Acoustics

Abatement and Distance from Source

The disruption of sound pressures waves which reduces the noise is called attenuation - Sound Pressure Level Calculator

Acceptable Noise - dBA - Levels

Acceptable noise - dBA - levels at some locations

Acoustic Calculation of Ventilation Systems

A procedure for acoustic noise calculation of ventilation systems

Adding Decibels

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

Blade Dampers and Noise Generation

Noise generated in blade dampers

Blade Pass Frequency - BPF

The fan Blade Pass Frequency noise can be very intense - vary with number of blades and rotation velocity

Classification of Noise Reduction Silencers

Eliminating noise with reactive silencers - diffuser type silencers - active silencers and/or dissipative silencers

Comparing Noise Criteria

Comparing Noise Criteria - Noise Criterion (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.

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Decibel A, B and C

Sound pressure is not equally sensed by human ear at different frequencies - compensated with dB(A), dB(B) or dB(C) filters

Directivity Coefficient and Sound Attenuation

The attenuation in a room depends on the location of the source and the receiver, and the room constant

Doppler Effect

Change in frequency of a sound due to relative motion between source and listener

Ducts - Noise Generation

Air flow and noise generated in ducts

Ducts - Noise Generation

Air flow and noise generated in ducts

EPA Protective Noise Levels

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

Fans and Noise Power Generation

Sound Power Level from a fan depends on motor power, capacity, static pressure and discharged volume

Floor Vibration

Human activities like walking, running, dancing and operating machines can induce high levels of vibration in floors

Frequency Limits for Octave Bands

Frequency limits for octave bands and 1/3-Octave bands

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

Machines - Sound Level Reduction

Reducing machines sound level

Maximum A-Weighted Sound Levels Allowed

Maximum A-weighted sound levels allowed by OSHA

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

NR - Noise Rating Curves

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

Noise Exposure - Permissible Level and Duration

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

Noise from Road Traffic

Online calculating of road traffic noise levels for non-complex situations

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

Outdoor ambient sound level (dBA) in 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 - Fresnel Number

RC - Room Criteria

Room Criteria - RC - measures the background noise 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 the time it takes until the sound pressure level in a room is decreased with 60 dB

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 Duct 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

Noise attenuation in a duct elbow is caused by reflected sound. It is only in larger ducts and at higher 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 - 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

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

Sound Power, Intensity and Pressure

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

Sound Pressure

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

Sound Pressure - Recommended Maximum Levels in Rooms

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

Sound Transmission Through Massive Walls or Floors, and other Building Elements

Sound and noise transmission through massive walls or floors - concrete or similar

Sound Transmission through Duct Walls

Estimating sound transmission from ducts to surrounding rooms

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

Speed of Sound Formulas

Calculation formulas for velocity of sound in gases, fluids or solids

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