Sound level

Noise. Technical differences exist between personal noise dosimeters and high accuracy sound level meters and these may alter the usual preference for personal monitors. But it is exposure to noise rather than general room noise that must be estimated for comparison with noise exposure criteria, the logarithmic expression and alternative means of summation (3 vs 5 db doubling) compHcate statistics. Exposure criteria for both dose and peak exposure must be evaluated, and space and time variabiUty of noise intensity can be immense. 

Safety Standards (enclosures) for construction and guide for selection, installation and use of rotating machines Sound level prediction for insulated rotating electrical machines Energy management guide for selection and use of three phase motors Polyphase induction motors for power generating stations... 

Sound level prediction for in >iallcd rotating electrical machines. 

When the unit was initially plaeed in serviee, sound level measurement data were eolleeted. Within 3 ft of the expander ease, sound levels were measured at 92-99 dBA. At the property line 25 ft away from the ease, the levels were 68-85 dBA. At the time of installation, there were no stmetures near enough to the faeility to be impaeted by any noise. However, as the surrounding area eontinues to develop, it may be neeessary to install sound attenuation equipment. 

Airborne material affecting the quality of indoor air may be classified as gases or particulate matter. Gases which may be potential problems are radon, CO, NOj, and hydrocarbons. Particulate matter may come from tobacco smoke, mold spores, animal dander, plant spores, and others as shown in Table 23-1. Other factors interact to influence our perception of indoor air quality, including humidity, temperature, lighting, and sound level. 

Noise monitoring is usually located in the HASP as part of the monitoring program. Noise monitoring should be performed in accordance with acceptable practices. Typically, noise levels are monitored in the field with either a Type I or Type II sound level meter (SLM). Noise dosimeter readings can also be obtained to determine the percent (%) noise dose. Noise levels and % doses measured are then compared to limits listed in OSHA standard 29 CFR 1910.95, Hearing Conservation [3]. 

Not performing monitoring that is required hy the SSHAP may have potentially serious consequences. For noise monitoring, guidance should he written into the plan that specifies when noise monitoring will he performed. For instance, how should one handle the following situation Let s say you are on site hut you do not have a sound level meter. At what point do you need to monitor One rule of thumb for this situation is as follows if you cannot conduct a normal conversation with fellow employees that are within three feet, you are likely at or above 85dBA. Your plan should state this. And it should state when and if the site would need to have a sound level meter on site. 

The roof and walls of the fan room should be lined internally with absorbent materials in order to reduce the sound level in the fan room. The wall insulation should be sufficient to reduce the transmission of sound to adjoining silent premises. 

Holmberg, K., Landstrom, U., and Kjellberg, A. (1993). Effects of ventilation noise due ro frequency eh.iracteristics and sound level. /. Low Frequency Noise and Vibration 12(4). 

Sound-level problems with high speeds... 

Inherently higher sound levels than most efficient centrifugal fans for the same duty... 

This fan design is capable of the highest efficiency with the lowest sound level of all the centrifugal fans for a given duty, particularly those with airfoilshaped double blades. 

Highest sound level of all centrifugal fans for a given duty. 

Therefore, acoustic science has introduced different kinds of weighting curves in order to correlate as accurately as possible the sound level with the level really perceived by a generic listener. In practice, A-weight-ing correction is used. It consists of a series of coefficients, shown in Table 9.17. These are added to sound levels expressed in dB for each frequency. 

The high sound levels produced by an electric arc furnace can be contained within a furnace enclosure if a proper acoustical design is carried out. Any design should be checked by a competent acoustician. The following points should be considered ... 

The sensor is the element of an instrument directly influenced by the measured quantity. In temperature measurement the thermal mass (capacity) of the sensor usually determines the meter s dynamics. The same applies to thermal anemometers. In IR analyzers used for concentration measurement, the volume of the flow cell and the sample flow rate are the critical factors. Some instruments, like sound-level meters, respond very fast, and follow the pressure changes up to several kHz. 

Weighting A The frequency-selective device on a sound level meter used to measure the A frequency network. 

On January 9,1964, a test was run at Los Alamos Scientific Laboratory to measure the acoustic sound levels developed during the release of gaseous hydrogen at high flow rates. The released hydrogen ignited and exploded. 

Reider et al. (1965) describe the incident at Los Alamos Laboratory in Jackass Flats, Nevada. An experiment was conducted on January 9, 1964, to test a rocket nozzle, primarily to measure the acoustic sound levels in the test-cell area which occurred during the release of gaseous hydrogen at high flow rates. Hydrogen discharges were normally flared, but, in order to isolate the effect of combustion... 

I.D. of duct, ft decibels sound level polytropic efficiency, = m/m ... 

Steam transmission will produce noise. Low steam velocity will help to reduce this. One specific noise area will be if a pressure-reducing valve set is employed. Therefore it is desirable to have this within the boiler house or other building and not outside. Some types of pressure-reducing valves operate at lower sound levels than others, and therefore if environmental noise could be a problem then this should be investigated. Insulated valve boxes will also help to contain any noise. 

In the case of the subtraction of levels. The difference between the total sound level and the one to be subtracted is plotted onto the graph and the correction obtained as above. In this case the correction is subtracted from the total level to give the remaining sound level. 

The simplest sound level meter consists of a microphone, an amplifier and a meter of some type. Sound level meters are graded according to British and international standards, and the most common type used for accurate measurement purposes it known as the Precision Grade or Type 1 meter. In practice, a basic sound level meter will incorporate weighting networks with either in-built octave filters or provision for connecting an external filter set (Figure 42.6). 

Portable sound level meters are also available which can measure percentiles. These either hold the results in a memory which can be separately interrogated or may be connected to a computer for a printout. Larger machines (known as environmental noise analyzers) are available which can record percentiles and Leq readings and produce a printout. These are resistant to weather and can be left on-site for up to a week. 

In practice, measurements are made with the use of an accelerometer. This device is connected to a sound level meter and may make measurements of acceleration in terms of decibels (or by changing scales or use of a device similar to a slide mle, in direct terms). An integrator can be connected between the accelerometer and the meter to express the results in terms of velocity or displacement. 

Figure 42.6 Schematic diagram of a sound level meter...

Permanent damage to hearing can be caused at sound levels above about 90 dB(A), and it is normal practice to provide ear protection in areas where the level is above 80 dB(A). 

Blast pressure gages, heat flux transducers, and sound level meters are to be located at the probable head location of the operator and at representative positions where transient personnel may be located. 

Distance is a major factor in reducing nuisance noise and suitable spacing should be considered in the plant initial layout. The acceptable amount of noise generation should be specified on the purchase order for the equipment. Where sound levels cannot be alleviated by purchasing a different make of equipment, sound attenuation devices should be fitted (i.e., enclosures) as an alternative. 

The noise level was also measured using Interacting Sound Level Meter (NL04) from RION for blower speed setting of normal-speed near the inlet and outlet of the Prototype Unit. The average noise levels are 23 and 48 dB at the inlet and outlet, respectively. These values are low compared to most air dehumidifier and air purifier appliances. 

The signal, amplified to a good sound level at the loudspeaker, is fed to the vertical input of the oscilloscope. A stationary trace is obtained on the oscilloscope. The frequency of the sine wave of the oscilloscope is varied until a single trace is obtained. This frequency is then equal to the frequency of bubble formation. 

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