Sound meter

A weighting scale, dBA The unit of sound intensity expressed as a logarithmic scale, related to a reference level of 10 W m"-. The A weighting scale is the most commonly used scale, as it reduces the response of sound meters to very high and low frequencies and emphasize those within the range audible by the human ear. 

Industrial sound meters include a filter network to give the meter a response that corresponds roughly to that of the human ear. This is termed the A weighting network and the readings are reported as dB(A). 

Different laboratories use different criteria for determining whether a drop-test resulted in an explosion ( go ) or failure ( no-go ). In many test facilities any visual observation of smoke, flash or flame, or any crackle, pop or bang detected by the operator is taken to signify a go result. Sometimes sound-meters are used to detect the audible signals of a drop test. In still more elaborate tests, the volume of gas, produced by a go result, is measured. In general, for sensitive explosives like PETN, distinguishing between go ... 

The units for the values in Table 5.11 are shown as dB A impulse for A, dB F impulse for flat, and dB L impulse for linear. One must pay attention when using a super low frequency sound meter to the linear reading. The linear range of its dynamic response is l-90Hz when the frequency component is over 90Hz, it becomes a low level frequency. 

The sound meter was not able to measure completely the sound going in three directions hence, the sound intensities in each direction could not be directly compared. However, regarding an analysis based on a reduced distance (the difference in a frequency component caused by distance and direction), it may be understood in the following manner ... 

The Taylor sound meter measures the sound generated by a textile when it is drawn over glass pins. 

Field Light, sound meters measurements tape measures Ambient environment workstation dimensions... 

Using a sound meter, the fiillowiog measurements were made for the fellowii sources Rock band at a concert (100 X 10 /tPa), a Jack hammer (2 X 10 juPa), and a whisper (2000 /uPu). Convert these readings to dB values. 

One of the drawbacks of the two-microphone transfer function method is that the absorption coefficient determined may not be a true representation of the material s characteristic. In the case of a porous material, such as silica aerogels, the reflected wave from the rigid wall could contribute to a rise in the absorbed energy by the material. To account for this uncertainty, the four-microphone impedance tube setup is usually used to determine the transmission loss (TL) and absorption coefficient (Feng 2013). In the absence of additional microphones downstream of the specimen, a sound meter could be used instead to measure the TL of the specimen under test. However, the sound meter picks up discrete transmitted signals at periodic interval, which could result in a mismatch with the generated signals from the source. 

Fig. 7.3 Schematic of InTLM experimental setup for transmission loss measurement using 2-miciophone and sound meter without the rigid wall backing...

Granule size (mm) No of Layers Thickness, r(mm) Frequency (Hz) Absorption coefficient Transmission loss (dB) TL (avg) (dB) Sound meter TL (avg) (dB)... 

The second aspect is the proposed novel Inferential Transmission Loss method (InTLM) in determining TL using 2-microphone impedance tube. The approach is a modification to the usual transfer method that infers transmission coefficient with and without the rigid wall. The calculated results showed high accuracy from —0.2 to -3.2 dB compared with sound meter measurements. Thus, the InTLM can be applied for 100 mm diameter specimens which use the large tube in estimating the TL without the need to use 4-microphone impedance tube... 

In cases where the use of these weightings is deemed appropriate, equipment somewhat beyond the technical capability of most inexpensive sound meters is required. Where the facility does exist, however, then BS/EN/ISO 11064-6 2005 would recommend the nse of dB in preference to dB(A). Likewise, when encountering control... 

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