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Acoustics

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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Air - Speed of Sound

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

Decibel

Logarithmic unit used to describe ratios of signal levels - like power or intensity - to a reference level.

Decibel A, B and C

Sound pressure filters compensating for hearing sensed by the human ear.

Fans - generated Noise Power

The sound generated by a fan depends on the motor power, the volume capacity, the static pressure increase and the discharged volume.

Floor Vibrations

Human activities like walking, running and dancing - and operating machines - can introduce floor vibrations due to resonance.

Gases - Speed of Sound

Speed of sound in some gases at zero degrees Celsius and atmospheric pressure.

Liquids - Speed of Sound

Speed of sound in common fluids like water, glycerol, kerosene and more.

Maximum Sound Pressure Level in Rooms

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

NC - the Noise Criterion

Noise Criterion - NC - level is a standard describing relative loudness of a space with a range of frequencies

Noise - Acceptable dBA Level

Acceptable noise - dBA - level at typical common locations.

Noise - EPA Protective Levels

The noise level should not exceed certain values to protect public health and welfare.

Noise - Maximum Daily Dose Level

Maximum daily noise dose level when exposed to periods with different levels.

Noise - Recommended Exposure Limits (REL)

The NIOSH noise Recommended Exposure Limit - REL - for occupational noise

Noise Criterion (NC) - Free Online Calculator

Calculate Noise Criterion (NC) from octave band pressure levels.

Noise Criterion vs. Noise Rating and dB(A)

Comparing Noise Criterion (NC, NCB, RNC) to Noise Rating (NR) and dB(A).

Noise Exposure - Permissible Level and Duration

Exposure to noise should be controlled so that it is less than a maximum combination of exposure level and duration.

Noise from Machines - Sound Pressure Level Reductions

Barriers and enclosures to reduce noise sound pressure levels from machines.

Noise generated by Fans - Blade Pass Frequency (BPF)

TheBlade Pass Frequency noise generated by a fan can be very intense and varies with the number of blades and the rotation velocity.

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Noise generated by Road Traffic

Estimate noise level generated by traffic.

Noise generated in Air Ducts

Estimate noise generated by air flow in ducts.

Noise generated in Blade Dampers

Sound power noise generated by blade dampers in ventilation systems.

Noise Rating (NR) - Free Online Calculator

An online Noise Rating (NR) calculator.

Notes, Octaves and Frequencies

Frequencies vs. notes and octaves.

NR - the Noise Rating Curve

The Noise Rating (NR) Curve used to determine acceptable indoor environments for hearing preservation, speech communication and annoyance.

Octave Band Frequencies

The octave and the 1/3 octave band frequencies.

Outdoor Ambient Sound Pressure Levels

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

PNC - the Preferred Noise Criterion

A 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 outdoor sound through and around barriers - the Fresnel Number.

Propagation of Sound Indoors - the Room Constant

In a room the sound or noise will reach the receiver as direct and reverberant sound.

Propagation of Sound Outdoors - Attenuation vs. Distance

The propagation of outdoors sound vs. distance and attenuation.

RC - the Room Criteria

The Room Criteria (RC) is used to measure background noise in buildings for frequencies ranging 16 to 4000 Hz.

Required Voice Level at Distance

Distance and perception of voice.

Signals - Adding Decibels

The logarithmic decibel scale is convenient when adding values for signals like sound power, pressure and more from two or more sources.

SIL - the Speech Interference Levels

Background noise frequencies that interferes with speech.

Solids and Metals - Speed of Sound

Speed of sound in solids and metals like aluminum, brass, concrete and more.

Sound - Abatement vs. the Distance from Source

The disruption of the sound pressure wave and the reduction of noise is called attenuation - Sound Pressure Level vs. distance calculator.

Sound - Attenuation and Speed vs. Sound Frequency and Air Humidity

The speed and attenuation of sound in moist air varies with sound frequency and air humidity.

Sound - Attenuation and the Directivity Coefficient

The attenuation in a room depends on the location of the sound source and the receiver - and the room constant.

Sound - Doppler Effect

The doppler effect is the change in sound frequency due to the relative motion between a source and a listener.

Sound - Frequency, Wavelength and Octave

An introduction to the nature of sound with frequencies, wave-lengths and octaves.

Sound - Hearing Threshold vs. Age

Shift in hearing threshold for men and women vs. age.

Sound - Ldn - Day and Night Level

The EPA A-weighted sound level day and night equivalent definition - Ldn - for a 24 hour period.

Sound - Leq - Equivalent Level

The EPA Equivalent Sound Level - Leq - quantifies the noise environment to a single value of sound level for any desired duration.

Sound - Ls - Exposure Level

The EPA Sound Exposure Level - Ls - describes the noise from a variable source.

Sound - Reverberation Time

The sound reverberation time indicates how long it takes until the sound pressure level in a room is decreased with 60 dB.

Sound - Room Absorption Characteristics

Mean absorption coefficients and reverberation times in typical rooms.

Sound - Room Absorption Coefficients

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

Sound - Room Attenuation in Direct Sound Fields

Room size, absorption characteristics - and attenuation in direct sound fields.

Sound Attenuation - Duct split to Terminals

Estimating sound attenuation where ducts splits to terminals.

Sound Attenuation - Main Duct to Branch Ducts

Sound attenuation from main ducts to branch ducts.

Sound Attenuation in Duct Elbows

Noise attenuation in duct elbows by reflected sound.

Sound Attenuation in Ducts due to End Reflection

Low frequency noise transferred from main duct to end terminals is reflected back to main duct.

Sound Attenuation in Unlined Sheet-Metal Ducts

Attenuation in unlined sheet-metal ducts

Sound Attenuation of Lined Sheet-Metal Ducts

Sound attenuation in rectangular straight, lined, sheet metal ducts

Sound Intensity

Acoustic power of sound per unit area.

Sound Intensity, Power and Pressure Levels

Introduction to decibel, sound power, intensity and pressure.

Sound Level - Online Calculator

Calculate sound level, pressure and intensity.

Sound Power

Sound power from sources like fans, jet engines, cars, humans and more.

Sound Pressure

Sound Pressure is the force of sound on a surface perpendicular to the propagation of sound.

Sound Pressure Level - OSHA A-Weighted per Day

OSHA maximum A-weighted sound pressure levels allowed per day.

Sound Propagation - the Inverse Square Law

Doubling of the distance from a noise source reduces the sound pressure level with 6 decibel.

Sound Transmission through Duct Walls

Sound transmission from ducts to surrounding rooms.

Sound Transmission through Flanking Paths

Sound transmitted through duct walls, floors and ceilings.

Sound Transmission through Massive Walls or Floors

Sound transmission and attenuation in building elements like massive concrete walls or floors.

Speed of Sound - Online Calculator

A free online speed of sound calculator.

Speed of Sound Equations

Calculate the speed of sound (the sonic velocity) in gases, fluids or solids.

Subjective Effect of Change in Sound Pressure Level

Change in sound pressure level and the subjective human perception.

Use of Telephone in Noisy Areas

Satisfactory, difficult and impossible noise levels for telephone use in noisy areas.

Ventilation Systems - Acoustic Calculation Procedure

Acoustic noise calculation procedure HVAC systems.

Ventilation Systems - Classification of Noise Reduction Silencers

Noise in a ventilation system can be reduced by reactive, diffuser type, active and/or dissipative silencers.

Water - Speed of Sound

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

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