SpeakerTalk

bilbobat · Introductory Contributor Joined: 25 Nov 2014 Posts: 7

hi KEF lovers,

I have 105,4 and 107,2 speakers, and 2 bass cabinets from a 105,2 pair. the bass modules are complete, they only lack the head for high and mid frequencies.

I have some work to do with the 107,2. the surrounds were changed but they installed a bigger surround and cut it to fit the woofers. they do not respond as well as they should. my kube also need repair.

so I want to try the 105,2 bass modules with the 107,2 heads ideally, or with the 105,4 heads. is the thing possible? are the specs close enough to authorize this test? If it is possible with the 107,2 heads, I will make an adaptor for the DIN plug, and will ask if someone have the pin out.

thank you

SaSi · Senior Contributor 200+ Joined: 24 Aug 2008 Posts: 256

Should be fun to try. Not difficult and not much harm could be done. One word of caution on the 107.2 heads though. The 107 and 107.2 were using conjugated crossovers to present a resistive 4Ohm load to the amplifier. The drivers on the 107 heads are 4Ohms. The 105.2 uses 8Ohm drivers on the heads so it would generate a loudness mismatch and possibly a load mismatch. Nothing a decent amplifier would not handle in low listening levels though.

So, the 105.4 heads would be a closer match to the 105.2 bass cabinet, although it would still be a FrankenKEF.

If you are adventurous, and have access to 4xB200SP1014 and can do some woodworking, I would suggest to make wooden flanges for the SP1014 drivers (if needed) and mount these in the 107 bass cabinets. I've built R107 lookalike cabinets, using the original crossovers and heads as well as various B200 drivers and settles for the SP1014s. They sound terrific and I don't use a KUBE.

BTW, could you help me on a question I have? What is the nominal DC resistance of the R107 woofers measured with a multimeter? I am wondering if they are 8Ohm drivers or something else.

audiolabtower · VIP Contributor 500+ Joined: 06 Jan 2009 Posts: 686

If you have a spare power amp the simplest solution would be to drive each half from its own dedicated amp. Final balance is then no problem, just relative volume control, and less chance of impedance interaction problems.

bilbobat · Introductory Contributor Joined: 25 Nov 2014 Posts: 7

I will measure the resistance of a woofer the next time I work on the cabinets.

bilbobat · Introductory Contributor Joined: 25 Nov 2014 Posts: 7

I removed the woofers from one of the cabinets. DC resistance is 7,8 ohms.
I will finally change the foam surrounds in the 107/2, and hope this will get the speakers to factory specs.

SaSi · Senior Contributor 200+ Joined: 24 Aug 2008 Posts: 256

Thanks for the measurement. If the refoaming is done correctly, it will bring them back nicely to where they should be...

bilbobat · Introductory Contributor Joined: 25 Nov 2014 Posts: 7

I did the refoaming job on one of the 2 cabinets. The former job was done with heavier surrounds, actually 11 inches cut down to fit the woofers; they were glued in the rear of the cones, and finally the dustcap were generic models with a homemade hole in the center.
My kit is coming from Audiodog, via Ebay. The surrounds are lighter than the ones I had, and fits perfectly. For the donuts, their outside diameter is almost 1/4 inch less than the generic dustcap.
I am wondering if the donut can affect the performance of the woofer, since I had to force the outer diameter down to reach the cone for gluing them.

speakerguru · Posted: Tue Mar 03, 2015 9:40 am Post subject:

It's the back suspension (corrugated spider) which dominates the total unit setup and behaviour re total compliance, maximum excursion and resting position of the voice coil in the gap. The front inner and outer roll surrpunds are intended to act mainly as seals. They also have to resist the dynamic air pressure from the back of the woofer. I would not worry too much about minor deformations during the glueing stage.