Calling on KEF 104/2 Yodas, restore woes

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ParleyW

Junior Audioholic
I picked up a really beautiful pair of 104/2 for cheap. Not a mark on them. I dug in and got to work. The center doughnuts are new now, I restored the tweeters next, crud removed fresh fluid. I get everything back in and do some testing. The midrange to the top end is very clean but not a stitch of low end. Dig back into the cabinets looking for possible air leaks. Some of the little rubber isolation pads were shot so I direct coupled them woofers to the cabinet, then swapped out the old cabinet seals for the top and bottom panels for new. I put them both on the mic and ran a pass. I see a low bump just above 20hz now, and the bass is starting to climb at 40 hz and remarkably flat from 50 hz to 20 KHz. These old girls can still tangle with newer models. Just Beautiful imaging. I used a product I ran across in my lathe turning that brings out the beauty in wood like none other. The grain sucked in three heavy coats, and is three times darker now.

So I assume that I’m going to need to order new isolation grommets for the woofers (three posts per) Anyone know where I can find fresh seals for the woofers? It appears they use sort of what looks like weather stripping. I may just leave them as they are. They sound great. I assume the lack of low bass was due to air leakage with one or both woofers. Sealed systems are touchy that way. I believe they are operating normally now.

thanks
 

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Pogre

Pogre

Audioholic Overlord
Those look really nice! Nice work man. I've been eyeballing a pair of those on craigslist for a few weeks now and have been wanting to give them a listen. Interesting design.
 
P

ParleyW

Junior Audioholic
Those look really nice! Nice work man. I've been eyeballing a pair of those on craigslist for a few weeks now and have been wanting to give them a listen. Interesting design.
They are the finest imaging speakers I’ve had in this spot. I’ve had some damn fine speakers there. They date back to ‘85 for heck sakes. I’ll have the grills done tonight.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Grills finished. While I don’t have mad skills, I can do more than some, not as much as others. Very happy with them for $350.
Those speakers need an active equalizer that goes in the tape loop that modern receivers do not have. So you will need a separate preamp and power amp, assuming you have, or can find the equalizer. Bass performance is poor without that KEF Cube as it was called.
 
P

ParleyW

Junior Audioholic
Those speakers need an active equalizer that goes in the tape loop that modern receivers do not have. So you will need a separate preamp and power amp, assuming you have, or can find the equalizer. Bass performance is poor without that KEF Cube as it was called.
I don’t believe that was the issue. When I bypassed the aged speaker mounting hardware that isolates the woofers , and just bolted them directly to the cabinet, they drastically improved. My one sweep showed nothing under 150 hz. After the change I had some low end energy showing at 20hz, then a large climb starting at 30hz to 50hz, then ruler flat all the way to 20Khz. It’s the flattest speaker I’ve seen. When I only had one cabinet done, then compared the sweeps, it was so visible that something was amiss. After fixing both, overlaying the sweeps, they were virtually identical. Sealed speakers are super snotty with leakage.

The are very impressive. Especially on my big main beast amp. Beautiful.
 
Pogre

Pogre

Audioholic Overlord
Yours look a lot cleaner than the craigslist ones.
Those speakers need an active equalizer that goes in the tape loop that modern receivers do not have. So you will need a separate preamp and power amp, assuming you have, or can find the equalizer. Bass performance is poor without that KEF Cube as it was called.
I read about that in their literature and assumed the "Cube" was a subwoofer. It's an active crossover?
 
TLS Guy

TLS Guy

Audioholic Slumlord
I don’t believe that was the issue. When I bypassed the aged speaker mounting hardware that isolates the woofers , and just bolted them directly to the cabinet, they drastically improved. My one sweep showed nothing under 150 hz. After the change I had some low end energy showing at 20hz, then a large climb starting at 30hz to 50hz, then ruler flat all the way to 20Khz. It’s the flattest speaker I’ve seen. When I only had one cabinet done, then compared the sweeps, it was so visible that something was amiss. After fixing both, overlaying the sweeps, they were virtually identical. Sealed speakers are super snotty with leakage.

The are very impressive. Especially on my big main beast amp. Beautiful.
They work a lot better with the KUBE. Your speakers have a fourth order coupled cavity bass system. Both woofers fire into sealed enclosures. They share a common vented enclosure between them on they magnet sides. They are linked with a rigid metal rod. They was designed as 6th order system.
KEF were keen on 6th order alignments at that time. A sixth order alignment always requires active electronics to implement. There is no entirely passive solution for a sixth order alignment. This is what the KUBE is for. It extends f3 down significantly but with a 36 db per octave roll off rather than 24 db per octave. So if you can snag a KUBE you should should insert it between a preamp and power amp, es modern equipment no longer has tape loops.

At that time, the flagship KEF speaker was a large three way with 12 woofer, in a standard vented cabinet, not compound like yours. It was also a 6th order alignment and also required a KUBE.
 
P

ParleyW

Junior Audioholic
They work a lot better with the KUBE. Your speakers have a fourth order coupled cavity bass system. Both woofers fire into sealed enclosures. They share a common vented enclosure between them on they magnet sides. They are linked with a rigid metal rod. They was designed as 6th order system.
KEF were keen on 6th order alignments at that time. A sixth order alignment always requires active electronics to implement. There is no entirely passive solution for a sixth order alignment. This is what the KUBE is for. It extends f3 down significantly but with a 36 db per octave roll off rather than 24 db per octave. So if you can snag a KUBE you should should insert it between a preamp and power amp, es modern equipment no longer has tape loops.

At that time, the flagship KEF speaker was a large three way with 12 woofer, in a standard vented cabinet, not compound like yours. It was also a 6th order alignment and also required a KUBE.
They are hard to come by but I’m looking. I’m using old school equipment so the original cube config will be fine. Thx very much for the info. Even if I can’t find one, they are still a very fine sounding speaker. My hats off to the designer.
Thanks for the data.

My Lexicon preamp has a “loudness” option in the config. Wow do these have low frequency abilities. Ain’t this fun?
 
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Pogre

Pogre

Audioholic Overlord
I'm on craigslist a lot. If I stumble across one I'll give you a poke.
 
TLS Guy

TLS Guy

Audioholic Slumlord
Yours look a lot cleaner than the craigslist ones.

I read about that in their literature and assumed the "Cube" was a subwoofer. It's an active crossover?
No it is not an active crossover, but an active equalizer, which are required for all Qb6 alignments.

We should visit the coupled cavity bass systems once more. They are compact and efficient, and their major attraction is being able to control Q. The KUBE for these speakers gave the, owner wide selection of Q, over the bass system.

Those speakers I built as monitors, I used in Eagan, I did design and build an active crossover, variable Q system for. However, when I moved to Eagan I drove that bass system from Sub outs of the pre/pro. I had designed the native Q at 0.7 which was fine.

These coupled cavity systems have fallen out of favor with the developments of HT. The problem is that bandwidth is limited. Also bandwidth is dependent on Q. The lower the Q is the lower the bandwidth. So at Q 0.5, bandwidth is very limited, but bass quality is good. As you widen the bandwidth of the design, Q gets very high and bass quality falls off the cliff.

So the issue for HT becomes the LFE signal that does not roll off until 120 Hz. If you design a coupled cavity sub with a bandwidth of 20 Hz to 120 Hz, it would have a high Q, and a sloppy oozy bass, ala Bose.

So they work best as a passive crossover. Since roll off is 24 db per octave at both ends, then you can make a nice acoustic crossover for a ported speakers. Say you have a speaker, Qb4 ported box with an F3 of 50 Hz, then you can design a coupled cavity sub with a bandwidth of 20 Hz to 50 Hz, and low Q and get a perfect acoustic splice at crossover. However it will not handle the LFE channel. I have done designs like that, and I'm using one now in our family room. However I have an elegant WAF friendly solution up my sleeve, to change that in the near future.
 
P

ParleyW

Junior Audioholic
No it is not an active crossover, but an active equalizer, which are required for all Qb6 alignments.

We should visit the coupled cavity bass systems once more. They are compact and efficient, and their major attraction is being able to control Q. The KUBE for these speakers gave the, owner wide selection of Q, over the bass system.

Those speakers I built as monitors, I used in Eagan, I did design and build an active crossover, variable Q system for. However, when I moved to Eagan I drove that bass system from Sub outs of the pre/pro. I had designed the native Q at 0.7 which was fine.

These coupled cavity systems have fallen out of favor with the developments of HT. The problem is that bandwidth is limited. Also bandwidth is dependent on Q. The lower the Q is the lower the bandwidth. So at Q 0.5, bandwidth is very limited, but bass quality is good. As you widen the bandwidth of the design, Q gets very high and bass quality falls off the cliff.

So the issue for HT becomes the LFE signal that does not roll off until 120 Hz. If you design a coupled cavity sub with a bandwidth of 20 Hz to 120 Hz, it would have a high Q, and a sloppy oozy bass, ala Bose.

So they work best as a passive crossover. Since roll off is 24 db per octave at both ends, then you can make a nice acoustic crossover for a ported speakers. Say you have a speaker, Qb4 ported box with an F3 of 50 Hz, then you can design a coupled cavity sub with a bandwidth of 20 Hz to 50 Hz, and low Q and get a perfect acoustic splice at crossover. However it will not handle the LFE channel. I have done designs like that, and I'm using one now in our family room. However I have an elegant WAF friendly solution up my sleeve, to change that in the near future.
So I understood “no”?? :)
 
P

ParleyW

Junior Audioholic
They work a lot better with the KUBE. Your speakers have a fourth order coupled cavity bass system. Both woofers fire into sealed enclosures. They share a common vented enclosure between them on they magnet sides. They are linked with a rigid metal rod. They was designed as 6th order system.
KEF were keen on 6th order alignments at that time. A sixth order alignment always requires active electronics to implement. There is no entirely passive solution for a sixth order alignment. This is what the KUBE is for. It extends f3 down significantly but with a 36 db per octave roll off rather than 24 db per octave. So if you can snag a KUBE you should should insert it between a preamp and power amp, es modern equipment no longer has tape loops.

At that time, the flagship KEF speaker was a large three way with 12 woofer, in a standard vented cabinet, not compound like yours. It was also a 6th order alignment and also required a KUBE.
I have access to a Kube 200. It was designed with the 107 I think. Would it still work with the 104/2?
 
Pogre

Pogre

Audioholic Overlord
I have access to a Kube 200. It was designed with the 107 I think. Would it still work with the 104/2?
Not according to the research I did yesterday. The KUBE for the 104/2 is made specifically just for that model. The other ones (like the 200) won't work. I did a bit of a deep dive yesterday looking into it. You should double check my findings of course, but yeah. From what I found, no the 200 won't do it.
 
P

ParleyW

Junior Audioholic
Not according to the research I did yesterday. The KUBE for the 104/2 is made specifically just for that model. The other ones (like the 200) won't work. I did a bit of a deep dive yesterday looking into it. You should double check my findings of course, but yeah. From what I found, no the 200 won't do it.
Dang. Thanks for your effort’s. Saved me $300
 

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