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Sound is a traveling longitudinal wave, which is an oscillation of pressure. Humans perceive the frequency of a sound as its pitch. Each musical note corresponds to a particular frequency. An infant's ear is able to perceive frequencies ranging from 20 Hz to 20 000 Hz; the average adult human can hear sounds between 20 Hz and 16 000 Hz. [11]
The initial multichannel audio application was called 'Fantasound', comprising three audio channels and speakers. The sound was diffused throughout the cinema, controlled by an engineer using some 54 loudspeakers. The surround sound was achieved using the sum and the difference of the phase of the sound.
The standard example of a longitudinal wave is a sound wave or "pressure wave" in gases, liquids, or solids, whose oscillations cause compression and expansion of the material through which the wave is propagating. Pressure waves are called "primary waves", or "P-waves" in geophysics. Water waves involve both longitudinal and transverse motions ...
1.5 kW is the maximum legal power output of a US ham radio station. [12] 60 dBm: 1 kW = 1,000 W: Typical combined radiated RF power of microwave oven elements 55 dBm ~300 W: Typical single-channel RF output power of a K u band geostationary satellite: 50 dBm: 100 W: Typical total thermal radiation emitted by a human body, peak at 31.5 THz (9.5 μm)
millimeter wave radar research, molecular rotational spectroscopy and other kinds of scientific research W band: 75 to 110 GHz: 2.7 mm to 4.0 mm satellite communications, millimeter-wave radar research, military radar targeting and tracking applications, and some non-military applications, automotive radar F band: 90 to 140 GHz: 2.1 mm to 3.3 mm
A speaker 3 dB more sensitive than another produces double the sound power (is 3 dB louder) for the same electrical power input. Thus, a 100 W driver (A) rated at 92 dB for 1 W @ 1 m sensitivity puts out twice as much acoustic power as a 200 W driver (B) rated at 89 dB for 1 W @ 1 m when both are driven with 100 W of electrical power.
The current device has two settings: the high frequency sound targeted at youth, and another that can be heard by everyone. The range of the sound is 140 feet (43 m) with the sound baffle, and 200 feet (61 m) without. It requires a 24-volt DC or 15-volt AC power supply.
The operation of engines typically has a negative impact upon air quality and ambient sound levels. There has been a growing emphasis on the pollution producing features of automotive power systems. This has created new interest in alternate power sources and internal-combustion engine refinements.