Can you measure Impedance with an Ohm Meter..

Impedance is the total opposition to current flow -- a combination of both resistance AND reactance (capacitive and inductive). As you suggest, impedance does change with frequency, except in purely resistive networks.

I just did a quick Google and found the following hit, which might help further:

You are correct in stating that you cannot measure impedance using an ohm meter.

This is sort of a "No Brainer", since impedance is typically frequency dependent and an ohm meter measures only dc resistance.

Harry C.

In article , snipped-for-privacy@yahoo.com mentioned...

You can measure the real part of the impedance, since the impedance is going to be _at_least_ as much as the resistance.

But then the speaker may measure 4 ohms at 1kHz, but some widely differing impedance at another freq. Especially if it has a xover network.

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You can't even do that. As someone else posted, consider the case of a

1/4-wave, end driven antenna.

Harry C.

In article , snipped-for-privacy@yahoo.com mentioned...

The OP asked a Q about measuring a speaker and I'm still referring to that context. I didn't think that we were discussing RF radiators.

Obviously one has to use good judgment when making the measurement. If you're measuring a coil in parallel with a resistance, the coil's DC resistance will predominate in the resistance measurement. And of course if you're measuring a coil, cap, and resistor in series, the resistance is going to measure infinite because the cap is blocking the DC. So obviously in these cases, the resistance measurement is not going to be valid.

If we're just talking about speakers, there is the possibility that the speaker has a crossover network between it and the terminals. And of course that can throw a whole new set of variables into the resistance measurement.

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You may want to go back and refresh your memory about the OP's question. It was: "Is it possible to measure Impedance with an ohm meter."

The answere is of course not, and it doesn't depend on if you want to measure the impedance of an audio speaker or an antenna system. The identical concepts and rules apply.

The OP's question was not about resistance, it was about impedance.

Rather than debate the point endlessly, I strongly suggest that you go crack an EE 101 or AC Circuits 101 text and learn about impedance. You'll find that it is a complex quantity containing both a real and an imaginary component, neither one of which can be measured using a d.c. ohm meter.

As an example, take a conventional 10-Watt, 8-Ohm speaker and compare its d.c. resistance to that of a 100-Watt, 8-Ohm speaker. The d.c. resistance may vary as much as 20 to 1, which tells you absolutely nothing about the speakers' impedances.

If you want to measure the impedance of anything, be it a speaker or an antenna, you have to employ a.c. measurements. For speakers these techniques are quite simple, for antennas more complex. The bottom line being, impedance is definitely not d.c. resistance, nor does a d.c. resistance measurment tell you anything about impedance.

Harry C.

In article , snipped-for-privacy@yahoo.com mentioned...

I have already said that previously. The crossover network would add other elements to the speaker and the measurement would be open circuit if there was a cap in series.

I don't want to hear your put-downs. I want to hear your explanation on how I "cannot" as you say, make a DC resistance of a speaker that has no other components connected to it, as I say in the following paragraph, and which, as you say, 'hasn't sunk in'.

I don't care. And I don't need to be told that the way it actually is is anything different than how ai perceive it. Stop being condescending and treat me like an adult.

So you're telling everyone, not just me, that one *cannot* deduce that if a speaker, by itself, measures 5 or 6 ohms DC resistance, as _you_ say above, that that very same speaker has _at_least_ an impedance of

5 ohms, or more?

I think we would all really like to hear your answer to this, Mr EE.

And what about yourself? Perhaps you've discovered a new physical property, negative impedance, that will subtract from DC resistance?

[chest thumping and condescending insults about intelligence snipped]

Next stop: The Twilight Zone.

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Obviously that's not what I posted. Deterermination or measurement of a speaker impedance provides a specific value. If I measure the d.c. resistance of a speaker voice coil be to 1.2-Ohms, it tells ABSOLUTELY NOTHING about the impedance of the speaker.

You're assuming that if a speaker has a restance of say N-Ohms, it has an impedance greater than N-Ohms. In most cases this is true, but not always, plus it doesn't provide the value of the speaker's impedance hence you haven't measured the speaker impedance and still don't know its value. (Note also that there are exceptional cases where the speaker resistance will be greater than its imedance, but I'm sure you already know this.)

It is also quite possible for an 8-Ohm speaker to have a voice coil resistance of 0.5-Ohm, and a 3.2-Ohm speaker to have a voice coil resistance of 2.5-Ohms, and here again your Ohm meter reading will tell you nothing about impedance.

Again this is pretty basic stuff, and every competent electroincs technician is familiar with the difference between resistance and impedance measurements.

Harry C.

Watson, deducing incorrectly, I believe, posted in part:

In article , snipped-for-privacy@yahoo.com mentioned...

I see that now you're backpedaling, you've gone from "Again, you cannot measure the real part of impedance with a d.c. ohm meter!" (your exact words), to "In most cases this is true, but not always".

As I stated before, and you seem to have ignored, the measurement does not have to give an exact value. I also stated that the measurement had to be of just a simple speaker, not a speaker with a crossover or capacitor, etc.

I have NOT claimed that the measurement would give the exact impedance of the speaker. And you keep saying that "your Ohm meter reading will tell you nothing about impedance."

You also claim that "(Note also that there are exceptional cases where the speaker resistance will be greater than its imedance, but I'm sure you already know this.)"

I have already limited the measurement to a simple speaker, without any other components, such as a capacitor. I'm talking about only a simple inductance and resistance.

You're telling me that the impedance of this speaker could be less than its DC resistance. Could you explain how you come to this conclusion?

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ROFL!!!!! Clueless Dork!

Then it obviously isn't a measurement.

Impedance is impedance, and quite different from resistance.

It obviously won't! Do you work at being a Clueless Dork, or does it come natural to you? :-)

Now where do you suppose the distributed capacitance vanished?

AC Circuits 101, of course. Ever hear about speakers without a moving (dynamic) voice coil? How about headphones, electrostatic tweeters, etc., etc., etc. Ever wonder what happens to the impedance of a speaker as it approaches its resonant frequency? No, I suppose that the answer is obviously not.

The below is worth repeating:

It's been fun playing, but I'm growing weary of trying to educate someone in the basics who is evidently resistant to opening a textbook on basic a.c. circuits and comprehending its content.

Harry C.

I asked some questions, expected a simple explanation, and got called a "clueless dork." He has graduated from degree waving to name calling. I would settle for the simple explanation of what's wrong with my assumptions, but I won't settle for being insulted. Again.

In article , snipped-for-privacy@yahoo.com mentioned...

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Correct. And none of those is still following your rants.

Like I said, none of those will realize, even though your sight is totally correct.

False beliefs are not corrected by reading flame wars. Let those who want "measure impedance" with an ohm meter and let them find out the hard way. Pro's won't and know why, they don't need your flame war either.

Whatever. EOT for me, fup2p, score adjusted. Michael

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