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How Should The Fan Sound?

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How Should The Fan Sound?
How Should The Fan Sound?

Video: How Should The Fan Sound?

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Video: REALLY AWESOME FAN SOUND FOR SLEEP | White Noise For Superb Slumber, Studying & Relaxation 2023, February
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Our ears pick up noise 24 hours a day, because hearing works continuously, without a break. Around 15,000 hearing cells inside the ears intercept the sound waves of each tone, process them into signals and send them to the brain. There they are evaluated. This is where psychoacoustics comes in as a branch of psychophysics. It deals with the description of the individual noise perception in relation to the measurable sound level, so it wants to define why we find a noise pleasant or annoying. In the meantime, manufacturers are also taking into account the results of corresponding investigations when developing fans.

If we are disturbed by a noise, for example if we feel disturbed by it, we speak of noise pollution. When this is the case depends on many factors. Among other things, the situation in which we are currently playing a role, the volume and the type of noise. This also applies to fans, which should meet different requirements depending on the situation and location. Are you z. B. used on a heat exchanger in the cold store, it is less of a low or pleasant noise, because such a room is rarely entered. Air and air conditioning units for living and working areas have to meet completely different expectations. However, this does not mean that fans should then work silently. In many applications, their working noise serves as a function check;a typical example of this is the extractor hood above the kitchen stove.

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Graphic 1: By using a Flowgrid pre-grille, a remarkable noise reduction can be achieved, in combination with the Axitop diffuser even more
Graphic 1: By using a Flowgrid pre-grille, a remarkable noise reduction can be achieved, in combination with the Axitop diffuser even more

The noise spectrum of a fan

For fans, the noise level is therefore often a decisive factor in purchasing. In addition to the aerodynamic data (air power), sound power becomes an important parameter. The noise spectrum of a fan usually contains tonal and broadband components. Their mechanisms of origin are completely different: the cause of most tonal components is the interaction of the rotating impeller with disturbances in the adjacent air flow, which are caused by struts, guide vanes, asymmetrical inlet, etc. They are therefore dependent on the installation situation of the fan impeller. They can often be reduced or even avoided by improved arrangement of the impeller.

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Most broadband noise components, on the other hand, are caused by the unavoidable turbulence of the inflow and the principle-related flow around the blades. The broadband components determine the basic level of the noise spectrum of a fan. The manufacturing industry has already done a lot here and there are many known ways to reduce noise in fans. These include e.g. B. fluidically optimized fan wheels, winglets, diffusers and inlet grille, with which the sound power and sound level of the fans decrease significantly. Figure 1 shows an example of the remarkable noise reduction that can be achieved by using the Flowgrid inlet grille and the Axitop diffuser.

Figure 2: The sound spectrum of a piece of music (blue) and a size 250 EC fan (red) is similar, but is perceived very differently
Figure 2: The sound spectrum of a piece of music (blue) and a size 250 EC fan (red) is similar, but is perceived very differently

Different perception despite the same volume

If the sound level drops by a few decibels, this means that the fan works much quieter. The sound level physically measured in the test stand says nothing about whether we find the remaining noise pleasant or annoying. Playing the trumpet, for example, and the excavator on a construction site have roughly the same sound power, but are assessed completely differently psychoacoustically. Graphic 2 shows another example: in this case the spectra can be distinguished (it is the two curves), but the overall level is (almost) the same: 69.7 dB (A). The crucial point here is that due to the spectrum, no statement about the annoyance / comfort of the noise can be made, possibly because of the low-frequency components the blue spectrum (music!) Would be assumed to be more disturbing.The human ear classifies the sounds completely differently.

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Content of the article:

  • Page 1: How should the fan sound?
  • Page 2: Quiet is not enough

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