The sound level meter

The majority of noise control work imdertaken by the safety adviser will involve the measmement and possibly the analysis of noise. It is therefore important that the use and the limitations of sound pressure level measurements and soxmd level meters are understood. Errors in measurement technique or interpretation could lead to costly mistakes or over-specifying in remedial measures. 

The difference between the two available grades of soimd level meter, precision and industrial, is effectively the degree of accuracy of the measurements particularly at high and low frequency. Meters should comply with the current appropriate standard.  

For the operation of soxmd level meters of different types the safety adviser should refer to the manufacturer s instruction book. The prime requirement for any instrument for noise measurement is that it should not be more sophisticated than necessary and it should be easy to use and calibrate. A typical sound level meter for use by the safety adviser should have the facility for measuring dBA and octave band soxmd pressure levels. More sophisticated meters have facilities for measuring equivalent noise level (Leq, Lepci) (see section 3.5.6) and xmderlaking statistic analysis. 

---

Frequency weighting Weighting for loudness and type of sound by means of various weighting networks fitted in the sound level meter mainly these are the A, B, C and D weightings (weighting curves are given in DIN 45633). 

Configure the sound level meter to read in dB(A) and take a number of measurements at individual workstations. Take the average of the readings at each woikstation. 

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. 

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 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. 

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. 

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. 

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. 

Noise—with the assessment of permissible noise levels lor communication and warning signals and the development of technology for noise abatement and control. Developments have included an audio dosimeter to replace conventional sound-level meters, discriminating earmuffs, and a noise control muffler system to reduce pneumatic drill noise. 

Exposure monitoring is another element of HCP. The sound level and exposure time should be measured. It is very important that sound levels measured are typical of those encountered by the worker. Proper survey techniques include sound-pressure-level (SPL) meters that should be vigorously apphed at monitored workplaces. They measure the smallest pressure changes initiated by the vibrating source and transmitted through the air. 

Both OSHA and the EPA have provided information on permissible noise exposures. Protection from noise is required when sound levels exceed those provided below. These are measured on the A scale at a slow response on a standard sound-level meter (except for certain alarms, etc.) as provided by OSHA. 

Sound level level of sound measured with a sound level meter and one of its weighting networks. When A-weighting is used, the sound level is given in dBA. 

Weighting network an electronic filter in a sound level meter, which approximates under defined conditions the frequency response of the human ear. The A-weighting network is most commonly used. 

Noise of a constant level as measured over at least one second using the slow setting on a sound level meter. Note that a noise that is intermittent, e.g., on for over a second and then off for a period, would be both variable and continuous. 

A weighted sound-pressure level obtained by use of metering characteristics and the weighting A, B, or C as specified in American National Standards Institute (ANSI) Standard S1.4, Specifications for Sound Level Meters. If the frequency weighting employed is not indicated, A-weighting is usually implied. 

A device to measure instant noise levels. It is comprised of a microphone, amplifier, output meter, and frequency-weighting networks, which are used for the measurement of noise and sound levels. Sound-level meters are often made with various filtering networks that measure the sound directly on A, B, C, etc., scales. Sound-level meters may also incorporate octave-band filters for measuring sound directly in octave bands. Since sound levels are specific to the areas being measured, the sound levels are called area sampling. Sound level meters used for measuring noise for compliance requirements must meet American National Standards Institute (ANSI) Standard S1.4, Specifications for Sound Level Meters. See also Noise Dosimeter Weighted Measurements. 

In areas where noise is a problem, the sound level should be established using a sound level meter and if above the stipulated minimum operatives must be provided with ear protection. 

Where sound levels exceed the PNEs, you must also implement a hearing conservation program. An effective program monitors employee exposure, administers annual audiograms, trains workers, and maintains proper recordkeeping. You should keep records on the noise created by different machines and operations at your construction site. Measurements should be taken with a sound level meter, at slow response, measured on the A-scale. 

The other type of survey has the purpose of finding out if conditions could create excessive exposures. In this kind of survey, measurements taken at various locations help determine noise sources or potential noise exposures at locations where people may be. During a survey, a user takes readings with a sound level meter in a grid pattern or at specific worker locations. The survey data then help with decisions on reducing noise exposures. 

The 3M Sound Detector SD-200 is a compact, lightweight sound level meter designed for measurement of workplace noise levels. Its intuitive design makes it easy to measure sound levels and determine the level of hearing protection that may be required. 

Make the maximum noise level of the equipment 80 dBA, 8 Hour Time Weighted Average when measured on the A scale of a standard sound level meter or noise dosimeter within 3 feet of the equipment. 

There are many sound level meters on the market, but all work in a similar manner. The basic hand-held set Figure 20.6) consists of a microphone, an amplifier with a weighting network and a read-out device in the form of a meter or digital presentation. The microphone converts the fluctuating sound pressure into a voltage which is amplified and weighted (A, B or... 

Figure 10.1 The effect of the linear (L), A and C weighting filters of a sound level meter on actual sound pressure level...

---