Very often one reads the specification of audio equipment and comes across the term – impedance. Often people are a bit unsure of the exact meaning of this term and how it affects their audio system. We will explain the term and take the mystery out of it by answering the question -what is impedance?
Impedance explained
All devices ruining on an alternating current (AC) circuit will experience resistance. This resistance is known as impedance and is measured in ohms. You might see the symbol which looks like this – Ω. The principal is often referred to in electronics but also applies to audio equipment as they operate on an AC circuit.
So when you connect, for example, an amplifier to speakers, there is resistance or impedance in the AC circuit between the two devices.
If you purchase a complete system, it will be designed and optimized to perform correctly. If you are building a system using a range of components it is necessary to understand a bit about impedance. Getting it wrong could result in poor audio and even cause damage to equipment.
Don’t be intimated by the concept. We will try and keep it simple so that you get it right for your system. It can get rather complex but that is the domain of professional sound engineers and technicians. They generally work on extremely complex rigs with multiple parts. For home use, it is relatively simple.
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Ohms law
OK, so we said we are not going to get too technical but Ohms Law is the foundation of impedance. Simply put, it states that the “current through a conductor between two points is directly proportional to the voltage across the two points.”
Yeah, that is a mouthful, I know. It goes on to state that “Introducing the constant of proportionality, the resistance one arrives at the usual mathematical equation that describes this relationship.”
To try and keep it simple, we are not going to go into mathematical equations. All you need to know is that it is a scientific principle that is universally accepted. Georg Ohm, a German physicist, and mathematician developed the law as far back as 1827.
It is the basic law of electrical power and allows those that have the need to work out the voltage, current, efficiency, power, and, most importantly, in this case, the resistance of a circuit.
Why is impedance important?
For most home users, the importance of impedance relates to your speaker system. Current is needed to create motion in the speaker cone in order to produce sound. A loudspeaker transfers energy from electrical action to deliver sound.
Impedance is the resistance the system or transducer faces in making this conversion. More impedance results in less current from the power amplifier. More power results in more sound but what is important is that the components are matched. Power, measure in Watts, needs to be matched with the impedance.
Generally, higher impedance is needed for better and louder audio. This is particularly true in headphones. It allows for a deep rich sound and is especially important for low-frequency bass sounds.
Input & Output Device Impedance
Following on from the above point, one needs to note that components will either have input or an output impedance. Something that generates voltage would create output impedance. Those components that receive this voltage receive impedance from the source.
Matching Impedance to Power
In order to achieve a high power output current and voltage are needed. It is, however, important that the output and input impedance, as explained above, are equal, in words matched. It is also important to note that the cable, especially if lengthy, will add to impedance.
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Are resistance and impedance the same thing?
While the principal is very much the same the term resistance is used when referring to direct current (DC) circuits while impedance refers to AC circuits.
Final thoughts
It is not important that you understand the technical details of impedance. Just know that it needs to be correct for quality audio.
