Sound power level

I oise Transmission Reduction in HVACSystems. One common use of sound-absorbing treatment is to reduce noise transmission in heating, ventilating, and air-conditioning (HVAC) systems (6). The treatments ate used to reduce the transmission of fan noise and air turbulence noise through ducts into occupied spaces. Noise transmission reduction in duct systems is described in terms of insertion loss, the difference in sound power level or sound pressure level measured at a given location before and after installation of the treatment or sound attenuation, the reduction in sound power between two locations affected by a sound source. The units ate decibels. 

When measuring the noise level, i.e. the limiting mean sound power level in dB for airborne noise emitted by a machine, reference may be made to the following lEC and ISO publications ... 

ISO 3740, Acoustics - Determination of sound power levels of noise sources - Guidelines for the use of basic standards and for the preparation of noise test codes. 

Guidelines on t ualily management and quality system elements Test code for the measurement of airborne noise emitted by rotating electrical machines Engineering method for free field conditions over a reflecting plane Survey method Determination of sound power levels of noise sources 14004/1991 BS EN ISO 9004/1994-1/1994 BS 7458-1/1991 BS 7458-2/1991 B.S 4196 9004/1987 1680-1/1986 1680-2/1986. 3740... 

Octave band frequency The band in frequency scale that is split into bands, each assigned a sound power level, that is twice the power level of the lower limit. 

P[3 = P[ = fan input power D = fan size (impeller or wheel diameter) N = fan speed Nj = fan specific speed p = fan air density Q = fan flow rate Kp = compressibility coefficient L, = sound power level Pjt = fan total pressure Pjy = fan velocity pressure Pj-s = fan static pressure... 

Sound power is the total energy emitted from a fan that is a function of the fan s speed and point of operation and is independent of the fan s installation and surrounding environment Sound power level is the acoustical power expressed in decibels (dB) radiating from a source. Sound power can be converted into predictable pressure levels (dBA) after the acoustical environment surrounding the fan is defined. Sound pressure for a specific fan varies with... 

The power of a source (measured in watts) can be similarly expressed in terms of decibels (in this case, called the sound power level) ... 

It can thus be seen that it is important not only to express the unit but also to state sound pressure level, sound intensity level or sound power level. 

Acoustics—Determination of Sound Power Levels of Noise Sources—Precision Methods for Broad-Band Sources in Reverberation Rooms Acoustics—Determination of Sound Power Levels of Noise Sources—Engineering Methods for Free-Field Conditions Over a Reflecting Plane Acoustics—Determination of Sound Power Levels of Noise Sources—Survey Method... 

If specified, the vendor shall provide both maximum sound pressure and sound power level data per octave band for the equipment. Control of the sound pressure level (SPL) of all equipment furnished shall be a joint effort of the purchaser and the vendor having unit responsibility. The equipment furnished by the vendor shall conform to the maximum allowable sound pressure level specified. ISO 3740, ISO 3744 and ISO 3746 may be consulted for guidance. 

ISO 3744, Acoustics — Determination of sound power levels of noise sources using sound pressure — Engineering method in an essentially free field over a reflecting plane. 

SPL at a point, typically 30 m distant from an SRV vent of sound power level (PWL) is calculated by using the following equation ... 

In the context of acoustics the power level is called the sound power level and given the symbol Lw, and the reference power P0 = 1 pW. 

There is a subtle but important difference between the terms Sound Power Level (PWL), and Sound Pressure Level (SPL). Sound power level is used to indicate the total energy emitting ability of a sound source. In other words, sound power is an attribute of the source itself. Sound pressure level, on the other hand, is used to indicate the intensity of sound received at any point of interest, from one or more sources. The illustration in Eigure 8.4 shows the formula to calculate the SPL to be expected at a distance r from a spherically radiating source of power level L. ... 

Ip = sound pressure level in dB = Sound power level in dB r = Distance from source in ft. 

If the above conditions are sufficiently fulfilled, fhen Equation 8.2 can not only be used to calculate the SEE expected at a certain distance r from the source if the sound power level is known, but also to back-calculate the PWL of a source from a measurement of the sound pressure level at a known distance r from fhe source. The laffer procedure is a fechnique fhat is sfandardized in ISO 3744 [2]. 

Sound power level calculated from measured noise data, plotted versus heat release rate for different types of industrial flares... 

Example for the acoustic optimization of a steam injector for a steam-assisted flare at the John Zink Company test facilities in Tulsa. A-weighted sound power level for identical steam pressure and steam mass flow rate. 

Example for the noise emissions of a steam control valve of a steam-assisted elevated flare. A-weighted sound power level L , as in Figure 8.32 of the flare with standard control valve and uninsulated piping and with low noise valve and acoustically insulated steam pipes. 

Sound power level fundamental measure of sound power defined as = 10 log P/Pq dB, where P is the RMS value of sound power in watts and Pq is 1 pwatt. 

ISO 3744 "Acoustics - Determination of Sound Power Levels of Noise Sources Using Sound Pressure— Engineering Method in an Essentially Free Field Over a Reflecting Plane." May 1,1994. 

ISO 3744 (E), Acoustics Determination of Sound Power Levels of Noise Sources. 

ISO/DIS 8297 Acoustics Determination of Sound Power Levels of Multi-Source Industrial Plants for the Evaluation of Sound Pressure Levels in the Environment-Engineering Method, 1988. 

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