Noise and Attenuation

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

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


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

Ducts and Noise Generation

Noise generated in air ducts

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

Human Effects of Low-Frequency Noise and Vibration

Physiological effects of low-frequency noise and vibration

NR - Noise Rating Curve

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

Noise Attenuation by Changing Duct Area

Changing of duct size and attenuation of noise

Noise Attenuation in a Chamber

Chamber noise attenuation

Noise Rating - NR - Online Calculator

An online Noise Rating - NR - Calculator

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

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

Noise attenuation in rotating heat exchangers

Sea Water - Attenuation of Sound

Sea water and attenuation of sound

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

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