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Impedance
Headphones are available with low or high impedance measured at 1 kHz. Low-impedance headphones are in the range 75 to 150 ohms and high-impedance headphones are about 600 ohms.[4] High impedance headphones have been popular among tube amplifier aficionados,[citation needed] and in classroom or studio situations requiring many headphones connected in parallel to the same source. Low impedance headphones yield a louder sound from a standard headphone jack, and require less voltage to achieve a target sound pressure level—an important consideration for portable electronics.[4]