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Old 27th November 2003, 02:01 AM   #1
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Default noob needs help designing crossover

What I have: (1) tweeter- 6 ohm nominal impedance, (2) 6.5" woofers - 8 ohm nominal impedance.

What I want: A 2nd-order Linkwitz-Riley crossover at 2KHz that also gives an 8 ohm impedance for the entire speaker.

Ok, so in my searchings I have come across numerous "crossover network calculators" such as

http://www.ajdesigner.com/crossover/crossoversecond.php

and

http://www.mhsoft.nl/spk_calc.asp

they are very nice and I was happy to find these, but the only problem is they all give different results!

Why is this? It seems like there should be only one soulution to this problem. I don't doubt that they xover at 2KHz but do they have an 8 ohm input impedance?

Any help would be nice, thanks.
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Old 27th November 2003, 10:40 PM   #2
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One thing i do know,is that you cant assume the impedence will be 8ohm ul have to measure.
woofers have a rising inductance as frequency goes up.

what are u actualy using? passive or active?

http://www.sound.westhost.com/
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Old 28th November 2003, 02:11 AM   #3
GM is offline GM  United States
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Uh, you can't get a nominal 8ohms using two 8ohm and one 6ohm driver. Two 8s in parallel = 4ohm, and in series = 16ohm, and as Mikee noted, for the calculators to work you have to input the right impedance at the XO point. If you use impedance compensation and a zobel, their effects have to be factored in also.

This one is correct: http://www.mhsoft.nl/spk_calc.asp

Good XO design is no trivial pursuit unless you have good measurement/design tools/software.

GM
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Old 21st December 2003, 11:22 PM   #4
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Thanks for your comments guys.

Sorry I forgot to mention that the 2 6.5's are in parallel, which of course gives 4 ohms.

I've done a little analysis myself and found that the crossover network gives back the speaker's impedance when above or below the crossover point. Meaning in my case, for freqs above 2k the impedance is 6 ohms and below 2k the impedance is 4 ohms.

Seems to make sense since a low/high crossover is supposed to be transparent for freqs that it passes. For freqs that it doesn't pass, it just takes the speaker in question out of the picture by raising the impedance. I should have known this already.

I have decided to put a 12 ohm resistor in parallel with the 6 ohm tweeter to give an equivalent resitance of 4 ohms to match the 6.5's. So the speakers, as a whole, should have about a 4 ohm resistance across all freqs making it simpler for the amp. In the end 8 ohms was just too complicated.
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