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The amplifying devices in audio and radio equipment are vulnerable to a variety of feedback problems, which can cause distinctive noise in the output. The term motorboating is applied to oscillations whose frequency is below the range of hearing, from 1 to 10 hertz , [ 3 ] so the individual oscillations are heard as pulses.
Somewhat later, farm radios were made to be run on 6 V from a car or tractor battery, using an electromechanical vibrator to create a pulsating DC current that could be stepped up through a transformer to create the high voltage needed for the plates of the tubes- exactly as contemporary car radios did.
Upsweep is an unidentified sound detected on the American NOAA's equatorial autonomous hydrophone arrays. This sound was present when the Pacific Marine Environmental Laboratory began recording its sound surveillance system, SOSUS, in August 1991. It consists of a long train of narrow-band upsweeping sounds of several seconds in duration each.
Mains hum, electric hum, cycle hum, or power line hum is a sound associated with alternating current which is twice the frequency of the mains electricity. The fundamental frequency of this sound is usually double that of fundamental 50/60 Hz , i.e., 100/120 Hz, depending on the local power-line frequency .
The torsional deflection of a simple cylinder cannot radiate efficiently acoustic noise, but with particular boundary conditions the stator can radiate acoustic noise under torque ripple excitation. [8] Structure-borne noise can also be generated by torque ripple when rotor shaft line vibrations propagate to the frame [9] and shaft line.
The AM/FM radio combined with a CD player has remained a mainstay of car audio, despite being obsolescent in non-car applications. [17] [18] In the 2010s, internet radio, satellite radio, streaming, and podcasting came into competition with AM/FM radio. By this time some models were offering 5.1 surround sound.
Subjects could locate the hum of the internal combustion engine car at 36 feet (11 m) away, but could not identify the hybrid running in electric mode until it came within 11 feet (3.4 m), leaving just less than two seconds to react before the vehicle reached their position. In a second trial, the background sounds of two quietly idling ...
A previous hum in Sausalito, California, also on the West Coast of the United States, was determined to be the mating call of the male midshipman. [37] However, in that case the hum was resonating through houseboat hulls and affecting the people living on those boats. In the West Seattle case, the University of Washington researcher determined ...