160608 RT in Large Rooms-PRESENTATION for IOA

Reverberation Time in Sports Halls

Paul Doyle - BSc MSc MIOAIon Acoustics Ltd

8th June 2016

Institute of Acoustics, South-West BranchYoung Members’ Presentations

Presentation Summary Research context Reasons for underestimation of RT Modelling used for project Research findings Further research

Paul Doyle - BSc MSc MIOA. 8th June 2016. ‘Reverberation Time in Sports Halls’.Institute of Acoustics, South-West Branch. Young Members’ Presentations

Research context


Typical Sports Hall Layout (photo taken by Ion Acoustics)

Research context RT design requirements

Tmf 1.5 – 2.0 sec (BB93, Sport England)

Historical design of sports halls Large volume (2,000m3 – 5,000m3) Shoebox geometry, parallel walls Hard surface materials Constraints on location of absorption


Research context Is Tmf RT appropriate? What about low frequency RT? Acoustic comfort

Not enough to simply ‘meet the Tmf target’ Health effects


Research context


Arup Acoustics Dataset - Predicted and Measured Tmf Reverberation Time (Oeters, 2012)

Research context Dane Court sports hall

33m x 18m x 8.65m - volume 5183m3

Perforated metal soffit, αw 0.45 Sabine Tmf 2.1 sec - actual Tmf 3.8 sec 150m2 αw 0.9 at high level - Tmf 3.0 sec 150m2 αw 0.9 to soffit - Tmf 2.8 sec Scattering elements (nets) - Tmf 2.0 sec


Reasons for underestimation of RT1. Prediction method2. Location of absorption3. Effect of scattering


1. Prediction Method Sabine // Erying // Fitzroy

Only suitable under specific conditions Do not account for room effects

Ray-tracing Room effects (flutter echoes, diffraction) User knowledge Scattering - (BS ISO 1749-1 (2004) +A1 (2014))

‘Wave-based’ methods, hybrid methodsPaul Doyle - BSc MSc MIOA. 8th June 2016. ‘Reverberation Time in Sports Halls’.

Institute of Acoustics, South-West Branch. Young Members’ Presentations

1. Prediction Method Importance of scattering in ray-tracing


Single ray modelled in a rectangular room; reflections with different scattering coefficients (Rindel, 1995)

1. Prediction method Frequency-dependent scattering behaviour


Relationship between surface roughness, D, and wavelength, λ , which illustrates the frequency dependent behaviour of scattering (James et al, 2012)

2. Location of absorption

Absorption at high level Sports hall typically 8 - 10m tall Sound energy travels in horizontal plane Sound energy does not ‘see’ the absorption


2. Location of absorption


Acoustics of Schools: a design guide. Appendix 4 (November 2015) Sport England: Affordable Sports Halls, Appendix 5 (July 2015)

3. Effect of scattering

Scattering will direct sound energy to the absorption at high level

Not necessarily a lightweight diffuser…



Sports Hall Tmf 2.8 sec reduced to Tmf 1.8 sec - Oeters (2012)




Sports Hall Tmf 4.0 sec reduced to Tmf 3.1 sec - Oeters (2012)


Initial RT 1.03 sec (250Hz – 4kHz)


With scattering RT 0.59 sec (250Hz – 4kHz)

Alternative to scattering elements

Design approaches for tilting walls in smaller & larger rooms (Chmelik et al, 2012)


Modelling used for research Finite Element Modelling

Geometry split into a mesh Solving wave equation at nodes

Limitations 2D (visualising a section as a ‘slice’ of 3D) Non frequency-dependent absorption No scattering (impedance)


Modelling used for research Dane Court sports hall Comparison between Sabine, ray-tracing, FEM

Original model: absorptive ceiling only Location of absorption:

(1) abs ceiling, 150m2 abs at high level (2) abs ceiling, 150m2 abs at low level (3) 150m2 abs at low level only

Effect of angled wall: absorptive ceiling onlyPaul Doyle - BSc MSc MIOA. 8th June 2016. ‘Reverberation Time in Sports Halls’.


Modelling process – ray-tracing


Modelling process - FEM


Research findings Absorptive ceiling only (αw 0.45)


Prediction Method Tmf (sec) Comment

Measured RT (Arup Acoustics) 3.8Sabine calculation 2.0 much lower than measured

CATT Acoustic T20 3.4 close to measured

FEM side wall T20 4.8 higher than measured

FEM rear wall T20 2.6 lower than measured

Research findings Effect of location of absorption on Tmf


Prediction MethodAbs ceiling & panels

at HIGH level, Tmf (sec)

Abs ceiling & panels at LOW level,

Tmf (sec)Comment

Sabine calculation 1.5 1.5 No changeCATT Acoustic T20 2.8 2.6 Small reduction

FEM side wall T20 4.5 1.6 Significant reduction

FEM rear wall T20 3.0 1.5 Significant reduction

Research findings Effect of location of absorption on decay


Absorption to ceiling & walls high level Absorption to ceiling & walls low level

Research findings Is soffit absorption necessary with

absorption at low level?


Prediction MethodAbs ceiling & panels

at LOW level, Tmf (sec)

Abs panels at LOW level ONLY,

Tmf (sec)Comment

Sabine calculation 1.5 2.6 Significant increaseCATT Acoustic T20 2.6 2.6 No change

FEM side wall T20 1.6 2.2 Moderate increase

FEM rear wall T20 1.5 2.0 Moderate increase

Research findings Effect of angled wall


Prediction MethodShoebox model,

Tmf (sec)Angled wall model,

Tmf (sec)Comment

Sabine calculation 2.0 2.0 No changeCATT Acoustic T20 3.4 2.9 Small reduction

FEM side wall T20 4.8 1.1 Significant reduction

FEM rear wall T20 2.6 1.0 Significant reduction

Research findings Effect of angled wall on pulse propagation


Research findings Effect of angled wall on decay


Shoebox with absorption to ceiling Angled wall with absorption to ceiling

Research conclusions Sabine

Lower than measured values Unsuitable for non-uniform absorption distribution

Ray-tracing Comparable to measured values Location of wall absorption does not affect RT prediction Angling side wall - no significant reduction in RT

FEM Location of absorption has significant impact on RT Angling side wall reduces RT Difficult to determine ‘accuracy’ due to 2D model


Further research FEM

Expansion to 3D Frequency-dependent absorption coefficient Addition of scattering (impedance)

Ray-tracing Comparison between different software

Tmf – consideration of lower frequency range?


Conclusion Sports halls – challenging acoustic design Prediction method Location of absorption Effect of scattering Can we model room effects accurately?

Thanks for your time! - Questions?Paul Doyle - BSc MSc MIOA. 8th June 2016. ‘Reverberation Time in Sports Halls’.


160608 RT in Large Rooms-PRESENTATION for IOA

Documents

Transcript of 160608 RT in Large Rooms-PRESENTATION for IOA