Noise control. Sound components. Transmission loss TL. reflected (reverberated) ρ absorbed α transmitted τ. TL = 10 Log(1/τ) = -10 Log τ.

Transcription

1 Sound components reflected (reverberated) ρ absorbed α transmitted τ Transmission loss TL TL = 10 Log(1/τ) = -10 Log τ Incident sound Transmitted sound Absorbed sound Reverberated sound

2 Mass law (Berger s law) theory: doubling of surface density ρ S [kg/m 2 ] -6 db i.e. TL 20 Log ρ S practice: - 5 db i.e. TL 17 Log ρ S Attenuation [db] Hz Theor. 565 Hz Exp Surface density [kg/m²]

3 Mass law (Berger s law) Frequency law doubling of frequency f [Hz] -6 db i.e. TL 20 Log f Attenuation [db] TL 20 Log (0.08 f ρ S ) ρ s [kg/m²] Frequency [Hz]

4 For low and high frequencies: resonance coincidence Sound reduction index : db Resonance region Mass law region Coincidence region 100 Hz 1000 Hz 10 khz Images by MIT OCW. Resonance Effect in a Panel Coincidence Effect in a Panel

5 Sound paths 1 - direct air transmission 2 - reverberation 3 - lateral transmission of airborne sound 4 - re-emission of impact sound 5 - transmission " Weakest path B A

6 Sound paths Weakest path 10log 1+ S' 10 S ΔTL 10 TL = TL0 1 S TL 0 S' TL'=TL 0 -ΔTL Loss of insulation [db] Δ TL [db] S'/S

7 Planning phase sensitivity to noise noise sources noise insulation requirements Design phase acoustic criteria in positioning and orientation calm vs. noisy zones construction elements technical installations e.g. cavities in walls, no connection between window layers

8 Environmental noise Noise control

9 Environmental noise θ 90 Anti-noise barriers of "infinite" length Attenuation [db] θ h/ λ 100 h

10 Environmental noise Anti-noise barriers of "infinite" length of finite length L 25 L d Noise control L/d Attenuation [db] Attenuation if L infinite.

11 Environmental noise Anti-noise barriers Acoustic urbanism Decibels > <55 Pesay

12 Environmental noise Anti-noise barriers Acoustic urbanism 69 db 74 db 69 db 72 db 78 db 66 db 50 db

13 Environmental noise Anti-noise barriers Noise source Noisy factory Very loud radio A Requisite noise barrier C Activity or situation B Threshold of audibility Acoustic urbanism Average workshop Lorry passing at 5 m Recording studio db(a) db(a) Noisy restaurant or dance floor Average light factory Office: typewriters Living room, loud radio Quiet car passing at 5 m Conversation Moderate radio Average office Special discontinuous construction 300 mm concrete rendered 240 mm brick or 150 mm concrete 120 mm brick or 100 mm concrete Double 3 mm glass, 100 mm space 140 mm hollow block 75 mm solid gypsum panel Timber studs, 10 mm plasterboards Timber floor plaster ceiling Single 6 mm plate glass 120 mm lightweight concrete block Single 3 mm glass Hospital ward, sleeping Studying Reading Houses Flats Hotels Quiet office db(a) Average home Quiet garden Subdued radio 13 mm fibreboard Badly fitting door Open door or window Quiet restaurant Average office Kg/m 2 Image by MIT OCW. Image by MIT OCW.

14 Structure-borne noise Noise control

15 Structure-borne noise Noise control

16 Structure-borne noise Noise control

17 Structure-borne noise Noise control

18 Structure-borne noise Noise control

19 Structure-borne noise Floating floor Flexible (soft) layer

20 Sound source in room Source Direct sound Reverberant sound: Sum of an infinite number of paths S 90 db 80 Image by MIT OCW. 70 Direct component Reverberant component Total sound level Distance from source (m) Image by MIT OCW.

21 Sound source in room I abs = I inc α s P abs = I A = I α s S Source Direct sound I = ¼ I stat Reverberant sound: Sum of an infinite number of paths L stat = 10 Log I stat /I o = 10 Log (4P/(I o A)) 90 db Direct component Reverberant component Total sound level Distance from source (m) Image by MIT OCW.

22 Sound absorbers Porous (a) (b) Absorption coefficient k 10kHz k 10kHz Image by MIT OCW.

23 Sound absorbers Porous Membrane Absorption coefficient k 10 khz k 10 khz Two layers of bitumenous felt 10 mm plywood Image by MIT OCW.

24 Sound absorbers Porous Membrane Cavity resonators Absorption coefficient k 10 khz V I 2r Image by MIT OCW.

25 Sound absorbers Porous Membrane Cavity resonators Absorption coefficient 100% 80% 60% 40% 20% 0% Porous Membrane Cavity Frequency [Hz]

26 Sound absorbers Porous Membrane Cavity resonators Perforated panels + Absorption coefficient With porous Without porous k 10 khz + Image by MIT OCW.

27 Absorbent baffles (a) (b) Sound partially absorbed Minimum 1 m Sound transmitted fully Absorber Bathroom flat 1 Ventilation duct Bathroom flat 2 (c) (d) Sound almost completely absorbed Sound partially absorbed Absorbent Ceiling Absorbent lining Street noise Sixth floor Fifth floor Absorber Section Plan Image by MIT OCW. Image by MIT OCW.

28 Noise Control Reading assignment from Textbook: Introduction to Architectural Science by Szokolay: 3.3 Additional readings relevant to lecture topics: "How Buildings Work" by Allen: p. 132 in Chap 14