Acoustic noise reduction consultations for industry
The subject of acoustics is of great importance in a wide range of industries where “noise” (unwanted sound) is generally the focal point of attention. Noise pollution is increasingly receiving attention as a disruptive and harmful entity that adversely affects the environment, everyday life and labour productivity. Noise levels and noise damping measures can be evaluated by conducting professional measurements and analysis and/or by simulating noise generation and attenuation. Based on the results of these studies, designs can be optimized and existing devices and environments altered to achieve acceptable and safe noise levels.
There is a myriad of targets for acoustic consultations such as the emissions from noisy fans at industrial exhausts, noisy impellers on ships, highways or even shooting ranges in residential areas and their environmental impacts. Other examples are found in building techniques, such as the proper acoustic design of churches, opera halls or offices and meeting rooms. Optimum acoustic design plays a key role even in sensitive micro-industries such as communication devices.
The acoustic design of industrial and production facilities is crucial and neglecting it can prove a costly error. Noise reduction can be rather expensive and requires advanced technical know-how. Exposure to harmful noise, either gradually or in the form of sudden impulses, can cause severe injuries and prove costly for both the employer and employees. Prevention is indeed better than cure!
Meeting environmental standards
All industries are required to meet minimum environmental standards with regards noise pressure levels in order to be certified by environmental authorities. The certificates are issued based on acoustic measurements or simulations according to the rules that exist in different countries. In Europe, for example, a request can be put in for these tests (calculations or simulations) to be conducted for any project during the basic design or design review phases, as well as for operating industrial plants at stipulated intervals, or when authorities have received complaints from local communities.
Taking acoustic measurements
The first phase for precise acoustic measurement is the selection of the most suitable acoustic measuring device. The conditions under which acoustic noise measurements are taken vary greatly and several factors need to be taken into consideration before selecting the device.
These include the contour of the sound pressure level, the sound reflection (for reverberation time), the sound absorption in various materials or sound dampers, the sound impulse tracking, the real-time spectrum responses as well as the acoustic measurement in diffuse or distant fields and sound power for indoor or outdoor cases. The acoustic measuring device selection is therefore extremely important. Care should be taken to choose a noise measuring device that has the appropriate acoustic class, sensitivity and microphones to fulfil the associated standards (for example EN/IEC 61672 A-weighting or IEC 60651 for C/Z-weighting).
There are a number of ISO and EN standards that govern acoustic measuring methods in free and diffuse fields, both indoors or outdoors, as well as for noisy equipment. The acoustic measurements can be an average or maximum sound pressure level that was logged over the time, in order to follow real-time responses, a sharp noise impulse sound pressure, or a measured contour taken from an array of measurement points.
Various noise-measurement parameters that indicate errors, such as equipment responses, calibrations or errors due to nearby reflecting walls must be considered in order to produce a reliable measurement report.
Acoustic simulations provide detailed information
The motion of sound in air or in any other material is studied with the help of a wave equation, which is a particular type of Navier-Stokes equation that is usually used in computational fluid dynamics (CFD). Computer simulation of a real acoustic system is rather complex as a result of the minuscule calculation time intervals (of 10-8 order) used. This means that advanced simulation methods and powerful hardware are required for the generation of acoustic noise sources, pressure waves and sound propagation.
Simulations can be conducted using different techniques and accuracy levels according to varying project requirements. There is, therefore, a vast range of computational acoustic simulations and related results. Variations exist for various frequencies, for example, in sound exposure levels, impulse peak pressure levels, the contours of sound pressure levels, noise attenuation in various materials or sound dampers, as well as sound reflections for reverberation times in diffuse or distant fields.
Noise sources can be measured (in the form of impulse, white or pink noise etc.) and the pressure wave that travels in the CFD domain can be analyzed. This eventually leads to the identification of the various receivers’ exposures in the domain as well as the efficacy of various sound attenuation systems.
Tangible benefits for industry
The simulation results can be very useful for many industries as they allow them to check various acoustic effects in different scenarios in their plant designs. For existing sites or machinery, noise defects can be identified and noise attenuation reviewed. It also allows for cost evaluation of the various sound attenuation techniques to be done in advance. By adhering to standards and conducting professional and systematic studies, industry can reduce noise pollution in the environment and reduce the risk of injury to employees, thereby improving long-term productivity and profitability.
Author: Amir Shakib-Manesh