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Application NoteSound Power Determination with or without IS09614-1byErik Cletus Petersen, Bruei&Kjser, Denmark

I In Europe, a new "Machinery Direc- \tive" has been written, coming intoforce from 1/1/95. The purpose of thisdirective is to ensure the health of peo

ple using machines.The directive states, among other

things, that equipment sold in Europemust fulfil specified noise demands.The equipment covered by this directive is everything from jacks and garden tractors, to chain saws and plasticmoulding machines.

What should be stated in the in

struction manual for the equipment?If the A-weighted sound pressurelevel is below 70dB(A), this must beindicated (L < 70 dB(A) re 20 Pa) .

Above 70dB(A), the A-weightedsound pressure level should be stated.

If the sound pressure level exceeds85 dB(A), the A-weighted sound powerlevel should also be stated.

If the machine is very large, thesound power level is replaced by thesound pressure level measured at significant positions.

If the noise contains peaks exceeding 130 dB(C), this must also be stated. / Fig.l In this particular case the measuring conditions was improved by raising the

V J vacuum cleaner 25 cm over the floor

Introduction the neces sary equ ipme nt and soft- st and ar d giving good advice about

Driven by the new directive, a large w a r e - w h a t t o d o n e x t -numb er of factories, producers and To perform mea sur eme nts accord- The sta ndar d provides thre e

small contra ctors will in the ne ar fu- ing to the ISO sta nda rd, you need a gra des of accuracy:

tu re begin to ma ke sound power compu ter with a Nati onal Ins tru - O Precisi on

meas urem ents . For some, these ment s IEEE interface board. The o Engineer ing

me as ur em en ts will be the ir first con- comp uter th en acts as controller and o Survey

tact wit h the acoustic envi ronm ent. the Sound Inte nsi ty Analyz er as Note th at only the surve y grad e

The purpos e of thi s applicat ion front end. supp orts A-weighted sound power de

note is to show novices how easily the ter min ati on.sound power measurements can ac- Making measureme nts For our vac uum cleane r we choose

tually be performed. For this purpose an arr ange men t of meas urin g points

we have chosen a modern "Nilfisk" With the ISO 9614-1 standard on a me asu rin g surface th at enclose

vac uum cleaner from the Dani sh To ens ure the quali ty of the sound the noise source. This surface is her e man ufa ctu rer F isk er & Nilsen. The power dete rmi nati on, the ISO stan d- a cubic box of 1 x1x 1 m wit h 4 meas -

me as ure me nts are first done accord- ard prescrib es a num ber of checks ur ing points on each surface.

ing to ISO 9614-1, a suit able stan d- (boolean expressi ons). Thes e checks The res ult of the me as ure me nt is

ard for this purpose, and then as are based on different mea sur eme nt illust rated in Fig.2. According to the

simply as possible. As you will see, calcula tions called Field indicators. mac hine directive, only the A-weight-

the res ult s are very close. Since the ISO sta nda rd came, peo- ed value is of inte res t:

pie ha ve sp en t a lot of ti me ma ki ng C^-RCA-\ I WInstrumentation advan ced spr ead she ets or trie d to ^ " " ^

For the sound power determ ination make the calculations by hand . But

of thi s vac uum cleaner we have cho- th at is all histo ry now. Without any standard

sen th e new soun d power, low-cost The PC-pr ogr am guid es you In th is case we will in st ead of fixed

package Type 3554, conta ining all thr oug h the difficult par ts of the ISO points use the sca nnin g metho d,

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Fig.2 When fulfilling themachine directive, only the A-weighted sound power isof interest

which is described in the ISO 96 14 -2 they are rai sed from the floor, and

sta nda rd. But we will mak e none of therefore emit a different power.

the field indicator checks, and we Regardi ng point me asu rem ent s,

therefore don't need the computer. one of the main problems which, es-

This simple method of determ ini ng pecially at low frequencies can real ly

the sound power is actually described influence the resul t, is that a rela-

in a Nordic standar d called INSTA tively high nega tive int ens ity flow ^ ^ f121, which is not very well-known. and/or sta ndi ng waves can occur. documentation directly to the PC

The resu lt of the mea sur eme nt is This is due to reflections from th e

illustrated in Fig.3, from where we wall s, and can be difficult to get rid d B g c o r r e s p o n d i n g t o t h e a r e a o f a

S et: of- 0 n e w a y * t 0 v e t h e v a c u 1u m hemi spher e of one metr e radius:

T /jo i JT>/A\ i xiT cleaner around m the room, ano ther .,AT /Q 2 oJ-DLw =68.1 dB(A) r e l p W . , , J ,, . ' 10Log(27cr

z) = 8dB.is to go closer to th e noise source, m, , -, n . ,, .

& n , - ,_ . , -, The sound pre ssure level is the n:

m facing nea r field problems ins tea d. 6 9 d B (A) - 8dB = 61dB(A)

w u n A + A - * + * , B e f r e m g m e a s u r e m e n t ' t r^ According to the machine directi ve,We have made two different types of checking the in tensit y flow in each t h e D a n i s n manufacturer Nilfisksound power determinati on, one ac- planne d position. This is easily done therefore only have to sta te th at t h e *cording to ISO 9614-1 and one very m 0 ving around with the 4437 dis- v a c u u m c l e a n e r i s l o w n oi s e>> B u t a ssimple according to no sta ndar d. playing "Fast" exponentially aver- a c o m p e titive parameter for the fu-From the results it appears that both a g ed intensity. t u r e , i t m i g h t b e a g o o d i d e a t o s t a t emethods have proved equally good. The point meas ure ment took near- ^ e s o u n d pressure (at lm) and/or

The machine directive does not say ly two hour s, calibration included, sound power level:

anything about how th e re sult s where the sweep mea sur eme nt was L : 61dB(A) re 20uPa

should be obtained, but for most peo- concluded in less th an half an hour! jj^: 69dB(A) re lp W

pie it is im po rt an t that th ei r me as - w h i c h corresponds to the manufac-

urements are made according to an The machine directive tur er' s specifications.inte rnat iona l sta ndar d. That gives a According to the machine directive,

sort of security. the noise specification depends of the How to operate the instruments is de-

During the pre-investi gation of the A-weighted sound pres sure level. tailed described in: Guided Tour;vacuum cleaner, it was establ ish th at This can be d eterm ined from the Sound Power Determination using

raisi ng the va cuum cleaner 25 cm sound power level. Type 3554, with or without ISO9614-1;over the floor improved the mea sur e- We need to find the sound pres- BS0167.

mertt conditions. But it is important sure level in free-field conditions All measurement ^results are repro-

to emphasize th at other noise sources one metr e from the vacuum cleaner. duced with the permission of Fisher

migh t be acoustically influenced if We there fore sub tra ct the number of & Nilsen A/S.

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