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Microphones, amplifiers and recording systems all add some electronic noise to the signals passing through them, generally described as hum, buzz or hiss. All buildings have low-level magnetic and electrostatic fields in and around them emanating from mains supply wiring, and these can induce hum into signal paths, typically 50 Hz or 60 Hz (depending on the country's electrical supply standard ...
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.
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.
A pair of headphones being tested inside an anechoic chamber for soundproofing. Soundproofing is any means of impeding sound propagation.There are several methods employed including increasing the distance between the source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound waves, using damping structures such as sound baffles for absorption, or using ...
A buzzer or beeper is an audio signaling device, [1] which may be mechanical, electromechanical, or piezoelectric (piezo for short). Typical uses of buzzers and beepers include alarm devices , timers , train and confirmation of user input such as a mouse click or keystroke.
The Mosquito or Mosquito alarm is a machine used to deter loitering by emitting sound at high frequency. In some versions, it is intentionally tuned to be heard primarily by younger people. Nicknamed "Mosquito" for the buzzing sound it plays, the device is marketed as a safety and security tool for preventing youths from congregating in ...
The people who do hear these sounds typically hear a faint hissing (cicada-like sound), buzzing or ringing, especially if they are otherwise in complete silence. [34] Hence, researchers who looked at the Taos Hum considered otoacoustic emissions as a possibility.
So while threshold levels of for the microwave audio effect of 267mW/cm² for 1.3GHz and 5000mW/cm² 2.9GHz, respectively, were reported by Frey in 1961, for the peak amplitude (providing the pops) and would only give an average (sustained) power density of only 0.4mW/cm² and 2mW/cm² respectively [7] similar to current cellphones.