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Sound power

Consumer awareness and sensitivity regarding noise and its associated sound power have never been higher. Product noise levels are increasingly important to customers when evaluating which tools, appliances, or other products to buy. Therefore, the lower the sound power emitted from the product, the better.

Product noise levels have become increasingly more important to buyers of tools, appliances, machinery and other equipment. Purchasers seek to ensure lower noise exposure for both users and bystanders.

To encourage lower product noise, regulations such as the EU Directive 2010/30/EU require that products clearly display their sound power levels. This provides open information that facilitates the consumer’s choice and promotes competition on lower sound levels.

Undisputable noise levels

In order for noise labels on products to be effective, they must be based on fair and comparable measurements. Sound power represents the absolute acoustic energy of a product, independent of the acoustic environment. To keep test methods identical, standards stipulate the exact methods you must use to measure noise from any type of equipment, from household appliances to earth-moving machinery. Brüel & Kjær’s solutions are designed to support a wide range of relevant EU and international standards and to guide users through each one of them.

Sound power measurements

It is possible to calculate sound power based on several different types of measurements, depending on your test object. Sound intensity-based methods are used for in situ measurements and product engineering, making them ideal for fixed objects like extractor fans.

Reverberation room-based sound power and free-field-based sound power measurements are most often used for production audits and high-volume testing of products such as household appliances.

Brüel & Kjær is deeply involved in the creation and maintenance of measurement standards. Important standards include IEC 60704-2-4 for washing machines, and ISO 6393, ISO 6394, ISO 6395, and ISO 6396 for outdoor machinery.

Traditionally, to measure sound power, the noise source had to be placed in specially constructed rooms such as anechoic or reverberant chambers. Sound intensity, however, can be measured on a source in any sound field allowing sound power to be determined directly. And, because steady background noise makes no contribution to the sound power determined when measuring intensity over a closed surface, measurements on individual machines or components can be made even when all the others are radiating noise. Because sound intensity gives a measure of direction as well as of magnitude, it is also very useful when locating sources of sound. Therefore, the radiation patterns of complex vibrating machinery can be studied in situ.

System suggestion

Sound intensity based sound power system overview

PULSE Sound Power Using Sound Intensity Type 7882 software enables sound power to be determined, stored and reported according to ISO 9614 Parts 1, 2 and 3, using dedicated templates. The hardware required is the same for all three standards. To fulfil the requirements of the chosen standard, a dedicated PULSE template leads you through all the necessary steps by means of a task list. The task list reflects the similarities between standards, making for an intuitive user interface.

A portable, hand-held sound intensity analyzer system comprising the 2-channel Hand-held Analyzer Type 2270 (with sound level meter), Sound Intensity Software BZ-7233 and a Sound Intensity Probe Kit Type 3654, is also available. 

Sound power with hand-held sound intensity system

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.

System suggestion

Sound pressure - reverberation room based sound power system overview

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

Sound pressure - free-field based sound power system overview

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.

> Sound Power and Noise Source Identification (Video)    

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