and Model Calibration
of Rose Auditorium
Class: Sound and Space (ME 465)
Year: Spring 2019
Goal: To create a model of a room, conduct acoustic measurements of the room and analyze it for its acoustic characteristics, calibrate the model using CATT Acoustics and validate the model using experimental results
Custom-made series of code for measurements, analysis, and functions
3 Part project: Acoustic Measurements, Model Creation and Calibration, and Recommendations and Final Presentation
Description, analysis, and understanding of the space and its purpose
Convergence between measured data and analyzed simulated data
Impulse Response that can be applied to anechoic recordings to experience the room through auralization
The Rose Auditorium was chosen as the room to be analyzed as it is used for various different activities, from guest speakers, lectures, theatrical performances, and musical (vocal and instrumental) performances.
The auditorium was measured for its dimensions using a laser pointer, due to the lack of blueprints and manuscripts. Then, an omnidirectional, dodecahedron speaker was placed in the center of the stage (as the sound source will be usually for the auditorium), and a flat-field microphone was placed in four different locations (front center, side center, back center, and middle center where AV usually records) that best characterizes the space. Acoustic measurements were then conducted by sending out sine sweeps, and conducting many averages for accuracy and to eliminate noise.
The frequency response and then the impulse response of the room for each receiver (microphone) location were found. Then, each impulse response were filtered through a bank of octave bands, and the energy decay curve (EDC) was calculated for both the unfiltered response and frequency-band filtered responses. The responses were then plotted against the EDC, on a log scale for computational efficiency and analysis.
Several acoustic measures, such as reverberation time, energy decay time, and clarity index, were then found for each receiver location and response. It was interesting to note that the reverberation times for the signals stayed consistent, regardless of the location of the receiver. This implies that the Rose Auditorium was designed so that each audience member has similar acoustical experiences. Not only that, the reverberation time (RT) of the auditorium lied in between the optimal RT for spoken word and performances, fitting as it serves multiple purposes. Using the analyzed data, auralization was possible to experience the space and its sound.
After the experimental measured data had been analyzed, a model was created using CAD software (OnShape, AutoCAD, and SketchUp) and was imported to CATT Acoustics to be analyzed and validated. Each surface of the model were assigned specific materials that best corresponded to the actual space. Then, the materials were changed to better match the analyzed parameters from the measured data. For example, scattering was added to the audience area, to accurately account for the effects of people sitting in the auditorium. Several iterations of the model were simulated to ensure that the measured and analytical data match closely.
After the model had been verified, the model was further calibrated by changing acoustic properties of the materials to match the actual purpose of the space. For Rose Auditorium, "spoken word" was chosen as its main purpose as it is served most often for lectures and guest speakers. To do so, the reverberation time had to be lowered and clarity index had to be higher. For both of these parameters, more absorption is needed, and the changes were made accordingly. Auralization for both the calibrated and the improved model was possible, and was compared to that from the measured data.
All code for the measurement, analysis (MATLAB), and simulations (CATT Acoustics) was custom-created. The technical report can be found here.