Model 17 Woofer

[jessiAV]

   Thanks to Norman's generosity, I now have a replacement for my one Seventeen woofer whose voice coil scrapes when manually pushed to the bottom of it's travel. The replacement woofer came from his Model 17 and looks very close to mine, only differing in that it's surround was treated with a black butyl rather than a clear, and dust cap that may(?) have been treated with the clear as it's not black.

      Strangely, this replacement driver has apparently less midrange than my two originals, I'm guessing maybe 3-4 db down? The bass amplitude is the same however. I'm at a loss to understand why this could be. Any ideas? Mr. Roy, Kent ?   Thanks!

[RoyC]

5 hours ago, jessiAV said:

   Thanks to Norman's generosity, I now have a replacement for my one Seventeen woofer whose voice coil scrapes when manually pushed to the bottom of it's travel. The replacement woofer came from his Model 17 and looks very close to mine, only differing in that it's surround was treated with a black butyl rather than a clear, and dust cap that may(?) have been treated with the clear as it's not black.

      Strangely, this replacement driver has apparently less midrange than my two originals, I'm guessing maybe 3-4 db down? The bass amplitude is the same however. I'm at a loss to understand why this could be. Any ideas? Mr. Roy, Kent ?   Thanks!

Hey Jessi,

I have worked with both woofers, but don't recall noticing a difference. I never, however, did a direct comparison between the two.

Before assuming there is an actual difference, I would try a couple of things if you haven't already done so:

-listen with the amp channels reversed.

-listen to the woofers without the tweeters connected.

-switch woofers to opposite cabinets.

-remove woofers and compare resistance and inductance.

Roy

[jessiAV]

  hi Roy,

  Thanks for your recommendations 😀 I will try them all, other than the electrical measurements since I've already done those (they measure almost identically). If I discover anything new, I will pass it on here, okay? It's always great to have your insights 😊

[jessiAV]

So after fiddling with these little guys, following Roy's logical methodology, here is what I believe is going on.

    The main take-away is that there is a difference in these woofers, with the black surround version sounding a bit more 'mellow' or if you will, less 'sharp', in their upper range. But it's VERY subtle and I would never have noticed if both weren't next to each other, and both have a very similar signature. Clearly, I'm just being stupid picky.

     FWIW, the damaged woofer measures 14% lower in inductance than the replacement woofer. I wasn't sure if that reflected the slightly melted voice coil or if it was within production tolerances. DC impedance is within .2 ohms.

     My thanks to Mr. Roy and Norman for their wonderful assistance 😀

[jessiAV]

 And I just noticed: The cone material on the woofer with the light colored surround is roughly twice as thick as in the one with the black surround... using my calibrated 😀fingers as a measuring device.

[RoyC]

53 minutes ago, jessiAV said:

 And I just noticed: The cone material on the woofer with the light colored surround is roughly twice as thick as in the one with the black surround... using my calibrated 😀fingers as a measuring device.

Interesting...Variations in cone mass or construction would have a greater impact on response than .2 ohms dcr (which is not very much).

Roy

[Norman Nicolai]

We may finally have our answer!

BTW, can you post photos of the two different woofers, showing all parts of the speaker, including cones, magnets, and surrounds? Over the years I've owned maybe 4 different sets of Seventeens, along with a set of their 4 ohm brother, the Model Twenty. I knew there were different generations of tweeters, some silver metallic, some painted black. I never realized that the woofers varied so much. Just kind of curious about the different appearances of the woofers as well.

Jessi, you may have made a discovery, adding to our knowledge of KLH speakers!

[jessiAV]

Well, the woofers are back in their cabinets and as they have been changed often the wood sealing surface is now pretty worn, so I'm reluctant to remove them again for photos. Below is a pic but it's only of the front.

  I can say that the cone on your spare Seventeen woofer is thinner in cross section than the one's I have, but both magnets are identical and the cone material appears very similar.