Acoustic product improvement

Sonobex undertake noise audits, which is a process is to identify the potential noise producing components or mechanisms and transmission paths. Enhanced analysis of the following factors are considered as part of the noise audit process.

Considered factors

Enhanced analysis of the following factors are considered as part of the noise audit process.

Types of noise
Noise levels and temporal patterns
Frequency distribution
Noise sources (location, power, directivity)
Noise propagation pathways, through air or structure
Noise rank order – in terms of contributions to excessive noise.

For example such sources may include the noise directly radiated by a motor when under load, structure-borne noise due to vibration transmitted from the same motor to various connected structures, the blade passage tonal noise associated with a cooling fan, noise due to gear mesh, noise due to airflow etc.

Following identification of the common noise sources, the next step is to determine the noise produced by each individual source. The most straightforward way to do this is to operate a source by itself while maintaining representative speed, load, temperature etc.

Sonobex is experienced in designing and constructing experimental test rig setups to ensure that operation is as close to real life as possible, ensuring accurate representation of the appliances "normal" sound field.

Airflow noise

Almost all airflow through products is turbulent, and air turbulence creates noise. This includes inlets, exhausts and all internal airflow channels in between. Impingement of the flow with a surface can result in significantly greater noise levels being generated, with path properties such as surface roughness and small radius turns increasing turbulence and thus noise.

Airflow can also excite vibrations that produce radiated noise when they reach the product surface, acting as a loudspeaker. This type of noise is typically broadband but can generate more tonal components.

Fan and rotating elements noise

Fans tend to produce broadband noise as well as tonal noise at the blade pass frequency as a result of turbulence and blade interactions with housings and airflows. The latter tends to be a greater problem for fans operating at higher speeds.

Motors and gear noise

These components can produce noise that propagates through the air and/or vibrations that find their way to outer surfaces of the product which then radiate noise. Housings for motors and gears are often large, lightweight contiguous panels that respond to vibration from internal sources with greater vibration levels and are also efficient radiators of noise.

Noise reduction strategy


Once all of the different sources, paths and noise radiation mechanisms have all been characterized and quantified during the noise audit procedure, they can be ordered based upon their contribution to the overall noise levels.

This approach then provides a basis for developing an effective noise reduction strategy, stating with the highest-level source, that contributes most to the total noise.

The noise reduction strategy then leads to making modifications and evaluating the resulting noise and performance.

Finite Element software enables Sonobex to perform acoustic design while not compromising the performance, weight, size and cost of the product. Whilst this can be a challenge, making use of a methodical approach offers the best chance of achieving noise reduction success.