What Is Impedance? And Why Does It Matter?

While almost everyone has heard the term impedance, very few actually know what it is and why it matters. Speakers, subwoofers, and amplifiers all come with specifications for their impedance level. Impedance is measured in ohms which is symbolized as Ω and is critical to getting the most out of your sound system. We’ll be the first to admit; trying to understand all there is about impedance can prove to be a daunting task. Here’s all you need to know about impedance and why it even matters without feeling like you’re sitting through a college lecture.

What is Impedance?

Impedance can be defined as the measure of opposition that a particular circuit presents when direct electric current is applied. This includes the resistance of electrical current that causes heat as well as the reactants which is a measurement of the opposition as the current alternates. In a speaker, the impedance is the particular characteristic of the speaker that restricts the flow of power from either the receiver or the amplifier. The main aim of impedance is to quantify how hard it is to drive a speaker as well as guide users towards compatibility among electrical components.impedance formula

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What Are Ohms?

Ohm is the unit of measurement for impedance. Often times you’ll see a subwoofer mention an impedance rating of 2, 4, 8 and 16 ohms telling you exactly what impedance you need when connecting to an amp. Max output will be delivered to the speaker when the impedance of that unit matches the amplifier. But be careful because if the impedance is too low, the unit will overheat causing a safety hazards.

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Power + Water

For learning purposes, the analogy of power and water is going to be applied to help you better understand impedance. Audio engineers use the analogy of water flowing through pipes to help create a visual representation. We’ll use it today because, well, it’s a great analogy and water is cheaper than oil.

Now, think of your speaker or subwoofer as a pipe and your music as the flowing water. The bigger your pipes the easier it is for water to flow and the more volume you can cram in there. As such, a sub or speaker with low impedance can be compared to a pipe with a larger diameter since they let in more electrical signals. At the same time, smaller tubes will only allow for the flow of less water, creating a high impedance situation.

So, does this mean that music lovers should only look for subs and speakers with lower impedance levels? No, it doesn’t; because amplifiers are not always designed to work at the same impedance level. To answer with our analogy, you can install a pipe as big as you’d like(lower impedance) but it will only carry more current (water) if you have an adequate pump with enough power to maintain the additional flow of water.

Why Does Impedance Matter?

So, what’s all this fuss about matching impedance in your car’s sound system? Is there any advantage of buying a 2 or 4 Ohm subwoofer versus an 8 Ohm speaker? Let’s examine the details more closely.

hz diagram

Since impedance restricts the flow of power from your receiver, it would stand to reason that the lower the impedance the better. However, the truth is that lower impedance only stresses the amplifier by asking it to push more current. This can be very bad, especially if your amp is not capable of putting out the required power. Using the water pipe analogy to explain low impedance; let’s picture a regular pipe. Increasing the diameter (lowering the impedance) will increase the flow of water (current) but will in turn cause the water pump (amp) to work twice as hard just to maintain the water pressure (voltage). If the pump (amplifier) attempts to drive the system with its small power levels, it’s likely to overheat and shut down. While there are many amplifiers built for low impedance and high currents, most of the common low cost amps cannot achieve this.

So, are we saying that higher levels of impedance are best? Again, not quite . If the impedance is too high (small water pipes), this restricts the flow of current (water). The flow is crucial to optimize the needs of your subwoofer and speakers. Most experts recommend impedance specifications ranging between 6 and 8 Ohms since almost all amplifiers and receivers can safely drive speakers and subs with such impedance specs.

Born in a subwoofer box, music has always been my passion. At the proud age of 9 I began driving. The two eventually met and led to my career at Sonic Electronix.

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