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The disruption of sound pressures waves which reduces the noise is called attenuation
Guidelines for acceptable noise levels in terms of dBA for different locations.
A procedure for acoustic calculation of noise in ventilation systems
Noise generated in blade dampers
The noise level intensity varies with type of fan
The logarithmic decibel scale is convenient when calculating resulting sound power levels and sound pressure levels for two or more sound or noise sources.
Noise can be eliminated with reactive silencers, diffuser type silencers, active silencers and/or dissipative silencers
Comparing Noise Criteria (NC), Noise Rating (NR), and dB(A)
Daily noise dose level when exposed in periods with different noise levels
Decibel is a logarithmic unit used to describe the ratio of the signal level - power, sound pressure, voltage, intensity, etc.
The sound pressure is not equally sensed by the human ear at different frequencies. This can be compensated with the dB(A), dB(B) or dB(C) filters
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The attenuation in a room depends on the receiver and source location.
The noise level should not exceed values protecting public health and welfare.
The Sound Power Level from fans depends on the motor power and the capacity of the fan - the static pressure and/or the discharged volume.
For every doubling of the distance from the noise source, the sound pressure levels - Lp, will be reduced by 6 decibels
The EPA has defined an A-weighted sound level day and night equivalent for a 24 hour period.
Equivalent Sound Level - Leq - quantifies the noise environment as a single value of sound level for any desired duration.
Sound Exposure Level - Ls - describes noise from a varied source.
For a given noise spectrum, the NC rating can be obtained by plotting its octave band levels on the set of NC curves
Noise exposure should be controlled so that exposure is less than the combination of exposure level and duration.
An introduction to Noise Rating - NR - curves - developed by the International Organization for Standardization (ISO) - NR diagram
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Calculate the attenuation in decibels in an outdoor free field
An online Noise Criterion - NC - Calculator
An online Noise Rating - NR - Calculator
Convert between sound level, sound pressure and sound intensity
Outdoor ambient sound level in different rural and urban business and industrial environments with or without limited traffic.
A noise measurement system for continuous or ambient noise in indoor environments proposed by Leo Beranek in 1971
An online Preferred Noise Criterion - PNC - Calculator
Sound and noise in a room will reach the receiver as direct and reverberant sound.
Outdoor propagation of sound - distance and attenuation.
The transmission of sound through and around outdoor barriers.
Room Criteria - RC - measures background sound in a building over the frequency range 16 Hz to 4000 Hz.
The NIOSH noise Recommended Exposure Limit - REL - for occupational noise.
The Sound Reverberation Time indicates how long it takes until the sound pressure level in a room is decreased with 60 dB
An online calculator for calculating road traffic noise levels for non-complex situations.
Mean absorption coefficients and reverberation times for some typical rooms.
An online acoustic calculator for estimating the reverberation time and designing the acoustics of rooms
Room size, absorption characteristics and attenuation in direct sound fields
Approximate speech interference levels
Sound absorption coefficients for some common materials as plaster walls, brickwork, plywood panels etc.
Estimation of sound attenuation when ducts are split to terminals
Sound attenuation for main ducts to branches.
Some of the low frequency noise transferred to the end terminals in a ventilation system, reflects back to the duct.
Attenuation in duct elbows is caused by reflected sound. It is only in big ducts and at high frequencies the attenuation is considerable.
Attenuation of sound in unlined sheet-metal ducts
Sound attenuation in rectangular straight, lined, sheet metal ducts.
An introduction to the nature of sound with frequency, wavelength and octaves.
The sound intensity level is the acoustic power of a sound per unit of area in relation to a fixed reference.
The definition of Sound Power Level and the Sound Power from some common sources as fans, jet engines, cars, humans ....
An introduction to decibel, sound power, sound intensity and sound pressure
The Sound Pressure is the force of sound on a surface area perpendicular to the direction of the sound.
Maximum recommended sound pressure levels in rooms with activities as kindergartens, auditoriums, libraries, cinemas and ...
Estimating sound transmission from a duct to the surrounding room.
Noise and sound transmitted through duct walls, through floors or through ceilings
An online Speed of Sound calculator for air
Calculation formulas for velocity of sound in gas, fluid or solid
Speed of sound in some common gases
Velocity of sound in common fluids as water, glycerol, kerosene ...
Velocity of sound in some common solids as aluminum, brass, concrete and ...
Changing sound pressure level and the subjective effect on human perception
Using telephones in noisy areas - satisfactory, difficult and impossible noise levels
The voice level at various distances
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