LJUD I BYGGNAD OCH SAMHÄLLE

(1)

LJUD I BYGGNAD OCH

SAMHÄLLE

DELPHINE BARD

(2)

Why address sound issues?

• Noise affects people physiologically and psychologically

• At least 25 % of EU citizens are

exposed to noise in such extent that it

affects health and quality of life

• …

• Today, approximately 2 million people in

Sweden are exposed to a noise level

that exceeds the regulations set up by

the Swedish parliament

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D. Bard / VTAF01 / 20 Jan. 2016

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)

(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

)

‒ p measured with microphones

‒ Frequency response of human hearing changes with amplitude

L

_p

= 10 log

p

2

p

_ref2

= 20 log

p

_ref p = p f = RMS pressure p_ref = 2·10−5 Pa = 20μPa p_atm = 101 300 Pa p_tot(t) = p_atm ± p(t)

(5)

D. Bard / VTAF01 / 20 Jan. 2016

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

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Frequency weightings (II)

• Filters and calculation

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D. Bard / VTAF01 / 20 Jan. 2016

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…)

Ex: Calculate the L_eq,8h that corresponds to 105 dBA for 15 min.

L

_eq,T

= 10 log

1

T

₀ T

p

2

(t)

p

_ref2

dt = 10 log

1

T

₀ T

10

L_p(t) 10

dt

(9)

D. Bard / VTAF01 / 20 Jan. 2016

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

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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.

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Psykoakustik

• Söker samband mellan ett

ljuds fysikaliska parametrar

och hur ljudet uppfattas av

hörsystemet.

• Psykoakustiska mått har

som mål att beskriva hur

ljudet uppfattas.

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D. Bard / VTAF01 / 20 Jan. 2016

(16)

A – ytterörat

2 - 2.5cm

/4 = 2 - 2.5cm



(17)

D. Bard / VTAF01 / 20 Jan. 2016

B – mellanörat

Hammaren Städet Stigbygeln

Trumhinna

Ovala fönstret

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D. Bard / VTAF01 / 20 Jan. 2016

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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

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D. Bard / VTAF01 / 20 Jan. 2016

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

(22)

Sound exposure

• Temporary and permanent threshold shift

• Hearing impairment and hearing loss

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D. Bard / VTAF01 / 20 Jan. 2016

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D. Bard / VTAF01 / 20 Jan. 2016

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SDOF – Single Degree of Freedom System

u

(

t

)

F

(

t

) =

F

_driv

cos(

t

)

• Mass,

M

• Spring,

K

• Energy storage elements (spring)

R or C

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D. Bard / VTAF01 / 20 Jan. 2016

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D. Bard / VTAF01 / 20 Jan. 2016

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)

M

K



0



M

K

f







2

1

0

(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







sin(

)

cos(

)



)

(

2 ₁ ₂ 2 1 2 0

A

e

A

e

0

B

t

B

t

e

t

u

_h t i dt i dt t



_d



_d      









  







2

MK

R

















2

1

0





_d

(31)

D. Bard / VTAF01 / 20 Jan. 2016

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

• Which gives the solution

)

cos(

)

sin(

)

(

t

D

₁

t

D

₂

t

u

_p













 





 

)

cos(

)

sin(

)

(

₁ ₂ 2 2 2 2 2 2 2 1

t

D

t

D

t

u

F

R

M

K

M

K

D

F

R

M

K

R

D

p driv driv























(33)

D. Bard / VTAF01 / 20 Jan. 2016

Total solution= homogeneous +

particular

u_h

u_p

(34)

Different driving frequencies

0





0











₀

(35)

D. Bard / VTAF01 / 20 Jan. 2016

Low frequency excitation (



<



₀

)

• The spring dominates

(36)

Excitation at resonance frequency (



=



₀

)

• Damping dominates

• Phase difference= 90 or 

• If no (or little) damping is present:

(37)

D. Bard / VTAF01 / 20 Jan. 2016

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:

(39)

Thank you for your attention!