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

Abatement and Distance from Source

The disruption of sound pressure waves reducing the noise is called attenuation - Sound Pressure Level Calculator

Acceptable dBA Noise Levels

Acceptable noise - dBA - levels at some common locations

Acoustic Calculation of Ventilation Systems

Procedure for acoustic noise calculation of ventilation systems

Adding Decibels

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

Blade Dampers - Noise Generated

Noise levels generated in blade dampers

Blade Pass Frequency - BPF

A fan Blade Pass Frequency noise can be very intense - and vary with the number of blades and the 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, NCB, RNC), Noise Rating (NR) and dB(A)

Daily Noise Dose Level

Daily noise dose when exposed in periods with different noise levels


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

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

The change in frequency of sound due to relative motion between source and listener

Ducts and Noise Generation

Noise generated in air ducts

EPA Protective Noise Levels

The noise level should not exceed certain values to protect public health and welfare

Fans - Generated Sound Power

Noise from a fan depends on the motor power, capacity, static pressure and discharged volume

Floor Vibration

Human activities like walking, running, dancing and operating machines can induce high levels of floor vibrations

Gases - Speed of Sound

Speed of sound in gases

Inverse Square Law

When doubling the distance from a noise source - the sound pressure level - Lp, will be reduced by 6 decibel

Ldn - Day and Night Sound Level

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

Leq - Equivalent Sound Level

Equivalent Sound Level - Leq - quantifies the noise environment to a single value of sound level for any desired duration

Ls - Sound Exposure Level

Sound Exposure Level - Ls - describes the noise from a variable source

Machines and Noise Level Reductions

Reducing noise levels from machines

Maximum A-Weighted Sound Levels

Maximum A-weighted sound levels allowed by OSHA

NC - Noise Criterion

Noise Criterion - NC - level is a standard that describes the relative loudness of a space examining a range of frequencies

NR - Noise Rating Curve

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

Noise Criterion - NC - Online Calculator

An online Noise Criterion - NC - Calculator

Noise Exposure - Permissible Level and Duration

Exposure to noise should be controlled so that the exposure is less than a max combination of exposure level and duration

Noise Rating - NR - Online Calculator

An online Noise Rating - NR - Calculator

Noise from Road Traffics

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

Octave Bands - Frequency Limits

Frequency limits for octave and 1/3 octave bands

Online Attenuation Calculator

Calculate the attenuation in decibels in an outdoor free field

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

Noise measurement system for continuous or ambient noise in indoor environments

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

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

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

Sound Level - Online Calculator

Convert between sound level, sound pressure and sound intensity

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 sound

Sound Pressure - recommended Maximum Level in Rooms

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

Sound Transmission through Building Elements like Massive Walls or Floors

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 - Online Calculator

An online Speed of Sound calculator

Speed of Sound Formulas

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

Speed of Sound in some common Liquids

Speed of sound in common fluids like water, glycerol, kerosene ...

Speed of Sound in some common Solids

Speed of sound in some common solids like aluminum, brass, concrete and ...

Subjective Effect of Change in Sound Pressure Level

Changing sound pressure level and the subjective human perception

Telephone use in Noisy Areas

Use of telephone in noisy areas - satisfactory, difficult and impossible noise levels

Voice Level and Distance

Voice level at various distance

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