Computer Simulation and Virtual Experiments for Architectural Acoustics Education Ralph Muehleisen Civil, Environmental, Architectural Engineering University of Colorado, Boulder CO
[email protected] http://acoustics.colorado.edu
Challenges of Arch ACS Education • Buildings/Rooms cannot be easily modified – Can only see/measure/compare one configuration – Cannot often isolate sources/fields/elements • Look at just one room mode • Look at transmission through one element • Look at effects of various sources
• Coordinating off campus trips can be hard – Students forced to measure evenings/weekends
• Measurement equipment is expensive and fragile – >$20k for a good analyzer, several mics, speakers • Don’t want students using alone
– Cannot have multiple/duplicate setups • Measurements only in large groups
Alternatives • Animation – Show difficult concepts in isolation (like modes)
• Acoustic CAD – Show/compute and modify a room
• Digital Filters – Show/compute TL of various constructions
• Virtual Experiments – “Pretend” measurements with properly obtained data
Animations • Animations can help explain difficult to understand concepts: – – – –
Plane and Spherical Waves Standing Waves and Modes Radiation Patterns Evanescent Waves
Plane and Spherical Wave
Standing Waves and Modes
Evanescent (from Dan Russell) Below Cutoff
Above Cutoff
Software • I use MATLAB, others use Mathematica – Complex numbers built in – Animation capabilities built in – Expensive but ubiquitous and student versions available for a reasonable price
• Convert to Animated GIF for best portability – I use Ulead GIF animator ($40) • Converts nearly any movie format (avi, mpeg, mov)
– Usually smaller in size and can be viewed with standard web browser
Interactive Programs • Interactive programs let users modify computation parameters that fixed animations cannot • Very useful for understanding multivariable concepts like modes RUN
Mode DEMO
Acoustical CAD Let students “measure” and auralize designs • Let students compare room treatments – Hear the effects of reverberation on different acoustic signals – Hear effects of reflective surfaces on speech
• Use for lecture or concert hall design projects problems – Objective measures allow for some comparison between student designs
Software • Several good programs on the market – CATT, EASE/EARS, Odeon, Raynoise, Ramsete/Aurora
I use CATT: – Generous site license agreement and good price – No hardware dongles (can use in dept. labs) – Good auralization performance (although other programs are getting better)
Example: Reverberation Speech in Auditorium
Speech in Concert Hall
Speech in Cathedral
Audio Editing / Digital Filtering • Use audio editor to modify prerecorded sound – Change spectral/temporal characteristics • Filter broadband noise to simulate the sounds of different sources (e.g. Neutral, Rumbly, Hissy HVAC)
– Filter recorded noises to simulate TL • Compare different wall/window constructions – See how the attenuation compares
• Compare different sources with one wall – See the how different spectra are attenuated differently
Software Dozens of good programs. • Editor: Cooledit (http://www.syntrillium.com) – – – –
Shareware program ($70) FFT filter, arbitrary response (to simulate TL) Noise and tone generators Missing octave and 1/3 octave spectral analysis
• Sources: http://www.sounddogs.com – Special effects site with ~100K royalty free sounds – Can sample at low fidelity before buying – Typical cost: $10 for a 1 min 16 bit/44.1k sample
Example: Relative TL of Walls 2x4in Standard Stud Wall (STC 37)
2x4in Staggered Stud Wall (STC 47) 2x4in Double Stud Wall (STC 58)
Virtual Experiments • Faculty/TA does a good measurement once – Save data in most raw form – Can introduce noise after measurement taken
• Students use computer based instruments to measure prerecorded data – Students can have access to good data without having to go into the field – Students do not have to worry about out of calibration or broken equipment – Well designed virtual instruments can still incorporate ideas like calibration
Software • Labview – Ubiquitous, student editions available – Many books about virtual instrument design
• MATLAB – GUI design tools in newest versions allows for virtual instrument design
Virtual Experiment Examples – Noise Level measurements with virtual SLM • See how integration time effects sound level measurements. • Compare Lp, LA, LEQ, etc. • Compare FFT, 1/3 Oct., Oct. and dBA
– Reverberation time measurements • Compare impulse response to decay methods
– TL/Impact noise measurements • Compare airborne sound levels to vibration levels
Computers can help students… • Visualize difficult concepts • Modify a building to see the effects on acoustic signals • Have access to experiments at home or in a computer lab at their convenience • See/hear/feel acoustics – maybe for the only time • Save money to be used elsewhere in the University/School
