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Old 8th January 2005, 07:50 PM   #1
sardonx is offline sardonx  Canada
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Default Need formula for contour network!! Anybody?

I need to design a contour network for a woofer and have been desperately looking for a formula. I found one at www.lalena.com but he is not sure if it's correct. Any information would be great..

sardonx
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Old 9th January 2005, 12:06 AM   #2
dooper is offline dooper  Canada
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Loudspeaker Design Cookbook by Vance Dickason - I have the sixth edition from 2000. Beginning at p. 147, there are descriptions of circuits for:
Quote:
situations where:

a) the response is rising with increasing frequency, and

b) the response is rising with decreasing frequency.
For situation a), a parallel RL circuit is used, and for situation b), a parallel RC circuit is used. Which network do you need the formulas for?

dooper
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Old 9th January 2005, 01:09 AM   #3
sardonx is offline sardonx  Canada
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Dooper,
I'm interested in situation A. It's for the SS 7 inch revelator.
The response starts to rise at 800hz and tops out at 1800 with a total rise of about 4db.
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Old 9th January 2005, 02:11 AM   #4
dooper is offline dooper  Canada
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1. L (in henries) = 0.15916 / f - in this case f = 400 Hz.

2. "R is selected so the combined impedance of the total circuit equals the amount of maximum-needed attenuation (or average if the rise is not well-defined), where:

Z = (RX) / ((R ^ 2 + X ^ 2) ^ 0.5)

Z = total circuit impedance

X = component reactance at frequency of maximum attenuation"

For an inductor, X = 2 * pi * F * L.

Dickason suggests R = 5 ohms would result in 4.8 dB attenuation.

The book has more info, formulas, and examples. It's well worth the money

EDIT: The formulas on the Web page you posted appear to be the same as the ones in Dickason's LDC.

Cheers,

dooper
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Old 9th January 2005, 01:41 PM   #5
Paul W is offline Paul W  United States
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Sardonx,
I used the 7" revelator in my previous system and as I recall, for the circuit you are asking about, L was .2 and R 2-3 ohms. I am not certain about either value...optimum reponse on your baffle may require different values anyhow.

I also used a very subtle series RLC trap across the VC tuned to the ~800Hz impedance glitch in the rev. I don't remember those values at all, but the overall result of the two networks was much flatter reponse. You're on the right track...keep going.
Paul

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Old 9th January 2005, 08:27 PM   #6
sardonx is offline sardonx  Canada
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Thang you v much guys.

Paul,
I came up with the same value of L too. As for the resistor I will experiment with it.

I still haven't ordered the revelators but i know they will sound good. Slit paper rules.

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