Linn Isobarik Drivers

There is a lot of information concerning the drivers used in the Linn Isobarik loudspeaker; some of it confusing and some of it conflicting. I have attempted below to identify the model of those drivers actually used during the years of production. Variants I don't believe were used are listed for completeness.

The bass driver is generically known as the KEF B139. Two of these are used in each loudspeaker, mounted front to back in a sealed enclosure called an isobaric chamber. These are also referred to as the B139 "racetrack" driver because of their shape. Some B139s have a copper coloured face but most appear to be black. I have seen one reference to an 8Ω B139C but can't find any details on it. In a table on comparative properties of materials, B139C is the number given to a phosphor bronze. Whether this has anything to do with the copper colouring used on the face of some B139s I don't know.

You may occassionally see a photograph of a B139 with a board on the back of it; the board having a label stating SP1004. This is the number given to KEF's DN12 dividing network board and is not part of the loudspeaker.

The midrange driver is generically known as the KEF B110. One is mounted on the front face of the loudspeaker, the other on the top face, firing upwards.

In March 1983, Linn started painting sound deadening material onto the standard bass and midrange units supplied by KEF. On the bass unit, liberal coatings of a black car underseal like substance were painted on the legs of the chassis, not visible from outside the cabinet. On the midrange, Linn painted a doping material onto the front face. One of the forum members has used a good quality PVA glue to dope replacement units by laying them face up and brushing with a slightly watered down glue from the outside to the centre, and reports that the thin coat on the cone dries clear but the thicker coat around the dust cap remains a little whiteish.

KEF B139 and B110 drivers are no longer in production. However, at the time of writing (February 2013), Falcon Acoustics have an exact replacement for the B110 SP2003. Whilst it does not have the sound deadening material painted on the cone it will be a viable alternative for those looking to replace blown or broken units.

I have not included photographs of these units as there are countless examples on the sites listed below under sources.

The original tweeter used was the Scan-Speak D2008. This was later changed to a Linn Products D20-LP-1, made by Hiquphon, which is recognisable by two concentric rings on the faceplate, with later models sporting a Linn logo on the front. Tweeter mounting uses the same layout as the midrange unit. The Scan-Speak tweeter is still produced but I have no information regarding changes to it's specification over the years. The Hiquphon unit is still made and is only available from Linn. Neither Linn nor Hiquphon are willing to supply the specification of this unit.

Sources:
john & Jake
sybil
Barnie
Colin Royle
The Linn Isobarik DIY-Mods Bible
hifiloudspeakers.info, formerly allansonline.com
Transmission Line Speakers
Falcon Acoustics
Scan-Speak
Hiquphon
Wilmslow Audio

I believe the information provided here is correct. If you know otherwise, or have any further information, please email me.