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

Adding Decibels

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

Blade Dampers - Noise Generated

Sound power level generated in blade dampers

Blade Pass Frequency - BPF

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

Classification of Noise Reduction Silencers

Eliminate noise with reactive , diffuser type, active and/or dissipative silencers

Decibel

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

Decibel A, B and C

Sound pressure sensed by the human ear - dB(A), dB(B) or dB(C) frequency filters

Directivity Coefficient and Sound Attenuation

Room attenuation depends on location of source and receiver - and the room constant

Ducts and Air Flow Noise

Air flow generated noise in air ducts

Fans - Noise Power Generated

Noise or sound generated by a fan depends on the motor power, volume capacity, static pressure and discharged volume

Floor Vibration

Human activities like walking, running, dancing - and operating machines can induce floor vibrations

Human Effects of Low-Frequency Noise and Vibration

Physiological effects of low-frequency noise and vibration

Maximum Sound Pressure Levels in Rooms

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

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

Outdoor Ambient Sound Levels

Outdoor ambient sound level (dBA) in rural and urban business and industrial environments with or without limited traffic

Propagation of Outdoor Sound - Partial Barriers

The transmission of sound through and around outdoor barriers - the Fresnel Number

Propagation of Sound Indoors - Room Constant

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

Propagation of Sound Outdoors

Outdoor propagation of sound - distance and attenuation

Room Absorption Characteristics

Mean absorption coefficients and reverberation times for typical rooms

Room Sound Absorption - Sound Absorption Coefficient

Room sound absorption and absorption coefficients for common materials like plaster walls, brickwork, plywood panels etc...

Rotary Heat Exchanger - Noise Attenuation

Noise attenuation in rotating heat exchangers

Sea Water - Attenuation of Sound

Sea water and attenuation of sound

Sound Attenuation - Duct split to Terminals

Estimation of sound attenuation when ducts are split to terminals

Sound Attenuation - Main Duct to Branch Ducts

Sound attenuation from main duct to branch ducts

Sound Attenuation due to Duct End Reflection

Some of the low frequency noise transferred from a main duct to the end terminals is reflected back to the main duct

Sound Attenuation in Duct Elbows

Noise attenuation in duct elbows are caused by reflected sound

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 octave

Sound Intensity

Sound intensity is the acoustic power of sound per unit area

Sound Level - Online Calculator

Convert between sound level, sound pressure and sound intensity

Sound Power

Sound Power Level from common sources like fans, jet engines, cars, humans and more ..

Sound Power -, Intensity - and Pressure Level

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 Transmission through Duct Walls

Estimating sound transmission from ducts to surrounding rooms

Sound Transmission through Massive Walls or Floors

Sound attenuation in building elements like massive concrete walls or floors

Sound Transmissions through Flanking Paths

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

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