BBE Sound 262 Manual de usuario descargar pdf (Pagina 10)

MED ASSO C IAT E S I NC. ANL- 940 - 1 U L TR ASO NI C M I CRO PH ONE AND AMPL I FIE R

- 7 -

MED Associates, Inc.

NOTE: Sound Pressure Level is often abbreviated simply as SPL. Sometimes variants of the actual

measurement unit are used, such as dB (SPL), dBSPL, or dB

SPL

. These variants are not recognized as units

in the ANSI standard. The unit dB (SPL) is sometimes abbre viated to just "dB", which can give the

erroneous impression that a dB is an absolute unit by itself. Keep in mind that SPL measures (L

) are not

absolute measures in and of themselves. They are expressing one sound pressure relative to a reference

sound pressure.

The commonly used reference sound pressure level (p

ref

) in air is 20 µPa (rms), which is usually

considered the threshold of human hearing (roughly the sound of a mosquito flying 3 m away)

. Most

sound pressure level measurements will be made relative to this level, meaning 1 Pa will equal a SPL of

94 dB (20 log(1 Pa/0.00002 Pa) = 94 dB).

If a sound pressure p

, is measured at a distance r

, one can calculate the sound pressure p

at another

position r

using the following equation:

Converting the resulting pressure to Sound Pressure Level (in dB) allows the correction for distance to be

accomplished by simply adding logarithms.

20 log(p

) = 20 log(p

) + 20 log(r

) - 20 log(r

)

In the case where r

= 1 meter,

@1 meter = L

+ 20 log(r

)

Figure A.1 - Graph of 20 log(r

) for distances less than 1 meter

1 2 ... 5 6 7 8 9 10 11 12

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BBE Sound 262 Manual de usuario Pagina 10