The Inverse Dynamics of Flow

When matching speaker cabinets to use with your amplifier, there are a number specifications to consider (power handling, frequency response, sensitivity, etc). While some specs are straight forward, others can be confusing, especially when we talk about impedance which can vary depending on your setup.

Impedance is a measure of the resistance to the current flow through an electric circuit when voltage is applied. It is measure in ohms and is designated by the greek letter omega (Ω). Speaker impedance refers to the resistance a speaker places on the current supplied by an amplifier, or the load a speaker places on an amplifier. It’s essential for amplifiers, receivers, or speakers connected to each other because mismatched impedance can cause distortion as well as damage to the components.

The signal that drives a speaker is the electrical equivalent of the audio input signal. The actual impedance of a speaker is not constant across all frequencies, so for convenience, rather than provide the impedance for every frequency, we use the term “nominal impedance”, which refers to the impedance that a speaker presents to an amplifier at a reference frequency. Most speakers are rated by at 4Ω, 6Ω, 8Ω or 16Ω.

A speaker with higher impedance will limit the signal flow. The lower the impedance of a speaker, the more easily the current will flow, and more power will be developed by the amplifier. For example, a 4Ω speaker will extract more power from your amplifier than an 8 ohm speaker.

To help visual the concept, let’s use the analogy of a dam. A dam is a barrier that stops or restricts the flow of water in a river or stream.

In this circuit, the water pressure acts as the voltage, the dam gates can be the impedance and the flow of water is the current. 

When the gates are closed, they act as a barrier that oppose the flow of water into the river. This represents very high impedance, which in a circuit will allow very little or no current to flow. 

Once the the gates start to open, the water begins to flow. This represents a lower impedance and an increased current flow. There is an inverse relationship between the current and the impedance. This is called Ohm’s law and is represented with the formula: Impedance = Voltage / Current

Most amplifiers are designed for a speaker load impedance of 4–16 ohms. This means the minimum speaker impedance is 4Ω. Therefore if you connect a speaker with a rated impedance of 4Ω, 6Ω, 8Ω or 16Ω, the amplifier will function without any issue. If you connect a speaker with an impedance lower than the rating of the amplifier’s output, the amplifier can overheat and damage the power output section.It is important to learn how to connect multiple speaker cabinets safely without damaging the speakers or the amplifier in this way.  Let’s look at some examples of different speaker configurations that can be used to connect multiple speakers to a single amplifier channel.

Series Wiring

When speaker are wired in series, it means the speakers are daisy chained. Their total impedance can be found by simply adding the nominal impedance of each speaker together.  Two 8 ohm speakers in series present a 16 ohm load to the amplifier. To wire speakers in series, connect the positive terminal of the amplifier to the positive terminal of the first speaker. Then, connect the negative terminal of the first speaker to the positive terminal of the next speaker. The negative terminal of the last speaker will connect to the negative terminal of the amplifier, completing the series circuit.

Parallel Wiring

Typically, amplifier speaker output jacks and speaker cabinet input jacks are parallel connections, and will follow the rules described in this section. When speakers are connected in parallel, the impedance is reduced. The formula to calculate the total impedance of your speaker system is:

Rt = 1/(1/R1 + 1/R2 + 1/R3 + … 1/Rn)
Where “R” is the impedance of a speaker cabinet

To wire speakers in parallel, connect the positive terminal of the amplifier to the positive terminal on each speaker. Then, connect the negative terminal of the amplifier to the negative terminal on each speaker.

You must be careful when connecting speakers in parallel to an amplifier. The impedance can quickly fall below safe levels. This is especially true when connecting speakers in parallel to a bridged amplifier. When choosing speakers, make sure that they can match or exceed the output power of the amplifier, or you can damage the speakers.

Series/Parallel Wiring

There are times when you can use a combination of both series and parallel wiring to get the optimal impedance for your amplifier. This can be thought of connecting multiple sets of speakers wired in series connected in parallel. This type of wiring can be a bit harder to calculate, so we are going to assume an even number of the speakers with all of the same impedance to make this easier. You will have to have a minimum of 4 speakers to use this method. If all four speakers have the same impedance, with series-parallel wiring, the final impedance will be the same as the impedance of a single speaker. You will simply series two sets of two speakers and then wire one group of two speakers in parallel with the other group of two speakers.

So, as you make decisions on building your audio system, you must take note of operating range your amplifier is designed for, and how you are wiring all of the components together. Taking the time to determine your speaker system’s impedance can be the difference between an optimized sound system and one that is on the edge of disaster. Hopefully this article helped you understand why impedance is important and how to calculate impedance based on different wiring configurations.