Radio Shack multi meter battery powered?

[djlivex]

I have loaded and wired my T24 double BP102 (4Ohm) loaded and I already installed the Neutrik NL2 female jack in the back of the cab. I wan to read the ohm on the multi meter it is a small red box do not know how to use it with the sub loaded should'nt I be reading 10 ohms since it is series wired I get a reading of 1 set at 200 ohm which is the 1st notch on the meter? I am also connecting on the female jack the lead wires from the multi meter? Thanks for the help!

[Tom Smit]

By the sounds of things, you have the BP102 (4 ohm) wired in parallel. If the nominal Re of one driver is 4, then the total Re of both drivers would be two. Therefore, your meter is reading pretty close.
But, you were thinking 10 ohm. This may be with an 8 ohm driver since the horn add 2 ohms impedance. Remember, the voice coil resistance...is an impedance, and, the air load in front of the moving cone is an impedance. Two different things. Resistance is impedance, but impedance is not resistance necessarily.

[J_Dunavin]

Yes. You won't see the 10ohms on your meter, but your amp will react as it were a 10ohm load when playing.

[sine143]

only if he has series wired his 2 4 ohm bp102s.... else it will react like a 4 ohm box (2 ohm driver load)

[J_Dunavin]

Yup.

[djlivex]

Thanks guys for the reply the T24 is dual loaded 4 ohm BP102 wired series, even if I don't touch the metal pieces inside the connector it still reads 1 on the selector it is set at 200 ohm since it is the first notch on the meter range. So it should read something if I move it to on position on the meter?

[Hackomatic]

What does it read if you short the two probes together?
I'm trying to figure if you might have a short or an open . . .

[djlivex]

If I touch the two probes together it reads 103.3 then goes to 1 then 15.0 then back to 1, 89.9 then to 1? I connect back to the metal parts of the female NL2 nothing? Thanks!

[djlivex]

I touched one woofers -/+ and it reads 4.3 ohm, is the wiring wrong? Thanks!

[Hackomatic]

If I touch the two probes together it reads 103.3 then goes to 1 then 15.0 then back to 1, 89.9 then to 1? I connect back to the metal parts of the female NL2 nothing? Thanks!

Something is amok with yer meter. Does it have a fresh battery (batteries) ?

[djlivex]

Sorry Hackomatic I was touching the wrong metal on the body of the NL2 female it now reads 7.9 ohm, but should n't it read 10 ohm because of the added 2 from air load I still have to put the access panel and the left side BB piece? Thanks!

[sine143]

a multi meter does not measure impedance. it measures RE. your multimeter has no way of knowing what type of enclosure the drivers are in.

[Grant Bunter]

Here we go, with actual V nominal impedance.

As sine143 has rightly pointed out, you can't measure additional impedance from the cab with your multi meter. After your mesuring, you can add 2 ohms for the cab though, to work out your cab loading and consequent amplifier requirements. (edit: even then, some sources say you need to study impedance charts for drivers because a large percentage of your drivers impedance across the chart will be below amplifier impedance handling capability when you connect more than one cab per channel)

The nominal impedance (the target for a drivers impedance at the design stage) rarely = the actual impedance.

So for the BP 102 "8" ohm, the Re or DC resistance is measured by Eminence as 5.59 ohms.
So 2 x BP102 8 ohms in parallel should measure close to 2.8 ohms and if wired in series, 11 ohms.

The Re for the BP102-"4" is measured by Eminence at 2.7 ohms.
For that driver, 2 in parallel should be 1.35 ohms and if wired in series, 5.4ohms.

There will be variations from batch to batch, but the figures above are about what you would expect to see measuring drivers in cab...

[djlivex]

So as I posted before just checked again it reads 7.9 then 7.4 and both woofers are 4 ohm out of the box X 2 series wired? Am I doing something wrong since Grant says it should be 5.4 ohms??? Thanks!

[Grant Bunter]

So as I posted before just checked again it reads 7.9 then 7.4 and both woofers are 4 ohm out of the box X 2 series wired? Am I doing something wrong since Grant says it should be 5.4 ohms??? Thanks!

Nah don't sweat it mate!

As I said, there will be manufacturing variance batch to batch from Eminence, and the reading you get at the speakon would be different to the reading from one driver to another.
You've added wire from the speakon to the driver chamber, and back to the speakon. If your sepakons are way down the bottom of the cab compared to the driver chamber, that wire adds to resistance as well.

What you should have done if you were really concerned with a result was to measure each driver straight out of the box before installing, and add them up.
If it didn't measure much the same when the cab was finished, then there would be a problem somewhere...