Audio Fundamentals
Impedance is the measure of opposition a circuit presents to the flow of alternating current, such as an audio signal. It is expressed in ohms (Ω) and determines how efficiently electrical energy is transferred between connected audio devices.
In audio systems, impedance describes how much resistance and reactance (from capacitance and inductance) a device offers to an AC signal. It plays a critical role in matching equipment such as microphones, preamplifiers, amplifiers, and loudspeakers to ensure optimal signal transfer and minimal distortion.
Two main types of impedance exist: input impedance and output impedance. Input impedance defines how much load a device places on the source feeding it, while output impedance represents how strongly the source can drive that load. For efficient operation, the input impedance of a receiving device should typically be at least ten times higher than the output impedance of the device feeding it. This is known as impedance bridging.
In professional audio, balanced line inputs commonly present an impedance of around 10 kΩ to 20 kΩ, while microphones typically have output impedances between 150 Ω and 600 Ω. Loudspeakers, on the other hand, often range from 4 Ω to 8 Ω, requiring power amplifiers capable of supplying significant current at those loads.
Mismatched impedance can cause loss of signal level, frequency response changes, and distortion. Modern audio equipment is generally designed with standardised impedance characteristics, making proper interfacing straightforward. Understanding impedance remains essential for system design, troubleshooting, and achieving accurate signal performance across the audio chain.
