Sound Pressure - Reverberation Room Based Sound Power

For determining the noise emissions of products, the preferred quantity to investigate is sound power because it measures the absolute power of a noise source independently from its acoustic environment.

One of the main methods used for this is reverberation room-based sound power, where you place the source in a reverberation room (diffuse sound field) and determine its sound power from sound-pressure measurements.

Laboratory reverberation rooms as described in ISO 3741 are particularly suitable when performing precision-grade tests on comparatively small machines where the sound emitted is predominantly steady in character. Special reverberation rooms constructed to fulfil the requirements of ISO 3743-2, on the other hand, are less expensive and, since their methods provide engineering-grade results, particularly suitable for direct measurement of A-weighted sound-power levels of a series of small noise sources. Hard-walled test rooms as described in ISO 3743-1 are used for engineering-grade measurements; most ordinary, unfurnished rooms without special acoustical treatment comply with these requirements.

Built on the powerful PULSE platform, PULSE Sound Power in Reverberation Rooms Type 7884 software provides measurement and calculation procedures based on ISO 3741, ISO 3743-1 and ISO 3743-2 for determining the sound power of noise sources operating in reverberant test environments. A dedicated PULSE template enables determining, storing and reporting noise-emission quantities according to the various standards. Other components for the solution include a LAN‐XI data acquisition hardware, a set of microphones or a single rotating microphone.

Noise emission quantities from machinery and equipment are increasingly becoming the subject of national and international regulations with the aim of a safer and healthier working place and of environmental protection.

For example, all household appliances sold in the EU, from vacuum cleaners to refrigerators, must feature an energy label including sound power information. For washing machines, for example, this must cover both wash and spin cycles.

Noise declarations are meant to help buyers to compare noise emissions of machinery on the market and thus to choose comparatively quiet machines. Simultaneously, any company that manufactures certified products fulfilling the EU noise emission requirements has the opportunity to enter a bigger market with fewer import barriers.

One of the three main methods for determining the noise emission of products is through free-field based sound power, where the source is placed in an acoustically open area (free field) and its sound power determined from sound pressure measurements.

System suggestions

Depending on need, two complete turnkey systems are available that enable you to determine sound power in essentially free-field environments and that simplify the measurement procedure right up to the final report. For infrequent or variable testing needs, a sound level meter-based product noise application is a good fit for measuring sound power levels according to ISO 3744 and ISO 3746 and  EU Directive 2009/125/EC.

For more frequent measurements under static conditions, the PULSE- and LAN-XI-based system adds additional microphone and tachometer probe possibilities along with compliance with a wider range of ECMA and ISO standards and test codes. A reference sound-source for determining environmental correction can be used with either system.

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