Input Impedance
Input impedance is the electrical load an analogue input presents to the source driving it.
It is commonly given in ohms or kilohms. Line-input impedance is separate from phono-cartridge loading, source output impedance and a loudspeaker’s nominal impedance.
Input Impedance — Headphone Amp
For a headphone amplifier, input impedance describes the load on the connected line-level source. It is not the impedance of the headphones at the output.
Compare it with the source’s output characteristics and keep connector and frequency conditions attached. A higher line-input impedance usually loads the source less, but the number alone does not establish gain or maximum input level.
Input Impedance — Power Amp
For a power amplifier, this value describes the load on the preamplifier or other line source. Named balanced and unbalanced input ratings are separate when provided.
Compare the relevant source and input path rather than the amplifier’s supported speaker load. A single unspecified value should not be assumed to describe every connector if separate input ratings differ.
Input Impedance — Equalizer
For an equalizer, input impedance describes how its analogue input loads the preceding component. The value belongs to the specified input path.
Compare the source’s output requirements and retain any frequency or connector condition. Input sensitivity and overload voltage are different quantities; neither can be inferred from an impedance figure alone.
Input Impedance — Crossover
For an active crossover, input impedance describes the load placed on the preamplifier or source feeding the crossover. The downstream amplifier inputs are a separate part of the chain.
Compare the actual input connection with the source’s drive requirements. An input-impedance figure is not a crossover frequency, output impedance or speaker-load rating.
Input Impedance — Subwoofer
For an active subwoofer, this figure normally describes the specified input electronics, such as a line-level input. It is not the woofer’s own nominal load.
Compare the correct input path, especially when both line-level and speaker-level inputs are available. Values from different input types are not interchangeable, and sensitivity is a separate measurement.