Controlling equipment noise High noise levels produced during operation of fans and compressors can most directly be reduced by using which measure at the source or on the duct?

Introduction / Context:
Mechanical equipment such as fans and compressors generate broadband noise from aerodynamic turbulence, blade-pass tones, and mechanical vibration. Environmental and occupational noise control aims to attenuate these emissions cost-effectively while maintaining system performance (airflow, pressure).

Given Data / Assumptions:

• We are concerned with typical plant fans, blowers, and compressors.
• Noise is carried via air paths (intake/exhaust) and structure-borne paths.
• Question asks for a primary, direct reduction method.

Concept / Approach:
Mufflers (silencers) installed on intakes and discharges target the dominant airborne path and are specifically engineered for attenuation across target frequencies. They incorporate reactive and/or absorptive sections that interrupt sound transmission while allowing flow. Acoustical absorbents and lagging can reduce reverberant-field levels and transmission through ducts but are often supplementary; the most direct and effective first measure for air-borne fan/compressor noise is a properly designed silencer close to the source.

Step-by-Step Solution:

Verification / Alternative check:
Noise control handbooks consistently recommend silencers as primary controls for duct-borne noise from fans and compressors, with lining and lagging as complements.

Why Other Options Are Wrong:

• Acoustical absorbent: Helps in room treatment and duct lining, but not as directly effective alone as a tuned silencer.
• Lagging of noisy duct: Reduces breakout, but leaves the main intake/exhaust path less treated.
• None of these: Incorrect as silencers are standard practice.
• Raising fan speed: Increases noise; counterproductive.

Common Pitfalls:
Overreliance on room treatment while ignoring source-path controls; neglecting pressure drop considerations when selecting silencers.

Final Answer:
Mufflers (silencers)