PDF - 1.84 Mo
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PDF - 1.84 Mo
C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 The decibel (1/2) dB 9 The sensitivity of human ear depends on the frequency 9 The auditive sense is proportional to the logarithm of the acoustical intensity I of the wave with I s = 10 W.m 120 100 80 60 40 −2 20 ULTRASOUNDS INFRASOUNDS Chapter 2 ( ) L = 10 log 10 I I s −12 Threshold of pain 140 Audible area Speech Threshold of audibility 0 1 Hz 20 Hz 1 kHz 2 kHz 20 kHz frequency The unit for the sound level is the decibel (dB) (one tenth of a bel), named like this in honour of the physicist Alexandre Graham Bell. This unit has the advantage of being based very well on the differential sensitivity of human ear, since 1 dB gap between two sound levels substantially corresponds to the smallest difference (in sound level) detectable by the human ear. Physiological acoustics, decibel Alexandre Graham Bell (1847-1922, american inventor) http://en.wikipedia.org/wiki/Alexandre_Graham_Bell Sound levels (1/2) Sound levels (2/2) z Sound level which results from two non-correlated sources dB 9 The sensitivity of human ear depends on the frequency 9 The auditive sense is proportional to the logarithm of the acoustical intensity I of the wave ( ) L = 10 log 10 I I s INFRASOUNDS 140 120 100 80 60 40 20 with I s = 10 −12 W.m ( r p r m s (r ) = 20 Hz ( ⎛ I1 + I 2 ⎞ ⎟ = 10 log 10 10 L 1 10 + 10 L 2 L res = 10 log 10 ⎜ ⎜ Is ⎟ ⎝ ⎠ ) [p(rr ; t )] 2 20 kHz [p(rr ; t )] 2 PE ) 3 2.5 frequency p s = ρ 0 c 0 I s = 400 ⋅10 −12 = 2 ⋅10 −5 Pa with 10 Lres-L1 (dB) 1 kHz 2 kHz averages over time, over an acoustic period T: r r r r r r ∀r p (r ) = 0 v (r ) = 0 ρ (r ) = 0 p T Speech 0 L = 20 log 10 p r m s p s Ptot Audible area Threshold of audibility −2 1 Hz I ∝ p 2rms ULTRASOUNDS Threshold of pain 1⌠ ⎮ T →∞ T ⎮ ⌡ 1.5 1 +T 2 [p(rr ; t )] 2 d t = lim 2 −T 2 0.5 L2-L1 (dB) [p(rr ; t )] 2 ≠ [p(rr ; t )] time (s) 2 Acoustic pressure level dB 140 threshold of pain 100 000 000 130 rjet engine (distance: 25 m) 10 000 000 110 100 pop band take-off (distance: 100 m) 120 1 000 000 pneumatic drill 90 80 truck 100 000 road traffic -10 ( -9 -8 ) L res = L res − L 1 + L 1 The decibel Acoustic pressure µPa 0 -7 -6 with -5 -4 -3 ( -2 -1 L res − L 1 = 10 log 10 1 + 10 (L 2 −L 1 ) 10 ) 0 Equal loudness contours Pa pressure level Lp (dB) dB 200 20 2 0,2 0,02 0,002 0,0002 0,00002 threshold of pain 140 120 100 80 60 40 20 0 70 speech 60 10 000 office 50 40 1 000 living room = 2 X 43 dB 30 library threshold of audibility 20 100 10 mountain bedroom + 40 dB and 40 dB = 20 0 threshold of audibility noise bruit = + 40 dB and 140 dB = frequency (Hz) loudness: subjective intensity of a sound; unit: the phon 140 dB Example: A 70 phons sound provokes the same auditive perception than a 1000 Hz sound, the physical level of which is 70 dB 1 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 A weighting curves: dB(A) Structure of human ear high pitch and low pitch sounds malleus temporal lobe of brain incus semi-circular canals oval window auditory nerve are less perceived cochlea pinna temporal bone auditory canal eardrum eustachian tube stapes circular window Outer ear Middle ear Inner ear Ossicles The tympanic membrane (eardrum) incus stapes malleus From Robier Transfer of acoustic pressures (sonic waves) from air medium to fluid media and to inner ear structures (cochlea) incus malleus "small" displacement (not very compressible liquid) strength "higher" and S smaller ==> higher pressure Transfer of acoustic pressures (sonic waves) from air medium to fluid media and to inner ear structures (cochlea) - animation The sound wave moves the eardrum and attached ossicular chain. The stapes footplate, in the oval window, transfers the vibrations to the perilymphatic compartment (scala vestibuli) and to the inner ear structures. Depending on the frequency, the vibration has a maximum effect (resonance) at a different point along the basilar membrane, accounting for passive tonotopy. stapes stapes pivot ossicles eardrum eardrum "large" displacement (compressible gas) "less large" strength and greater S ==> smaller pressure a high frequency sound affects a basal portion of the cochlea a low frequency sound affects a more apical part of the cochlea Text and images from website "Promenade 'round the cochlea" (http://www.cochlee.info) by R Pujol et al., Université Montpellier 1 et INSERM - France http://www.iurc.montp.inserm.fr/cric51/audition/fran%E7ais/ear/fear.htm 2 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 Schematic functioning of the eardrum Cochlea - Organ of Corti - Hair cells scala vestibuli ear cochlear tunnel eardrum outer hair cells organ of Corti scala tympani inner hair cells nose healthy cells equilibrium of pressures damaged cells nerve fibers of the auditory nerve http://ile-de-france.sante.gouv.fr/santenv/bruit/notions/celcil.htm http://ile-de-france.sante.gouv.fr/santenv/bruit/notions/corti.htm Hair cells Audiograms Hearing loss (dB) Hearing frequency (Hz) Too much silence? z Danger 9 at work (wearing of hard hat) 9 in the streets (noiseless vehicles) z Deprivation of sound information 9 noise of an engine 9 functioning of a machine 9 lack of pleasantness (the good noise!) normal hearing hearing loss reaches 2000 Hz hearing loss at 4000 Hz important or irreversible deafness Sound levels - Noise annoyance The audible sounds range from 0 dB (threshold of hearing) and 140 dB. The threshold of pain is around 120 dB. Annoyance, which is a subjective concept, is felt with a great variability from one person to another. Consequently, no objective noise level can give an absolute indication of the annoyance. z Discomfort 9 public transports (train) 9 open-plan offices http://www.acnusa.fr/bruit_et_mesure/bruit_et_mes_echelle.asp 3 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 Terrestrian transports Noise contour maps (Paris - France) Exposure of population to roadway noise: number of road black points Leq ≥ 70 dB(A) between 8 h -20 h Nord Pas-de-Calais Picardie Haute Normandie Lorraine Ile de-France Basse Normandie Bretagne Champagne Ardenne Alsace Pays-de-Loire Centre Bourgogne Franche Comté Poitou Charentes Limousin Rhône-Alpes Auvergne 100 From data bank of LRPC Strasbourg - France (results 1998) Aquitaine Provence Alpes Côte d'Azur 1st district Midi-Pyrénées Languedoc Roussillon 16th district www.paris.fr/FR/Environnement/bruit/carto_bruit/default.ASP French noise annoying plan (plan de gène sonore - PGS in french) French noise annoying plan (plan de gène sonore - PGS in french) Document provided by French law 92-1444 of 31 December 1992 (Article 19) which permits to define the areas in which residents are eligible for assistance for soundproofing. Roissy CDG Airport (1999) http://www.adp.fr/labo/web/surenv/bruit/index.html French noise exposure plan (plan d'exposition au bruit - PEB in french) French noise exposure plan (plan d'exposition au bruit - PEB in french) Orly Orly- France Document provided by the French law 85-696 of 11th July 1985 which regulates urbanism near airports so as not to expose new populations to noise annoyance. Specific measures can take into account the specificities of the pre-existing context. Orly airport Precautionary principle http://www.adp.fr/labo/web/surenv/bruit/index.html 4 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 Example of solution: traffic management (noise mitigation) PEB - PGS: merger? z Maximum number aircrafts movements (Orly airport : 200.000 per year) z Time of day restrictions (Orly airport : 7 am to 11 pm) z Choice of air lanes z Departure flight path and slope An french interministerial working group studied the question of bringing together the procedures relating to the noise exposure and noise annoying plans in France. A report released in December 2007 weighs the advantages and disavantages of a merger of the two zonings, and makes proposals. or Report of the working group « Rapprochement des procédures PEB et PGS » - report n°004577-01 - june 2007 (format pdf - 784,9 Ko) - Authors : Gilles Rouques (CGPC) and Annick Helias (IGE) http://publications.ecologie.gouv.fr/publications/IMG/pdf/Rapport_GT_Rapprochement_PE B_et_PGS.pdf Perception and room acoustics (1/10) Perception and room acoustics (2/10) z Sounds z Perception 3 Location: comparison by the brain of • intensities • times of arrival 3 noise (annoyance, alert function) 3 speech (intelligibility) 3 music (esthetic) organization of sounds • time (rythm, melody) • spatial (fill the space) - visually space - auditively to the two ears 3 Attributes: perceived • monaural hearing • binaural hearing loundness, pitch, timbre (timbre), soundscape ∆L d B ∆t ms 0dB 0 ms 3 spectrum 3 intensity 3 duration 3 Continuous: formants for the voice 3 Transient: consonants, musical attack Perception and room acoustics (3/10) z The sound space 3 Location of one source • binaural • pinna • scattering 0dB 0 ms 3 Location of two sources • coherent sources: impossible • non coherent sources: distinct Perception and room acoustics (4/10) ∆L d B ∆t ms z Soundscape: intelligibility and noise 3 Noise masking speech • Example: pernicious effect of reverberation 3 Reverberation which permits to the speaker to hear himself 3 Too high reverberation: tiredness | h(t) | 3 Delay between two coherent sources • summation effect (~ 1ms) • precedence effect (loudness + space effect) • space effect (3D) 3 These three effects can be simultaneously perceived (reflections in a room) 3 Large number of reflections, late effects: reverberation ≈ 100 ms straightforward sound 1st (geometrical) reflections time reverberation (statistics) 5 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 Perception and room acoustics (5/10) z Soundscape, room acoustics (2/6) z Soundscape, room acoustics (1/6) ¾ Expectation of the listener ¾ Expectation of the performer Perception and room acoustics (6/10) ¾ Listeners blooming, esthetic pleasure interpretation of music Sonorous sound Orchestra: 10 to 100 W (in facts < 110 dB) 9 good distribution of sound energy 9 increase the number of reflections The listener try to: 9 benefit from a sonorous sound (avoid tiredness) 9 make the most of his two ears (space effect) 9 well understand music (but small "fuzziness") 9 have a good adjustment of tones (instrumental equilibrium, tonal equilibrium, …) increase the volume of the room (6 to 11 m3 per listener) Use of the two ears 9 initial side reflections (close to the listener) improve the clarity Good understanding 9 limited reverberation (compromise with sonorousness) Moreover, the musician try to: 9 well listen what he is playing 9 have a good contact with other musicians favor the small "fuzziness" Good adjustement of tones (delicate) 9 avoid front reflectors (above and behind the orchestra), coloration if the reflector are present, split them Perception and room acoustics (7/10) z Soundscape, room acoustics (3/6) Perception and room acoustics (8/10) z Soundscape, room acoustics (4/6) ¾ Impulse response ¾ Musicians p r (t ) = h (t )* p anechoic (t ) listen what they are playing 9 return of sound towards stage 9 good coupling stage / room good contact between them 9 reflectors above the orchestra | h(t) | ¾ The room Room acoustics ≡ question of geometry 9 arrangement of volumes 9 arrangement of walls • contact listeners / musicians • coupling stage / room ≈ 100 ms straightforward sound 1st (geometrical) reflections time reverberation (statistics) Absorbant acoustical treatment does not improve anything 9 (permits eventually to remove some echoes) Perception and room acoustics (9/10) z Soundscape, room acoustics (5/6) ¾ Subjective characterization 9 9 9 9 9 9 9 9 Reverberation Clarity Loudness Intimacy Uniformity Diffusion Envelopment Performer's satisfaction ¾ Questionnaire ¾ Binaural hearing 9 numerical simulation, scale model Perception and room acoustics (10/10) z Soundscape, room acoustics (6/6) ¾ Objective characterization (examples) 9 sound amplitude 9 reverberation duration at -60 dB 9 early decay time (1st reflections) 9 timbre ⎛ ⎜ ⌠ 80 ms 10 log10 ⎜ ⎮ p 2 (t ) d t ⎜⎜ ⌡ 0 ⎝ ⎡ ⎛ 5000 Hz ⎢ ⎜⌠ 10 log10 ⎢ ⎜ ⎮ M(f ) d f ⎢ ⎜⎜ ⌡ 500 Hz ⎣⎝ ⎞ ⎟ 4500 ⎟ ⎟⎟ ⎠ ⎛ ⎜ 10 log10 ⎜ ⎜⎜ ⎝ ∞ ⌠ 2 2 ⎮ p (t ) d t p ref ⎮ ⌡0 ⎞ ⎟ ⎟ ⎟⎟ ⎠ ⎞ ∞ ⎟ ⌠ 2 ⎮ p (t ) d t ⎟ ⎟⎟ ⌡ 80 ⎠ ⎛ 500 Hz ⎜⌠ ⎜⎮ M(f ) d f ⎜⎜ ⌡ 50 Hz ⎝ ⎞ ⎟ 450 ⎟ ⎟⎟ ⎠ ⎤ ⎥ ⎥ ⎥ ⎦ ¾ Numerical simulation ¾ Scale model 6 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 Example of mistakes (1/2) large movie projection screen on a perfectly reflecting wall McKinnon Theater, Kettering University, Flint, MI Example of mistakes (2/2) z flutter echo succesive echoes large movie projection screen on a perfectly reflecting wall 400 seats http://www.kettering.edu/acad/scimath/physics/acoustics/McKinnon/McKinnon.html McKinnon Theater, Kettering University, Flint, MI http://www.kettering.edu/acad/scimath/physics/acoustics/McKinnon/McKinnon.html Animation courtesy of Dr. Dan Russell, Kettering University 7 C. Potel, M. Bruneau, "Acoustique générale (...)", Ed. Ellipse, collection Technosup, ISBN 2-7298-2805-2, 2006 Slides based upon C. POTEL, M. BRUNEAU, Acoustique Générale - équations différentielles et intégrales, solutions en milieux fluide et solide, applications, Ed. Ellipse collection Technosup, 352 pages, ISBN 2-7298-2805-2, 2006 8