Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Verdons
 
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Default Can you measure Impedance with an Ohm Meter.......

You are correct

"Denny B" wrote in message
...
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







  #2   Report Post  
Damir
 
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Default Can you measure Impedance with an Ohm Meter.......

Yes,you are correct.
Impedance is complex resistance.

Damir


On Wed, 16 Jul 2003 22:59:29 -0600, "Denny B" wrote:

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





--------------
Regards,
Damir
--------------
  #3   Report Post  
John Bachman
 
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Default Can you measure Impedance with an Ohm Meter.......

On Wed, 16 Jul 2003 22:59:29 -0600, "Denny B"
wrote:

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.

Impedance is the algebraic sum of the dc resistance and ac reactance.
An ohmmeter measures only the dc resistance and cannot measure
impedance.

You are correct.

John

  #4   Report Post  
waxhead
 
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Default Can you measure Impedance with an Ohm Meter.......

Further, the impedence will vary across the frequency range of the
speaker. The quoted impedence is a nominal impedence. An 8ohm (nominal
impedence) speaker can quite easily have a coil resistance as low as
6.0ohm.

On Thu, 17 Jul 2003 19:13:42 +1000, Verdons wrote:

You are correct

"Denny B" wrote in message
...
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





  #5   Report Post  
petrus bitbyter
 
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Default Can you measure Impedance with an Ohm Meter.......


"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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  #6   Report Post  
Patch
 
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Default Can you measure Impedance with an Ohm Meter.......


"Denny B" wrote in message
...
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



You are 100% correct.



  #7   Report Post  
jakdedert
 
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Default Can you measure Impedance with an Ohm Meter.......

Not withstanding the below...you can get an 'idea' of the VC impedance with
an ohmeter...it will always be a few ohms below the actual ac impedance.
The frequencies involved are not so high as to make a major difference;
although the readings will not necessarily be the same for two dissimilar 8
ohm speakers (around 6 ohms), or speaker systems.

jak

"waxhead" wrote in message
...
Further, the impedence will vary across the frequency range of the
speaker. The quoted impedence is a nominal impedence. An 8ohm (nominal
impedence) speaker can quite easily have a coil resistance as low as
6.0ohm.

On Thu, 17 Jul 2003 19:13:42 +1000, Verdons wrote:

You are correct

"Denny B" wrote in message
...
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








  #8   Report Post  
Mike Russell
 
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Default Can you measure Impedance with an Ohm Meter.......

jakdedert wrote:
Not withstanding the below...you can get an 'idea' of the VC
impedance with an ohmeter...it will always be a few ohms below the
actual ac impedance. The frequencies involved are not so high as to
make a major difference; although the readings will not necessarily
be the same for two dissimilar 8 ohm speakers (around 6 ohms), or
speaker systems.


I would add that you can measure impedance precisely by driving the speaker
at a particular frequency, and measuring the ac voltage and current with
your VOM..

Which begs another question: will playing normal audio material through a
speaker, and measuring the ac voltage and current match the nominal
impedence reasonably well, say within 10%?

--

Mike Russell
http://www.curvemeister.com
http://www.zocalo.net/~mgr
http://geigy.2y.net


"waxhead" wrote in message
...
Further, the impedence will vary across the frequency range of the
speaker. The quoted impedence is a nominal impedence. An 8ohm
(nominal impedence) speaker can quite easily have a coil resistance
as low as
6.0ohm.

On Thu, 17 Jul 2003 19:13:42 +1000, Verdons wrote:

You are correct

"Denny B" wrote in message
...
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



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RWatson767
 
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Default Can you measure Impedance with an Ohm Meter.......

Mike
Can you measure Impedance with an Ohm Meter


Which begs another question: will playing normal audio material through a
speaker, and measuring the ac voltage and current match the nominal impedence
reasonably well, say within 10%?

We used to measure voice coil and other audio impedance by inserting a low ohm
resistor in series with the load. We did have an idea of the actual impedance.
We onfirmed this by reading the voltage across the resistor. We also checked
the procedure by using actual carbon resistors to "calibrate" the procedure.
Bob AZ
  #10   Report Post  
jakdedert
 
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Default Can you measure Impedance with an Ohm Meter.......

I don't know what your tolerance would be...the way to check accurately is
to run a plot using an audio generator, sweeping from 20 Hz to 20k Hz and
taking an average...or merely using the plot like you see in speaker spec
sheets. Running a few of those compared to your 'quick & dirty' procedure
below will give you your tolerance. White (or pink) noise would be
preferable to 'normal' (just what is 'normal' anyway) program material, as
you will have a consistent measurement.

jak

"RWatson767" wrote in message
...
Mike
Can you measure Impedance with an Ohm Meter


Which begs another question: will playing normal audio material through a
speaker, and measuring the ac voltage and current match the nominal

impedence
reasonably well, say within 10%?

We used to measure voice coil and other audio impedance by inserting a low

ohm
resistor in series with the load. We did have an idea of the actual

impedance.
We onfirmed this by reading the voltage across the resistor. We also

checked
the procedure by using actual carbon resistors to "calibrate" the

procedure.
Bob AZ




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