Hence we see that we can choose a frequency-response shape and engineer the loudspeaker accordingly. It gives the flattest possible response down to f C where it is 3 dB below the pass-band level. The curve for Q T C = 1 / 2, also known as critical damping, has a Butterworth high-pass frequency-response shape. This can only be done if details of the way the fan is to be used, together with details of the environment it is serving, are known and a detailed acoustic analysis is carried out. What he cannot do is unequivocally state what sound pressure levels will result from the use of the fan. However, the manufacturer can calculate this level after measuring the sound pressure levels in each octave band with the fan working in an accepted standard acoustic test rig. It is impossible to measure directly the sound power level of a fan. He must also appreciate that dB re 10 −12 watts and dB re 2 × 10 −5 Pa are different units.
Note: The engineer must clearly distinguish and understand the difference between sound power level and sound pressure level. Pneumatic chipping and riveting (operator's position)Īutomatic punch press (operator's position)
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