VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...

More documents

Recommendations

Info

48 CHAPTER 3. MEASURING SOUNDFigure 3.13: Dosimeter. Source: Bruël&Kjær.Typical cumulative distributions are the L 99 , L 95 , L 50 , L 10 , L 5 and L 01 distributions.L x indicates that during x% of the time, a sound pressure levelis present larger than or equal to the indicated value. For example; L 95 = 60dB indicates that 95% of the time, the sound pressure level is at least equalto 60dB. L95 and L 90 can be interpreted as the sound pressure levels thatare continuously present, whereas L 10 and L 05 indicate sound pressure levelsthat are caused by accidental noises (eg. passing vehicles).3.8.4 The Noise Rating valueNoise pollution is related to the loudness and the frequency spectrum of thesound. This is the case because of the following reasons : a) high tones proveto contribute more to the nuisance of sound than the low tones; b) whendealing with noise one wants to track the source, and this is only possiblewith a frequency spectrum analysis. One has searched for a better one digitsystem, thatalso takes into account thespectrum. Inthis wayonegetsthesocalled ISO-limit curve for noise, also called the N.R. or Noise Rating curves(see Figure 3.14), presented by Kosten and Van Os. These are prescribedfor e.g. the determination of noise of ventilators and HVAC units. Theydisplay an octave band level (dB) in function of the frequency. They areenumerated according to the number of dB sound pressure in the 1000Hz
3.8. QUANTITATIVE PARAMETERS 49octave band. One only needs to analyse the noise in the octave bands andconnect themeasuring pointsto getapolygonal figure, this figureneeds to besuperimposed on the NR-curves. The NR number of the lowest not crossedcurve is a measure for the noise pollution caused by that noise. One mayinterpolate. The value obtained, has to be corrected to take into account theduration of the disturbance, the season, the surroundings etc. In the ISO-1996-standard all these notions are fixed. Tolerable limits for the sound thatmay enter a living room, bedroom, bureau, hospital etc. are also proposedin this standard. Or the sound that may be caused in a factory, central, at atransformation station, etc. A few examples, as presented in the ISO-1996-standard. - in a bedroom : NR 25, concert hall : NR 30 - in offices : NR 40,typing pool : NR 55 - in a factory : NR 85Figure 3.14: Noise rating curve.3.8.5 The nuisance of fluctuating soundThe NR method is interesting to represent the nuisance of a sound by asingle value, taking into account the frequency spectrum of that sound. Neverthelessthis is only valid for a sound with constant magnitude in time. Inlater research one has tried to express the nuisance of a fluctuating sound bya single value, assuming the nuisance is not only dependant of the averageloudness of the sound (L eq ) but also of the changes the loudness is undergoes.
Page 1:
VRIJE UNIVERSITEITBRUSSELAcousticsB
Page 4 and 5:
iiWhen sound becomes noise, it will
Page 7 and 8: ContentsI Introduction to acoustics
Page 9 and 10: CONTENTSvii4.3 Measuring the acoust
Page 11: Part IIntroduction to acoustics1
Page 14 and 15: 4 CHAPTER 1. FUNDAMENTAL CONCEPTS O
Page 20 and 21: 10 CHAPTER 1. FUNDAMENTAL CONCEPTS
Page 34 and 35: 24 CHAPTER 2. THE HUMAN HEARING SYS
Page 44 and 45: 34 CHAPTER 3. MEASURING SOUNDconver
Page 46 and 47: 36 CHAPTER 3. MEASURING SOUNDFigure
Page 54 and 55: 44 CHAPTER 3. MEASURING SOUNDfactor
Page 60 and 61: 50 CHAPTER 3. MEASURING SOUNDFor ex
Page 62 and 63: 52 CHAPTER 3. MEASURING SOUNDderiva
Page 64 and 65: 54 CHAPTER 3. MEASURING SOUNDThe so
Page 66 and 67: 56 CHAPTER 3. MEASURING SOUND
Page 69 and 70: Chapter 4Sound AbsorptionAll(constr
Page 71 and 72: 4.1. ACOUSTIC TRANSMISSION BETWEEN
Page 73 and 74: 4.1. ACOUSTIC TRANSMISSION BETWEEN
Page 75 and 76: 4.2. REALIZATION OF ACOUSTIC ABSORP
Page 81 and 82: 4.3. MEASURING THE ACOUSTIC ABSORPT
Page 87 and 88: 4.4. THE DIRECT AND DIFFUSE SOUND F
Page 89 and 90: 4.4. THE DIRECT AND DIFFUSE SOUND F
Page 91 and 92: Chapter 5Sound InsulationWhen consi
Page 93 and 94: 5.1. MEASURING SOUND INSULATION 83F
Page 95 and 96: 5.1. MEASURING SOUND INSULATION 85F
Page 97 and 98: 5.2. AIRBORNE SOUND INSULATION OF A
Page 105 and 106: 5.3. THE ACOUSTICAL BARRIER 95For t
Page 107 and 108: 5.3. THE ACOUSTICAL BARRIER 97Figur
Page 109 and 110:
Chapter 6Noise control6.1 Origin of
Page 111 and 112:
6.1. ORIGIN OF NOISE 101Figure 6.2:
Page 113 and 114:
6.2. REDUCING NOISE AT THE LEVEL OF
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
6.3. TACKLING NOISE TRANSMISSION 11
Page 123 and 124:
6.3. TACKLING NOISE TRANSMISSION 11
Page 125 and 126:
6.4. RADIATION NOISE 115Figure 6.17
Page 127 and 128:
6.4. RADIATION NOISE 117Figure 6.20
Page 129:
Part IIINoise directives119
Page 132 and 133:
122
Page 134 and 135:
124CHAPTER 7. DIRECTIVE 2000/14/EG:
Page 136 and 137:
126CHAPTER 7. DIRECTIVE 2000/14/EG:
Page 138 and 139:
128 CHAPTER 8. NOISE ON THE WORK FL
Page 140 and 141:
Page 142 and 143:
Page 144 and 145:
Page 146 and 147:
Page 148 and 149:
Page 150 and 151:
140 CHAPTER 9. COMMUNITY NOISE2. No
Page 152 and 153:
142 CHAPTER 9. COMMUNITY NOISE
Page 154 and 155:
144 APPENDIX A. MATERIAL PROPERTIES
Page 156 and 157:
Page 158 and 159:
Page 160 and 161:
Page 162:
152 BIBLIOGRAPHY[12] Bruel and Kjae
show all

VRIJE UNIVERSITEIT BRUSSEL Acoustics - the Dept. of ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?