstairs system speakers, as I had Raymond on my mind when I designed them, so I made the speakers totally impedance compensated. The part count is 27!

 

[Seth=L]

Oh, there are two woofers inside the cabinet? I'm curious, can the OP verify the second driver inside the cabinet is working? Is that what driver he is refering to as the "upper"?

 

[Mika75]

Just for the record, some 20 years ago it was the KEF 104.2 that initially opened my eyes to how emotionally powerful a home system could be, and stirred my interest in the audio field and music in general

 

[TLS Guy]

Oh, there are two woofers inside the cabinet? I'm curious, can the OP verify the second driver inside the cabinet is working? Is that what driver he is refering to as the "upper"?

Yes, he is. I was confused at first. He has confirmed that the upper of the two interconnected woofers are working, but the lower is not, and all connections seem to be in order.

The two woofers have a rod between the magnets to cancel vibration. The rear of each driver has its own sealed enclosure behind. The fronts of both drivers see a common ported cavity. This is the standard second order dual woofer coupled cavity band pass arrangement.

 

[The Rang]

I've had a pair of 104.2 s since '86, never a problem
Still my primary 2 channel speakers to this day


You may be able to get help via the Forum at this website:

http://www.hifiloudspeakers.info/

The site is basically dedicated to KEF.