D-140 8 0hm resistance ???

David Mullis · Post by **David Mullis** » 30 Jan 2003 10:11 am

The other day I measured across the leads of the D-140 I'm trying to trade and I noticed the reading was alot higher than it should have been. (like into the mega ohms) Where before it had been reading close to 8. However, the speaker appears to be functioning fine because I have it in my session 400 now. What's up with that? I just want to make sure there is nothing wrong with this thing before I trade it off. I don't want anyone to end up with a speaker that may have a problem. What do y'all think?

thanks
David

Donny Hinson · Post by **Donny Hinson** » 31 Jan 2003 2:25 am

What you describe is just about impossible...unless the problem is intermittent. Of course, you could have just made a mistake when you measured.

Rich Paton · Post by **Rich Paton** » 31 Jan 2003 2:53 am

Donny is probably right. A while back I was horsetrading for a pair of pre-owned JBL 2118 mid drivers and found one locally. Measuring it at home with a Fluke 79 Series II digital multimeter, I got no indication of contiuity at all, Now, I've been into electronics since I first encountered ham radio in 1966, and felt like an idiot when I took it back the seller complaining about this bogus driver. He whipped out an analog multimeter, on which the voice coil measured good. But it had been re-coned as a 16 ohm unit and it was supposed to have been an 8 ohm, so the whole feal was down the tubes anyway.
Moral of the story is...I've seen all sorts of weird symptoms & indications with electronic gear, and this was just one more for the book. Try another meter, test lesds, DVM battery, etc.
"It's always something!"
BTW, I forgot to mention this...on a good JBL 8 ohm driver, you should see around 6 ohms or so resistance on a meter. The remaining impedance components making it "8" ohms vary in value with the applied frequency(s) and can only be measued with an "impedance bridge" and/or certain other types of slightly more exotic test gear.
The ULTIMATE JBL / Altec Lansing web site is: http://www.audioheritage.org/ [This message was edited by Rich Paton on 31 January 2003 at 03:06 AM.]

David Mullis · Post by **David Mullis** » 31 Jan 2003 5:54 am

Thanks guy's. I did try another meter. Both digital. Just for grins I'll check it again later today. I wasn't expecting it to be dead on 8 ohms, but definitely not into the mega ohms!

I'll let y'all know what I come up with.

thanks
David

David Mullis · Post by **David Mullis** » 31 Jan 2003 6:01 am

OK, I just checked it again. and it read 6 ohms. Go figure, the only thing different between the last time I checked it and this time was, before, it was sitting on top of my work bench and I measured across the terminals on the speaker, this time, the speaker was mounted in my session and instead of measuring across the terminals of the speaker itself, I just pulled the 1/4 plug out of the speaker jack and measured it. All I can figure is maybe I just wasn't getting a good connection by merely touching the test leads to the terminals? Thanks for the help!

Take Care
David

Ken Fox · Post by **Ken Fox** » 31 Jan 2003 8:17 am

David, I have done that same thing with a meter. Sometimes there is enough oxidation at the terminal or solder point to not get a reading.
Here is another note of interest, perhaps! An 8 ohm driver will not read 8 ohms on a DC ohmmeter. It will on an impedance meter. A JBL 16 ohm speaker I purchased recently read just over 8 ohms on a meter and 16 ohms with my impedance meter. The impedance meter injects a tone at around 700hz or higher (depends on the model, brand). The speakers true impedance (resistance to an alternating current) is then measured and displayed. A speaker's impedance is not a true constant, it varies somewhat with the signal frequency. [This message was edited by Ken Fox on 31 January 2003 at 08:20 AM.]