Simcenter Testing Solutions Noise level certification, how to select the right standard?

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Siemens Digital Industries Software has created a new Guide to Measuring Sound Power to provide assistance to manufacturers who need to do noise certification testing for their products.

Background

Within the European Union (EU), there are explicit limits on how much noise outdoor machinery can produce, putting pressure on manufacturers and end users.

Producers of equipment both made outside and inside of the EU are affected by this legislation if they wish to sell products to EU countries. Anyone who wants to sell certain equipment on the European market has to measure its emitted sound power level and stay below the specified target set by national legislation.

Figure 1: European energy label including sound power declaration (lower right)

Other types of equipment do not need to meet specific targets, but the standards and directives require manufacturers to label (Figure 1) their products with noise declarations; their guaranteed sound power levels.

Standards that specify measurement procedures for a particular type of machinery or equipment are called the noise test codes, or C-standards. Following these standards ensures reliable and repeatable results.

Standards

Choosing the correct standard for qualifying an acoustic source can be a challenge. The decision must take into account a number of factors: Type of noise source, available equipment and testing environment, regulations, etc.

Standards on specific products include:

• EC/2000/14 directive on noise emission by equipment for outdoor use
• ISO 15744: Hand-held nonelectric power tools
• ISO 7779/ECMA-74: Information technology and telecommunications equipment
• ISO 9296/ECMA-109: Declared noise emission values of computer and business equipment
• IEC 60704: Household electrical appliances
• DIN 45635 standards
• ISO 6393: Earth-moving machinery measured in stationary test conditions
• ISO 6395: Earth-moving machinery measured in dynamic test conditions

Measuring of Sound Power

Sound power is expressed in units of watts [W]. It is a measure of the acoustic power of a product that is independent of the environment, distance or direction. Measuring sound power is not a straightforward process.

Sound power can be determined either through the measurement of sound pressure [Pa] or sound intensity: the rate of energy flow through a unit area, expressed in watts per unit area [W/m2].

Sound pressure-based sound power measurements (Figure 2) can only be performed in very specific environmental conditions, usually only met in acoustic rooms (anechoic or reverberant chambers).

Figure 2: Fixed array microphone method of sound pressure-based sound power measurements. Microphones are arranged in a fixed arrangement around the object under test.

The sound pressure-based approach is most commonly used when performing certification measurements. A set of ISO standards governs these requirements and indicates measurement procedures that are necessary to obtain quality results.

Sound pressure-based sound power standards include 2000/14/EC, ISO 3744, ISO 3745, ISO 6394, ISO 6395, and ARI 260.

Sound intensity-based sound power can be measured in any sound field, but certain requirements with regard to the type of sound must be met. The measurements can be performed on individual machines or sound sources in the presence of other components radiating noise, because steady background noise does not contribute to the measured sound intensity (Figure 3).

Figure 3: Sound intensity-based sound power measurements

However, this approach has a limited usable frequency bandwidth, time demanding measurement procedures and limitations on the characteristics of the noise source.

ISO standards govern sound intensity-based measurements and describe the procedures that are required to obtain quality results. ISO standards for intensity-based sound power include ISO 9614-1 and ISO 9614-2.

Conclusions

Choosing the correct standard to follow can be a challenge. The decision must take into account a number of factors: Type of noise source, available equipment and testing environment, regulations, etc.

This Guide to measuring Sound Power provides an overview of the existing standards as well as the applicable regulations and noise codes, but the decision to execute which tests which tests and measurements ultimately rests with the product manufacturer.

Questions? Check out the free on-demand webinar Fundamentals of Acoustics or email Scott MacDonald (macdonald@siemens.com).

Related links:

• Index of Testing Knowledge Articles
• History of Acoustics
• Microphone Basics
• Sound Pressure
• What is a decibel?
• What is A-weighting?
• Octaves and Human Hearing
• What is Sound Power?
• Sound Intensity
• Decibel Math
• What is the Acoustic Quantity called Q?
• Sound Absorption
• Sound Transmission Loss
• Sound Pressure, Sound Power, and Sound Intensity: What is the difference?
• Sound Fields: Free and Diffuse Feld, Near and Far Field
• Loudness and Sones
• Articulation Index
• Speech Interference Level
• Auditory Masking
• Tone-to-Noise Ratio and Prominence Ratio
• Tonality
• Fluctuation Strength and Roughness
• Critical Bands in Human Hearing
• Kurtosis
• Sound Quality Jury Testing
• Fundamentals of Sound Seminar - Part I
• Fundamentals of Sound Seminar - Part II
• Acoustic Testing YouTube Playlist