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ls3/5a clone- which KEF crossover?

 
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Martijn Bosch
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Joined: 01 Feb 2006
Posts: 7

PostPosted: Wed Feb 01, 2006 12:50 pm    Post subject: ls3/5a clone- which KEF crossover? Reply with quote

Hello all, I just joined this group, wonderful info!

I'm assembling a ls3/5a, and I wonder what KEF crossover is suitable (apart from the 'originals' from Falcon. Can I use a CS1 or CS1a? What b110 should I use, sp1003/sp1057? I found conflicting opinions on this- I'm confused.

Thanks in advance, Martijn
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Wed Feb 01, 2006 5:05 pm    Post subject: Reply with quote

What do you want?

KEF CS1 or CS1A are not LS3/5a clones, they’re 8 Ohm impedance mini monitors capable of reasonable spl’s with good power handling capacity, using drive units that were generally available to “us mortals” in the 80’s.

The CS1 is a 100 Watt design using a B110B SP1057 and T27 SP1032, a little like a Reference 101 without the S-STOP circuit.

The CS1A is a 50 Watt design using a B110A SP1003 and T27 SP1032, a DIY KEF Coda.

Neither were originally designed to model the acoustics of the Queen Elizabeth Hall at half scale (1/2”: 1’) and subsequently modified by a broadcasting organisation, they were both designed by a computer!



The term “based on the famous LS3/5a design” is always taken out of context these days; it properly refers to the use of a B110 and T27 in a small box.

“LS3/5a inspired design” referring to JR149’s is also suspect, as my understanding is that it’s a rework of the KEF Coda.



If you really want to build a 15 Ohm LS3/5a clone, buy a hundred or so B110A’s and measure the frequency response of each and choose those with the flattest frequency response.

Or find a pair of B110A SP1228’s for the 11 Ohm variant.

Similarly choose T27’s which have the shallowest rising output cf frequency.

Then go to Malcolm Jones’ “LS3/5a” and Paul Whattons “what’s inside” pages and depending upon the age of drivers select the appropriate crossover and build them according to Malcolm Jones’ unsuccessful formula of component matching, when Falcon Acoustics were after a licence to build LS3/5a’s.
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Martijn Bosch
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Joined: 01 Feb 2006
Posts: 7

PostPosted: Wed Feb 01, 2006 5:40 pm    Post subject: Reply with quote

...point well made and taken Smile

I realise the rather big difference between the two.
Hence I'm planning to follow the dimensions of the ls3/5a, hoping to get a result resembling the original whilst knowing that it is almost impossible achieving the measurements of the venerable BBC...

Reading up on this great site this afternoon I found out the difference between cs1/cs1a design and that the cs1a crossover has been recommended and used in projects like these. Would it be wise using them or would it be better using the Falcon-crossovers?
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ColinR
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Joined: 31 Jul 2004
Posts: 1175
Location: Staffordshire

PostPosted: Wed Feb 01, 2006 8:43 pm    Post subject: Reply with quote

Very Happy

Quote:
cs1a crossover has been recommended and used in projects like these. Would it be wise using them or would it be better using the Falcon-crossovers


What can you afford?

If you have an LCR Meter for measurement and have access to buckets of components you can follow the tolerances on the distruction sheet and make your own.

I've seen that some German is flogging KEF Constructor crossovers on ePay, but bear in mind after this time the electrolytics will be starting to go off.

As for Malcolm's offering, Falcon do a good product.

I'm discriminating against Wilmslow on the grounds of cost btw.

Finally I know this bunch do driver repairs, do they do anything else?

AUDIOLAB LUIDSPREKERSYSTEMEN

Doniagaweg 20
Follega
Friesland
8535 WD
Nederland
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Parts
Senior Contributor 100+


Joined: 13 Jan 2006
Posts: 174
Location: Edinburgh

PostPosted: Thu Feb 02, 2006 2:06 pm    Post subject: Reply with quote

Hi,

Considering the price of the drive units second hand, you would probably be better going for a pair of LS3/5a from stirling broadcast.

My own views will not go down well here but, you could still probably have a decent musical speaker by having a custom external crossover made. Use a cabinet with the same volume as the Coda, but with no grill and a flush baffle, with the baffle being narrow and cabinet deep.
Round the edges of this cab, fit the mid/bass only near the top and fit the treble unit onto a panel on top of the cab. If using a T27 try out a pair of those felt rings from Russ andrews.

My views on the LS3/5a are its a fine speaker which was (I think) designed for voice reproduction in the back of a broadcast van, active LS3/5a variants were also used as monitors in the news booth at Scott FM.
I personally prefer using the Linn Kan for music as it has more snap and percussion with better power handling.

I believe the LS3/5a had a mild hump around 150hz and dip around 500hz. And was rated as an above average and recomended.

The Kef Coda at around half the price was considered a best buy, and comparable with models up to £300 in its day, I am sure this had a smoother responce than the LS3/5a ? Though the model im refering to used an Audax 25mm fabric dome.

Steve
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boyzo
Intermediate Contributor 25+


Joined: 10 May 2003
Posts: 44

PostPosted: Wed Feb 08, 2006 12:27 am    Post subject: Re: ls3/5a clone- which KEF crossover? Reply with quote

Martijn Bosch wrote:
Hello all, I just joined this group, wonderful info!

I'm assembling a ls3/5a, and I wonder what KEF crossover is suitable (apart from the 'originals' from Falcon. Can I use a CS1 or CS1a? What b110 should I use, sp1003/sp1057? I found conflicting opinions on this- I'm confused.

Thanks in advance, Martijn


Martin have a look here

http://member.melbpc.org.au/~jkaso/loudspeakers.htm#LS3/5a%20Resource
CSA1a is the best it uses the old B110 SP1003 which has a robust surround and superb bass.

Build the box 3" deeper and the hump goes and the bass is extended.
The BEEB box is cheap thin ply with damping go ultra rigid braced and use the CS1a KEF C/o design but use polyprop caps.

The KEF design is NOT equaled by any other in terms of using the B110/T27 at their best.
Response....
http://member.melbpc.org.au/~jkaso/LS35_FR_curve.jpg

Building an LS3/5a clone is a lot of work it can't be taken lightly.
Get the contructors CS1a C/o replace the caps
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Martijn Bosch
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Joined: 01 Feb 2006
Posts: 7

PostPosted: Wed Feb 08, 2006 12:56 pm    Post subject: Reply with quote

Thanks for the info Boyzo. I now have had 15 ohm crossovers made, hardwired, with up-to-date electronics but true to original spec. Also found original cabinets at Stirling Broadcast and T27+B110 sp1003 drive units, so apart from not having bbc-spec-matched b110's I've got some nice speakers for a total of around 375 euros, which suits my budget nicely Very Happy
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Martijn Bosch
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Joined: 01 Feb 2006
Posts: 7

PostPosted: Fri Mar 03, 2006 6:07 pm    Post subject: Reply with quote

...And they are ready! They sound fantastic- I've listened to several original LS3/5a's and I must say this comes very close. The hard-wired 15-ohm crossovers turned out very nice, thanks to PLSaudio in The Hague. I've got the reference cabinets with the srewed-on backs in maple via Stirling, with all the tit-bits you need, e.g. the original sealing-strip for the B110's, felt-strips etc. I recommend them highly.
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