Yes, Kef Kube is missing.

[richardpp]

Hi,

I've found a pair of Kef 102 Reference speakers for sale but without the Kube. I understand from the user manual that these speakers are designed to work with the Kube which, as a separate item, is not so commonly available. I'm wondering if these speakers, as good as their drivers are recognised to be, are not really worth much at all without the Kube?

Many thanks, Richard

[PeteMcK]

102s + Kube is essentially a sub + Sat system, you could probably use any other sub crossed over correctly...???

[phase_accurate]

IIRC the Kube was a little equaliser designed for this speaker. It won't go as deep without it. On the positive side it was just a 2nd order HPF with a hump causing the system to act as a sixth order highpass (4th order is coming from the reflex tuning of the speaker).

The one who desigend it (can't remember his name) is also a member of this forum and he once posted something about it. With the search function you may probaly find it.

The circuit as such isn't complicated - you just have to find the right dimensioning.

Regards

Charles

[speaker dave]

I worked for KEF during that era. Be aware that some of the KUBEs did a lot more than just bass EQ, giving considerable midrange flattening also. Can't exactly remember which camp the 102 fell into.

Try this website
SpeakerTalk :: View Forum - KEF Speakers from the 1970s

Either search there or contact speakerguru, a long time KEF engineer.

Nothing would stop you from careful equalization on your own with either analog or digital means.

David S.

[richardpp]

Thanks very much for your replies. Having followed up on the posts as suggested I find again I'm bewildered by the height of expertise available on these forums. Congratulations!

Back on the Kefs a moment, 'speaker dave'. You think I can with careful EQ bring these speakers back, within reason, to how they were meant to sound, albeit without the extended bass. Sounds like a good place to start.

My amp is a Stereo Reciever NAD 7020e rated at 35w into 4ohms. The Kef 102 speakers require an amplifier capable of delivering 50 to 200 watts into 4 ohms. I am a little under powered here, would it be alright or should I be looking for another amp?

Thanks again, Richard

[speaker dave]

The systems that used the Kube were generally designed for maximum efficiency rather than flat response. The addition of the Kube then flattened the response. By the way, this is not much different than the original Bose 901 and its EQ. So the 102 will rise considerably in the mids (say around 2k) and will be soft in the bass. If you set up and equalizer with the opposite of that curve, that is a good start. You can have the extended bass as well, with some modest EQ at a frequency just below the natural rolloff.

I would still urge you to visit the KEF site. If you can find a graph of the Kube curve you will be that far ahead in creating the right curve, even with a graphic EQ just trying to approximate it. I think speakerguru has even been able to link some people up with missing Kubes, so it doesn't hurt to ask.

Regarding power, give your NAD a try before you discard it. Required power is a funny thing. 5 or 10 watts is usually way more than you need, but some times 300 watts isn't nearly enough. It really depends on how loud you like to listen, how far from the speakers you are, how dead your room is, etc. The benefit of the Kube is that the system efficiency could be maximized rather than thrown away to extend the bass. I don't think you need 50 to 200 watts.

Regards,
David S.

[richardpp]

It's interesting that the Kube tended to flatten response. Perhaps at some stage I might be able to find a Kube to try, though now I'd be very curious to hear what can be done with some equalization.

As you suggest I think I'll give my NAD a go. I'm sure I'll be happy with it for now. Most of my listening is done at low volume and fairly close in to the speakers.

I really appreciate your help and if I turn up some good results I'll let you know.

Regards,
Richard

[AndrewJ]

SpeakerDave is correct. I designed most of the KUBE EQ's, and other than the KUBE for the 104.2, most of them applied midrange EQ in addition to bass extension.
This was done so as to maximise the available midrange efficiency of the system that normally gets "thrown away" in the xover.
As Dave says, without the KUBE, not only will the bass response be mis-aligned, but the midrange will sound "forward", being too strong by typically at least 6dB.
You could attempt to compensate this by tone controls or an equaliser, but you are not likely to readily get the correct compensation without measurement tools.
Documentation on all the different KUBEs is sparse. I have attempted to get this myself from time to time but with limited success.
The circuit for the bass correction was certainly not a simple humped 2nd order filter, but was variously at least one "Friend Biquad" topology or a "Double Integrator Loop Biquad", the former very tricky to design without access to the computer program we wrote to help with the design (thanks Ric!).
On a side note, this October is KEF's 50th anniversary! Get ready to wish them happy birthday!

Andrew

[vcoppola]

Andrew,

Do you have any idea where I can get a hold of a Kef Kube for a pair of 103|3 Reference speakers ? I've been searching for one for some years.

Thanks so much for your help,

Victor

[dbphd]

I have a Model 200 KUBE that was given to me years ago. Is it suitable for use with KEF R107.2s and/or R104.2s? As I understand it, the KUBE is required for the R107.2s but optional for the R104.2s. Is that correct?

db