Noise control is affected in a number of ways. Machinery can be redesigned to reduce noise. The basic principle is similar to controlling indoor air pollution: eliminating the source of the noise. This can be accomplished through improved machinery design and maintenance or by damping vibrations by increasing stiffness or using rubber or plastic bumpers or shock absorbers. Larger, slower machines typically produce less noise than smaller and faster devices. Belt drives can be used to replace gears and cams, and hydraulic or electric devices can be substituted for mechanical ones.
Noise screens of various types can be designed and constructed. Noise baffles are effective, particularly for higher frequencies. Cosmetic correction, such as tree plantings or visual screens, may provide better acceptance of noise levels, but do little to reduce actual SPLs. Distance is a very effective noise control strategy. It is noted that higher sound frequencies are more easily attenuated than lower frequencies.
There are other means and ways to reduce noise from moving parts and machineries as follows:
- Reduce frictional resistance
- Reduce rotating areas
- Reduce noise leakage
- Isolate and dampen vibrating elements
- Provide mufflers or other silencers
- Noise control in the transmission path
- Apply noise absorbing materials
- Enclosures
EXAMPLE 5.17 NOISE CONTROL
A turbine has an acoustic power output of 10 W. A workstation is to be located 10 ft from the turbine in an acoustically shielded booth providing a 29 dB reduction. What will the SPL be in the booth? Will it be low enough to permit normal conversation?
SOLUTION
For a free‐field, omnidirectional source, use Eq. (5.12) to calculate the intensity at d = 10 ft.
Converting to sound pressure using Eq. (5.14):
With no attenuation
80.3 dB (unweighted), which is higher than 60 dB for normal conversation (Table 5.12); therefore, it will interfere with normal conversation.
Leave a Reply