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Old 19th September 2006, 01:48 AM   #11
lndm is offline lndm  Australia
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Quote:
Originally posted by georgehifi
[B]Thanks lndm, then again Martin Logan used a 2nd order at the 125hz (C2A & L3) and it's just as steep on both sides, so maybe it would work fine at 200hz also,
I don't believe I suggested it wouldn't work, if I gave you that impression. Using a crossover sim, I have been able to do things with crossovers that previously I would have considered impossible without a complex crossover.

A textbook crossover for 14 ohms and 200Hz could be 33uF and 20mH giving a theoretical bessel slope. In your case, though, this would not work. The effect of the impedance on either side of the centre point shouldn't be ignored as the crossover has a heavy influence within a range of frequencies.

Generally speaking though, you could start with the spirit of Rabbitz' first suggestion of reducing the values so the resonance frequency is in proportion by the same as the proportion of 125Hz vs 200Hz.

Then, to compensate for the increased impedance you could reduce the value of capacitance, and increase the value of inductance by the same amount as each other. This way, the frequency is the same, but the Q is adjusted to suit the new impedance.

Going this way, and taking a stab in the dark, and wanting to make life easy, you could start by keeping your 5mH inductor, and changing your capacitor to 39uF. Go from there

BTW, it is interesting that 100uF and 5mH resonates at 225Hz.
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Old 19th September 2006, 02:10 AM   #12
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Quote:
Originally posted by lndm



BTW, it is interesting that 100uF and 5mH resonates at 225Hz.
This is throwing me, as the specs clearly show that with these components it's 2nd order at 125hz, I'm scratching my head, also being new at this xover voodoo.

Mine is the IIIp not the IIIx

I wonder if the L3 @ 5mh could be a typo on the the circuit I posted and it's really 15mh?


Cheers George
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Old 19th September 2006, 02:21 AM   #13
lndm is offline lndm  Australia
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Maybe, maybe not. Assuming it's not a typo, I feel it only serves to illustrate how it isn't so straightforward. I still feel that reducing the value of capacitance is a starting point in the right direction.
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Old 19th September 2006, 02:52 AM   #14
v-bro is offline v-bro  Netherlands
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dunno but since you use an active sub system, isn't it more easy to create a passive line level filter(as used in very high end pre's):
http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
http://www.marchandelec.com/xm46.html
I did, and it sounds very good to my opinion...

I use two subs with 17cm(5 inch?) woofers combined with quad esl-57's. Pre's are also passive with ladder attenuators...

Just use high qualiy caps and resitors, but the end result is only a few components in the signalpath, as any signal benefits from simplicity....
And you don't need any BIG and expensive components between the amp and the speaker. So you can fully benefit from the dampeningfactor from your amp.
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Old 19th September 2006, 04:40 AM   #15
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Quote:
Originally posted by v-bro
dunno but since you use an active sub system, isn't it more easy to create a passive line level filter(as used in very high end pre's):
http://www.t-linespeakers.org/tech/f...ssiveHLxo.html
http://www.marchandelec.com/xm46.html
I did, and it sounds very good to my opinion...

I use two subs with 17cm(5 inch?) woofers combined with quad esl-57's. Pre's are also passive with ladder attenuators...

Just use high qualiy caps and resitors, but the end result is only a few components in the signalpath, as any signal benefits from simplicity....
And you don't need any BIG and expensive components between the amp and the speaker. So you can fully benefit from the dampeningfactor from your amp.
This cross my mind a few times, it would be so much easier to have a passive 12db filter at the input of the power amp.
But correct me if I'm wrong, when you series two 1st orders to make a second order together of identical components, don't you get a hump, or is it a smooth 12db per octave roll of at the frequency that they are calculated for, ( 200hz) in my case.
The input impedence of my amp is a steady 68k

Cheers George
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Old 19th September 2006, 09:55 AM   #16
v-bro is offline v-bro  Netherlands
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to make a second order filter this way(I use this for the sub in my car) in the second series(as is stated in the theory in the linkhttp://www.t-linespeakers.org/tech/filters/passiveHLxo.html)
C2 should be one tenth the value of C1 and R2 ten times the value of R1.
No "hump" should appear...
At least I don't experience one, the only down side to a filter like this is slight insertion loss, but that is easy solveable with more power or more efficient speakers....
Or you might allready have plenty...

Max. cone displacement can be severall meters only once...
(joke).
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Old 19th September 2006, 10:36 AM   #17
v-bro is offline v-bro  Netherlands
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To overcome amplifier impedance effects you can use a pot for R2, rest of the values I would buy cheap first to experiment with in different values.

Make it sound exactly the way you want it and buy the values in a good quality(polypropene caps will mostly do just fine...).

Can be a lot of fun and revealing to make such a filter....
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Old 6th October 2006, 12:21 PM   #18
v-bro is offline v-bro  Netherlands
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The manual foor marchand xm-46:
http://www.marchandelec.com/ftp/xm46man.pdf

This has just helped me a lot......
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