SpeakerTalk

iso · Posted: Sun Apr 15, 2012 1:00 pm Post subject: B139 SP1044

Does anybody know how B139 was upgraded during SP1044:s quite long production run.

From spec sheets you can see that voice coil former was probably upgraded sometime. Early spec sheets confirm more modest working temperatures than late spec sheets. Colin also mentioned sometime, that late production units after mid 80´s are most consistent in performance.

So if anybody has inside information about upgrades during SP1044 production, please let us know. Most important issue is which units are most suitable for vented box, TL or IB usage... and of course why.

Best Regards,

speakerguru · Posted: Mon Apr 16, 2012 10:30 pm Post subject:

Sorry I can't help with dates. I have no memory for that sort of thing. I did most of the prep work in reducing voice coil tolerance from +/-10% to +/-5%. To that end there was a change from self bonding (nylon) coated wire to wet wound (epoxy) polyester coated wire. The split nomex VC former gained a nomex tube over the unwound portion at the same time. The material did not change. All versions were nomex, therefore Qm remained the same.

The magnet changed from a bolted design with a staked pole to a bonded one with a pole/backplate forging. This resulted in about 1~2% increase in gap flux density. Not a significant amount as regards box alignment.

speakerguru · Posted: Fri May 18, 2012 7:54 am Post subject:

There are small pictures of the two different types of voice coil construction, in KEFTOPICS here: http://www.hifiloudspeakers.info/Anatomy/KEFDocuments/KEFTopics/KEFTOPICS_Vol_4_No_1.pdf
It also contains a lot of knowledge on power handling, voice coil temperature and protection circuits.

Thanks to Terry for putting it up.