Welcome to Speaker Impedance. This website calculates the nominal impedance created with different combinations of wiring speakers together. Remember calculations are only to be used as a guide; in reality, the impedance will vary with frequency and more factors such as coil temperature come into play.
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The ohm. It's a unit. It's symbol: Ω It's the unit of Impedance. So what's impedance? It's a measure of something that opposes/restricts the flow of current in an electrical circuit. In this case, that something is a speaker.
So why should you care? If your mixing speakers together; plugging more than one into the same channel on an amplifier, or maybe you are building your own cabinets and connecting cones together, it is definitely worth paying attention to. If you don't then your amp could break/explode/catch fire/cease to work/implode/end the world. Your speakers may not be looking too healthy either.
Resistors in Parallel & Series
There are a few facts to know about connecting resistors in parallel and series.
Resistors in Series are simple; their values add up. Total Resistance = R1 + R2 + R3 etc..
Resistors in parallel are a little tricky. Their reciprocals add up.
So 1/Total Resistance = 1/R1 + 1/R2 + 1/R3 etc..
How does this relate to speakers? Speakers are a resistance in a circuit. (But they make more noise than a resistor, and have magnets, diaphragms, cones...
Basics of Impedance If you think of a basic electrial circuit involving a bulb, there is a power source and a light bulb. There is a flow of electrons in the circuit; this is known as the current.
The power source is providing voltage that effectivley pushes the elctrons round the circuit. The bulb is the resistance in the circuit. This takes the current and turns it into light and a bit of heat energy. This light bulb or resistance impedes the current flow in the circuit. If you connect another light bulb in a series connection, then the brightness will half because the voltage is being shared between the two bulbs. However, if you connect in a parallel way, the brightness stays the same in both bulbs, as does the voltage. (It's the current that changes - halves in this case)
Now convert this series/parallel fact to speakers. If you connect them in series, the voltage is shared between them. But in Parallel, the voltage going to them stays the same. BUT, there is more current needed to sustain the two bulbs, and the power source - in this case - them amplifier needs to work harder.
There is a relationship between the voltage, current, and resistance; Known as Ohm's Law. It states that Voltage = Current x Resistance or V = IR (I is symbol for current.. don't ask..
Resistance in AC circuits (such as an audio system) is called Impedance. (Although you can't swap the terms because Impedance contains resistance and reactance - reactance varies with frequency - although can be ignored in simply calculating impedance of simple speaker setups.) So, you have an equation to work out the impedance. Simple. You could use this to calculate the load impedance of the amplifier. R = V/I - Which is what the calculator on this website will enable you to do.
Click here to have a look at a list of some equations used on thie website.