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Old 5th July 2006, 06:24 AM   #1
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Default Still can't get reasonable numbers

Y'all might remember that I have begun measuring the params on some of my old drivers lying around. I was having trouble getting reasonable results with the little 5" ratshack full ranges so I tried switching to another amp. Still no luck. I am getting Fs of around 250Hz. These look like Fostex OEM. They have whizzers and a small hole in the center of the dustcap. It doesn't feel like the drivers are dragging (though they are stiffly sprung). They were originally used as car drivers so I don't think that they were intended as midranges.

Both speakers measure very close to the same so I don't think that it is bad solder joint at the speaker lugs.

Any ideas? This is very strange.

mike
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Old 5th July 2006, 06:52 AM   #2
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Have you tried measuring the Qts, then taking a close-spaced mic reading of the how far the SPL is down from the midrange at 250 Hz?

The formula for the relationship at Fc or Fs to the midrange is
20LogQts. So a speaker with a Qts of 0.5 will be -6 dB at Fc or Fs.

If nothing else, the test will tell you if the Qts reading agrees with the Fs reading.
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Old 5th July 2006, 06:54 AM   #3
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By the way, what are the Radio shack part numbers for those speakers?

I have some old catalogs that I might be able to look up the published figures. At least the Fs.
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Old 5th July 2006, 01:27 PM   #4
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I haven't gone beyond the Fs (and approximate at that) since the readings were so screwy. I will give that a try the next chance I get.

Cat# is 12-1848.

mike
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Old 5th July 2006, 04:15 PM   #5
Ron E is offline Ron E  United States
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How are you measuring? What equipment, what method, etc....

IMO, the easiest way is the constant current method you can find at epanorama - do a searh for 'epanorama theile' and you should find it.

Even easier is to build a jig and get speaker workshop going - at least once you figure out how to get things set up and calibrated correctly.
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Old 5th July 2006, 07:51 PM   #6
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Quote:
Originally posted by mashaffer
Cat# is 12-1848.
I'm not at home to check, but if it is the one i'm thinking of, then if they have developed stiff surround syndrome the Fs could easily be 250 Hz

dave
planet10/still searching for a cure for stiff surround syndrome
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Old 6th July 2006, 01:54 AM   #7
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Well they are pretty old. I suppose the fix would be to replace the surrounds or... use them as midranges.

mike
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Old 6th July 2006, 06:02 AM   #8
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I'm convinced there is a fix... some solvent somewhere that removes the treatment that has gone hard -- i've at least 30 drivers that would become useable.

dave
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Old 8th July 2006, 03:32 AM   #9
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Do we know what they used for treatment? Something that a patroleum solvent (sea foam e.g.) might get out? The surround does in fact look like a light cloth with some sort of snot soaked in.

Have you experimented with this idea at all? Anyone ever ask Fostex folks about the issue?

mike
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Old 8th July 2006, 04:02 AM   #10
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Quote:
Originally posted by mashaffer
[Do we know what they used for treatment? Something that a patroleum solvent (sea foam e.g.) might get out? The surround does in fact look like a light cloth with some sort of snot soaked in.

Have you experimented with this idea at all? Anyone ever ask Fostex folks about the issue?
I have some drivers that are fine... seem to be untreated cloth and then the same driver with SSS (Stiff Surround Syndrome). I've also many with SSS where the surrounds seem coated in a hard varnish -- i know they didn't start that way. I've tried a number of things, acetone working best (but still not adequately)... I have a long list of potential solvents from SY but no chance to try them out. I'd be happy to send some candidates to a honourrs organic chem student for some research.

dave
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