LJUD I BYGGNAD OCH SAMHÄLLE

Transcription

1 LJUD I BYGGNAD OCH SAMHÄLLE DELPHINE BARD DIVISION OF ENGINEERING ACOUSTICS, LUND UNIVERSITY

2 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

3 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

4 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 = Pa = 20 μpa p atm = Pa p tot (t) = p atm ± p(t) p measured with microphones Frequency response of human hearing changes with amplitude

5 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 Fallen into disuse

6 Frequency weightings (II) Filters and calculation L weighted = 10 log 10 (L n+weighting) 10

7 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

8 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.

9 Regulations environmental noise Infrastrikturprop. 1996/97:53 Noise-maps Location Measure Road Track Flight Indoors L Aeq,24h Indoors L AFmax Outside (façade) L Aeq,24h Outside L AFmax

10 Malmö actions for noise exposure 2014 Citizens exposed to >30 dba indoors: , >55 dba outdoors: Estimated cost (incl. health care and loss of work): 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

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14 Psykoakustik Söker samband mellan ett ljuds fysikaliska parametrar och hur ljudet uppfattas av hörsystemet. Psykoakustiska mått har som mål att beskriva hur ljudet uppfattas.

15 Örat

16 A ytterörat /4 = 2-2.5cm f = 3-4 khz 2-2.5cm

17 B mellanörat Hammaren Städet Stigbygeln Ovala fönstret Trumhinna Runda fönstret

18 C innerörat, cochlea

19 Basilarmembranet

20 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

21 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 ( Hz) f (Hz) 31, L (db)

22 Sound exposure Temporary and permanent threshold shift Hearing impairment and hearing loss Tinnitus

23 Threshold shift

24 Tone audiogram

25 Age-Related hearing Loss

26 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)

27 Basic system

28 Free Vibration

29 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 K M

30 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( ) ( 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 d

31 Damping function It represents the dissipation of energy of the system Ex: Without damping With damping

32 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)

33 Total solution= homogeneous + particular u h u p u = u h + u p

34 Different driving frequencies 0 0 0

35 Low frequency excitation ( < 0 ) The spring dominates Force and displacement in phase

36 Excitation at resonance frequency ( = 0 ) Damping dominates Phase difference= 90 or If no (or little) damping is present: The system collapses

37 Tacoma narrows 1600 m long Collapsed in 1940 due to wind loads exciting the structure at the resonance frequency

38 Excitation at high frequencies ( > 0 ) The mass dominates Force and displacement in counter phase: Phase difference = 180 or

39 Thank you for your attention!