"Denny B" schreef in bericht
...
Is it possible to measure Impedance with an ohm meter.
For example can you measure the Impedance of a 4 ohm
car speaker with an ohm meter?

When I tell people they cannot measure Impedance with an
ohm meter, you need an impedance meter and the impedance
must be measured with the speaker in operation, with a signal generator
supplying a fixed frequency, this always leads to disagreements
with the person who demands an ohm meter to measure what he calls
Impedance, when I tell him an ohm meter can only measure the resistance
of the coil there is always disagreement.

I tell them Impedance is AC resistance and what they measure
with an ohm meter is DC resistance. Disagreement here again.

Will somebody take me up on this and clarify the situation.

Thanks in advance
Denny B



Denny,

It's an understandable misunderstanding. The resistance of an conventional
speaker is some Ohms. It's an aircoil with only some microhenry of
selfinduction and only some pF or less capacity. So if you measure the
resistance you can easily distinguish between a 4Ohm and an 8Ohm speaker for
instance. As a rule of thumb you may say that the resistance and the
impedance will be almost the same.

The real story of measuring impedances you described already. (Although the
practice of this measurements is more complicated.) More expensive speakers
often come with a impedance characteristic measured under well defined
circumstances. You will find impedance depends on frequency (Amongst other
things). If you do the same measurements in changed circumstances, another
box for instance, you will find other results.

But.... There are a lot of people out there knowing everything better. They
heard about the rule of thumb, take it for the whole truth and never ever
realize what impedance means anyhow. I consider discussions with this people
useless. Their knowledge of electricity and electronics is below the level
needed for exchanging arguments. As they want neither listen nor learn
you're only waisting your time.

pieter






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