KEF B139 Subwoofer [Archive] - Audio & Video Forums


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04-26-2008, 03:47 PM
Has anyone got a good subwoofer enclosure design for using a pair of B139's? There was an interesting idea around a while ago for 'back to back' 12" drivers (sealed enclosure that acted like a reflex port) which used the speakers, driving on front and back panels but phased the same, to control - dampen - each other. Or maybe something more conventional that someone has used with B139's that works well.

04-26-2008, 07:36 PM
First, I've never thought of the B139 as a "subwoofer". It was a credible bass driver by 1970s standards, but is not the window rattling DVD movie explosion device connoted by the term subwoofer.

I used a pair for 25 years in a set of transmission line cabinets that I built in 1980 or so. The cabinets were very large (to allow for the long transmission line duct). I don't know if I still have the plans, but there should be a number of suitable TL construction plans still available.

05-05-2008, 11:14 AM
See also 'isobaric' enclosures. Not 'back to back' - but mounted face to face and ported.

More complex/expensive cabinetry , but a really good sound for a smaller footprint than just two subs in ported enclosures.

I have never heard of a back-to-back config - not impossible.... But not practical IMHO.

05-27-2008, 08:40 AM
Perhaps you're thinking of an 'isobaric' loading, where both driver cones are coupled together either face-to-face or via a very short tunnel that's separate from the main enclosure volume. I've got a lot of respect for isobaric designs when it comes to getting musical, deep low end out of inexpensive drivers in a smaller sealed or vented enclosure, and wouldn't hesitate to try this with other drivers, but probably not the B139 -- the racetrack frame would complicate things. When you couple the drivers together, you double the motor power, but not the cone area, so your sub will still only be capable of moving as much air as one driver on its own, and output volume will be limited.

For a musical sub, I've heard great things about the B139s, but I'd prefer a driver with more grunt for a home theater subwoofer, where air movement is king, not necessarily finesse.

06-07-2008, 05:10 PM
are worth more to you as something to sell. on them should be a SP number which would qualify them as to what speakers they can be used in.

i suggest listing them on agon with their sp #s for at least $100 or more apiece. use the proceeds to purchase a powered sub.

otherwise, look into building a transmission line cabinet like the imf IIIs or fried model IVs which can produce bass to 16hz. it wont be cheap, but may be worth the money.