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KLH Twelve vs Five (drivers)--another piece of the puzzle


JKent

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KLH's best classic speakers, their only 3-ways and two of my all-time favorites: The Twelve and the Five (OK. The Nines are probably better but I have never heard them and they were really JansZens labeled as KLH).

I always thought these models had identical drivers: a tweeter, two "twelve point five" mids and a so-called 12" woofer (really a bit under 11"). The Twelves provided more bass extension because of their 4 cu. ft. cabinets and they had the cool external "Contour Controls."

I sold my Fives and the Twelves a couple of years ago but the new owner of the Twelves recently called to say one speaker was not working. He's only about 5 miles away so I went to take a look and he had managed to blow both the woofer and the tweeter in one speaker (the twin mids are fine).

No problem. Roy had a spare tweeter and there were some woofers on ebay from Model Fives and Model Twenty-threes (and when I replace them I'll also install fuses, Vern ;))

I knew some Model Five woofers had square magnets and some had round. The Twelves in question had round magnets so I'll just use a Model Five woofer with a round magnet, right? Wrong!

Below are photos of a Model Five woofer and a Model Twelve. The Twelve has a deeper magnet structure, with 2 rings. The Five is shallower, with 1 ring. The baskets also appear to be different but I don't have a Five on hand to compare side-by-side.

So I guess we'll have to watch for some Twelve woofers OR replace both woofers with Model Fives.

Hope this information is useful to other restorers. Comments welcome.

Kent

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I believe it was Tom Tyson who pointed out the 12s needed more magnet to control woofer cone travel, as a function of its larger volume (= less damping).

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Thanks Ken--you are correct. I just did a search and found that in many old threads it was asserted that the Five, Twelve and Twenty-Three all used the same woofer (even by some very knowledgeable members). But in this thread http://www.classicspeakerpages.net/IP.Board/index.php?showtopic=2500&hl=%2Bmodel+%2Btwelve+%2Bwoofer Tom wrote; "I had always heard that the KLH Five and KLH Twelve shared basically the same woofer, but that may not be exactly right. The enclosure volume in the twelve is much larger than in the Five, and the magnet structure would surely have to be different to address the different characteristics. Ironically, a larger enclosure usually denotes a *smaller* magnet -- all things equal -- for appropriate damping, but I think KLH designed significant contouring in the Twelve crossover, but I'm not sure what was done on the low-frequency end. It is very difficult to significantly change anything (read "equalize") down in the very low frequencies with a passive crossover, so I suspect that damping was worked on in that speaker. That Twelve woofer on eBay shows stacked magnets for additional motor strength. Since the cabinet is much larger than the Five, the woofer may have utilized a stiffer mechanical suspension to offset the reduced acoustic restoring force, all the while retaining a long overhang in the voice coil. This would call for additional magnetic strength."

Live and learn....

Kent

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