Noise and Attenuation

Noise is usually defined as unwanted sound - noise, noise generation, silencers and attenuation in HVAC systems

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

Attenuation of Sound in Sea Water

Sea water and sound attenuation

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

Chamber Noise Attenuation

Noise attenuation in chambers

Classification of Noise Reduction Silencers

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


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

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

Ducts - Noise Generation

Air flow and noise generated in ducts

Effects of Low-Frequency Noise and Vibration on People

Physiological effects of low-frequency noise and vibration

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

NR - Noise Rating Curves

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

Noise Attenuation - Changing Duct Area

Changing duct size and noise attenuation

Online Attenuation Calculator

Calculate the attenuation in decibels in an outdoor free field

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

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

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

Rotary Heat Exchanger - Noise Attenuation

Sound attenuation in rotating heat exchangers

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 Level 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

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