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Old 21st March 2009, 10:33 PM   #1
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Default For anyone using wooden phase plugs. . .

I posted this over on the Fullrange Driver Forum , too.

Take a strip of Aluminum Foil , about 1/2"-3/4" wide, wrap it one time around the base of the phase plug. Leave it just long enough to overlap the starting edge, about 1/16" or so. Use a small piece of Scotch tape (clear) to affix the foil at the overlap point. Re-install and enjoy !

You have just created a shorting ring. Obviously performance will vary depending on level of care you exercise during installation , but this will reduce the natural impedence rising characteristic commonly found in many drivers.

Give it a try, it will only take 15 minutes to install.

You must make sure the foil is in contact with itself at the overlap point , it has to make a continous ring to make the "shorting" ring.

I'd love to hear what you have to say after trying this.



...........................Blake
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Old 22nd March 2009, 01:28 AM   #2
badman is offline badman  United States
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I've been thinking of doing something similar, but with copper foil, and attempting to get it into the gap creating a sleeve.

Just adding a 'shorting ring' to the top of the polepiece can actually create additional distortion, as you can introduce Le/X variance. Some drivers have removed shorting rings from motors to improve Le/X linearity, the top line eminence, AFAIK, changed over in this fashion.

But certainly no harm in experimentation!
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Old 22nd March 2009, 02:16 AM   #3
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I also thought of using copper foil, and actually bought some, but went for the aluminum foil as it is cheap and easier for a quick trial .

Eminence driver's design does NOT impress me. They are designed to take a beating during PA use, not exhibit linear response.

Massive deviations in impedence response of 99% of their drivers is a good indicator of what I mean.

Some of their drivers have impedence peaks at Fs over 200 ohms ! ! !

Le/X ?

Le= inductance

X= ? , Xmax or movement of the coil ?


Seriously, I think you would be very hard pressed to insert a foil sleeve over the pole piece of a FR unit. I know that it would be VERY difficult to do in my CalRads as the gap is pretty narrow.

If your drivers have aluminum coil formers , then you could just bridge the gap/split section of the former . This will act as a sleeve .

If you have non-metal phase plugs, try the aluminum foil. What have you got to lose besides about 15 minutes of install time ?




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Old 22nd March 2009, 03:27 AM   #4
badman is offline badman  United States
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Le/X is inductance vs. excursion. It's a standard plot for any in-depth speaker testing.

Care to elaborate on impedance variations? A really huge Fs spike isn't a problem, it's just the result of the motor particulars.

Bridging the gap on an aluminum former doesn't make it act as a sleeve, since it's in motion. It acts as a brake, which lowers Qms.

I never said inserting a sleeve would be easy, only that I'm going to try it
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Old 22nd March 2009, 11:11 PM   #5
G is offline G  United States
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This is a interesting thread. I had some phase plugs made out of solid bronze with a countersunk steel bolt threaded into the tail end. My Fostex FE206Es sure sounded different when I installed them. It was a good different though.
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Old 23rd March 2009, 12:58 AM   #6
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Quote:
Originally posted by G
Fostex FE206Es sure sounded different when I installed them. It was a good different though.
It was the plugs not any shorting, as the 206 alreadt has a copper cap on the pole piece

dave
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Old 23rd March 2009, 01:13 AM   #7
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I needed to understand better, so I went out and found this which I share, from free patents online, patent #6768806

...shorting rings have no effect on a steady state magnetic field but act in opposition to any change in flux density or any displacement of the flux lines such as those that occur under the loading imposed when the voice coils are driven hard with audio frequency current. The location of the shorting rings determines their effect: location close to a voice coil reduces the voice coil inductance, location entirely within the magnetic flux loop centerline favors reduction of second harmonic and higher order even harmonic distortion, a centered location on the flux loop centerline, i.e. centered in the magnetic gap, favors reduction of third harmonic and higher odd order harmonic distortion, while location outside the flux loop as defined by its center line but near the voice coil acts generally to reduce harmonic distortion and reduce the voice coil inductance. Thus a plurality of rings can be strategically deployed at different locations so as to optimally suppress both even and odd order harmonic distortion and to reduce the voice coil inductance.
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Old 23rd March 2009, 02:56 AM   #8
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Nililist- do you know which eminence drivers have 200 ohm resonant peak? thanks
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Old 23rd March 2009, 05:47 AM   #9
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Ed LaFontaine,

Excellent info ! Thanks .


lms,

Here goes. . .


Cast Frame models of various sizes.

http://www.eminence.com/pdf/kappapro-10a.pdf

A few that aren't quite 200 ohms, but very close.


http://www.eminence.com/pdf/kappapro-15lf-2.pdf

http://www.eminence.com/pdf/definimax-18lf.pdf

http://www.eminence.com/pdf/sigmapro-18-2.pdf


Stamped Steel frame drivers :


I know, this is a 16ohm driver but. . .

http://www.eminence.com/pdf/delta-10b.pdf

8 ohm

http://www.eminence.com/pdf/delta-12b.pdf

http://www.eminence.com/pdf/kappa-15a.pdf

This is a 4 ohm unit ;

http://www.eminence.com/pdf/kappa-15c.pdf


So only 1 that actually exceeds 200 ohms , but many that are 150 ohms or so, and if you browse the rest of the PDF files like I just did, you'll see most of their drivers are about 100 ohms at Fs.

That's no Gouda in my book. I know there are many people who think that the impedence peak at Fs is nothing to worry about, but I disagree.


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Old 23rd March 2009, 06:22 PM   #10
badman is offline badman  United States
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Time to look at a variety of impedance traces. Pro drivers in general have big impedance spikes due to the powerful motors.
You can always use a TL to damp the impedance spike.
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