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Electrical resistance (internal resistance) of a headphone speaker measured at 1 kHz.
The rated impedance allows you to compute the input signal voltage required to generate the rated sound pressure level (stated as sensitivity) and the reference power of 1 mW. The lower the rated impedance, the lower the required input signal voltage.
Example:
19 ohms 0.138 V
32 ohms 0.179 V
55 ohms 0.234 V
120 ohms 0.346 V
600 ohms 0.775 V
In day-to-day practice, the rated impedance is important when using headphones with portable equipment. Battery operated devices usually provide low output voltages for headphones. Therefore, it is better, or even necessary, to use low-impedance headphones to achieve adequate loudness levels. |