Still can't get reasonable numbers

[mashaffer]

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

 

[kelticwizard]

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.

 

[kelticwizard]

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.

 

[mashaffer]

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

 

[Ron E]

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.

 

[planet10]

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

 

[mashaffer]

Well they are pretty old. I suppose the fix would be to replace the surrounds or... use them as midranges.

mike

 

[planet10]

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

 

[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?

mike

 

[planet10]

[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

 

[mashaffer]

Since I didn't pay anything for mine I would be willing to experiment on them a little bit. I did think of acetone but it is a strong chemical and I was afraid that it might quickly ruin the driver. Have you found it to be a pretty safe thing to try?

mike

 

[planet10]

I did think of acetone but it is a strong chemical and I was afraid that it might quickly ruin the driver. Have you found it to be a pretty safe thing to try?

I was worried about it, but it proved to not hurt cloth surrounds & paper cones.

Use outside and avoid breathing the fumes... etc

dave

 

[mashaffer]

Could you share the process that you used? Did you just dab it on with a Q-tip and wipe with a cloth? Drizzle it through from the back side?...

mike

 

[planet10]

Could you share the process that you used? Did you just dab it on with a Q-tip and wipe with a cloth? Drizzle it through from the back side?...

I tried all sorts of schemes. But all using q-tips. Seemed more effective if the surround was heated up with a hot-air gun 1st. I went as far as having a little lake in the surrounds (all the surrounds i played with were inverted half-round), and let the acetone sit (it does evaporate fairly quickly), alternatly working it with the q-tip the whole time. On occasion i was able to visibly pull out yellow gunk on the q-tip. Repeat.

Let us know how you make out.

dave