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Sound power of domestic appliances

There is an uniform label for domestic appliances in the European Union. Apart from energy consumation, several icons illustrate specific categories with certain performances and properties: including noise emission in decibel. These measurements are executed according NBN EN ISO3744.

To determine this noise emission, specific guidelines for the device category refer to certain measuring methods. Usually, these methods are based on the NBN EN ISO 3744. This method describes the determination of the sound power of a device based on measurements of sound pressure levels at a certain distance (measuring surface) around this device. According to the standard, these measurements must take place in a measuring environment with an "acoustic free field" approached over one (or more) reflecting surface.

In the eco-scan sound laboratory these measurements take place in the so-called "semi-anechoic chamber". This is a measuring chamber in which the four walls and the ceiling are very sound-absorbing. The floor is made of smooth concrete and therefore sound-reflecting. For the test setup with one sound-reflecting surface, the device to be measured is positioned centrally on the floor of the test chamber. Depending on the application, the device can also be placed on an elevated tripod. For the test arrangement of hoods, for example, the appliance is placed at a height of 63 cm. Around the device, 9 microphones will now be built up according to the standard distances and positions. The typical measuring distance is 1 m.

With a completely disabled device, the background sound pressure level is first measured. Then the device is put in a certain operating mode, waited until the produced sound has reached a stable level and then the sound pressures are measured in this operating mode. Based on these sound pressure measurements (and other input parameters such as the dimensions of the device, including any height, measuring distance, correction factors for the measuring environment ...), the sound power of this unit can now be calculated in this operating mode. As a certificate for this measurement, an ISO 17025 accredited test report is issued.

Especially because the same unit dB is used, these two variables (sound power and sound pressure level) are often mixed-up. The sound power can be seen as the cause. The sound pressure level is then the result.

For other test arrangements in this measuring chamber, one or more wall surfaces can also be covered with sound-reflecting panels.

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