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Old 6th December 2009, 04:46 PM   #1
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Default Woofer speed/Inductance

Hi there,

Just wanted clarification. Woofer speed (how high or low in frequency the cone moves) is dependent on inductance as

A) Inductance limits how high in response the cone moves

B) Limits how low it can move /

Just wanted to understand a little more concerning the mass situation. If you add mass, you reduce efficiency. So more power is needed. But you also lower Fs, right ? So the cone can respond to lower frequencies.

So inductance ultimately limits the frequency response of the driver but mass can shift it up or down and limits efficiency. Is that correct ?

Many people I know still cling to the belief that smaller woofers have better transient response because the smaller woofer has less mass. But to my understanding, less mass has nothing to do with the speed of the cone.

If the cone is moving slower then it is reproducing a lower frequency and if it's moving very quickly then it's much higher up the frequency scale and inductance limits this. And since woofers are bandwidth limited (hence due to inductance do not operate in that region) speed is not a concern.

Woofers are also low pass filtered. So at what point does the inductance dominate ? The low pass filter limits things as well, correct ? Just want to put these things into perspective. Sorry, I'm typing all of this really quickly so forgive me if I don't make any sense here.

I'm sure there are many far more knowledgeable than I. I look forward to hearing from you. Thanks.

Regards,

Last edited by Vaughan; 6th December 2009 at 04:50 PM.
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Old 6th December 2009, 06:18 PM   #2
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Any views ?

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Old 6th December 2009, 10:46 PM   #3
MaVo is offline MaVo  Germany
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the thing about inductance and mass as the limiting factors in the high and low frequency response seems to be right. its just, terms like speed have no meaning with speakers, so people get confused when you use such terms. also, its no use to speak about an individual drivers impulse response - you have to look at the whole system. after all, the points you want to understand have to real use in building a speaker, so i didnt look into them so much.
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Old 7th December 2009, 12:19 AM   #4
MaVo is offline MaVo  Germany
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should read "have no real use"
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Old 7th December 2009, 03:52 AM   #5
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Velocity and frequency aren't interchangeable terms. When you add in displacement, you can convert to any of the three. Acceleration is in the mix as well. link
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Old 7th December 2009, 04:01 AM   #6
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Quote:
Originally Posted by Vaughan View Post
A) Inductance limits how high in response the cone moves
Inductance of the coil indicates where the power through the coil begins to fall off as frequency is raised: Fc = 2*pi*Re*Le roughly. Yes, less power will mean less acoustical output. It's an electrical property, not a physical.
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Old 7th December 2009, 07:31 AM   #7
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Inductance is similar to a low pass filter in that it filters out high frequency components. It limits how high in frequency the cone responds.

Mass affects resonance, I know it's a physical, not electrical component. Just trying to separate the two components. Mass can shift the resonant frequency up or down but inductance limits how high or low it goes. Like a hard limit.

Dan Wiggins said in his article some time ago that if the cone has infinite changes in current that transient response would be infinite. That makes sense to me, since current is the driving force.

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Old 7th December 2009, 09:56 AM   #8
Henkjan is offline Henkjan  Netherlands
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Dan Wiggins wrote a white paper on this..

http://www.adireaudio.com/Files/WooferSpeed.pdf
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Old 7th December 2009, 10:52 AM   #9
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Thanks, I've been looking for that article for some time. Does Dan still post around here ?

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