Acoustics

Room acoustics, acoustic properties - decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity, attenuation ..

Abatement and Distance from Source

The disruption of sound pressures waves which reduces the noise is called attenuation

Acceptable dBA Levels

Guidelines for acceptable noise levels in terms of dBA for different locations.

Acoustic Calculation of Ventilation Systems

A procedure for acoustic calculation of noise in ventilation systems

Blade Dampers and Noise Generation

Noise generated in blade dampers

Blade Pass Frequency - BPF

The noise level intensity varies with type of fan

Calculate Decibel

The logarithmic decibel scale is convenient when calculating resulting sound power levels and sound pressure levels for two or more sound or noise sources.

Classification of Noise Reduction Silencers

Noise can be eliminated with reactive silencers, diffuser type silencers, active silencers and/or dissipative silencers

Comparing Noise Criteria

Comparing Noise Criteria (NC), Noise Rating (NR), and dB(A)

Daily Noise Dose Level

Daily noise dose level when exposed in periods with different noise levels

Decibel

Decibel is a logarithmic unit used to describe the ratio of the signal level - power, sound pressure, voltage, intensity, etc.

Decibel A, B and C

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

Directivity Coefficient and Sound Attenuation 

The attenuation in a room depends on the receiver and source location. 

EPA Protective Noise Levels

The noise level should not exceed values protecting public health and welfare.

Fans and Sound Power Generation

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. 

Inverse Square Law

For every doubling of the distance from the noise source, the sound pressure levels - L_p, will be reduced by 6 decibels

L_dn - Day and Night Sound Level

The EPA has defined an A-weighted sound level day and night equivalent for a 24 hour period.

L_eq - Equivalent Sound Level

Equivalent Sound Level - L_eq - quantifies the noise environment as a single value of sound level for any desired duration.

L_s - Sound Exposure Level

Sound Exposure Level - L_s - describes noise from a varied source.

NC - Noise Criterion

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 - Level and Duration

Noise exposure should be controlled so that exposure is less than the combination of exposure level and duration.

NR - Noise Rating Curves

An introduction to Noise Rating - NR - curves - developed by the International Organization for Standardization (ISO) - NR diagram

Online Attenuation Calculator

Calculate the attenuation in decibels in an outdoor free field

Online Noise Criterion - NC - Calculator

An online Noise Criterion - NC - Calculator

Online Noise Rating - NR - Calculator

An online Noise Rating - NR - Calculator

Online Sound Level Calculator

Convert between sound level, sound pressure and sound intensity

Outdoor Ambient Sound Levels in Decibel

Outdoor ambient sound level in different rural and urban business and industrial environments with or without limited traffic.

PNC - Preferred Noise Criterion

A noise measurement system for continuous or ambient noise in indoor environments proposed by Leo Beranek in 1971

Preferred Noise Criterion - PNC - Calculator

An online Preferred Noise Criterion - PNC - Calculator

Propagation of Sound Indoors

Sound and noise in a room will reach the receiver as direct and reverberant sound.

Propagation of Sound Outdoors

Outdoor propagation of sound - distance and attenuation. 

Propagation of Sound Outdoors and Partial Barriers

The transmission of sound through and around outdoor barriers. 

RC - Room Criteria

Room Criteria - RC - measures background sound in a building over the frequency range 16 Hz to 4000 Hz.

REL - Noise Recommended Exposure Limit

The NIOSH noise Recommended Exposure Limit - REL - for occupational noise.

Reverberation Time

The Sound Reverberation Time indicates how long it takes until the sound pressure level in a room is decreased with 60 dB

Road Traffic Noise

An online calculator for calculating road traffic noise levels for non-complex situations.

Room Absorption Characteristics

Mean absorption coefficients and reverberation times for some typical rooms.

Room Acoustics Calculator

An online acoustic calculator for estimating the reverberation time and designing the acoustics of rooms

Room Attenuation in Direct Sound Fields

Room size, absorption characteristics and attenuation in direct sound fields

SIL - Speech Interference Levels

Approximate speech interference levels

Sound Absorption Coefficients for some common Materials

Sound absorption coefficients for some common materials as plaster walls, brickwork, plywood panels etc.

Sound Attenuation - Duct split to Terminals

Estimation of sound attenuation when ducts are split to terminals

Sound Attenuation - Main Ducts to Branches

Sound attenuation for main ducts to branches.

Sound Attenuation due to End Reflection

Some of the low frequency noise transferred to the end terminals in a ventilation system, reflects back to the duct.

Sound Attenuation in Duct Elbows

Attenuation in duct elbows is caused by reflected sound. It is only in big ducts and at high frequencies the attenuation is considerable.

Sound Attenuation in Unlined Sheet-Metal Ducts

Attenuation of sound in unlined sheet-metal ducts

Sound Attenuation of Lined Sheet-Metal Ducts

Sound attenuation in rectangular straight, lined, sheet metal ducts.

Sound Frequency, Wavelength and Octave

An introduction to the nature of sound with frequency, wavelength and octaves.

Sound Intensity

The sound intensity level is the acoustic power of a sound per unit of area in relation to a fixed reference.

Sound Power

The definition of Sound Power Level and the Sound Power from some common sources as fans, jet engines, cars, humans ....

Sound Power, Intensity and Pressure

An introduction to decibel, sound power, sound intensity and sound pressure

Sound Pressure

The Sound Pressure is the force of sound on a surface area perpendicular to the direction of the sound.

Sound Pressure - Recommended Levels in Rooms

Maximum recommended sound pressure levels in rooms with activities as kindergartens, auditoriums, libraries, cinemas and ...

Sound Transmission through Duct Walls

Estimating sound transmission from a duct to the surrounding room.

Sound Transmissions through Flanking Paths

Noise and sound transmitted through duct walls, through floors or through ceilings

Speed of Sound Calculator

An online Speed of Sound calculator for air

Speed of Sound Formulas

Calculation formulas for velocity of sound in gas, fluid or solid

Speed of Sound in Gases

Speed of sound in some common gases

Speed of Sound in some common Liquids

Velocity of sound in common fluids as water, glycerol, kerosene ...

Speed of Sound in some common Solids

Velocity of sound in some common solids as aluminum, brass, concrete and ...

Subjective Effect of Change in Sound Pressure Level

Changing sound pressure level and the subjective effect on human perception

Telephones in Noisy Areas

Using telephones in noisy areas - satisfactory, difficult and impossible noise levels

Voice Level and Distance

The voice level at various distances

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