Speakerphone
Encyclopedia
A speakerphone is a 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...

 with a microphone
Microphone
A microphone is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. In 1877, Emile Berliner invented the first microphone used as a telephone voice transmitter...

 and loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

 provided separately from those in the 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...

. This device allows multiple persons to participate in a conversation. The loudspeaker broadcasts the voice or voices of those on the other end of the telephone line, while the microphone captures all voices of those using the speakerphone.

Many telephones have an integrated speakerphone function which can be activated by pushing a single button. This button transfers the sound input and output from the handset to the ambient microphone and loudspeaker. Devices designed specifically for speakerphone use often have multiple microphone inputs arranged radially around the device to maximize sound input, such as may occur around a conference table. The most sophisticated units allow the connection of additional satellite microphones that can be placed some distance from the main unit.

Types of speakerphones

Speakerphones may be broadly divided into two classes of Duplex
Duplex (telecommunications)
A duplex communication system is a system composed of two connected parties or devices that can communicate with one another in both directions. The term multiplexing is used when describing communication between more than two parties or devices....

:
  • Half-duplex
  • Full-duplex


Half-duplex speakerphones only allow sound to travel in one direction at a time, either: 1) into the speakerphone from the telephone line and out of its internal speaker to its user, or 2) from its user, into the microphone, and out through the telephone line. While the users of the speakerphone are speaking, the phone only transmits sound to the telephone line; its internal speaker is cut-off and no sound arriving from the telephone line can be heard by the user. While the user of the speakerphone is quiet, the speakerphone only receives sound from the telephone line and its internal speaker broadcasts that sound to its user. There is a very definite, noticeable switching action each time the phone "changes directions" and a cough or other transient noise in the room may interrupt incoming sound from the far end of the telephone connection.

Full-duplex speakerphones are able to transmit and receive simultaneously and there is no discernible change of transmission direction. These phones are much more complicated and often employ sophisticated digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...

 algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

s to sort out the incoming sound and the sound in the room for echo cancellation
Echo cancellation
'The term echo cancellation is used in telephony to describe the process of removing echo from a voice communication in order to improve voice quality on a telephone call...

. Their cost is also higher than for a half-duplex speakerphone.

Speakerphone setup

Many modern speakerphones must first be calibrated
Calibration
Calibration is a comparison between measurements – one of known magnitude or correctness made or set with one device and another measurement made in as similar a way as possible with a second device....

 to the acoustic
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...

 characteristics of the room in which they will be used. During this calibration phase, they may make a variety of noises including ascending tones or chiming sounds. This calibration may be automatic or manually invoked by the user, and it may need to be repeated if the speakerphone is relocated within the room. A failure to be properly calibrated can be indicated by the occurrence of echoing, ringing sounds, or feedback
Audio feedback
Audio feedback is a special kind of positive feedback which occurs when a sound loop exists between an audio input and an audio output...

.

Handset vs. base speakerphone

Many cordless telephone
Cordless telephone
A cordless telephone or portable telephone is a telephone with a wireless handset that communicates via radio waves with a base station connected to a fixed telephone line, usually within a limited range of its base station...

s have a handset speakerphone as well as a base speakerphone. The handset speakerphone allows hands free conversations away from the base unit. The base speakerphone is located in the base unit. The user must be at the base unit, but still gets the added benefits of having hands free conversations. Most base speakerphones have a secondary keypad for dialing calls on the base unit.
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