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