Pssst! Quiet blades: the noise generated by fans

For the application developer, a fan represents a challenge –on the one hand because of its properties as an electromechanical component, here in the sense of a moving part, and on the other because of its function-specific noise development.

Whereas noise development is a relatively minor criterion for industrial applications, it is crucial for applications used in noise-sensitive environments, including medical engineering, IT telecommunications systems, power supplies and printers, but also everyday appliances such as ticket machines, gaming machines and household appliances, including fully automatic coffee makers and other kitchen appliances, small and large.
In these applications, fans can significantly improve performance and reliability, but only if they are not a source of unpleasant noise.

Various factors contribute to the noise level of a fan:

• Most of the noise can be attributed to the aerodynamically generated noise caused by the air flow and the required supply pressure
• Structure-borne sound, i.e. oscillations and resonances that propagate by e.g. vibration
• Mechanical noises, such as the bearing systems of the fan
• To a small extent: the power and control electronics.

Fan manufacturer Sunon has taken up these challenges and developed a special series of fans for such applications, with particular attention paid to aerodynamic noise generation.

The sound pressure level for fans is usually given in decibels and is determined by taking the A-weighting curve into account. However, this assessment does not relate to a physical value, but is rather based on various contributing factors and a standard defined from them. Thus, one criticism with this procedure is that the dB(A) value has no relevance for the noise perception experienced by humans.

To be able to evaluate this, the generated noise is determined in phon instead of with the dB(A) method. Here, the 20-phon threshold is seen as a value below which a fan in a normal working environment such as an office or laboratory is no longer perceived by humans as a single noise source.

Manufacturer Sunon has thus specifically adapted the components that influence aerodynamic noise generation to reduce noise to below the 20-phon threshold. The solution includes improvements and new developments of the large components – e.g. the impeller and fan housing – but also significant optimisation of such details as the parts that connect the motor and housing.

The resulting HA fan series has "quiet blades" in the truest sense – generally speaking, it is no longer acoustically noticeable that the fans are actively running in the unit at all.

The HA series is available from Schukat electronic:

• Fan with low-noise and maintenance-free magnetic Vapo bearing
• Air-flow rate from 9.2 to 93.4m³/h
• Available housing dimensions from 40x40 to 120x120mm
• Base-level 12VDC version available direct from Schukat stock