>Simon BAILHACHE, Michel VILLOT Prediction of structure-borne noise generated by a water evacuation duct in heavyweight and lightweight frame constructions ACOUSTICS 2012 April 23-27 Nantes, France PAGE 1
Contents 1. Introduction 2. Description of the prediction method 3. Application to a realistic case 4. Comparison between heavy and lightweight structures 5. Conclusions ACOUSTICS 2012 April 23-27 Nantes, France PAGE 2
Introduction Structure-borne noise from building service equipment > May cause discomfort to building occupants > Resulting noise levels are often subject to regulatory limits > Existing standard methods for prediction: > EN 15657-1: laboratory method for source characterization > EN 12354-5: model for transmission through the building structure and radiation in the adjacent rooms > Based on SEA: valid only for equipment installed in heavy construction! Lightweight structures inhomogeneous vibration fields due to stiffeners and high damping ACOUSTICS 2012 April 23-27 Nantes, France PAGE 3
Introduction Recent developments > CEN/TC126/WG7: draft standard pren 15657-2 > Source characterization for equipment in lightweight structures > Mobility-based estimation of injected power > COST Network FP0702 > Work on EN 12354-1 for lightweight structures > CEN/TC126/WG2 > Future work on EN 12354-5 for lightweight structures ACOUSTICS 2012 April 23-27 Nantes, France PAGE 4
Prediction method 1 > Installed power = structural power injected into the receiving structure > Mobility method Y=v/F W s, inst 1 2 Y Re R Y 2 R Y S 2 v sf 2 > Wall velocity > Heavyweight: power balance equation > Lightweight: empirical relationship Ws, inst 2 f m s v² C exp W s, inst S v 2 3 > Radiated noise > From radiation efficiency W ray 0c ss v² ACOUSTICS 2012 April 23-27 Nantes, France PAGE 5
Equipment Prediction method Assumptions and simplifications > Direct transmission only > Rigid point connections between equipment and supporting structure > Simplification with 2 single-point sources > Excitation in the direction normal to the receiver plane only F 1 F 2 ACOUSTICS 2012 April 23-27 Nantes, France PAGE 6
Case of a waste water duct System description > Source > PVC duct (Ø110 mm) > Variable water flow rate > 2 fixation points (1.25 m spacing) > Heavy receiver > 100 mm thick concrete blocks > Lightweight receiver > 10 mm OSB + 12.5 mm gypsum board > Wood studs every 600 mm > Contact points at bay SOURCE SIDE Duct Point connection RECEIVER SIDE Microphone Separating wall ACOUSTICS 2012 April 23-27 Nantes, France PAGE 7
Case of a waste water duct Characterization measurements > Source and receiver mobilities > Method similar to ISO 7626-2 > Separate sensors for velocity and force > Source free velocity > Method similar to ISO 9611 > Water flow rates: 1 l/s, 2 l/s, 4l/s > All tests performed in 1/3 octave bands (50-5000 Hz) > S. Bailhache, M. Villot, «Comparison of structure-borne sound power injected to heavyweight and lightweight constructions», Proc. 19th ICSV, Vilnius, Lithuania, 8-12 July 2012 ACOUSTICS 2012 April 23-27 Nantes, France PAGE 8
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 Maghitude (m/ns) Magnitude (m/ns) Case of a waste water duct Measured point mobilities > Receivers > Source 1,00E+00 1,00E+00 Concrete wall - Contact point 1 Contact point 1 1,00E-01 Concrete wall - Contact point 2 1,00E-01 Contact point 2 Lightweight wall - Contact point 1 1,00E-02 Lightweight wall - Contact point 2 1,00E-02 1,00E-03 1,00E-03 1,00E-04 1,00E-04 1,00E-05 1,00E-05 1,00E-06 1,00E-06 Frequency (Hz) Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 9
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 L V (db re 5.10-8 m/s) Case of a waste water duct Measured source free velocity > Maximum at low frequencies > Differences between the 2 contacts at low frequencies 80 70 60 50 40 30 1 l/s - Contact point 1 1 l/s - Contact point 2 2 l/s - Contact point 1 2 l/s - Contact point 2 4 l/s - Contact point 1 4 l/s - Contact point 2 20 Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 10
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 L Ws, inst (db re 10-12 W) Prediction results Installed power (2 l/s) > Predominant at low frequencies > Lightweight wall ~20 db higher > Missing values: wrong mobility measurement results 70 60 50 40 Heavyweight receiver Lightweight receiver 30 20 10 Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 11
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 L V - L Ws,inst (db re 10-12 W, 5 10-8 m/s) Prediction results Differences between heavy and lightweight structures > Mobility higher power injected into the lightweight wall > Damping of the vibration field higher losses in the lightweight wall 0-10 -20-30 -40 Heavyweight wall (estimated) Lightweight wall (measured) -50-60 Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 12
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 L v (db re 5.10-8 m/s) Prediction results Wall velocity (2 l/s) > Predominant at low frequencies > Lightweight wall 10-15 db higher > Gap decreases with frequency 50 40 30 20 Heavyweight receiver Lightweight receiver 10 0-10 Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 13
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 10 log(σ S ) (db) Prediction results Difference between heavy and lightweight structures > Radiation efficiency higher for the heavy wall (except at high frequency) 20 10 0-10 Heavyweight wall (estimated) Lightweight wall (measured) -20-30 -40 Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 14
50 63 80 100 125 160 200 250 315 400 500 630 800 1000 1250 1600 2000 2500 3150 4000 5000 L sn (db re 2.10-5 Pa) Prediction results Radiated noise (2 l/s) > Predominant at low frequencies > Heavy wall higher by 5 db(a)! > Comparison against measured values (heavy receiver) > L sn as defined in EN 14366 > Discrepancies up to 8 db > Similar global shapes 50 40 30 20 10 0 Heavyweight receiver - Prediction: 29 db(a) Heavyweight receiver - Measured: 25 db(a) Lightweight receiver - Prediction: 24 db(a) -10 Frequency (Hz) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 15
Prediction results Possible error sources > Neglect of moment excitation > Neglect of coupling between dynamic forces at the contact points > Simplified calculation of the installed power with regard to source/receiver mobility ratio > 1/3 octave band characterization measurements > Inaccurate input data > Measurement uncertainty ACOUSTICS 2012 April 23-27 Nantes, France PAGE 16
Conclusions Prediction method > Installed power calculation according to pren 15657-2 > Mobility approach > Separate characterization for source and receiver > Transmission through structure > Heavyweight: SEA-based model > Lightweight: empirical approach > Work in progress within CEN and COST ACOUSTICS 2012 April 23-27 Nantes, France PAGE 17
Conclusions Results > Radiated noise is not likely to be higher in the case of the lightweight structure > Higher structural losses > Lower radiation efficiency > Agreement between predicted and measured noise levels is rather acceptable (heavy wall) ACOUSTICS 2012 April 23-27 Nantes, France PAGE 18
Conclusions Upcoming work > Prediction considering a 2-contact source > Transfer mobility required > Use of effective mobilities > In situ experimental validation for lightweight constructions > Other source/receiver configurations ACOUSTICS 2012 April 23-27 Nantes, France PAGE 19
Simon.bailhache@cstb.fr Thank you for your attention ACOUSTICS 2012 April 23-27 Nantes, France PAGE 20