1、ECMA Technical Report TR/27 Second Edition - June 1995 ECMA Standardizing Information and Communication Systems Method for the prediction of installation noise levels Phone: +41 22 649.60.00 - Fax: +41 22 849.60.01 - ECMANEWS: +41 22 735.33.29 - internet: Helpdesk ECMA.CH ECMA Technical Report TR/27
2、 Second Edition - June 1995 ECMA Standardizing Information and Communication Systems Method for the prediction of installation noise levels Phone: +41 22 849.60.00 - Fax: +41 22 849.60.01 - ECMANEWS: +41 22 735.33.29 - Internet: Helpdesk ECMACH Gino Laud - ETR27-ll.DOC - 24.01.96 14,42 Brief History
3、 In 1979 ECMA set up its Technical Committee TC26 for Acoustics. As a first task TC26 drafted a standard for determining the noise out-put of different categories of individual items of computer and business equipment. This Standard ECMA-74, was first issued in 1981, and was adopted by ISO/TC43 as t
4、he basis for International Standard IS0 7779:1988. ECMA-109 followed and covered the subject of Declared Noise Emission Values for Computer and Business Equipment. ECMA-109 was adopted by IS0 TC43 as the basis for IS0 9296 and both are now widely used by the industry. ECMA-74. Edition 3, was adopted
5、 in 1993, slightly modified in 1994 and submitted to IS0 TC43 for adoption under the fast-track procedure as new edition of IS0 7779. Standard ECMA-74 facilitates the assessment of the NOISE EMISSION of a given piece of equipment, that is the level of noise emitted by this equipment when measured un
6、der standardised test conditions. In contrast, when several pieces of equipment are installed and operated in a room, the resulting sound pressure level is called INSTALLATION NOISE LEVEL that depends not only on the noise emitted by the installed equipment, but also on its arrangement in the room,
7、on the acoustical properties of the room, and the location of interest. Knowledge of the installation noise level is required in order to assess the NOISE IMMISSION level at workplaces in the room, that is the personal exposure to noise of people working in an installation. This personal exposure, t
8、he so-called RATING LEVEL, depends on the installation noise level and on the exposure duration of the individual person. Limits for the rating level have been set in a number of countries by law or regulation. ECMA TW62 gives details of legislative and normative requirements applicable to computer
9、and business equipment. When planning an installation it is therefore important to be able to predict the likely installation noise level. This ECMA Technical Report describes a method for such prediction. It is based on mathematical models developed by KRAAK and JOVICIC (see annex C). For the purpo
10、ses of this Technical Report applying to computer and business equipment, the method has been simplified to provide a practical tool for those concerned with machine and system installation as well as early installation planning. Whilst actual calculations and measurements by members of TC26 have ge
11、nerally shown that the difference between the predicted and the actual measured levels is within 3 dB, users are cautioned that conditions unique to each installation may result in the measured values being more than 3 dB different from the predicted values. The principal reasons for this situation
12、are as follows: - In a given installation it is possible that the operation conditions are for a certain time more stringent than the standard operating conditions specified in ECMA-74. - The predicted noise levels include steady background noise but do not include the additive effects of personal c
13、ommunication (speech, telephone, etc.). It is the intention of TC26 to consider the experience made when applying the method described in this Technical Report with a view to issuing improved editions. Readers and users of this Technical Report are therefore invited to communicate their views to ECM
14、A. This ECMA Technical Report has been adopted by the ECMA General Assembly of June 1995 Table of contents 1. Scope 1 2 References 1 3 Acoustical terminology 3.1 General 3.2 The nature of sound 3.3 The decibels scale 4 Glossary 4.1 Sound pressure, p, in pascals 4.2 Sound pressure level, Lp, in decib
15、els 4.2.1 Single machine 4.2.2 Adding sound pressure levels 4.3 Equivalent continuous sound pressure level, LPeq in decibels 4.4 A-weighted sound pressure level, Lp, in decibels 4.5 C-weighted peak sound pressure level, LpCpek 4.6 Sound power, W, in watts 4.7 Sound power level, LW ,in decibels 4.8 A
16、-weighted sound power level, LWA, in decibels 4.9 Noise emission 4.10 Emission sound power level and sound pressure level 4.1 1 Declared noise emission values 4.1 1.1 Declared sound power level, LWAd, in bels 4.1 1.2 Declared sound pressure level, Lp, in decibels 4.12 Noise immission 4.13 Rating sou
17、nd level, L, in decibels 5 Noise emission 5.1 General 5.2 Measurement of noise emission 5.3 Use of noise emission values 6. Noise immission 6.1 General 6.2 Determination of noise immission 6.3 Use of noise immission values 7. Installation noise 7.1 General 7.2 Measurement of the installation noise l
18、evel 7.3 Prediction of the installation noise level 7.3.1 Overview and assumptions of the method 2 2 2 2 2 2 2 2 2 2 2 3 3 3 3 3 4 4 7.3.2 Guidance through the method 7.3.3 Room categories 7.3.4 Prediction methods 7.3.5 Adjustments for screens 7.3.6 Multiple equipment in a room 7.3.7 Adjustments for
19、 background noise 7.3.8 Calculations for several locations of interest 7.4 Actual installation noise level 7.5 Rating level Annex A - Corrections for the determination of the installation noise level Annex B - Absorption coefficients of some typical building materials Annex C - Supplementary informa
20、tion on the prediction theory Annex D - Bibliography Annex E - Computer programs for installation noise prediction 9 10 11 15 16 17 18 18 18 19 31 33 37 39 1. 2 3 3.1 3.2 3.3 Scope This ECMA Technical Report specifies a method for the prediction of installation noise levels. This method takes into a
21、ccount the acoustical properties of the room in which computer and business equipment is installed, the location(s) of the noise emitting equipment and their noise emission level), determined in accordance with Standard ECMA-74, and the locations(s) of interest. References ECMA-74 ECMA-1 O8 ECMA-1 O
22、9 ECMA-160 ECMA TW62 Measurement of Airborne Noise emitted by Computers and Business Equipment. Measurement of High Frequency Noise Emitted by Computer and Business Equipment. Declared Noise Emission Values of Computer and Business Equipment. Determination of Sound Power Levels of Computer and Busin
23、ess Equipment. Product Noise Emission of Computer and Business Equipment. Acoustical terminology General In noise control a variety of terms and definitions have been introduced during the past two decades of standardization. When dealing with acoustical values a basic understanding of the most comm
24、only used expressions is essential. These definitions are listed in clause 4 of this ECMA TR. An important area of understanding relates to the distinction between the noise level emitted by an individual machine or a piece of equipment operated under well defined standard conditions in a controlled
25、 acoustical room (called EMISSION), and the noise which may occur at a receivers location in a given environment under actual working conditions as a result of the influence of multiple noise sources, and to which individuals are exposed during their daily work (called IMMISSION). This interrelation
26、ship is explained in clause 5 of this ECMA TR. The following descriptions summarise some of the physical quantities which form the basis for noise measurements and noise ratings with regards to human hearing. The nature of sound Mechanically vibrating bodies put the surrounding air particles into mo
27、vement which eventually reaches the human ear. For computer and business equipment typical sound sources are printing mechanisms, moving paper, cooling devices, rotating disks, and transformers, which emit sound power ranging from about Air pressure fluctuations in the frequency range of 20 Hz to 20
28、000 Hz are perceived as sound. The sensitivity of the human ear is strongly frequency dependent: at 1000 Hz it is sensitive to sound pressure fluctuations as low as 20 micropascals, whereas at 100 Hz its sensitivity is reduced to 10 percent. It also perceives sound pressure fluctuations at about 20
29、pascals and above as painful. Because of this large range of sensitivity of the human ear it is common practice to use a logarithmic scale when dealing with sound pressure fluctuations. The decibels scale The rating of sound pressure fluctuations on a logarithmic scale yields the sound pressure leve
30、l in decibels, abbreviated dB, and is being a dimensionless quantity. The audible sound pressure fluctuations range from O dB to about 120 dB. A sound pressure level change of 1 dB may be just detected by the human ear, 3 dB are clearly perceived and 6 dE3 are significant. If a sound pressure level
31、is increased by 10 dB, the ear normally perceives it as a doubling in loudness. A decrease of 10 dB is similarly perceived as a halving in loudness. Note 1 The decibel scale may be applied to both quantities, the total sound power emitted by a source, and the sound pressure, to which the human ear i
32、s sensitive. As this may easily lead to confusion, ECMA-109 reserves the decibel for sound pressure level measurement and declaration and uses the unit “bel” (1B = 10 dB) when declaring sound power levels. watts to watts. -2- 4 Glossary 4.1 4.2 4.2.1 4.2.2 4.3 4.4 4.5 4.6 4.7 4.8 Sound pressure, p,
33、in pascals The sound pressure, p in pascals is the incremental variation in pressure above and below the static pressure at a given location in air. These variations are extremely small; e.g. for normal speech, they average about 0,l pascals above and below atmospheric pressure at a distance of one
34、metre from the speaker. For practical reasons the root-mean-square value (rms or effective value) of the instantaneous sound pressures averaged over a time interval is determined. Sound pressure level, Lp, in decibels Single machine The sound pressure level, Lp in decibels is ten times the logarithm
35、 to the base 10 of the ratio of the square of the (rms) sound pressure, p, to the square of the reference sound pressure, pot of 20 micropascals (p, = 20 pPa, the approximate threshold of hearing at 1000 Hz): P2 P L, = lo log = 20log-(dB ) Po PO Adding sound pressure levels In many practical situati
36、ons the emitted noise of several machines may be combined to obtain a total level. A simple rule of thumb is: - Add two equal sources: The total value is 3 dB higher - Add ten equal sources: The total value is 10 dB higher A more detailed explanation is given in annex A. Equivalent continuous sound
37、pressure level, Lpq, in decibels The equivalent continuous sound pressure level, Lpes,. in decibels is equal to a steady sound pressure level which would produce the same sound energy over stated penod of time as a specified time-varying sound, also known as time-averaged sound pressure level. A-wei
38、ghted sound pressure level, LpA, in decibels The A-weighted sound pressure level, LpA, in decibels is a frequency weighted (equivalent continuous) sound pressure level, where the standardized A-weighting accounts for the frequency dependent hearing characteristics. the A-weighted sound pressure leve
39、l is the commonly used value for noise measurements and noise ratings with regard to its influence on man. The correct terminology is to express the value of LpA in decibels (dB) re 20 pPa, although it is commonly expressed in units of dB(A) or dBA. C-weighted peak sound pressure level, LpcpeA The C
40、-weighted peak sound pressure level, LpCpeak, in decibels is the highest instantaneous value of the C-weighted sound pressure level determined over an operational cycle. Sound power, W, in watts The sound power, W, in watts is the rate per unit time at which airborne sound energy is radiated from a
41、source into its environment. The sound power of a source is essentially independent of the environment. Sound power level, L, in decibels The sound power level, L, in decibels is a logarithmic quantity of the measured sound power of a source with reference to i picowatt (wo=i0-2 watts): W this level
42、 may include, or may be supplemented with corrections to account for the impulsive or tonal character of the rated noise. 4.13 5 Noise emission 5.1 General The term “Noise Emission“ is used to describe the characteristics of the acoustical output of equipment. It refers always to one functional unit
43、 and requires standardized test conditions for the acoustical measurements as weii as the installation and operation of the equipment under test; this is illustrated in figure 1. Noise emission is preferably expressed in terms of sound power, which, for practical purposes, is one real invariant, ind
44、ependent of the environment. It may also be expressed in terms of sound pressure which however is dependent on the measurement location, the distance from the equipment and the test environment. -5- Standard Measurement (II Procedure n Standard Declaration 83MA-8402tQA Figure 1 - Noise emission 5.2
45、Measurement of noise emission The basic noise emission quantity is the A-weighted sound power level, LWA in decibels re 1 pW. For computer and business equipment it is determined according to Standard ECMA-74 (or IS0 7779) andor ECMA-160 (IS0 9614-2) and declared in accordance with ECMA-109 (IS0 929
46、6), as the declared A-weighted sound power level LwAd. Generally, for mass-produced equipment, the declared noise emission value takes into account production variations and measurement uncertainties (IS0 4871, IS0 7574). The declared value may therefore be 3 dB to 5 dB higher than the value for the
47、 average production unit. These factors must be taken into consideration, when using declared values for the determination of the installation noise level; further details are given in 5.3. The measurements are performed in either of the two acoustical environments, a semi-anechoic room (providing a
48、 free field over a reflecting plane), or a reverberation room (providing diffuse field conditions). Other noise emission quantities of interest are the sound pressure level, LpA in dB re 20 pPa (decibels with reference to 20 micropascals), measured at the specified equipment operator position(s) or
49、at an otherwise defined position(s), the bystanders position(s). Furthermore the noise spectrum and the directivity of the noise radiation may be useful information when planning an installation. It should however be clearly understood, that these noise emission quantities are not personal exposure values (rating levels). Generally there exists no simple relationship between the (equipment) emission levels and the (personal) rating level. However, the rating level can be determined if all relevant parameters, as indicated in figure 2, are known. Use of noise emission values Pr
