A sound-powered telephone is a

communication Communication (from la, communicare, meaning "to share" or "to be in relation with") is usually defined as the transmission of information. The term may also refer to the message communicated through such transmissions or the field of inqui ...

device that allows users to talk to each other with the use of a

handset A handset is a component of a telephone that a user holds to the ear and mouth to receive audio through the receiver and speak to the remote party using the built-in transmitter. In earlier telephones, the transmitter was mounted directly on ...

, similar to a conventional

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

, but without the use of external power. This technology has been used since at least 1944 for both routine and emergency communication on

ship A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research, and fishing. Ships are generally distinguished ...

s to allow communication between key locations on a vessel if power is unavailable. A sound-powered phone circuit can have two or more stations on the same circuit. The circuit is always live, thus a user begins speaking rather than dialing another station. Sound-powered telephones are not normally connected to a telephone exchange.

Operation

The microphone

transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and cont ...

converts sound pressure from a user's voice into an electric current, which is then converted back to sound by a transducer at the receiver

node In general, a node is a localized swelling (a "knot") or a point of intersection (a vertex). Node may refer to: In mathematics * Vertex (graph theory), a vertex in a mathematical graph *Vertex (geometry), a point where two or more curves, lines ...

s. The most significant distinction between ordinary telephones and sound-powered telephones is in the operation of the microphone. Since the microphones used in most telephones are designed to modulate a supplied electric current they cannot be used in sound-powered transducers. Most sound-powered telephones use a

dynamic microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and public ...

. A common approach to transducer design is the balanced armature design because of its efficiency. The number of simultaneous listeners is limited because there is no amplification of the signal. A sound-powered telephone circuit can be as simple as two handsets connected together with a pair of wires, which is defined as the "talk" portion of the circuit. Talk circuits can be realized over a pair of wires that are 50 km (30 miles) long. More complex circuits include

magneto A magneto is an electrical generator that uses permanent magnets to produce periodic pulses of alternating current. Unlike a dynamo, a magneto does not contain a commutator to produce direct current. It is categorized as a form of alternator, ...

s, selector switches and bells to allow one user to select and call another, which is defined as the "calling" portion of the circuit. The voice communication ("talk") circuit is completely separate from the "call" circuit, allowing communication to take place without external power.

Usage

Sound-powered telephones are widely used on ships. A typical example on a

U.S. Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage o ...

ship is the "JL" circuit which is used by the

lookout A lookout or look-out is a person in charge of the observation of hazards. The term originally comes from a naval background, where lookouts would watch for other ships, land, and various dangers. The term has now passed into wider parlance. ...

s to report visual contacts to the pilot house and the

Combat Information Center A combat information center (CIC) or action information centre (AIC) is a room in a warship or AWACS aircraft that functions as a tactical center and provides processed information for command and control of the near battlespace or area of op ...

(CIC). In this case there would be five stations on the circuit (stern lookout, port lookout, starboard lookout, pilot house and CIC).

U.S. Coast Guard The United States Coast Guard (USCG) is the maritime security, search and rescue, and law enforcement service branch of the United States Armed Forces and one of the country's eight uniformed services. The service is a maritime, military, mul ...

Regulations require this emergency communication capability in most vessels today and dictate where phones should be located. A dial telephone system with a battery backup will not meet the USCG Regulations as they currently exist. Other uses for sound-powered telephone technology today include emergency communications systems for high-rise buildings, draw bridges, ski lifts, and temporary locations where reliable communication is necessary. These types of systems allow for two or more parties to be able to talk to one another in areas that experience loss of power or when

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...

communication is hampered by RF signal losses and/or limitations.

Ski lift A ski lift is a mechanism for transporting skiers up a hill. Ski lifts are typically a paid service at ski resorts. The first ski lift was built in 1908 by German Robert Winterhalder in Schollach/Eisenbach, Hochschwarzwald. Types * Aerial ...

s use sound-powered phones extensively. Because there are only two handsets (rarely three, where there is a mid station), sound-powered phones are ideal. They are used to confirm actions of the lift with the other operator, and abnormal operation of the lift machinery. Many different types of equipment have attempted to replace sound-powered telephones on ships. Due to the rugged, reliable and power-free nature of this equipment, it remains in use on all US military vessels, commercial vessels and work boats.

References

External links

The Sound Powered Web Page
Recording of a US Navy "growler" magneto. Archived October 2, 2011. {{Authority control Telephony equipment