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How to work out impedance

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2.9K views 7 replies 4 participants last post by  Krazeedude  
#1 ·
You may need a calculator if you aren't good with fractions.

You work out the parallel parts first, by finding the reciprocal (one divided by the number) of all the components' reciprocals added together. EG, I have two 4ohm subs, wired in series. .
1/(total resistance) = (1/R1) + (1/R2) + (1/R3)...
1/(total resistance) = 1/4 + 1/4
1/(total resistance) = .25 + .25
1/(total resistance) = .5
Total resistance = 2 ohms, so I get a two ohm load

Then you work out the series part, by adding the impedances together. So for 3 subs, 4ohms each, two in parallel and one in series.
I'd have 1/4 + 1/4 = 1/2, so 2ohms + 4ohms gives a 6 ohm load.

(found this image and text with sums it up nicely)
Image

Parallel components:

Total parallel resistance = (R1*R2)/(R1+R2)
Total parallel resistance = (4*8)/(4+8)
Total parallel resistance = 32/12
Total parallel resistance = 2.67 ohms

Total parallel plus Series:

Total resistance = R1 + R2
Total resistance = 4 + 2.67
Total resistance = 6.67 ohms total

Further more, if a component is parallel to a series, the series component is worked out first, followed by the parallel and then any other series. But that's just good maths. Just made this quickly in paint to explain what I mean:

Image


Think of it like rules to working out an equation, but instead of BIDMAS, it's paralleled series, parallel, then series.
 
#4 ·
Really impressed with that Alex. Really impressed.
I hold my hands up, I am useless with fractions so impedance has always been a calculator moment for me.

Any chance we can have this stickied?
 
#7 ·
nice bit of info but hate to say but I am feeling pedantic, impedance is the wrong term to use in this instance, Impedance is resistance offered by an electric circuit or component, with both a real and imaginary part (thus, a complex entity). However, not all components' impedance is represented by a complex number. For example, the resistance offered by a resistor consists of only the real part, and no imaginary part. In most texts, this is referred to as RESISTANCE, and not impedance and is denoted by Ohms.
Other components, like capacitors have resistance that consists of both a real and imaginary part. So, this is referred to as IMPEDANCE and not resistance.


the title just needs changing, I will be quiet now...
 
#8 · (Edited)
Impedance may not be the correct term, however it is what is used. 'Redtop' isn't 100% correct, but to those who don't know, it means the same as the correct term, and is what they'll look for.

If someone is setting up a system, they want to find the 'impedance' and so will look here and find their answer. They may not think that resistance is what they need, and this will show up under searches for impedance, so personally, I believe the title should stay ;)

Where do the imaginary parts come in? I've studied complex numbers, but not in this context.