Designing your home music system is generally a very easy task, there are only a few things to look out for and one of them is impedance. This is a brief guide to help you understand the basics.




"The ohm (symbol: Ω) is the SI derived unit of electrical resistance, named after German physicist Georg Simon Ohm"

Ohms are the units used to measure impedance, which is basically something that restricts the flow of current in a circuit... in this case, your speaker is that resistor.


What You're Trying To Avoid


Basically, if you get this wrong you'll risk damage or destruction to your amplifier and/or your speakers.... not ideal!


Speaker Resistance


The most important thing to start with is to say that there are a lot of different makes and models of speakers out there, and impedance varies greatly. The most commonly found is 8Ω but you'll need to check when you're designing and buying your system to ensure it meets all your requirements. The following diagrams show some examples of how wiring types and speaker impedance works. Take note that I've included the speaker impedance next to each speaker as an example only.


Let's show you how resistors work...


Resistors in SERIES - Add them together, so two 4Ω speakers connected in series will create a resistance to the amplifier of 8Ω

Resistors in PARALLEL - Divide by two! So two 8Ω speakers connected in parallel will create a resistance to the amplifier of 4Ω Once you connect more than 2 speakers this gets a bit more complicated. See further in the guide.


Speakers In Series

Speaker Impedance In Series

How To Wire Speakers In Series

As you can see, two 4Ω speakers connected in series (amplifer + to first speaker +, first speaker - to second speaker +, second speaker - to amplifier -) will mean the two speakers resistances are added together to create 8Ω

Another thing to note with this method is the fact that the higher the impedance, the lower the sound output. So whilst your amplifier might be able to handle 16Ω per channel, wiring 4 speakers in series may produce poor sound output.



Most amplifiers aren't rated at more than 16Ω please ensure you check your amplifier before you get carried away wiring speakers around your home!








Speakers In Parallel


 Speakers Wired In Parallel

Speakers Wired In Parallel

Wiring speakers in parallel has the opposite affect, now instead of adding the resistances together you're going to start halving them. 

When you get past two speakers the calculations get a bit more complicated, you're not simply going to keep halving. Instead you multiply the impedances of each speaker and then divide the result by the sum of the speakers’ impedances.

Example: You have an amp rated at 4-ohm power (100 watts x 2), and is also 2-ohm stable.

Zt = (Za x Zb)/(Za + Zb)  Zt = (4x4)/(4+4)
Zt = 16/8
Zt = 2 ohms 



Most amplifiers aren't rated at less than 4Ω please ensure you check your amplifier.





Speaker Switches


Speaker switches allow you to connect multiple sets of speakers to one amplifier in a safe and convienient manner. You simply wire the speakers to the switch and then connect the amplifier via speaker cable. The speaker switch will have a safety feature which means the amplifier will always see the correct amount of resistance to avoid damage.

You'll also get the added benefit of being able to turn sets of speakers on or off which could be useful for some applications such as kitchens and dining rooms. 




Speaker impedance can be complicated, but for the majority of home speaker systems you'll be using no more than two pairs of speakers.

If in doubt use an impedance matching speaker switch.


Handy Tools


Impedance Calculating Tool