Speakers and microphones both use diaphragms, typically made of paper or plastic, that vibrate to produce or detect sound, respectively. The diaphragms in the new devices are graphene sheets a mere one atom thick that have the right combination of stiffness, strength and light weight to respond to frequencies ranging from subsonic (below 20 hertz) to ultrasonic (above 20 kilohertz). Humans can hear from 20 hertz up to 20,000 hertz, whereas bats hear only in the kilohertz range, from 9 to 200 kilohertz. The grapheme loudspeakers and microphones operate from well below 20 hertz to over 500 kilohertz.