Bass Units

The following table shows likely candidates for the original B139 fitted to the Isobarik based on age and specification. Each specification has been taken from a KEF document. Unfortunately, none of the documents are dated. The KEF specification (SP) number denotes a specific drawing, manufacture and test procedure. They are all the same; SP1044 in this case; hence the confusion. It looks like only real way to tell is for someone to weigh one.

KEF B139 a) B139 SP1044 b) B139 SP1044 c) B139B SP1044 d) B139B SP1044
a.k.a. B139 Type II B139 Type II    
Age late 70's   mid 80's  
Dimensions 11.82" x 8.25"
300mm x 210mm 		  300mm x 210mm 300mm x 210mm
Weight 3.6kg/8lb 3.85kg/8.56lb 3.72kg  
Nominal Impedance 8Ω 8Ω 8Ω 8Ω
Minimum Impedance   6.7Ω @ 160Hz    
Programme 50W in a 3 way reflex enclosure 100W 100W 100W
Continuous 20v rms 40W in a 3 way reflex enclosure 20v rms 50W 28.7v rms 114W  
Frequency Response 20-1000Hz 20-1000Hz 25-500Hz 23-500Hz
Voice Coil 5.08cm/2in 55mm/2in 52mm 55mm
Dividing Frequency 400Hz in a 3 way reflex enclosure      
Fundamental Resonance 23Hz 25Hz 25Hz  
Comments I have included this one purely on the basis of age, in that it was around when Isobarik production started. However, programme power rating seems rather low so it may not have been used. I think this is the most likely driver used for the original Isobarik. Programme and continuous ratings don't tie up on this specification. Linn may have changed to this driver or the one in column (d) for later model Isobariks, however I have seen no documentation to substatiate this. Linn may have changed to this driver or the one in column (c) for later model Isobariks, however I have seen no documentation to substatiate this.

The following table shows other B139 drivers I've found information on. These are not likely to have been used in production Isobariks as we know them today.

I've been told the B139 6171 in column (e) was used in a first generation Isobarik between 1974 and 1977. They were styled differently to later models; about the size of an Isobarik swivelled on its base through 90°. They used two pairs of KEF T27 tweeters, but a very early variant with a plastic face plate and no visible wires on the front. The orientation of the midrange and treble units on the top was also reversed. I have not been able to find any other details about these but it would explain the revision history for September 1976 which states 'Current cabinet style adopted'.

KEF B139 e) B139 6171 f) B139 SP1037 g) B139B SP1044
a.k.a.      
Age late 60's early 70's    
Dimensions 13" x 9.5"
330 x 241mm 		  300 x 210mm
Weight 4.5kg/10lb   3.85kg
Nominal Impedance 8Ω   8Ω
Minimum Impedance      
Programme 50W in a 3 way reflex enclosure, 40W in a 2 way infinite baffle enclosure   100W
Continuous 50W in a 3 way reflex enclosure, 40W in a 2 way infinite baffle enclosure    
Frequency Response 20-1000Hz   20-1000Hz
Voice Coil 5.08cm/2in    
Dividing Frequency 400Hz in a 3 way reflex enclosure, 1000Hz in a 2 way infinate baffle enclosure    
Fundamental Resonance 20Hz 28Hz 25Hz
Comments This B139 has a wider chassis than the others so would not fit into an Isobarik cabinet. However, see the note above regarding the first generation of Isobariks. I believe this had been wrongly documented because an SP1037 is also listed as a BD139 auxilliary bass radiator with a foam surround. I believe this unit is the same as that in column (b) above, although again, the model number and information presented here was taken from a KEF document.

KEF B139 h) B139 SP1333 i) B139 SP1212
a.k.a.   TS1212
Age circa 1997  
Dimensions    
Weight    
Nominal Impedance 8Ω 4Ω
Minimum Impedance    
Programme 125W  
Continuous    
Frequency Response    
Voice Coil    
Dividing Frequency    
Fundamental Resonance    
Comments This is the specification number given to the B139 before production ceased. I am told it was specified by IMF for the TLS 80 and others and had the distinctive feature of three annular slots in the magnet to give a ventilated pole-piece. With the power handling increased from 100 to ~125 Watt, all other parameters such as voice coil size remained the same (but the same as which version, I know not). I have not been able to find any KEF specifications for it but one of the forum members has fitted 4 in a pair of Isobariks. I have not been able to find any KEF specifications for this but have been told it is the model used in the KEF C80.