Midrange Units

The following table shows likely candidates for the original B110 fitted to the Isobarik. The information shown is taken from KEF specifications.

KEF B110 a) B110 SP1003 b) B110 SP1057 c) B110B SP1057
a.k.a.      
Age      
Dimensions 130mm 130mm 130mm
Weight 1.13kg/2.5lb 1.13kg/2.5lb 1.13kg/2.5lb
Nominal Impedance
Minimum Impedance 7.8Ω @ 280Hz 7.8Ω @ 280Hz 7.8Ω @ 280Hz
Programme 80W in a 3 way reflex enclosure, 30W in a 2 way infinite baffle enclosure 150W in a 3 way reflex enclosure, 50W in a 2 way infinite baffle enclosure 150W when used as a midrange unit, 50W when used as a bass/mid unit
Continuous 15v rms 28W 28v rms 98W 28v rms 98W
Frequency Response 55-3500Hz 55-3500Hz 55-3500Hz
Voice Coil 26mm/1in 26mm/1in 26mm/1in
Dividing Frequency      
Fundamental Resonance 35Hz 37Hz 37Hz
Comments I think this is the most likely driver used for the original Isobarik. Linn may have changed to this driver for later model Isobariks, however I have seen no documentation to substatiate this. The KEF specification for this unit is identical to the B110 SP1057 in column (b).

The following table shows other B110 drivers I've found information on. These are not likely to have been used in production Isobariks.

KEF B110 d) B110 A6362 e) B110 SP1003 f) B110A SP1003 g) B110 SP1228
a.k.a.        
Age 1970      
Dimensions   140mm/5.5in    
Weight   1.6kg/3.62lb    
Nominal Impedance    
Minimum Impedance        
Programme   50W in a 3 way reflex enclosure, 20W in a 2 way infinite baffle enclosure    
Continuous   30W in a 3 way reflex enclosure, 20W in a 2 way infinite baffle enclosure    
Frequency Response   55-3500Hz    
Voice Coil   2.54cm/1in    
Dividing Frequency   400 and 3500Hz in a 3 way reflex enclosure, 3500Hz in a 2 way infinate baffle enclosure    
Fundamental Resonance   30Hz    
Comments This was used in the original LS3/5. It is unlikely this was used in production Isobariks. This has a wider chassis than the others so would not fit into an Isobarik cabinet. This may be the same driver as the B110 SP1033 in either column (a) or (e). I have been unable to find any figures for it, only a reference to it.

This version of the B110 was designed with the assistance of the BBC specifically for the LS3/5a. The earlier SP1033 had variations in the consistency of the neoprene used in construction that the BBC were not happy with.

As a 6Ω unit, it would not have been fitted into production Isobariks but it has been used as an effective replacement for blown drivers.

If fitting these, official advise from KEF suggests listening to the 'speaker and if it sounds right, it probably is. There may be a slightly forward presentation of the midrange but it would really be system dependant.

If you want to experiment they suggest either a good quality 2Ω resistor can be fitted in the positive line to the 'speaker or two 1Ω, one in the positive and one the negative line.