Audio lovers around the world, whether it be musicians, audio engineers, or just your casual home music buff will have come across something called impedance but possibly have not realized its importance in audio. This is especially true when it comes to hooking up equipment that has different impedance values. A common mismatch is hooking up a 4-ohm amplifier to 8-ohm speakers.

Hooking up an amplifier to a set of speakers usually requires matching the impedance of the two devices in order for proper sound to be reproduced. An amp is typically rated at either 2 or 4 ohms while most speakers are rated at 6 or 8 ohms. However, there are many times when the audio equipment we have do not have impedances that match. What can we do in situations like this?

The short answer to whether 8-ohm speakers can be hooked up to a 4-ohm amplifier, is yes, by wiring the speakers in parallel to the amp but with some caveats. If you want a longer explanation, then please read on.

Ohms, Resistance, and Impedance

In the simplest terms, an ohm is an SI-derived unit of measurement that represents how much voltage or current can pass through a circuit. It actually refers to electrical resistance in the circuit.

An impedance, on the other hand, is a complex term used to describe what kind of resistance exists in an alternating current (AC) circuit. Impedance can be used to represent everything that resists current in an AC circuit like capacitance, inductance, or sometimes even the physical resistance of a material.

The term impedance is associated with speakers as it represents the speaker's ability to handle electric signals that range in frequency and amplitude. It is important to know the speaker's impedance value so that you don't overload the circuitry and fry components.

4 Ohm and 8 Ohm

To determine what the difference is between 4 ohm and 8 ohms we need to look at the circuit from an electrical resistance point of view. 4 ohm and 8-ohm speakers are both low impedance speakers, which means they don't require much power to produce sound. However, 4 ohm is 4 times less than 8 ohms so 4 ohms will allow a 4 times increase in current flow and 4 times more voltage than 8ohms when exposed to the same amount of power (watts).

So when we have an amplifier impedance that is 4 ohm and a speaker impedance that is 8 ohm it is on the face of it a mismatch, but thankfully there are things that can be done to solve this problem.

Impedance Matching

This leads us nicely to discuss the concept of impedance matching. We know already that impedance is a measure of the amount of resistance in an AC circuit. The impedance of a device is the total opposition to flow that is presented to a current by a load (amplifier signal).

It is a combination of two components: inductive reactance and capacitive reactance. To match impedances, the impedance of one device must be equal to the other (Z 1 = Z 2) so energy moves smoothly from one device to another with little loss between them.

If the impedance of an amplifier is lower than the speaker impedance, then energy does not flow easily from the amplifier to the speakers. Large currents flow and power output is small in comparison with what should be obtained for the input signal. Effectively, the speakers will not produce the loudest audio but the equipment is safe from overheating.

If the impedance of an amplifier is much higher than a speaker's impedance, then signals cannot smoothly pass between them, and energy is lost as heat in the resistor or capacitor that provides resistance. This could potentially cause components to fry in theory. With solid-state devices, this is not much of an issue compared with older, vintage or valve tube equipment.

What is Nominal Impedance?

Nominal impedance refers to the average impedance value of a speaker, although in reality, it varies from that for any number of reasons. For example, a speaker that is rated as 8 ohms can vary between around 6 ohms and 12 ohms, and this can change over time.

Obviously, this is also true for an amplifier as well, so an amp with a nominal impedance of 4 ohms, can range between 2 ohms and 6 ohms. Keep this in mind when trying to match the impedances of amplifiers and speakers.

Solution - Wiring two 8 ohm speakers in Parallel

So the solution to wiring 8-ohm speakers to a 4-ohm amp is to wire them in parallel. Wiring two 8 ohm speakers in series will effectively mean that the speakers' impedance is 8 ohms still. (See diagram)

Wiring the speakers in parallel, however, means that the speakers' overall impedance is halved to 4 ohms and therefore we have now matched the nominal impedance value of the 4-ohm amp with the speakers. (see diagram)

Summary

If you're looking to power your speakers, it's important to know the difference between 4 ohm and 8 ohm. It is also imperative that you take into account the impedance of each device (speaker or amplifier) in order for them to work together effectively. If one has a lower impedance than the other, then there will be more voltage flow through the circuit due to higher current levels which can cause damage when not handled properly.

The solution? Matching impedances by wiring two speakers in parallel with an amp rated at 4 ohms or less! This solves any mismatch problems without causing too much noise pollution.