Agenda - 06-27-1983 - Laserfiche WebLink

Browse Search

Awal • In some cases , a noise spectrum must be studied in finer detail than is possible with octave frequency bands . In such cases - and they are common in acoustics - one-third octave bands may be used . For instance , FAR Part 36 specifies one-third octave-band analysis . Remember , you must always specify the bandwidth and the identifying frequency of the band ( as in "Data were recorded and later reduced in octave bands with center frequencies of 31 , 63 , and 125 14 ." ) . If you don't , you are giving as little information as if youf said , "The distance is two." Two what? Miles? Feet? Inches? Give all the necessary information. 1 A set of filters used to separate a complex sound into octave bands is called an octave-band analyzer. When a sound pressure level includes all the audio range of frequency , the resulting value i called the "overall" level. When the level refers to the sound in one specific octave frequency band , it is called an octave-band le41 , and the frequency band is either stated or clearly implied . 1 411 Weighting Network Sound level meters are usually equipped with weighting networks that represent the way the human ear hears certain sounirls. Overall readings can be taken with these settings , which are calle A-scale or B-scale or C-scale settings on the meter . The A-scale setting filters out as much as 20 to 40 dB of the sound below 100 Hz as illustrated in Fig . 4 , while the B-scale setting filters out as much as 5 to 20 dB of the sound below 100 Hz . The C-scale setting retains almost all the sound signal over the full frequency range . However , the B-scale and C-scale settings are rarely used. Always make sure that you identify the scale setting used when measuring sound levels; refer to it as a dBA reading , and remember that !it does not S 12 •