Clarke Band Saw Manual
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The relative attenuation of the octave bands of a sound is defined as the ratio of the attenuation of the higher frequency band to the lower frequency band. The use of octave bands in this way is only correct when the measurements are made at the exact same volume (the relative frequencies are equal). If the worker's ears are not completely sealed to the earplug, the octave band intensities may not be equal. For example, if the worker's ears are unsealed, the octave band intensity of the lower octave band (f1) will be lower than the octave band intensity of the higher octave band (f2).
For example, assuming that a worker is wearing earplugs and a hearing band for protection against a noise source of 80 dB, calculations for two different octave band intensities are shown in Table 2. The ratio of the two octave band intensities equals the ratio of the volumes of the two bands (see Figure 12).
For noise attenuation calculations, the sounds in an octave band are not just present, but they are also present in the exact same relative proportions. For example, a sound that is 3 dB lower in one octave band than another is twice as loud in the other. Octave band intensities are also always positive; therefore, a sound that is twice as loud as another is equal to a sound that is 3 dB lower in frequency.
If the worker's ears are sealed against the earplug, but the worker is exposed to a higher volume level than the worker is exposed to when the ears are fully sealed, then the ratio of the two octave band intensities will be less than the ratio of the volumes of the two octave bands.
When setting up a calibration range for a sound level meter or an octave band analyzer, follow the procedures prescribed for the equipment you are using. Otherwise, the meter or analyzer may give a false reading. Depending on the range and the instrument, you may need to obtain two calibrations for each reading. Consider the following:
4. When using an octave band analyzer, you will obtain two calibrations. One reading is for the ambient sound level, while the second reading is for the calibration source. The ambient reading is for the reading in the environment you are working in. The calibration reading is obtained by setting the range to 0 to 90 dB. The ambient reading will be approximately the same as the calibrated source.
The proper care and maintenance of sound-measuring instruments is critical to their reliability and accuracy. All sound level meters, noise dosimeters, and octave band analyzers require the same basic care. 827ec27edc