© Photo | ebm-papst

“Numbers alone say nothing”

The level of noise emis­sions is a deci­sive quality factor for fans. Dr Marc Schneider, ebm-papst’s Group Leader for Acoustics, explains how the company keeps its prod­ucts quiet

At what point is fan noise perceived as disturbing?

That is not an easy ques­tion to answer. There are of course phys­ical char­ac­ter­is­tics like the noise level that you can measure on a test bench. But numbers alone often say nothing about how the human ear perceives this kind of noise. For a subjec­tive assess­ment, what is impor­tant is how “raw” the noise is perceived. This percep­tion can happen when the signal is given a temporal struc­ture through a change in the frequency or ampli­tude.

A lot of noises also have tonal compo­nents which can be extremely disturbing. This percep­tion differs from person to person, which makes assess­ment even more compli­cated. One person reacts nega­tively to low-frequency noises, another winces at higher-frequency noises.

How do you measure this personal percep­tion?

At ebm-papst, we have the “AudiMax”, a so-called psychoa­coustic labo­ra­tory. In this noise-insu­lated facility, we have space for up to eight test listeners to whom we can play the noises of our prod­ucts in different config­u­ra­tions.

How does this method help achieve usable results?

After hearing the noises, our staff ask the test subjects about how they perceived them and thus create a data­base with scien­tific consid­er­a­tions. Using this data­base, we can eval­uate together with our colleagues from produc­tion which measures need to be taken and which not. Our overall aim is to create a fan that is perceived as comfort­able by as wide a spec­trum of test subjects as possible.

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