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If any of you have looked at my other main post, I'm beginning to restore a pair of Speakerlab K horns and have been asking for advice. Since my new digital multi-meter came in yesterday, I decided to go out to the garage to test my existing drivers and tweeter to check for continuity and measure impedance.

 

Tweeter - K-77-M or equivalent (x1) - PASS (measuring about 6.5 ohms (is that right?))

 

Midrange horn drivers (x2) - EV 1823M - PASS (measuring about 8 ohms each)

 

Woofer - here's where I ran into trouble. One is gone, pulled for some project of @rigma's. The other one has been safely secured in its bass bin since the 70's. When I say secured, I mean SECURED. It was overbuilt in the way of German cars, tanks and aircraft. I believe had these been on the Titanic, you could have pulled them from the sunken wreckage and there's a good chance they would play once drained.

 

I had to remove at least 15 screws that were completely coated in thick silicone and tightened into threaded inserts by scraping them clean, one by one. Then I had to use a razor to cut through even more silicone and get a small pry bar to separate the "access panel" from the bin.

 

That's where I messed up.

 

I should have known. The speaker cable going to the driver had also been still securely soldered to the driver inside, which pulled the little soldering tabs loose from the speaker.

 

Damn.

 

After removing 3 wingnuts, 1 3/4" nut and two wood screws securing the motor board to the cabinet (then prying it loose with said pry bar), the speaker came out.

 

It is a Speakerlab W1500D 4-ohm woofer and seems to be in OK shape (minus my screwing up the connecting tabs). I was able to test it by connecting the multi-meter probes to the little wires coming off the woofer. It does PASS continuity and looks to be reading 4.5 ohms(?) My hands were a little shaky by this point.

 

So, CAN the driver be repaired? Is it WORTH being repaired and finding a similar K-33 or equivalent? How much money did @rigma spend on sealants in 1970-whatever and what is that in today's dollars? These and other questions linger.

 

The line to take shots at me forms to your left. The line for helpful comments, on your right.

 

Thanks!

20200306_173241-COLLAGE.jpg

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Somehow I thought you were going to go with Eminence Kappa 15C woofers?  Or did I misunderstand?

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3 minutes ago, jimjimbo said:

Somehow I thought you were going to go with Eminence Kappa 15C woofers?  Or did I misunderstand?

It's still very much a possibility. Existing woofer functionality and funds will determine what I'm able to do.

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And here I thought you were going to say you jabbed the pry bar through the cone or slit it with the razor. 

 

The terminal pad can be fixed (replaced), but will be a little bit of a PITA. You'd have to drill out that rivet, get a small piece of masonite drill three holes through it, rivet it to the basket, safely and quickly desolder the leads off of the old tabs, screw new ones onto the new piece of masonite and safely and quickly re-solder the leads to the new tabs. Like I said, a PITA. But if funds are tight, you'll suffer through the fix and make it work. 

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If both soldering tabs still have that little piece of wire soldered to them, you could use those little pieces to zip tie the tabs back onto the masonite tab as a temporary fix to keep anything worse from happening. But I'm pretty sure you'll have to buy a pair of 15's, regardless of that tab. If you really just want to get them running, zip tie those tabs, remount that speaker and buy yourself the cheapest 15 you can find. You can always buy better woofers when resources permit, and you can move onto all the other stages of the project, plus you'll be able to use them. These are around 30 bucks.

4 OHM: https://www.ebay.com/itm/15-Raw-DJ-Pro-Audio-Subwoofer-4-Ohm-Sub-Woofer-2-5-KSV-High-Power-voice-coil/303234358532?hash=item469a2d1d04:g:Cp4AAOSwPCFeU-0A

8 OHM: https://www.ebay.com/itm/400-Watt-15-Raw-DJ-Pro-Audio-Replacement-Subwoofer-Sub-Woofer-8-Ohm/392363991768?epid=17022511745&hash=item5b5ab762d8:g:5K0AAOSwmbRd51X4

 

A 4 ohm driver usually measures around 3 ohms (4 ohms is the impedance (A/C resistance), you're measuring the D/C resistance), and an 8 ohm driver can measure around 6 ohms. If your midranges are measuring 8 ohms, they might be very efficient 8 ohms drivers, or very non-efficient 16 ohm drivers.

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I just looked online and found that the 1823M mids were available in 8 ohm, so that's my guess.

 

Is the tweeter measuring 6.5 ohms acceptable? I may check it again.

 

Do I need to get a pair of 8 ohm woofers to match (the Speakerlab one I damaged is a 4 ohm) or does that just get sorted out at the crossover? I'm unclear on this. Do driver impedances need to match or can you use different ones together?

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I'm sorry to hear about all this. 

 

I know I'm spending your money.  I think you should buy some Crites woofers for use on both bass bins and just abandon the salvage effort.  Clean up things.  Make sure you have gasket material between the motor board and the slot.  Check the assembly manual.

 

The guys at Speakerlab were a bit of hippy types and said there is no problem so big that RTV can't solve it.  Comments like that invite sloppiness as you've found out.

 

OTOH my friends who built SKs were very careful craftsmen as I'm sure were many others.

 

WMcD

 

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14 minutes ago, danalog02 said:

I just looked online and found that the 1823M mids were available in 8 ohm, so that's my guess.

 

Is the tweeter measuring 6.5 ohms acceptable? I may check it again.

 

Do I need to get a pair of 8 ohm woofers to match (the Speakerlab one I damaged is a 4 ohm) or does that just get sorted out at the crossover? I'm unclear on this. Do driver impedances need to match or can you use different ones together?

If you buy 8 ohm woofers recommended by k-horn experts on this forum, you should be ok with the crossover recommendations they also make. If you get your own set of 8 ohm woofers that are close matches, then you might have to do some attenuation, which is easily done with the addition of resistors to the crossover. You'll get plenty of help with all that here. With that said: There are several factors, other than size and impedance, that affect how a driver will perform. Since you're going for a k-horn setup, I would without a doubt stick to the info you're gonna be given here. 6.5 ohm for the tweeter is fine. Listening tests will determine the final series of adjustments.

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If you are going to use a crossover designed for a khorn, the proper woofer should be 4 ohm. The slot in the baffle and horn will raise the effective impedane to 8 ohms.

 

The k33 as well as Bob Crites woofers are all 4 ohms.

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