LJUD I BYGGNAD OCH SAMHÄLLE DELPHINE BARD DIVISION OF ENGINEERING ACOUSTICS, LUND UNIVERSITY
Why address sound issues? Noise affects people physiologically and psychologically Today, approximately 2 million people in Sweden are exposed to a noise level that exceeds the regulations set up by the Swedish parliament At least 25 % of EU citizens are exposed to noise in such extent that it affects health and quality of life
Hearing process Pressure waves For a sound to be perceived Frequency: 20 Hz 20 khz Sound pressure level (SPL): frequency dependent Inner ear detects: p ϵ [20 μpa, 200 Pa] wide range Use of logarithmic scale (in decibels) Source Conveying medium Receptor
The decibel (db) & SPL Logarithmic way of describing a ratio Ratio: velocity, voltage, acceleration Need of a reference Sound pressure level (SPL / L p ) L p = 10 log p 2 2 = 20 log p ref p p ref p = p f = RMS pressure p ref = 2 10 5 Pa = 20 μpa p atm = 101 300 Pa p tot (t) = p atm ± p(t) p measured with microphones Frequency response of human hearing changes with amplitude
Frequency weightings (I) Correlate objective sound measurements with subjective human response A-weighting [db(a)/dba]: designed to reflect the response of how the human ear perceives noise, i.e. 20 Hz-20 khz Only really accurate for relatively quiet sounds and pure tones? Low frequency noise is suppressed (wind turbine noise?) C-weighting [db(c)/dbc]: developed for high level aircraft noise Z-weighting: zero frequency weighting (un-weighted values) B-weighting: covers the mid-range between the A- and C-weighting D-weighting: designed for use when measuring high level aircraft noise *Filters are defined in the standard IEC 61672 Fallen into disuse
Frequency weightings (II) Filters and calculation L weighted = 10 log 10 (L n+weighting) 10
Single event noise metrics Maximum sound level (L max ): Accounts only for sound amplitude [db/dba ] Sound exposure level (SEL) & Single event noise exposure level (SENEL) Total noisiness of an event. It takes duration into account If SENEL is measured for the period when the level is within 10 db of the L max, it will be essentially the same as SEL
Cumulative exposure metrics Equivalent SPL during the measurement time T (units: db, dba ) L eq,t = 10 log 1 T p 2 (t) T 2 dt = 10 log 1 0 p ref T 0 T 10 L p (t) 10 dt Ex: Calculate the L eq,8h that corresponds to 105 dba for 15 min.
Regulations environmental noise Infrastrikturprop. 1996/97:53 Noise-maps Location Measure Road Track Flight Indoors L Aeq,24h 30 30 30 Indoors L AFmax 45 45 45 Outside (façade) L Aeq,24h 55 60 55 Outside L AFmax 70 70 70
Malmö actions for noise exposure 2014 Citizens exposed to >30 dba indoors: 48 000, >55 dba outdoors: 126 000. Estimated cost (incl. health care and loss of work): 1 100 MSEK Proposed long term measures (250 MSEK): Source: Lower speed limit, silent asphalt, driving style and silent car/tires Sound reduction: Noise barriers, allowance for improvement of sound reduction at dwellings Focus on sensitive places, e.g. schools, pre-schools and parks
Psykoakustik Söker samband mellan ett ljuds fysikaliska parametrar och hur ljudet uppfattas av hörsystemet. Psykoakustiska mått har som mål att beskriva hur ljudet uppfattas.
Örat
A ytterörat /4 = 2-2.5cm f = 3-4 khz 2-2.5cm
B mellanörat Hammaren Städet Stigbygeln Ovala fönstret Trumhinna Runda fönstret
C innerörat, cochlea
Basilarmembranet
Effekter vid exponering 30 db God sömn 35 db Tal 100% förståeligt (1m avstånd) 45 db Tal ganska förståeligt 50 db 10-25% ganska & mycket störda 55 db 10-25% mycket störda 65 db Ohälsosam röstansträngning vid tal 65 db Barns inlärning försämrad 65 db Risk för bullerorsakat högt blodtryck/hjärt-kärlsjukdom
Buller inomhus allmäna råd Maximalt ljud: L Amax = 45 db Ekvivalent ljud: L Aeq = 30 db Ljud med hörbara tonkomponenter: L Aeq = 25 db Ljud från musikanläggningar: L Aeq = 25 db Värden för låga tersband (32-200 Hz) f (Hz) 31,5 40 50 63 80 100 125 160 200 L (db) 56 49 43 41.5 40 38 36 34 32
Sound exposure Temporary and permanent threshold shift Hearing impairment and hearing loss Tinnitus
Threshold shift
Tone audiogram
Age-Related hearing Loss
SDOF Single Degree of Freedom System Mass, M Spring, K F(t) = F driv cos(t) Energy storage elements (spring) R or C u(t)
Basic system
Free Vibration
Eigenfrequency The frequency at which the system oscillates when it is left to free-vibration (after having set it into movement). Uttryckt i vinkelfrekvens (rad/s) resp. frekvens (1/s = Hz) 0 K M f 0 1 2 K M
Homogeneous solution Solution obtained when setting F(t) = 0 Determined by help of initial conditions Consists of an exponentialy decaying part... and a harmonically oscillating part ) cos( ) sin( ) ( 2 1 2 2 1 2 0 0 t B t B e A e A e e t u d d t t i t i t h d d 2 MK R 2 1 0 d
Damping function It represents the dissipation of energy of the system Ex: Without damping With damping
Particular solution The solution which shows the displacement due to the driving force Ex: F(t) = F driv cos(t) Apply u p ( t) D sin( t) D2 Which gives the solution cos( ) 1 t D D 1 2 R 2 2 K M R K M 2 2 K M R 2 2 F F driv driv u p ( t) D1 sin( t) D2 cos( t)
Total solution= homogeneous + particular u h u p u = u h + u p
Different driving frequencies 0 0 0
Low frequency excitation ( < 0 ) The spring dominates Force and displacement in phase
Excitation at resonance frequency ( = 0 ) Damping dominates Phase difference= 90 or If no (or little) damping is present: The system collapses
Tacoma narrows 1600 m long Collapsed in 1940 due to wind loads exciting the structure at the resonance frequency
Excitation at high frequencies ( > 0 ) The mass dominates Force and displacement in counter phase: Phase difference = 180 or
Thank you for your attention! Delphine.bard@construction.lth.se