What is impedance matching?

To match impedance means to take a group of speakers (usually more than three pairs) and forcing the combined impedance of the speakers to maintain an even 8 ohm level (or another number if required). On average, most home speakers have an impedance of 8 ohms. An Ohm unit measures the level of resistance—the resistance in a speaker varies based on the frequency it is using. A stereo receiver can operate speakers with total impedance of 4 ohms or more, depending on the quality of the receiver. By impedance matching the math is taken care of for you and gives your amplifier a steady 8 Ohm load. Impedance matching can be easily achieved by adding a speaker selector or impedance matching volume controls to your new sound system.

There’s a formula you can use to calculate the total impedance of your system when adding your speakers together in a parallel fashion (meaning adding + to +, and – to -). Every time you add parallel sets of speakers to a system, your impedance drops.

Here are some examples of common numbers:

2 – 8 ohm speakers together in parallel = 4 ohms

3 – 8 ohm speakers together in parallel = 2.67 ohms

4 – 8 ohm speakers together in parallel = 2 ohms

The formula to calculate this is as follows:

For a parallel circuit, the total Impedance (r) is given by the inverse of the sum of the inverses:

Parallel circuit graph

Therefore, by ‘impedance matching’, the math is taken care of for you and gives your amplifier a steady 8 ohm load which is ideal for your amplifier (and simpler for those of us who see only hieroglyphics when we look at that formula).

Impedance matching can be easily achieved by adding a speaker selector or impedance matching volume controls to your new sound system.

Customer Comments:

Still confused. Should I set my HD 650 speakers to 8 ohms or 4 ohms.
Inwallstore: Set them at 8 ohms. The 4 ohms setting is for knowledgable technicians with particular circuity needs. This article refers to the process of “needing” impedance matching and what’s going on for whole house audio.

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