Sref = signal reference (signal unit)
The Decibel Scale
Sound power is the energy rate - the energy of sound per unit of time (J/s, W in SI-units) from a sound source.
Sound power can more practically be expressed in a logarithmic scale named Sound Power Level as the ratio of sound power to the sound power at the threshold of hearing - 10-12 W:
LN = 10 log (N / Nref) (2)
LN = Sound Power Level (decibel , dB)
N = sound power (W)
Nref = reference sound power (10-12 W)
Sound intensity is the ratio acoustic or sound power to area. The SI-unit for Sound Intensity is W/m2.
The Sound Intensity Level can be expressed as:
LI = 10 log (I / Iref) (3)
LI = sound intensity level (dB)
I = sound intensity (W/m2)
Iref = 10-12 - reference sound intensity (W/m2)
The sound pressure is the force (N) of a sound on a surface area (m2) perpendicular to the direction of the sound. The SI-unit for the Sound Pressure is N/m2 or Pa.
The Sound Pressure Level in decibel can be expressed as
Lp = 10 log (p2 / pref2)
= 10 log (p / pref)2
= 20 log (p / pref) (4)
Lp = sound pressure level (dB)
p = sound pressure (Pa)
pref = 2 10-5 - reference sound pressure (Pa)
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.
Human physiology, air quality and comfort temperatures, activity and metabolic rates, health effects of carbon monoxide and more.
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.
Maximum recommended sound pressure levels in rooms like kindergartens, auditoriums, libraries, cinemas and more.
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.
Exposure to noise should be controlled so that it is less than a maximum combination of exposure level and duration.
Sound power noise generated by blade dampers in ventilation systems.
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 logarithmic decibel scale is convenient when adding signal values like sound power, pressure and others from two or more sources.
Shift in hearing threshold for men and women vs. age.
Acoustic power of sound per unit area.
Sound power from sources like fans, jet engines, cars, humans and more.
Sound Pressure is the force of sound on a surface perpendicular to the propagation of sound.
Change in sound pressure level and the subjective human perception.
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