The Environmental Protection Agency - EPA - has adopted a system of four "sound descriptors"
- A-weighted sound level
- Sound Exposure Level - Ls
- Equivalent Sound Level - Leq
- Day-Night Sound Level - Ldn
to summarize how sound is heard and measured and to determine the impact of noise on health and welfare.
Sound Exposure Level - Ls
The Sound Exposure Level - Ls - measures the sound change from moment to moment with variable sound. The maximum sound level and the length of time with the sound level greater than certain sound pressure levels are measured.
By accumulating intensity and exposure duration the total sound energy can be measured.
Sound Exposure Level - Ls - can be used to describe noise from moving sources such as airplanes, trains, trucks, etc.
Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.
Sound pressure filters that compensates for the hearing sensed by the human ear.
The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.
Noise Criterion - NC - level is a standard uesd to describe the relative loudness of a space within a range of frequencies.
Acceptable noise - dBA - level at typical common locations.
The EPA A-weighted sound level day and night equivalent definition - Ldn - for a 24 hour period.
The EPA Equivalent Sound Level - Leq - quantifies the noise environment to a single value of sound level for any desired duration.
OSHA maximum A-weighted sound pressure levels allowed per day.