Acoustics
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 and reduction of noise is called attenuation - Sound Pressure Level Calculator
Acceptable dBA Noise Levels
Acceptable noise - dBA - level at some 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
Age and Shift in Hearing Threshold
Shift in hearing threshold for men and women
Attenuation and Speed of Sound - Air Humidity and Frequency
Speed and attenuation of sound at varous frequencies and air humidities
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
Noise can be reduced by reactive , diffuser type, active 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
Decibel is a logarithmic unit used to describe the ratio of a signal level - like power or intensity 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
Doppler Effect
The change in frequency of sound due to relative motion between source and listener
EPA Protective Noise Levels
The noise level should not exceed certain values to protect public health and welfare
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
Gases - Velocity of Sound
Speed of sound in gases
Inverse Square Law
A doubling of the distance from a noise source will reduce the sound pressure level with 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
Maximum A-Weighted Sound Pressure Levels per Day
Maximum A-weighted sound pressure levels allowed by OSHA
Maximum Sound Pressure Levels in Rooms
Maximum recommended sound pressure levels in rooms with activities like kindergartens, auditoriums, libraries, cinemas and more ...
NC - Noise Criterion
Noise Criterion - NC - level is a standard describing relative loudness of a space with a range of frequencies
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 from Road Traffic
Estimate noise levels from traffic
Noise Generated in Air Ducts
Noise generated from air flow in ducts
Noise Level Reduction of Machines
Reduce the noise level from machines
Noise Rating - NR - Online Calculator
An online Noise Rating - NR - Calculator
Notes, Octaves and Frequencies
Frequency vs. notes and octaves
NR - Noise Rating Curve
An introduction to the Noise Rating - NR - Curve developed by the International Organization for Standardization (ISO)
Octave Band Frequencies
Octave and 1/3 octave band frequencies
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 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
RC - Room Criteria
Room Criteria - RC - measuring background noise in a building over frequencies ranging 16 Hz to 4000 Hz
REL - Recommended Exposure Limits for Noise
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 typical rooms
Room Attenuation in Direct Sound Fields
Room size - absorption characteristics and attenuation in direct sound fields
Room Sound Absorption - Sound Absorption Coefficient
Room sound absorption and absorption coefficients for common materials like plaster walls, brickwork, plywood panels etc...
SIL - Speech Interference Levels
Approximate speech interference levels
Sound - Frequency, Wavelength and Octave
An introduction to the nature of sound - frequency, wavelength and octave
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 in Duct Elbows
Noise attenuation in duct elbows are caused by reflected sound
Sound Attenuation in Ducts due to End Reflection
Some low frequency noise transferred from main duct to end terminals is reflected back to main duct
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 Intensity
Sound intensity is the acoustic power of sound per unit area
Sound Intensity, Power and Pressure Levels
Introduction to decibel, sound power, sound intensity and sound pressure
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 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
Subjective Effect of Change in Sound Pressure Level
Changing sound pressure level and subjective human perception
Telephone use in Noisy Areas
Use of telephone in noisy areas - satisfactory, difficult and impossible noise levels
Velocity of Sound - Online Calculator
An online Speed of Sound calculator
Velocity of Sound Formulas
Calculate velocity of sound - sonic velocity - in gases, fluids or solids
Velocity of Sound in Air
Velocity of sound in air at temperatures from -40 to 1000oC (-40 to 1500oF) at standard atmospheric pressure - Imperial and SI Units
Velocity of Sound in Liquids
Velcocity of sound in some common fluids - like water, glycerol, kerosene ...
Velocity of Sound in Solids and Metals
Velocity of sound in common solids and metals - aluminum, brass, concrete and ...
Velocity of Sound in Water
Velocity of sound in water at temperatures ranging 32 - 212oF (0 - 100oC) - Imperial and SI units
Voice Level at Distance
Required voice levels at distance
