Small speakers {earphone, speaker}| have electric-current waves that vibrate a thin plastic disc using piezoelectricity.
Receivers {microphone}| can change sound to electric current. In some microphones {ceramic microphone}, sound pressure makes voltage in a crystal {piezoelectric effect}. In some microphones {dynamic microphone}, sound pressure moves a magnet unidirectionally or omnidirectionally in a magnetic field.
Dropping a nickel into a machine {nickelodeon}| can select a record, put it on a record player, and start the record player.
To make sound-system media {records}, microphones can detect sound and make voltage changes that cause a pointed needle to vibrate sideways and cut a plastic disc {recording music}. Plastic discs are soft wax-like material and turn like a record as needle vibrates. Signals can make larger groove widths for high frequencies and smaller groove widths for low frequencies. Machine uses plastic disc to make a metal mold {master}. A press pushes soft vinyl into mold to make a disc.
TV remote controls {remote control}| use ultrasound tuning forks at 40,000 Hz. TVs have a microphone to convert sound waves to electric-current waves.
Machines {sonar, detector}| can emit sound waves and receive wave reflections, to determine speed and position by Doppler effect.
Electric voltage and current waves can go to a solenoid connected to a paper cone {speaker, electronics}|. Waves vibrate solenoid, and vibrations vibrate paper cone to generate sound. Speakers {bass reflex speaker} can have compartments, with a hole to outside. Speakers {air suspension speaker} can be airtight. Speakers {reflecting speaker} can send sound straight in front and reflect sound off walls. Speakers can be for bass {woofer}, middle {mid-range}, and high {tweeter} frequencies.
Telephone speakers {squawk box}| can be on trading floors to alert brokers.
To record sound {stereo system}| with spatial effects, two microphones, two meters apart, record on two tracks. Two speakers, two meters apart, play back sounds recorded by microphones. Input signal can come from record-player vibrating needle, laser light reflecting from CD, or changing magnetic field from tape-recorder tape head.
Cellulose acetate or Mylar ribbon {videotape} {audiotape} has an iron-oxide or cobalt-oxide coating. Ribbon passes over an electromagnet {magnetic head} {head, tape recorder}, of size 10^-3 square inches, at 1 7/8, 3 3/4, 7 1/2, or 15 inches per second. Recording head uses magnetic field to change coating magnetism pattern on tape {tape recorder}|. Tape magnetism pattern induces a magnetic field in receiving head, which makes an electric current. Demagnetizing heads use a random magnetic field to erase tape.
Devices {telephone}| can receive and transmit human speech sounds. After two telephones are on a circuit, direct current from telephone-central-office batteries flows through circuit.
microphone
Microphones {mouthpiece, telephone} can be a round box filled with powdered carbon, covered by a flexible diaphragm. Sound compresses diaphragm and carbon, to change carbon electrical resistance and make waves in electric direct current.
speaker
Speakers {earphone, telephone} can have an electromagnet and metal diaphragm, which current waves vibrate.
wire
Telephones use three wires: one to electrical ground, one for telephone line, and one for ringing line.
dialing
Dialing telephones activates relay switches that select correct wire pair to connect to dialing telephone. Dialing then activates ringing circuit. When other telephone answers, telephone-line circuit is complete. If other telephone line is already in use, the dialing process sends a busy signal.
People talk and listen at a telephone combined microphone and speaker {receiver, telephone}.
Compression algorithms {vocoder}| {voder} can make voice sounds into coded signals.
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Date Modified: 2022.0225