1) OSHA - Occupational Safety and Health Act - The OSHA criteria document reevaluates and reaffirms the Recommended Exposure Limit (REL) for occupational noise exposure established by the National Institute for Occupational Safety and Health (NIOSH) in 1972
The REL is 85 dB, A-weighted, as an 8-hr time-weighted average (85 dB(A) as an 8-hr TWA). Exposures at or above this level are hazardous.
2) The reference level - 10-12 - for the decibel scale
The sound pressure level from a number of sound pressure level readings can be calculated as:
La = 10 log (10 L1/10 + 10 L2/10 + ... + 10 Ln/10))
La = average sound pressure level (dB)
L1 .. Ln = sound pressure level source 1 .. n (dB)
n = number of sources
Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.
Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems.
Logarithmic unit used to describe ratios of signal levels - like power or intensity - to a reference level.
Sound pressure filters that compensates for the hearing sensed by the human ear.
Physiological effects from low-frequency noise or vibrations.
The rules of logarithms - log10 and loge for numbers ranging 1 to 1000.
Maximum recommended sound pressure levels in rooms like kindergartens, auditoriums, libraries, cinemas and more.
An online Noise Rating (NR) calculator.
The Noise Rating (NR) Curve used to determine acceptable indoor environments for hearing preservation, speech communication and annoyance.
The phonetic alphabet used in international aircraft communications.
The transmission of outdoor sound through and around barriers - the Fresnel Number.
In a room the sound or noise will reach the receiver as direct and reverberant sound.
The logarithmic decibel scale is convenient when adding signal values like sound power, pressure and others from two or more sources.
Background noise frequencies that interferes with speech.
The attenuation in a room depends on the location of the sound source and the receiver - and the room constant.
An introduction to the nature of sound with frequencies, wave-lengths and octaves.
Shift in hearing threshold for men and women vs. age.
Room size, absorption characteristics - and attenuation in direct sound fields.
Introduction to decibel, sound power, intensity and pressure.
OSHA maximum A-weighted sound pressure levels allowed per day.
Doubling of the distance from a noise source reduces the sound pressure level with 6 decibel.
Satisfactory, difficult and impossible noise levels for telephone use in noisy areas.
Acoustic noise calculation procedure HVAC systems.
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