It was those with over 2 drivers - hence the BC1 had a super tweeter 'to avoid purchase tax'.
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It may well be that 3 unit speakers were automatically "professional" for tax purposes but it also depended on woofer size. A 2 unit speaker with at least one dimension of 12" in the drive unit was it seems tax exempt and it is said this is the reasoning behind the KEF B139.
Not sure about that Jez. The B139 was a reduced size version of an older and much larger bass driver. Think it was the B1814 or something like that, it was damn big anyway.
http://i63.tinypic.com/ifqqlt.jpg
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Oh I'm well aware of the earlier incarnation of it yes. There was even a 2 way bookshelf with just a B139 and T27!
As far as purchase tax anomalies go well I don't know the full SP and it seems lost in the mists of time but there are many references I've seen over the years, some no doubt apocryphal, of "more than 2 drivers" being a criteria but even more mentioning size of bass unit and that it didn't specify that it had to be 12" or more in all directions.... so an elliptical driver was a tax loophole so long as 12" in biggest dimension. Think also of all those EMI 13" x 9" drivers with two tweeters on a metal strip across the front of them...
I even recall talk of some early ABR speakers being for tax purposes as the third driver didn't need a magnet or voice coil to qualify...
Sold by the thousands from Lasky's and W.H.Smith in Edgware Road. They were called the 'Set 450' with the nasty little plastic coned tweeters and the 'Set 350' with a single paper coned tweeter.
Not a patch on the various versions of the excellent 14A/770 alloy framed 13" x 9" jobs, as used by Celef, B&W, Mordaunt Short, Proac and Monitor Audio, amongst many others (although some of the 12" x 9" steel framed units shared the same cone and larger magnet).
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My Mordaunt Short MS 815's. I only use them to add a bit of oomph to the telly and I'm not in to the whole AV thing. They sounded OK until I heard the big Goodmans.
Well I grew up with a Dynatron radiogram and it subconsciously put me off elliptical looking drivers for ever.
Usually saw them in low fi gear that was knocking about as a kid.
They cant be that good if nobody uses them nowhttp://3.bp.blogspot.com/_6EzvmhURfx...0/DSC01379.JPG
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They were in this Van Der Molen garbage that I had when I was about 10. Im maybe being unfair as I enjoyed it as a kid until the built in amp starts crackling at the controls and failed...You could rock that BSR tonearm backwards and forwards on its rickety mounting and there was one elliptical speaker per cabinet :)
Picture below BSR version.... My pride and joy :D
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I seem to remember very well reviewed Monitor Audio MA3 used an elliptical driver.
That weren't no BSR deck. It was a late Garrard with a version of the ghastly cheapo 'Unimech' chassis which was based on their micro-changer CC10. Van Der Molen made some pleasant stereo record players, but the more expensive Hacker models were very much better and even had half decent speakers to boot (I think they were M-S sourced, but it would need Andr'e to confirm probably).