2x KEF B139 for home theatre challenge

I've 2x KEF B139 and need to enclose them for use in a home theatre system.

They are to accompany a pair of floor standers and need to play as low as possible. I'd love 10-80Hz, though a little off either end to the benefit of efficiency.

I've attached a T-TQWT design done by Bjorno, models very well but no longer fits with my living arrangements and despite my best efforts I cannot improve on it-I've managed to eek out a few more Hz lower in the register by MASSIVELY increasing it's size but at the detriment to both bandwidth and SPL, which I thought would go against Hoffman's Iron Law?!

Space is not really an issue (it was the limiting factor in previous designs) I have at least 4m (12ft) width to play with and depth/height can be anything you'd consider reasonable to sit a TV on top of (I will be building some storage on top/in front of/around the enclosure). The subwoofers will be powered off a 12ch Sonance Sonamp 1230 (12x 30wrms, 6x 60wrms @8ohm) which will also power the floor standers. A single fold design would benefit me in building the design, and would fit better with the depth of the room!

Anyway, I leave it open to you-can you better Bjorno's design?
 

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There's always the Linkwitz Transform

I used a sub in a rather small enclosure, per Sigfried Linkwitz 1978 article for several years. Went down very well, though it was limited by max excursion. b139 don't sound good when they hit stops.

Requires separate amp, includes schematic for crossover with transform. You may find it's not enough for home theater. I had to give it up when we moved to a bigger living room, just not enough travel. 4 12" drivers was big enough....

Linkwitz Lab - Loudspeaker Design
 

DrDyna

Member
2007-05-17 11:34 am
The subwoofers will be powered off a 12ch Sonance Sonamp 1230 (12x 30wrms, 6x 60wrms @8ohm) which will also power the floor standers.


If I read this right, you're planning to drive subwoofers with an amplifier that's 60w @ 8 ohm when you strap two of the channels together?

You might want to consider a dedicated subwoofer amplifier that has a little more guts, like a Behringer EP series or something, for HT I think you'll run a 60 wpc amp out of juice pretty quick.

Edit: I didn't realize the b139 was a fairly small driver.
 
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Power shouldn't be a problem, excursion will limit input power-if I ever get past the "design" stage!

Current design is just over 90dB with 1 watt input power - not sure whether for the two drivers you need to enter the voltage/wattage differently?
 
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Hi All,

FYI: Another suggestion, i.e. a ML-TQWT using 25% more Volume than the prior: T-TQWT.

b:)
 

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Wow, that is a significant improvement! Now, how do I translate that to full box dimensions?

The gross dimensions I get, though would need to know the:

Length of the internal wall, distance it is away from the front/rear face and the vent dimensions?

Am I missing these from the diagrams or is there an easy way to work it out?

Is there any way of sacrificing upper extension in exchange for more SPL/lower extension?
 
Wow, that is a significant improvement! Now, how do I translate that to full box dimensions?

The gross dimensions I get, though would need to know the:

Length of the internal wall, distance it is away from the front/rear face and the vent dimensions?

Am I missing these from the diagrams or is there an easy way to work it out?

Is there any way of sacrificing upper extension in exchange for more SPL/lower extension?

Hi TheBaronGroog,

It's DIY isn't it?:D

b:)

PS:
Is there any way of sacrificing upper extension in exchange for more SPL/lower extension?

This design has a + 4dB more output than the T-TQWT...More is affecting the SQ.
 
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Scott L

Member
Paid Member
2008-12-27 12:32 pm
Knoxville, TN
KEF B139's

Power shouldn't be a problem, excursion will limit input power-if I ever get past the "design" stage!

Current design is just over 90dB with 1 watt input power - not sure whether for the two drivers you need to enter the voltage/wattage differently?

Greetings !
I had used KEF B139's for many, many years (Just before Wilson decided on them for his WAMM). Used in pairs PER SIDE they are a wonderful mid-bass.
Now remember, they were designed to match the five inch unit(s) and the T-27 tweeter, all of which were low efficiency @ 82 db. Used in pairs per side
will give you 88db off a solid state amp, and is adaquate in most situations, but Home theatre is not one of them. They snap like a twig when Xmax is hit, you can do that a few times until they finally burn out, trust me, I know.
Used as a hi-fi midbass will gain you some protection. They are still fine units indeed and not being made any more. If I had 4 units I'd consider using as mid-bass, but I don't as I lost them all many years ago. Wilson bought all the stock from KEF a few years back. 60-400 Hz, what a dream :)
 
Right, made some progress last night and sketched out the enclosure as well as working out the cut outs. Did it the old way - biro, unsuitable for intended use tape measure and some lined writing paper!

See the attached drawing and let me know how far off the mark I am!
 

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