What is the point of an impedance curve ?? - diyAudio
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Old 10th November 2012, 03:51 PM   #1
aarvin2 is offline aarvin2  Mauritius
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Default What is the point of an impedance curve ??

HI guys I have searched everywhere but can't find any straight forward explanation about how the information found in an impedance curve should be interpreted. I know that it peaks at Fs and generally rises as we go up in the frequency range but what does it mean??

What is the use of the impedance curve?

In what way can it affect the sound of your speaker ?

How does a good amplifier react to this impedance curve and what sonic anomalies can happen ??

Why is the impedance curve important ??

What is the relationship between the impedance curve and the sound or the way the speaker reacts ?? Does impedance affect the transient speed ??

Thanks for your time guys
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Old 10th November 2012, 04:10 PM   #2
AndrewT is offline AndrewT  Scotland
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The picture does not affect the sound.
The picture lets the designer see what the driver does in response to a swept sinewave.
A knowledgeable designer can infer a lot from the picture, but he/she will usually want more. A phase plot and frequency response plot along with the impedance plot are probably the minimum he will be looking at to determine if he/she wants to use that driver or keep looking for another candidate.

I suspect, the designer will want to get his/her hands on a sample before committing to a design. Then it's down to development of the filters to gets the best out of that driver.

I know I have told you nothing, but I think the point I'm making is that one needs quite a bit of skill to really use those plots.
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Old 10th November 2012, 04:13 PM   #3
aarvin2 is offline aarvin2  Mauritius
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Quote:
Originally Posted by AndrewT View Post
The picture does not affect the sound.
The picture lets the designer see what the driver does in response to a swept sinewave.
A knowledgeable designer can infer a lot from the picture, but he/she will usually want more. A phase plot and frequency response plot along with the impedance plot are probably the minimum he will be looking at to determine if he/she wants to use that driver or keep looking for another candidate.

I suspect, the designer will want to get his/her hands on a sample before committing to a design. Then it's down to development of the filters to gets the best out of that driver.

I know I have told you nothing, but I think the point I'm making is that one needs quite a bit of skill to really use those plots.
Well, you have to know what those curves are in order to use your skills to do whatever you want.

could anyone can answer my questions please ?
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Old 10th November 2012, 04:24 PM   #4
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It's always referred to the amplifier, as it represents its load .
As you know -and Andrew knows it better - the impedance
varies with frequency....and in AC phase is very important because
when giving power to the load the amplifier works with voltage i.e.
it tries to maintain it ( trough the supply rails ) and when driven hard
the current demand may cause phase rotation that may cause overload
to the power devices ----- Let's go to school
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Old 10th November 2012, 04:31 PM   #5
RK1 is offline RK1
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The impedance curves are very important because:
- You read with their resonant frequency speaker,
- Selects the filter cutoff frequency,
- Adjusted increase in impedance due to inductance coil speaker for increasing frequency,
The more wavy characteristic impedance of the more difficult to match the appropriate amplifier. It is commonly said that the columns are difficult to drive.
Have a nice day
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Old 10th November 2012, 04:34 PM   #6
AndrewT is offline AndrewT  Scotland
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The questions are posed in Loudspeakers, not in Amplifiers.

How would a loudspeaker design use that curve?
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Old 10th November 2012, 04:46 PM   #7
RK1 is offline RK1
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crossover design
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Old 10th November 2012, 04:47 PM   #8
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the impedance curve will indicate the phase at any particular frequency. this is important to help you select crossover components based on phase as well as resistance.

also, small little wiggles in the impedance curve indicate resonances in the speaker itself or cabinet reflections.
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Old 10th November 2012, 04:48 PM   #9
aarvin2 is offline aarvin2  Mauritius
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Could anyone answer my questions please ? they were kind of precise I think

Thanks again in advance
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Old 10th November 2012, 04:48 PM   #10
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Quote:
Originally Posted by AndrewT View Post
The questions are posed in Loudspeakers, not in Amplifiers.

How would a loudspeaker design use that curve?
It is in the sub forum 'fullrange' , so it is quite meaningless ( the Imp-plot)
It is when there are more drivers connected thru a crossover network
that it has to be carefully studied . For example , a solid state amplifier
which has a lowish damping factor compared to a vacuum tube equipped one,
would guarantee a more stable response in all the audio spectrum.
In a tube amplifier, where DF is dictated by transformer's output impedance,
the current and voltage would 'follow' the impedance curve , causing peaks
and dips in the frequency response -not linear.
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