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Old 20th April 2011, 06:48 AM   #1
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Default First crossover - will it smoke?

I am a true beginner at crossover design. I am armed with edition 4 (1991) of Vance Dickason's cookbook and enthusiasm. I have fountek fr88-ex and dayton nd20-fb-4. Is the following design a good starting point or will it smoke my components? I was trying to cross at 5k. Thanks to anyone who spends the time to look over my attempt.
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Old 20th April 2011, 07:52 AM   #2
DaveG is offline DaveG  United States
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Hey, I'm really not alot of help here, but the 15uf may be too big, and I don't want you to pop the tweeter. I would think 5uf and .25 might be closer. I could not find my copy of cookbook to see how you were calculating, but I plugged the numbers into some online things and could not get the cap much above 8uf, and did not hit 15uf till I went down to 1500. Looks like about 3.2 ohms at 5k.
Get more opinions before you give it much power. Basic config looks fine.
Dave
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Old 20th April 2011, 08:47 AM   #3
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The attenuation of the tweeter is not enough. The FR88EX has 84dB/1m and if you include baffle step 81dB attenuation. The tweeter has 90dB/1m sensitivity.
5KHz is a good point of crossover.
Tweeter : you need to remove 9dB with a LPAD 2.2 series and 2.2 ohms parallel crossover 5Khz LR2 : 4uF 0.22mH
The woofer I calculate 1mH 4.7uF
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Old 20th April 2011, 11:16 AM   #4
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Quote:
Originally Posted by jerome69 View Post
The attenuation of the tweeter is not enough. The FR88EX has 84dB/1m and if you include baffle step 81dB attenuation. The tweeter has 90dB/1m sensitivity.
5KHz is a good point of crossover.
Tweeter : you need to remove 9dB with a LPAD 2.2 series and 2.2 ohms parallel crossover 5Khz LR2 : 4uF 0.22mH
The woofer I calculate 1mH 4.7uF

Erratum a schema is better : your woofer values are ok 0.5mH 2uF
For the tweeter C becomes 5.6uF
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Old 20th April 2011, 02:34 PM   #5
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Thanks all. I was worried about the tweeter atttenuation but did not know how to compute it properly.
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Old 20th April 2011, 02:36 PM   #6
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Jerome, that is much better than I could ever do as a first shot. Thanks for the lesson also.
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Old 20th April 2011, 02:42 PM   #7
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Ya know. If you wanna really do this "right"/better. www.zaphaudio.com has FR and impedance plots of both those drivers on his site. You could use SPL Tracer to make .frd and .zma files. Then download Jeff Bagby's PCD, free. You could then design the XO based on real measurements.

Now, those are infinite baffle measurements. So, even better would be to simulate diffraction, baffle step, etc. before doing the XO design. It's take quite some effort, but will likely do better than just throwing some calculated values in there.

I recently did something very similar for the first time. I can link you to my build thread if you want some guidance on how to go about it.

Oh ya, I agree with the above. 15uF to big and 1.2ohm to small. Make the resistor swapable so you play till you have it right.
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Old 20th April 2011, 03:24 PM   #8
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Quote:
Originally Posted by PlanoDano View Post
Thanks all. I was worried about the tweeter atttenuation but did not know how to compute it properly.
Tune it by ears. Don't worry. The value of 9dB is a good starting point.
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Old 20th April 2011, 04:20 PM   #9
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I will spend some time learning how Jerome set up the tweeter circuitry. Tuxedocivic please pm me the link to your build guide. I am a beginner with some good electronics experience. The software may be a bit complex for my current level but I would like to begin getting familiarity with it.
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Old 20th April 2011, 05:15 PM   #10
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I have some years of designing loudspeakers, there are a lot of tips.
I can give you useful links :
FRD Consortium
http://www.mh-audio.nl/index.asp
HOLM Acoustics
ARTA Home
You should read this first : crossovers

Hope this helps.

Note : Your set-up works and fortunately the theoretical values are closed to the actual values
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