Acoustics
Room acoustics, acoustic properties - decibel A, B and C - Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity, attenuation and more ..
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Abatement and Distance from Source
The disruption of sound pressures waves which reduces the noise is called attenuation - Sound Pressure Level Calculator
Acceptable Noise - dBA - Levels
Acceptable noise - dBA - levels at some locations
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
Classification of Noise Reduction Silencers
Eliminating noise with reactive silencers - diffuser type silencers - active silencers and/or dissipative silencers
Comparing Noise Criteria
Comparing Noise Criteria - Noise Criterion (NC), Noise Rating (NR) and dB(A)
Daily Noise Dose Level
Daily noise dose level when exposed in periods with different noise levels
Decibel
Decibel is a logarithmic unit used to describe the ratio of the signal level - power, sound pressure, voltage, intensity, etc.
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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
Ducts - Noise Generation
Air flow and noise generated in ducts
EPA Protective Noise Levels
The noise level should not exceed values protecting public health and welfare
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
Frequency Limits for Octave Bands
Frequency limits for octave bands and 1/3-Octave bands
Inverse Square Law
For every doubling of the distance from the noise source, the sound pressure levels - Lp, will be reduced by 6 decibels
Ldn - Day and Night Sound Level
The EPA has defined an A-weighted sound level day and night equivalent for a 24 hour period
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Leq - Equivalent Sound Level
Equivalent Sound Level - Leq - quantifies the noise environment as a single value of sound level for any desired duration
Ls - Sound Exposure Level
Sound Exposure Level - Ls - describes noise from a varied source
Machines - Sound Level Reduction
Reducing machines sound level
Maximum A-Weighted Sound Levels Allowed
Maximum A-weighted sound levels allowed by OSHA
NC - Noise Criterion
For a given noise spectrum, the NC rating can be obtained by plotting its octave band levels on the set of NC curves
NR - Noise Rating Curves
An introduction to Noise Rating - NR - curves, developed by the International Organization for Standardization (ISO) - NR diagram
Noise Exposure - Permissible Level and Duration
Noise exposure should be controlled so that exposure is less than the combination of exposure level and duration
Noise from Road Traffic
Online calculating of road traffic noise levels for non-complex situations
Online Attenuation Calculator
Calculate the attenuation in decibels in an outdoor free field
Online Noise Criterion - NC - Calculator
An online Noise Criterion - NC - Calculator
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
PNC - Preferred Noise Criterion
A noise measurement system for continuous or ambient noise in indoor environments proposed by Leo Beranek in 1971
Preferred Noise Criterion - PNC - Calculator
An online Preferred Noise Criterion - PNC - Calculator
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
RC - Room Criteria
Room Criteria - RC - measures the background noise in a building over the frequency range 16 Hz to 4000 Hz
REL - Noise Recommended Exposure Limit
The NIOSH noise Recommended Exposure Limit - REL - for occupational noise
Reverberation Time
The 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 some typical rooms.
Room Acoustics Calculator
An online acoustic calculator for estimating the reverberation time and designing the acoustics of rooms
Room Attenuation in Direct Sound Fields
Room size, absorption characteristics and attenuation in direct sound fields
SIL - Speech Interference Levels
Approximate speech interference levels
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
Speed of Sound Calculator
An online Speed of Sound calculator
Speed of Sound Formulas
Calculation formulas for velocity of sound in gases, fluids or solids
Speed of Sound in Gases
Speed of sound in some common gases
Speed of Sound in some common Liquids
Velocity of sound in common fluids as water, glycerol, kerosene ...
Speed of Sound in some common Solids
Velocity of sound in some common solids as aluminum, brass, concrete and ...
Subjective Effect of Change in Sound Pressure Level
Changing sound pressure level and the subjective effect on human perception
Telephones in Noisy Areas
Using telephones in noisy areas - satisfactory, difficult and impossible noise levels
Voice Level and Distance
The voice level at various distances
