SpeakerTalk

timsimmons · Introductory Contributor Joined: 10 Apr 2021 Posts: 2

I am a retired electronics engineer living near Matclock in Derbyshire. Like most of us it seems, I first encountered KEF loudspeakers in the mid to late 1960s, but I couldn't afford them as a teenage apprentice. So I built my own cabinets using Fane Drivers and they sounded awful! I decided to enhance the base with a central woofer 36x24x18 inches (parents were not impressed). I splashed on expensive B139-£11:10:0 from Henrys Radio in Edgeware Road, but I only had a 10W home made amplifier to power it. Waste of time of course.

I decided to look for some proper loudspeakers, not expecting to afford KEF's. I went to a shop called Studio 99 in London and amongst the Wharfedales etc. were a pair of loud speakers made by a company called Shepperd and the model was called 'Chesham'. It sounded much better than the others of comparable size - approximately 18 x 12 x 10 inches but they were cheaper. When I asked why I was told that they wouldn't sell as nobody had heard of them. We peeled the fret off one of them to reveal a D139, T15 and T27. Needless to say I tore the salesman's arm off, paid for the loud speakers and took them home.

I still listen to them every day and I have decided I can probably improve them by beefing up the mid range performance. A T15 and T27 are not that different in response so whatever the crossover frequency is between the B139 and T15 they are both struggling. I have just bought a pair of B110's (1974 vintage) and I intend to build speaker cabinets of about 50 litres, leave out the T15's, build 6 amplifiers and 2 electronic crossovers operating at 400 and 3500 Hz. I appreciate that B110's will need their own sealed enclosures within the cabinets - any ideas on optimum volume? But the T27's having a full 'metal jacket' can go within/without the B110 box.

Whilst on the subject, I bought a pair of B139's on eBay about 10 years ago for a subwoofer project (as yet not started), I have recently discovered the roll surrounds were of doped fabric rather than rubber. The suspension seems to be softer than rubber. They way almost 10 llbs each which is heaver than most B139's, and they do not have the 3 screws on the back to hold the pole piece in place. Instead there are 3 filled holes about 10mm diameter and the central screw. The filler may contain 3 screws and act as a thread sealant. One has a number which looks like BN065 or B1065 and the other is possibly BN265 or B1265. Could the 65 be the year of manufacture ? Has anyone ever seen this model?

Tim Simmons

KefHeir · Posted: Sun Jun 06, 2021 2:39 pm Post subject:

Hi There
On the B110 sub enclosure question, this might give you an indication
https://us.kef.com/pub/media/pdf/Constructor_Series_Model_CS7.pdf

timsimmons · Introductory Contributor Joined: 10 Apr 2021 Posts: 2

Thanks KefHeir, this is just what I was looking for. Regards, Tim

KefHeir · Posted: Sun Jun 20, 2021 10:42 pm Post subject:

Sounds like an interesting project. I have another blueprint in the Kef Constructor series which uses the B139 / B110 / T27 combination in a ported enclosure (as pictured in my profile image). By all means PM me if you'd be interested in seeing it as I can't find it online anywhere.

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

With a crossover at 400 Hz I don't think the volume of the box matters much. It is there to stop the bass inside the cabinet modulating the mid range cone, so just needs good damping inside the box for the midrange performance and enough volume not to compromise sensitivity. You can look at a 5 litre LS3/5a to see the volume needed for a bass down to 70Hz and box resonance around 90Hz. The minimum mid range box volume actually increases the volume available for bass extension, unless you have separate enclosures like the original Ref 105.