KEF B139 for sub woofer

[kennyb]

Hi All

Does anyone have any thoughts on using a pair of KEF B139 drivers for a subwoofer?

I've seen a design for a coffee table/subwoofer that used a pair of B139s front to front in a push/pull configuration. Unfortunately the folks that made the kit have died so I have to make my own.

I can still get the active crossover that the design used from Daan Jacobs here in Johannesburg, and he has some decent amp designs too.

Now, is there any advantage to using the push/pull configuration?

Can I use the pair of drivers individually and make a stereo subwoofer? Is that an overkill?

What volume of cabinet would be appropriate?

The B139s are currently in a pair of KEF Concord 2-way speakers dating back to the early 1970s. I always thought that the high frequency performance of these speakers was poor, but I have recently discovered that if placed in a fairly large room and with a lot more power than my parents ever used, they are better than I thought. Still, they have an impressive low end and I still think that I should make a sub with those B139s.

[mrfeedback]

I have a pair of Bailey TL cabinets using the B139's bi-amped and running 100 Hz down.
12" 3 ways provide 100 Hz up.
These Kef based TL's give quite serious low frequencies, but are not particularly high power handling, and old glues etc can let go.
If you are kind to these you can expect nicely satisfying lows.

Eric.

Daves TL site (tl.org ?) has pics of the Bailey TL's.

[Andy G]

slowly !!

http://users.tpg.com.au/users/gradds/KEF%20TL.htm

[sreten]

http://members.shaw.ca/t-linespeaker.../B139small.GIF

Are the specifications - which suggest very underdamped
bass alignments in my opinion.

I'd go for an isobaric push pull arrangement in a sealed box
40 litres to 50 litres to yeild a Q between 0.6 and 0.65.

With the low Fs of the drivers Fb will be 40Hz which is low,
in room it will give give very smooth and accurate bass.

This will make a ideal sub to be used in parralel with a very high
quality pair of 6.5" MT sealed box standmounting loudspeakers.
(Qtc i.e. in box, 0.6)

No more than 100w / 4 ohms will needed or should be used,
roll-off should be 2nd order Linkwitz/Riley with the ability to
set the c/o frequency to low values.

The above is ideal for music, for Home Theatre push/pull
parrallel should be used. this gets complicated as a huge
box is required, suggest you check this out :

http://www.linkwitzlab.com/sb80-3wy.htm

for ways to use the B139 in reasonable sized boxes.

sreten.