Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!


Room acoustics and acoustic properties - decibel A, B and C - Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation

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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 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

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Gas - Speed of Sound

Speed of sound in different 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 Attenuation in Direct Sound Fields

Room size - absorption characteristics and attenuation in direct sound fields

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 - Room Absorption Characteristics

Mean absorption coefficients and reverberation times for typical rooms

Sound - Room Absorption Coefficients

Room sound absorption and absorption coefficients for common materials like 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 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

Speed of Sound - Online Calculator

An online Speed of Sound calculator

Speed of Sound Equations

Calculate speed of sound - sonic velocity - in gases, fluids or solids

Speed of Sound in Air

Speed of sound in air at temperatures from -40 to 1000oC (-40 to 1500oF) at standard atmospheric pressure - Imperial and SI Units

Speed of Sound in Liquids

Speed of sound in some common fluids - like water, glycerol, kerosene ...

Speed of Sound in Solids and Metals

Speed of sound in common solids and metals - aluminum, brass, concrete and ...

Speed of Sound in Water

Speed of sound in water at temperatures ranging 32 - 212oF (0 - 100oC) - Imperial and SI units

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

Voice Level at Distance

Required voice levels at distance

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