Research On Key Technology Of Architectural Acoustic Scale Model Measurement

The architectural acoustic scale model serves as an important auxiliary predictionmethod to acoustics design. When designing opera houses and concert halls, scale models areusually required to be built beforehand to predict the sound performance. China promulgatedits national standard “Code for test of scale acoustic model for auditorium” in2007, in whichthe measurements of reverberation time, evenness of sound field and sequence distributing ofshort time sound reflecting were defined with clarity. However, the acquisition of preciseenergy ratios，speech intelligibility and spaciousness parameters via scale model still remainsas one of the hard issues in this field today. This paper presents a study on the key technologyof architectural acoustic scale model measurement. The main researches are listed as follows:1. Experiments were conducted to verify the measuring system of scale model. Soundpressure level attenuation with distant spark source, the radiation characteristics of sparksource and the directivity of microphone connected with nose cone were tested. It isconcluded that the efficient working range of the measuring system of scale model is within1/3octave frequency range from630Hz to125kHz, and also from562Hz to141.3kHz.2. Two scale reverberation chambers, scale factors1:10and1:20respectively, were builtfor sound absorption coefficient measurement. The reverberation radius and evenness ofsound pressure level of scale reverberation chambers were verified by the experiment. Thescale absorption materials are divided into porous sound absorption materials, resonantsound-absorbing materials and seats according to each material’s characteristics and its actualapplication in real halls. The aim of this experiment in reverberation chamber is to find out themost suitable materials for scale model. A kind of polyester fiber panel was chosen, for it canbe used to match the sound absorption of actual seat’s cushion. Seats made of differentcushions and with different row spacing were also measured to construct a database of scalesound absorption materials for future reference.3. A dual-channel measuring technique is applied to measure the room acousticparameters in scale model. One channel is the measuring channel and the other one is used asa referencing channel for fixed point measurement. for Three scale models, Guangzhou GrandTheatre (scale factor1:20), Tianjin Cultural Theatrical Center (scale factor1:20) and Tianjin Cultural Music Center (scale factor1:10) were used as examples to explain the constructionof scale model, the simulation of scale model materials and the measuring method of acousticparameters. The results of the measurements were then compared with the actual performingeffects of the real halls to decide the accuracy of acoustic parameters and the difference ofsound field between the scale models and the actual halls. The result of the comparison showsthat the acoustic parameters of single impulse response were predicted accurately by thetechnique of scale model measurement under the scale factor of1:10and1:20.4．Restricted by spark source and microphone, scale model can only be applied tomeasure the acoustic parameters of single impulse response. How to get spaciousnessparameters and realize auralization by scale model are crucial to the experiments. This studyproposes a new method which combines3D scanning,3D modeling and3D printingtechnologies together to make a1:10scale dummy head. It can be used to accurately measurethe binaural room impulse response (BRIR) because it simulates the actual dimension of face,pinna and torso. Experiment has shown that the scale dummy head could be used to predictspaciousness parameters and hopefully to realize auralization in architectural acoustics scalemodel measurement.