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Noise Reduction in Rotary Positive-Displacement Compressors

Screw compressors, Roots blowers: Understanding the sources of noise and how it propagates is essential before determining which solutions to implement. This note presents a comprehensive approach to reducing all sources of noise pollution.

Noise Problems and Mitigation Methods

Installing silencers is a prerequisite for properly designing a system to limit the noise generated by rotary positive-displacement compressors, but it is not sufficient for comprehensive noise management. It is important to understand the origin of noise sources and their propagation paths in order to identify the full range of solutions to be implemented.

Identifying Sources of Noise

A rotary positive-displacement compressor, particularly a Roots-type blower, can produce noise levels of up to 135 dBA. The noise level at the machine’s inlet will be significantly lower than that at the outlet, but it may be predominant when the inlet is connected to the atmosphere.

Major Sources of Noise

Pulsation-induced noise on the discharge side
Aerodynamic noises on the intake side
Mechanical noises, mainly from the transmission
Electric motor

Affected subassemblies

Admission
Repression
Roots Corps
Transmission

Noise Reduction in Rotary Positive-Displacement Compressors (2024-12)[91]

Pathways of Noise Propagation

There are three propagation paths through which noise and vibrations can travel from a source to a receiver, each requiring specific mitigation solutions.

Guided propagation

Sound propagates directly through the conduit. Attenuation over distance is minimal—this is the most efficient method of long-range transmission.

Airborne transmission

The transmission of sound waves through a fluid medium, usually air. It radiates from the walls of the machine and the pipes.

Solid-state propagation

Transmission of acoustic vibrations through solid materials—chassis, mounts, and rigid piping connected to the machine.

Key point: A distinctive feature of screw compressors and Roots blowers is that they generate significant noise through all three modes simultaneously. Using silencers alone is often insufficient—airborne and structure-borne noise mask their actual contribution.

A range of solutions for reducing noise

Intake and Exhaust Silencers — An Essential Prerequisite

Intake and discharge silencers designed to match the machine’s specifications are an effective and proven solution for reducing internal duct noise. Noise reductions in the range of 10 dB to 40 dB are typically achieved with this type of silencer.

Please note: Using silencers is not always sufficient to reduce the system’s overall noise level to the desired level. Airborne and structure-borne sound transmission often mask the actual effectiveness of the silencer. It is therefore necessary to apply acoustic treatment to all transmission paths in order to achieve the desired result.