The moving coil loudspeaker is without doubt the most common electroacoustic transducer in use. It consists of a circular coil suspended to move freely in a radial magnetic field. This transducer principle was first described by Ernst W. Siemens in his 1874 patent. He describes his transducer as a means for “obtaining the mechanical movement of an electrical coil from electrical currents transmitted through it.” He also mentions that the coil could be used to move visible or audible signals, but he had obviously nothing more elaborate in mind than a bell or buzzer.
In the preceding parts, I have mentioned several microphone (transmitters, in telephone lingo) types that were used in early telephone experiments. The first type, the one described by Borseul, was a make-and-break type transmitter, which was used by Reis. This type of transmitter is not very useful, and can hardly transmit understandable speech. The very closely related loose-contact transmitter, is the basis for the carbon microphone. Also related is the variable resistance transmitter used by Elisha Gray in his bid for the telephone. A needle was attached to the transmitter diaphragm, and the other end of the needle touched the surface of a conductive liquid in a conductive cup. When the diaphragm vibrated, the needle made more or less area in contact with the liquid, and the resistance of the circuit varied.
Two inventors with significantly improved, successful telephone devices made it to the patent office on the same day, February 14, 1876. These two inventors were Elisha Gray (1835-1901) and Alexander Graham Bell (1847-1922).
While electroacoustics is as old as lightning and thunder, man’s controlled application of it dates back to the 18th century. Early electroacoustic phenomena were mere replicas of the natural occurring ones; the crackles of electrostatic discharges in the early experiments in electricity. In 1729, it was discovered that some materials conducted electricity, and the idea that this could be used to transmit intelligence was born.
Imagine that a new road was planned for construction close to your house. Naturally, you might want to know how much this would impact the noise situation in the area where you live. Currently, what the developers would be able to tell you are numbers called equivalent levels that describe the noise increase in your area. While these numbers may be based on excellent simulations and may be entirely correct, numbers are no substitute for listening!
Aircraft noise unquestionably causes annoyance, but reactions to a given noise exposure vary wildly. The Norwegian Defence Estates Agency and SINTEF ICT Acoustics have teamed up to strengthen the connection between the aircraft noise situation and the annoyance response of airport neighbours.
For this purpose, we have assessed annoyance due to aircraft noise in Norway, by conducting noise annoyance surveys near five Norwegian airports. Respondents were asked about their annoyance from aircraft noise directly, but they also got questions that were more specific, like:
- When during the day are you most annoyed by aircraft noise?
- What kind of flight activities do you consider specifically annoying?
The aim of the research project is to use the obtained data to explain why respondents in different communities respond differently to the same noise dose.
In the research project MOVE, ARC is investigating methods and systems to estimate the environmental impact of road traffic. The project is financed by the Norwegian Research Council, through the BIA program. MOVE is managed by Acoustic One/Norsonic AS and SINTEF; other partners are NTNU and Norsk Elektro Optikk AS (NEO). The project started in 2012 and will be finished in 2015.