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Old 26th October 2011, 02:49 AM   #41
Einric is offline Einric  United States
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I don't suppose anything would stop a guy from buying a PE buyout woofer (12" $15) and cut the magnet off it.

That is half price from a 12" PR.
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Old 26th October 2011, 03:44 AM   #42
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Quote:
Originally Posted by Einric View Post
I don't suppose anything would stop a guy from buying a PE buyout woofer (12" $15) and cut the magnet off it.

That is half price from a 12" PR.
That sounds like an lot of money to spend on a PR experiment. I just wait until I find a pair of speakers on the side of the road and mod the woofers out of them for passive radiators.

Peace,

Dave
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Old 29th October 2011, 06:14 PM   #43
Ron E is online now Ron E  United States
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Quote:
Originally Posted by TerryO View Post
Ron,

I get the sense that you remember this from... (the Bass List?)
Dan certainly did the Math, although I checked his work and made any necessary corrections.
A copy of Adire's RDO paper is here:
http://stereointegrity.com/Files/RDOOperation.pdf

"The math behind RDO is fairly simple; the best explanation/set of equations we've seen comes from Ron
Ennega, and was posted at Brian Steele's DIYSubwoofer site:
First you need the original Rms:
Rms = 2 * pi * Fs * Mt / Qms
Next calculate:
Rms'=Bl^2 /(Re + R) where R is the shorting resistor
Rmt = Rms + Rms'
The new Qms is:
Qms' = 2 * pi * Fs * Mt / Rmt
Qes does not change:
Qts = 1/(1/Qes+1/Qms)"

To which I would make the correction that:
Qts = 1/(1/Qes+1/Qms')
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Last edited by Ron E; 29th October 2011 at 06:18 PM.
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Old 30th October 2011, 08:24 AM   #44
TerryO is offline TerryO  United States
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Quote:
Originally Posted by Ron E View Post
A copy of Adire's RDO paper is here:
http://stereointegrity.com/Files/RDOOperation.pdf

"The math behind RDO is fairly simple; the best explanation/set of equations we've seen comes from Ron
Ennega, and was posted at Brian Steele's DIYSubwoofer site:
First you need the original Rms:
Rms = 2 * pi * Fs * Mt / Qms
Next calculate:
Rms'=Bl^2 /(Re + R) where R is the shorting resistor
Rmt = Rms + Rms'
The new Qms is:
Qms' = 2 * pi * Fs * Mt / Rmt
Qes does not change:
Qts = 1/(1/Qes+1/Qms)"

To which I would make the correction that:
Qts = 1/(1/Qes+1/Qms')
Dan Wiggins did some of the preliminary math but, as been pointed out here, Ron Ennega did the really "deep" math (as was usual on the the old "Bass List"). I was being too hasty in replying and forgot to mention Ron's vital contribution.

Best Regards,
TerryO
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Old 2nd November 2011, 02:55 PM   #45
DAMIC is offline DAMIC  Seychelles
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Quote:
Originally Posted by Einric View Post
I don't suppose anything would stop a guy from buying a PE buyout woofer (12" $15) and cut the magnet off it.

That is half price from a 12" PR.
Is there something else wrong if magnet stays intact, beside reduced volume?
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Old 2nd November 2011, 08:58 PM   #46
djk is offline djk
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I generally leave the magnet on.

I do cut off the voice-coil below the spider joint (remove the dust cap, pull the cone up, and cut the coil former with an exacto knife, yank the coil out with pliers).
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Old 2nd November 2011, 09:24 PM   #47
Collo is offline Collo  Australia
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Usually you will need to add mass to tune the PR. Removal of the magnet gives you somewhere to put it.
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Old 2nd November 2011, 09:47 PM   #48
epa is offline epa  Netherlands
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question: why not leave the magnet/vc on.then you could tune the pr with a (variable)resistor between the poles?
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Old 2nd November 2011, 11:42 PM   #49
djk is offline djk
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"Removal of the magnet gives you somewhere to put it. "

Removal of the dust cap gives you a better place to put it, between the surround and the spider.

"question: why not leave the magnet/vc on.then you could tune the pr with a (variable)resistor between the poles? "

I would wonder about the excursion capacity. Cheap woofers will slam the coil-former against the back-plate, and you will probably be adding a bunch of mass too. The coil could also pop out of the gap in front and get hung up too, especially with some added mass.
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Old 3rd November 2011, 02:33 AM   #50
Ron E is online now Ron E  United States
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Quote:
Originally Posted by epa View Post
question: why not leave the magnet/vc on.then you could tune the pr with a (variable)resistor between the poles?
That won't "tune" it. The resonant frequency will stay the same, it will just reduce output.
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