KEF B139

[TheBaronGroog]

lol-will get the tape measure out and do some maths on the weekend!

 

[Salas]

Should be kinda short to KEF's by missing those curved side triangles between the two circles, we still got the ~350cm2 KEF spec. Its funny we even look in to it with interest when the two drivers have so wide a tolerance anyway. But inquiring minds wanna always know.

 

[TheBaronGroog]

I just want to be sure that what I am doing is right-if KEF can't do it right it's up to me to hold up the "British end"!

 

[soundalot]

Kef b139

I have used a Kef b139 as a subwoofer with both Quad esl 57 and martin Logan cls .They were very clean when not over driven, I don't know how low the went in my vented enclosure but organ pedals were heard. IMF used the b139 in their reference monitor and in its time had very good bass and could play fairly loud, Definitely not home theater loud. I owned a Morgan plus 4 for ten years in the sixties.I have very fond memories of the Morgan. My teeth still hurt.

 

[Boden]

Hi BaronGroog,

Would you care to also do the T?S parameter etraction with Delta V(olume) method? Often the Delta Mass method results in lower Fs and larger Vas than the Delta Vol method. Of course it should not theoretically speaking, but in practice it often does.

BTW the difference between the samples conforms my own experience. So far I enjoy your journey into KEF land!

Eelco

 

[planet10]

The area of the piston can be calulated as a circle with the diaphram width (including half the surround as Salas mentions) the diameter + the area of the rectangle left over when you slice off the semi-circles at either end.

Get those drivers on the breakk-in bench and get at least a couple hundred hours on them. One looks to be suffering fron SSS (stiff surround syndrome). Some Armour All or similar may be required if that doesn't help as much as you'd like. They will never return to as new thou -- one of the long term issues with rubber surrounds,

dave

 

[TheBaronGroog]

Soundalot, sounds good to me! ACn't wait to hook them up

Eelco-I will do at some point, need to make the box 1st Gonna do one with a removable baffle and make it large enough to accomodate a 15" (can't see me needing any larger)

Dave, as I have a small house and an "understanding, but not loving it" Missus I'll not really be able to do that-as the drivers are going into an isobaric clamshell config I can't see the difference being too huge a problem-anyone got any thoughts on that?

 

[revintage]

To break-in the 139s, as you must, place them close to each other, working out of phase. Will not be to much noise. I have used them in the 70´s and 80´s, both the OS and newer, and they can vary in parameters rom sample to sample. No need to judge yours without break-in, so do as Dave told you. It´s totally meaningless to measure them before.

 

[TheBaronGroog]

But the drivers are second hand so will have been "broken" in anyway. Playing them both for the same amount of time will surely just move them along the same amount-if any at all?

 

[revintage]

Hey Baron,
If they have been stocked for a while you should run them in anyway, albeit for a shorter time. Run them until Fs doesn´t get any lower.

 

[TheBaronGroog]

Off to China for a couple of weeks-so will hook them up and leave 'em running!

 

[revintage]

Great idea but what will the wife say?

 

[andersonpaulb]

Dear Baron: I am curious to learn if you ever got around to hooking them up and giving them a listen -apart from knocking them with a knuckle. With respect -since I enjoy spec-ulating in advance of listening as well as listening- the aluminum frame will respond to a knuckle rap quite differently when the rim is clamped to a baffle as intended in use. The most sonorous of bells will die acoustically when the bell mouth rim is damped by setting it down to rest onto a table or like surface. Moreover, when sealed into a box, the internal resonances of cavity or frame will have a devil of a time penetrating that diaphragm to the outside and thus to your ear. The B139 is one of the least dependent-upon-box size drivers I have played with. Any bass/mid driver can sound like hell in a bass-reflex box, but in a sealed enclosure in which it is happiest -IMF style TLs notwithstanding- they can sound quite lovely, even run full-range as in a KEF K2 Duette sans tweet, which I adore. Kef addressed the 400 and 1100 Hs resonances quite well with the resonant-trap baffle plate employed in this design. By the way, I have played the hifi game since Eisenhower was Prez, and have owned actively- WE, Altec, RCA theater rigs, KLH Nines, Quad ESLs, JBL, Jensens, Tannoys, Goodmans, Hartley , B&W,Spendor BC1&2, as well as many other BBC style boxes, Radford, ESS, and IMF TLSs Koss Model One ESLs, Acoustat ESLs, and many, many more. I have found it useful in all cases to give them a listen first, and only then to consult the specs and theory to aid in figuring-out why - not whether I like the sound or not. Cart before the horse, and so-on. Happy listening!. Regards, Paul, USA.

 

[TheBaronGroog]

Hi Paul,

Thanks for the comments, I've not listened to these yet-no, I have heard others B139 in different enclosures, had an awful lot going on, have just moved home and started a new business.

On the upside I've also got a new home with more space for audio and have acquired a 12ch amp and active crossover so intend to build a T-TQWT (movies) for the B139 along with a pair of floor standers using some Focal Utopia 6W mids and a ribbon and dome combo.

The floor standers I've yet to start designing, the T-TQWT Bjorno helpfully designed will probably be used, though I need to workout how to make it into a single fold deign-if possible. I've plenty of experience with sealed/vented enclosures and BBpro but horns and all their variants along with hornresp still mystify a little-particularly visualising the design. I've muddled around with his design and not succeeded in improving it. I lowered F3, but lost SPL across range and reduced the bandwith

Any input would be appreciated-did you try any T-TQWT?

 

[Jozua]

Hi

Is there a 'compact" box design available for these drivers ?

I have a niggling suspicion that Troels TL box for Jenzen Accu mkII will work ? It is roughly the same size of some TDL designs I have at home.

Jenzen-Accu

Regards

Jozua

 

[DrBoar]

The Speaker Builder magazine in the US had a TL fold for 10" unit in a shorter stocky box. My copies of SB is in storage but there should be some US members that have those issues at hand.

 

[jplesset]

I used to have a sub, based on the original Linkwitz 1978 article. Until I had a too large living room, I was quite happy with it. Not too large, played loud enough, and went plenty deep enough.

 

[ometbrnk]

KEF B139 passive radiators

Hi everybody, this is my first post on this fantastic forum, anyway, I´ve been here for while, lurking in the "dark" and digesting all those tips, ideas and knowledges...
I have a pair of KEF B139 SP 1082 passive radiators, anyone interested?

 

[TheBaronGroog]

Ooh, I would be-if I knew how to integrate them into a ML-TQWT and wasn't already under pressure to "do something" with of all my audio...

Do you have the TS for them?

 

[ometbrnk]

This is passive radiator type,without magnets and coils so You cannot integrate them into the ML-TQWT