SpeakerTalk

andy ashworth · Posted: Sun Feb 13, 2011 1:02 pm Post subject: Seven years later.....

Hello Everyone,

I don't know if there is a prize for the longest time between posts but I'd like to put my name forward Laughing

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Back in 2004, I was looking to build a pair of B139 based subwoofers for my Kef LS3/5a speakers. Well, to cut a long story short I didn't get round to it and have since sold the little Beebs (it was a moment of financial weakness and they went for twice the amount I paid new Shocked

).

Anyway, I've missed the little chaps and the B&W D5s I now use aren't quite doing it for me, despite them being quite good overall. So the plan is to build a 3-way setup using the B139, B110 and T27. I managed to get a full set on eBay last week and although the price was high-ish, the seller seemed reputable and he didn't appear to be stripping some old Concertos for profit (I share the hatred of pimps).

Here's a link to the auction - perhaps it was someone round here?.....

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=170596524965&ssPageName=STRK:MEWAX:IT

At the moment, I'm in two minds as to the best way to approach this. The first is to build a 'kit' Concerto and the second is to build a two enclosure setup which houses the B139 separately from the B110 and T27. If I choose the latter, it would seem to make sense to base the enclosure dimensions on the LS3/5a. After all, it's a setup which seems to work rather well. I'm fully aware that simply using any old SP1003 isn't going to give me an LS3/5a but is it likely to be hugely different? I appreciate the importance of the crossover network in the LS3/5a so I suspect this would be my biggest issue. However, as I'm not looking for bass from the B110, perhaps it actually makes things a lot simpler!

Ultimately, I'm not looking to re-create a BBC monitor and only hope to capture some of the magic in a well balanced diy build. This is only a pre-amble of course and given my record for completing projects, I wouldn't hold my breath for a finished photo! I'm sure I'll get there this time, mind Wink

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Any thoughts?

Regards,
Andy.

proffski · Posted: Sun Feb 13, 2011 7:40 pm Post subject: Re: Seven years later.....

Just Google B139 or B139 Subwoofer, plenty of ideas out there!

Food for thought: http://www.linkwitzlab.com/x-sb80-3wy.htm
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andy ashworth · Posted: Mon Feb 14, 2011 10:27 am Post subject:

Thanks Proffski, that's an excellent link and very close to what I intend to build Very Happy

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I've always liked the idea of putting the crossover before the amplifiers and this is one avenue I will look very seriously at.

I'm getting all excited now Laughing

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Cheers,
Andy.....

proffski · Posted: Mon Feb 14, 2011 12:20 pm Post subject:

andy ashworth · Posted: Mon Feb 14, 2011 12:35 pm Post subject:

I have indeed seen the coffin but unfortunately, I don't have the space for one!

I plan for the B139 enclosures to act as stands so in effect, it will be like building something similar to the Reference 105 (ish). Using a centrally spaced bass unit is out as my speakers will be placed either side of an open fire!

I'm pleased to hear active crossovers can make a big difference (more simple due to a more predictable impedance?), wasn't this the preferred rout of the BBC with their grade 1 monitors?

Cheers,
Andy.....

proffski · Posted: Mon Feb 14, 2011 7:18 pm Post subject:

Beware of crossovers making a "difference" as long as the difference is for better fidelity! Wink

I have bought many PCBs from this chap, very reliable and cheap.

http://sound.westhost.com/p-list.htm

See projects 48A, 28, 09, 68, 71!, 116, etc.
Do bear in mind that many circuits will not have all the details unless you buy the PCBs. He too has suffered from people stealing his material.
_________________
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

andy ashworth · Posted: Fri Feb 18, 2011 4:43 pm Post subject:

Thanks for the link Proffski, I'll be looking through the site with interest!

Well, the drivers are now here and I've really got to take my hat off to the seller. All units appear to be in good order and were very well packaged. Essentially, I've received the complete kit of parts pretty much as they were originally shipped in the late 70s. I even have the original Kef packaging for the drivers, along with instructions, templates acoustic wadding/panels and price list from Badger Sound Services! The crossovers are from Falcon and I'm wondering if they are the Concerto upgrade units they sold.

I'm going to approach this project in two stages. The first is to build the speakers as originally intended and the second is to build my own interpretation with the seperate bass enclosure. I'll then be able to perform a single speaker A-B comparison to see which I prefer. Fortunately, I use good quality birch plywood for a living and always have loads of offcuts to play with.

I'm really looking forward to this Very Happy

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So, if eBay member 'rootpruner' happens to read this - a big thank you for reminding me that that not all sellers are mercenary in their treatment of the hifi classics.

Cheers,
Andy.

Richie · Posted: Sat Feb 19, 2011 5:36 pm Post subject:

Hi Andy, would MDF not be better than ply ? much more inert and cheap .... either way good luck with your project
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Still learning ......

proffski · Posted: Sat Feb 19, 2011 10:27 pm Post subject:

andy ashworth · Posted: Sun Feb 20, 2011 1:49 pm Post subject:

Hello,

Thanks for the tip but I'm not really a fan of MDF. I favour the 'lossy' BBC approach of relatively thin but heavily braced and damped Baltic birch plywood. I checked out the design paper for the LS5/8 as well as LS3/5a and both point to this method as producing the lowest colouration. If Spencer Hughes and Dudley Harwood swore by the method - I think it's worth a shot.

I'm no stranger to damping (previous work with turntable plinths) so hopefully, I should be able to come up with a workable solution.

Initially though, I'll get a set of 'quick and dirty' boxes up and running to evaluate the drivers and crossovers.

This may take some time but I'm sure it'll be worth it Laughing

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Andy.....
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