SpeakerTalk Forum Index SpeakerTalk
This forum has been set up to facilitate discussion of 1970s KEF speakers and drive units. The owner of the Forum has no connection with KEF Audio.
 
 FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 

What to do with B139s and T15s

 
Post new topic   Reply to topic    SpeakerTalk Forum Index -> DIY with KEF drive units
View previous topic :: View next topic  
Author Message
thelandlord
Introductory Contributor


Joined: 23 Oct 2008
Posts: 9
Location: Near Bristol, UK

PostPosted: Fri Oct 24, 2008 12:10 am    Post subject: What to do with B139s and T15s Reply with quote

Hi - first post, so be gentle with me! Wink

I've just acquired some Kef drive units on a baffle-board but without crossovers, and I'm trying to decide how best to use them.

The bass units are B139 and look quite early, the tweeters weren't identified in the listing but have quite large domes so I'm presuming at this stage (they've not arrived yet) that they're T15s.

The existing baffle is only two-way, it looks from the photographs as though it's been correctly described as K2.

Questions:

How good would the K2 be 'as it stands' if I rebuilt the rest of a cabinet around the existing baffle?

What would be a suitable crossover frequency if I wanted to 'roll my own', and do I need to add any delay?
I seem to remember reading about B139s having quite a pronounced 'hump' around 1KHz, but would a T15 let me get away with crossing over below that, say 800Hz?

I'm open to the idea of starting from scratch and going to a 3-way system - does anybody have any ideas for a midrange unit, Kef or otherwise, that would integrate well - or am I better off with a more modern tweeter too?

In either case, is there a ready-rolled crossover available at a sensible price? I [i]hate[/o] winding coils... I won't be needing to bi or tri amp - if I even suggested it I'd be sleeping in the shed. Rolling Eyes

I don't need to go loud, but I do need to go down as far as reasonably possible as my listening includes classical organ music as well as live recordings of various acoustic instruments.
I have a wife who is very understanding about 'form following function' but (unsurprisingly these days) finance is going to be an issue...
_________________
Thought for today: Don't go knocking on death's door, ring the doorbell and run, he hates that!!
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Fri Oct 24, 2008 8:27 am    Post subject: Reply with quote

KEF produced a whole raft of B139/T15 variants in different size and style cabinets when they started out in the 60s. At that time you could probably sell on novelty and the "new" plastic diaphragms were certainly that. However, measurements revealed that the "flat pistonic" B139 had a violent diaphragm resonance at aound 800Hz and later designs would low pass filter it to use below 400Hz only. The T15's fundamental resonance was just below 1Khz so you can see there was a lot of wishful thinking in those old 2-way designs. KEF soon developed the B110 midrange to fill the gap.

I have to say that I've never heard any of those old 2-ways. My loss I suppose, but there were none around by the 70s. It might be nice to keep them "as is" to have an example from the very old "KEF" Raymond Cooke era (or as a terrible warning of how not to design speakers Twisted Evil Very Happy ).

If you don't care about originality then your best bet is to get a pair of B110s and convert to the 70s Concerto successor, whose name I've forgotten, but I think it was later marketed as a Constructor Series CS9.

Have fun.


Last edited by speakerguru on Sat Oct 25, 2008 11:08 am; edited 1 time in total
Back to top
View user's profile Send private message
thelandlord
Introductory Contributor


Joined: 23 Oct 2008
Posts: 9
Location: Near Bristol, UK

PostPosted: Fri Oct 24, 2008 9:26 am    Post subject: Reply with quote

speakerguru wrote:


If you don't care about originality then your best bet is to get a pair of B110s and convert to the 70s Concerto successor, whose name I've forgotten, but I think it was later marketed as a Constructor Series CS9.

Have fun.


Thanks for your reply.

I'm not a purist 'originality' wise, however I would like to see just what performance can be achieved by 1970s technology in the light of modern knowledge.

I was thinking along these lines myself - B110s would be an easy match to find the crossover details for, maybe even complete crossovers, as it was a combination that was marketed - I've already explored the various documents linked to from the 'main' site, that's what led me here. Smile

Given the resonance issues, would I be right in thinking a well-damped sealed box would be a wiser move than a reflex design?

I have a room about 20x12x8'6" feet high, and I have to fire down the length of it.
_________________
Thought for today: Don't go knocking on death's door, ring the doorbell and run, he hates that!!
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Sat Oct 25, 2008 11:25 am    Post subject: Reply with quote

Rolling Eyes Oh dear. My memory is fading. The CS9 used a B300 so forget what I said about that. The speaker I was trying to recall was the Cantata from the late 70s. There is a XO design is on this site http://www.hifiloudspeakers.info/Anatomy/Crossovers/Cantata/CantataCrossoverIndex.html. The early versions resulted in the impedance dipping below 4 Ohms (real part) in the LF/MF xo region. This caused early Quad 405 amplifiers to current limit. The later 405.2 were OK.Only happened at max output of course. I don't remember if the Cantata XO was tweaked for later production.

There was a kit version. I don't think the XO was sold with the kit, so, you will have to source your own R, L and Cs. If you don't like winding you can always buy bigger values and pull off turns - that's great fun. You'll have to get an LCR meter though.

You will need to put the B110s in a midrange enclosure else they will be pumped around by the B139s. For the woofers, a closed box is easier to design, construct and equalise. Let's hope the units are OK when you get them.
Back to top
View user's profile Send private message
thelandlord
Introductory Contributor


Joined: 23 Oct 2008
Posts: 9
Location: Near Bristol, UK

PostPosted: Sat Oct 25, 2008 7:58 pm    Post subject: Reply with quote

speakerguru wrote:
Rolling Eyes Oh dear. My memory is fading. The CS9 used a B300 so forget what I said about that. The speaker I was trying to recall was the Cantata from the late 70s. There is a XO design is on this site http://www.hifiloudspeakers.info/Anatomy/Crossovers/Cantata/CantataCrossoverIndex.html. The early versions resulted in the impedance dipping below 4 Ohms (real part) in the LF/MF xo region. This caused early Quad 405 amplifiers to current limit. The later 405.2 were OK.Only happened at max output of course. I don't remember if the Cantata XO was tweaked for later production.

There was a kit version. I don't think the XO was sold with the kit, so, you will have to source your own R, L and Cs. If you don't like winding you can always buy bigger values and pull off turns - that's great fun. You'll have to get an LCR meter though.

You will need to put the B110s in a midrange enclosure else they will be pumped around by the B139s. For the woofers, a closed box is easier to design, construct and equalise. Let's hope the units are OK when you get them.


That all makes good sense to me - I don't have an LCR meter, but I can calculate L from the resonance when I know C.

Current draw won't be a problem - I have a Mission 777 power amp and it can dump enough current to weld from the output - literally (just don't ask how I know this Wink ) it's stable at 2 Ohms even if the load is inductive because it's rather non-standard...

Cabinet wise, I'm thinking in the direction of placing a mid-treble sub-cabinet outside of a dedicated bass cabinet 105.2 style so things can be tweaked in one cabinet at a time without disrupting too many variables at once... the xo can be external for easy tweaking access too.

There are huge advantages to having a wife who's interested in how it all works too - you can get away with much more. Twisted Evil
_________________
Thought for today: Don't go knocking on death's door, ring the doorbell and run, he hates that!!
Back to top
View user's profile Send private message
ColinR
Über Contributor 1000+


Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Mon Oct 27, 2008 5:16 pm    Post subject: Reply with quote

speakerguru wrote:
Quote:
The early versions resulted in the impedance dipping below 4 Ohms (real part) in the LF/MF xo region. This caused early Quad 405 amplifiers to current limit. The later 405.2 were OK.Only happened at max output of course. I don't remember if the Cantata XO was tweaked for later production.



Although there is an "engineering varient" where the wafer switches are mounted on the mid/treble pcb.

The Cantata crossover was never tweaked as KEF happily repaired <200L in Maidstone or supplied replacement T52s and B139s until they ran out of stock in the 1990s.

My contact's Quad 405 was modified in 1992 by Quad Service after the loss of its eighth set of left channel output devices and someone finally asked the question!

The KIT Cantata did come with the crossovers fitted but you could also buy them as separate items (German pricelist) like the Ref 104aB retrofit.
_________________
This post or any other information supplied to this website or any other by myself is not available for any form of commercial purpose i.e. to hi-fi magazines or as sales and marketing material for sleezeBay or Audiodogging pimps and the like.
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Tue Oct 28, 2008 1:40 am    Post subject: Reply with quote

Interesting. The 405 MKI had problems running the B&W DM70 Continentals / Sony. Yet quite happy driving the veneered domestic versions.
The MKII was a much happier beast, I was concerned about the scorch marks left on the PCB of the MKI by some large resistors. Both were happy driving any KEF stuff I owned at the time.
Then the Amcrons came along but that is another story...
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill
Back to top
View user's profile Send private message Send e-mail
thelandlord
Introductory Contributor


Joined: 23 Oct 2008
Posts: 9
Location: Near Bristol, UK

PostPosted: Tue Oct 28, 2008 7:56 pm    Post subject: Reply with quote

Well, my B139s and T52s have arrived, and all work as they should without any unexpected noises or escapes of the 'magic smoke'... they're in pretty good nick, so now I have the basics to work with.

Having given a little more thought to what speakerguru said in his opening post about the early two-way units, I'm curious... I may build a pair of temporary 2-way cabinets to the original dimensions and the nearest I can manage to the original crossovers just to see what they sounded like in that form - without any expectations of a pleasant surprise.

I'll now be actively seeking some B110s, and practicing my coil-winding skills.

Here's a question for the crossover-techies among you... most crossovers seem to have a combination of air-cored and ferrite-cored coils - is there any good reason why I shouldn't wind ferrite ones on toroids rather than more conventional bobbins?

I ask because I'm used to winding coils for RF, and in that application toroids perform much better, being less prone to saturation, and keeping the magnetic field mostly within themselves to avoid interaction issues with neighbouring windings... has anybody experiemented with this in crossovers?
_________________
Thought for today: Don't go knocking on death's door, ring the doorbell and run, he hates that!!
Back to top
View user's profile Send private message
proffski
Über Contributor 1000+


Joined: 22 Aug 2003
Posts: 1297
Location: Tewkesbury UK

PostPosted: Tue Oct 28, 2008 9:43 pm    Post subject: Reply with quote

A crossover may incorporate an inductors DC resistance as part of the design, making it air cored, iron or ferrite will obviously have some influence on the DC resistance due to the amount of copper windings used depending on core.
Sure lesser designed ferrite can saturate, look at the iron cored devices in BBC designs.
Not only do you alter the inductance by using different cores but also the Q, as an RF engineer you will be aware of that I’m sure.

All good fun, then you could start measuring the Q of capacitors, maybe one reason why to some a change of capacitor may sound like an improvement rather than meandering away from the designers objectives... “ It sounds different so it must be better scenario... ”.

Over to you Mr Guru Sir! Smile
_________________
I contend that for a nation to try to tax itself into prosperity is like a
man standing in a bucket and trying to lift himself up by the handle.
-Winston Churchill
Back to top
View user's profile Send private message Send e-mail
thelandlord
Introductory Contributor


Joined: 23 Oct 2008
Posts: 9
Location: Near Bristol, UK

PostPosted: Wed Oct 29, 2008 12:09 pm    Post subject: Reply with quote

proffski wrote:

maybe one reason why to some a change of capacitor may sound like an improvement rather than meandering away from the designers objectives... “ It sounds different so it must be better scenario... ”.



You opened the can of worms called 'Subjective vs Objective performance' there...

And I'm not even going near it... in a previous life I sold HiFi for a living, and some of the bovine excrement magazine reviewers in particular spouted made me shudder... snake-oil anybody? Rolling Eyes

My take on things is quite a simple one - if you can hear the system, then it doesn't work... if it disappears, leaving only the music, that works.
_________________
Thought for today: Don't go knocking on death's door, ring the doorbell and run, he hates that!!
Back to top
View user's profile Send private message
speakerguru
VIP Contributor 750+


Joined: 18 Nov 2005
Posts: 959
Location: Green Hut, Tovil

PostPosted: Mon Nov 03, 2008 12:07 pm    Post subject: Reply with quote

thelandlord wrote:
.. is there any good reason why I shouldn't wind ferrite ones on toroids rather than more conventional bobbins?


see http://www.hifiloudspeakers.info/speakertalk/viewtopic.php?t=513&highlight=inductors for info on air core vs. cored

Re toroids, they are certainly low leakage, but only up to the point when they saturate and they will saturate at a lower level than an inductor with some air in the return path. You can't saturate air magnetically. When a toroid core saturates the flux will use the surrounding air instead.

Toroids would also be more variable (in production) because there would be no air gap to dilute the core magnetic characteristic variations from batch to batch. Toroids are also more difficult and therefore costly to wind.
Back to top
View user's profile Send private message
thelandlord
Introductory Contributor


Joined: 23 Oct 2008
Posts: 9
Location: Near Bristol, UK

PostPosted: Wed Nov 05, 2008 4:43 pm    Post subject: Reply with quote

speakerguru wrote:
Toroids are also more difficult and therefore costly to wind.


Thanks for linking the other thread, speakerguru - the biggest reason I asked about toroids was one I'd not mentioned - I actually find them easier to wind by hand than conventional coils because I have limited movement in one hand... they don't come unwound if I drop the wire. Embarassed

This project is going to have to go on hold for a week or two because a more pressing one has come along - my preamp has turned it's toes up so I'm going to be chasing a replacement.

'See' you all soon. Smile
_________________
Thought for today: Don't go knocking on death's door, ring the doorbell and run, he hates that!!
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    SpeakerTalk Forum Index -> DIY with KEF drive units All times are GMT + 1 Hour
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2005 phpBB Group