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Multi-Way Conventional loudspeakers with crossovers

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Old 8th February 2012, 08:23 PM   #41
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Originally Posted by system7 View Post
I'd incline to stick with that B200 for now. 18L is alright if you stuff a sock in the reflex. I was really trying to figure out a crossover for you. I'd think you won't have much difficulty matching it to a 89dB or better tweeter with a third order crossover, like a Seas Prestige 27TFFC or Morel Classic CAT298. But you could even just buy a cheapie dome and run it off a single 2.2uF.
...
Enjoy the pictures of your B200 in it's youth!
Haha, great stuff
Ok, i've found an italian seller who sells the tweeter you suggested (and many others...). Actually I've this dome:
- Audiokit E-commerce - Vendita componenti elettronici
pretty flat response, not bad I think but I can't find a review....

Anyway, I'm going to build a new cabinet: the one I have now is a bit "damaged"... Too many times I've opened and closed it due to vary experiments :-) .... 30/35 liters, port tuning at 45Hz even this time...
Anyway I prefer reflex design: one speaker is in a corner, the second along a wall .... So I can "match" the frequency response simply closing the reflex of the speaker in the corner...

RDLewis, I can't understand why KEF used this strange crossover design...
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Old 9th February 2012, 12:25 AM   #42
system7 is online now system7  United Kingdom
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Originally Posted by RDLewis View Post
Many years ago I aquired A B200 from a friend, who used it as the bass unit in a three way TL. I decided to try it in one of the 2 way designs common then using the above (largely Kef type), but using an Audax tweeter, I could not stand the T27. Anyway, the results were pretty poor, undynamic, flat, coloured. I could not understand why it was held in high regard.

A few days latter I decided to try it out with a simpler Crossover, namily a single inductor, I think it was 1mH, and second order tweeter section. The difference was amazing. It showed me that the B200 was a much better driver than I thought. I have heard similar improvements from those who did similar things with the B110. The old KEF crossovers just sapped the life out of those drivers, all with aim to get the flattest response.
I think you could be onto something there RD, bextrene is heavily damped and quite forgiving of programme material. I think a little liveliness at the expense of colouration is worth trying!

Michelino, don't dump that tweeter of yours on a whim. Is there any reason to think it's bad? But FWIW, Vifa XT19 and XT25 are pretty good too. The crossover design is definitely wrong. I'm thinking 1.2-1.5mH and 7uF now for the B200. Maybe a 2-3 ohms resistance on the shunt too.
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Old 9th February 2012, 07:22 AM   #43
DrBoar is offline DrBoar  Sweden
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One way to get good bass out of such a low Q driver is to use a quarter wave pipe of some sort. A Voigt pipe, a mass-loaded quarter wave pipe or a Transmission line with light damping in the line. I would go for Martin J Kings mass-loaded quarter wave pipe !
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Old 9th February 2012, 04:53 PM   #44
sreten is offline sreten  United Kingdom
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Click the image to open in full size.

Hi,

Come on people .... how can you take a x/o circuit that gives
a near short across an amplifier at high frequencies seriously ?
Its wrong, very wrong, people do make mistakes ....

If you swapped the position of the inductor and the notch
filter it would make a lot more sense*. As it stands you
have a 12uF path to ground (7uF + 5uF) which is 3 ohms
at 4.5KHz, 1.5 at 9KHz and a crushing 0.75 at 18KHz.

I guess circuit simulators still don't do smoke very well.

TinaTi has a nice option : an impedance meter, try that.

rgds, sreten.

*That would then be standard topology for a notch
filter below the x/o point, and pretty standard for
bextrene units, having a big midrange peak.

(Bextrene = rubberised polystyrene + a plastiflex
damping layer, which only controls the peak but
doesn't eliminate it, hence driver variability.)

The high value of the inductor may be due to it
doing BSC duty and reducing a midrange peak
in combination with the notch filter, hard to
say in a sim without the drivers response.
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Last edited by sreten; 9th February 2012 at 05:22 PM.
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Old 9th February 2012, 05:29 PM   #45
system7 is online now system7  United Kingdom
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You can see the trap is before the capacitor here, the 5uF being top right:

Click the image to open in full size.

So is the 3.29mH by the look of it.
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Old 9th February 2012, 06:08 PM   #46
sreten is offline sreten  United Kingdom
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Hi,

I don't care, perhaps the board is wrong. 12uF across the input is wrong.

i've seen completely wrong x/o boards before, somebody gets it wrong.

12uF to ground is 12uF to ground, very low high frequency impedance.
Its not intentional I'm sure. I'm sure the positions should be swapped.

It should look like those x/o's in post #33.

Here it won't stop the speakers working, but its wrong, very wrong.

rgds, sreten.
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Last edited by sreten; 9th February 2012 at 06:25 PM.
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Old 9th February 2012, 06:52 PM   #47
sreten is offline sreten  United Kingdom
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Quote:
Originally Posted by system7 View Post
You can see the trap is before the
capacitor here, the 5uF being top right:
So is the 3.29mH by the look of it.
Hi,

That is a viable arrangement, both before the capacitor.

rgds, sreten.
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Old 9th February 2012, 07:33 PM   #48
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I think the simple answer is that the x-over in #34 has an error. If you look at the lines near the bass inductor indicating wires there seems to be a cut and paste job that suggests a later alteration. Having the large inductor feeding the small cap across the bass unit would make complete sense and the values would not be outrageous. Both the B110 and B200 had peaks around 3k. Depending on the baffle size these could be 8-10 db. A over damped second order configuration was not uncommon. (I have schematics for at least 7-8 combinations of KEF bass units and various tweeters.) E.g. the Wilkinson 2-way stepped baffle design (B200//T15, Wireless-World from about 1978) had the bass signal passing through a 2mH coil to a 2uF cap for a 3kHz x-over. Totally non-standard values but measured fine apparently.

Cheers, Jonathan
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Old 9th February 2012, 07:40 PM   #49
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Btw sreten,
speaking of "good theories" there is a nice line in one of Gilbert Briggs books on Loudspeakers where he quotes a German proverb; "When theory and practice agree......both are wrong!" One for the cynics.....
Cheers.
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Old 10th February 2012, 12:56 AM   #50
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The higher order crossover does suck the life out of the speaker. That is why I prefer 6db per octave in series. Current is not wasted. Capacitors store and release current. Constant voltage is the key by the use of resistors. R1 and R2 in tweeter circuit.
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