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 26th October 2011, 02:49 AM #41 Einric   diyAudio Member     Join Date: Feb 2011 Location: Bozeman, MT 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.
dave_gerecke
diyAudio Member

Join Date: Dec 2007
Location: Phoenix, AZ
Quote:
 Originally Posted by Einric 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

Ron E
diyAudio Member

Join Date: Jun 2002
Location: USA, MN
Quote:
 Originally Posted by TerryO 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')
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley

Last edited by Ron E; 29th October 2011 at 06:18 PM.

TerryO
diyAudio Member

Join Date: Nov 2002
Location: Seattle,Wash.
Quote:
 Originally Posted by Ron E 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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"If you have to ask why, then you're probably on the right track."
quote from Terry Olson's DIYaudio Forum application

DAMIC
diyAudio Member

Join Date: Jan 2006
Quote:
 Originally Posted by Einric 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?

 2nd November 2011, 08:58 PM #46 djk diyAudio Member     Join Date: Feb 2001 Location: USA 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). __________________ Candidates for the Darwin Award should not read this author.
 2nd November 2011, 09:24 PM #47 Collo   diyAudio Member     Join Date: Nov 2004 Location: Newcastle, Australia Usually you will need to add mass to tune the PR. Removal of the magnet gives you somewhere to put it. __________________ Ports rule!
 2nd November 2011, 09:47 PM #48 epa   diyAudio Member   Join Date: Apr 2010 Location: amsterdam question: why not leave the magnet/vc on.then you could tune the pr with a (variable)resistor between the poles? __________________ one good thing about music ,when it hit you feel no pain. so hit me with music. hr driver db
 2nd November 2011, 11:42 PM #49 djk diyAudio Member     Join Date: Feb 2001 Location: USA "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. __________________ Candidates for the Darwin Award should not read this author.
Ron E
diyAudio Member

Join Date: Jun 2002
Location: USA, MN
Quote:
 Originally Posted by epa 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.
__________________
Our species needs, and deserves, a citizenry with minds wide awake and a basic understanding of how the world works. --Carl Sagan
Armaments, universal debt, and planned obsolescence--those are the three pillars of Western prosperity. —Aldous Huxley

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