A sound-powered telephone is a communication

Communication

Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...

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

Handset

On a telephone, the handset is a device the user holds to the ear to hear the audio sound. Modern-day handsets usually contain the phone's microphone as well, but in early telephones the microphone was mounted directly on the telephone itself, which often was attached to a wall at a convenient...

, similar to a conventional telephone

Telephone

The telephone , colloquially referred to as a phone, is a telecommunications device that transmits and receives sounds, usually the human voice. Telephones are a point-to-point communication system whose most basic function is to allow two people separated by large distances to talk to each other...

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

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s to allow communication between key locations on a vessel even if power, including batteries, is no longer available. A sound-powered phone circuit can have two or more stations on the same circuit. The circuit is always live, thus a user simply begins speaking rather than dialing another station. Sound-powered telephones are not normally connected to a telephone exchange

Telephone exchange

In the field of telecommunications, a telephone exchange or telephone switch is a system of electronic components that connects telephone calls...

.

Operation

The microphone transducer converts sound pressure from a user's voice into a minute electrical current, which is then converted back to sound by a transducer at the other end. 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 electrical current they cannot be used in sound-powered transducers. Rather, most sound-powered telephones use a dynamic microphone. 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 take place over a pair of wires that are thirty miles long. More complex circuits include magnetos

Magneto (electrical)

A magneto is an electrical generator that uses permanent magnets to produce alternating current.Magnetos adapted to produce pulses of high voltage are used in the ignition systems of some gasoline-powered internal combustion engines to provide power to the spark plugs...

, 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 naval vessels

Naval ship

A naval ship is a ship used for combat purposes, commonly by a navy. Naval ships are differentiated from civilian ships by construction and purpose...

. A typical example on a U.S. Navy

United States Navy

The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...

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

Lookout

A lookout or look-out is a person on a ship in charge of the observation of the sea for hazards, other ships, land, etc. Lookouts report anything they see and or hear. When reporting contacts, lookouts give information such as, bearing of the object, which way the object is headed, target angles...

s to report visual contacts to the pilot house and the Combat Information Center

Combat Information Center

The Operations Room is the tactical center of a warship or AWAC aircraft providing processed information for command and control of the near battle space or 'area of operations'...

 (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

United States Coast Guard

The United States Coast Guard is a branch of the United States Armed Forces and one of the seven U.S. uniformed services. The Coast Guard is a maritime, military, multi-mission service unique among the military branches for having a maritime law enforcement mission and a federal regulatory agency...

 Regulations require this emergency type communication 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

Power outage

A power outage is a short- or long-term loss of the electric power to an area.There are many causes of power failures in an electricity network...

 or when radio

Radio

Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

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

Ski lift

Ski lift

The term ski lift generally refers to any transport device that carries skiers up a hill. A ski lift may fall into one of the following three main classes:-Lift systems and networks:...

s use sound-powered phones extensively. Because there are only 2 handsets (on rare occasions 3, 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 also any abnormal operation of the lift machinery

Many different types of equipment have attempted to replace sound-powered telephones on ships, however, due to the rugged, reliable and power-free nature of this form of communication equipment, it is still in use on all U.S. military vessels, commercial vessels and work boats.

External links

• The Sound Powered Web Page
• How sound powered telephones work
• US Navy tips
• http://www.policeinterceptor.com/sounds/growler.wav Recording of a US Navy "growler" magneto