Acoustic Scale Model Research Articles

Advances of acoustic research in coupled spaces

Coupled space widely exists in theatres, concert halls, large religious buildings, factories and other buildings, and its sound field is complex. Although some scholars have carried out relevant studies by means of sound field computer simulation, acoustic scale model test and field measurement, there are still a lot of problems unsolved. In this paper, the characteristics of coupled space sound field and the research progress of coupled space sound field in concert hall and theater are reviewed.

The Performance of a Low Berm in Reducing Traffic Noise

Traffic noise measurements were made behind a low, earth berm and in an adjacent open field to estimate insertion loss. The traffic was comprised of a mix of light vehicles, heavy trucks, and some medium trucks. The berm had a height of 1.65 meters above the roadway and began at the outside shoulder of a four-lane highway along U.S. Highway 101 in Northern California. Two microphone positions were located on the far side of the berm at distances of 28 and 40 meters from the center of the near lane of vehicular traffic. Away from the berm, a microphone was placed in an open field at 28 meters from the highway at a site upstream of the berm. The difference between the open location and those behind the berm were 11.6 and 9.9 dB for the 28- and 40-meter locations, respectively. The reductions obtained with the berm are compared to double edge diffraction theory and acoustic scale model results from the literature. The results of this study are reviewed in this paper and a comparison to FHWA Traffic Noise Model results is presented.

Pre-Sabine Room Acoustic Guidelines on Audience Rake, Stage Acoustics, and Dimension Ratios

Prior to Sabine’s work on the Fogg Art Museum and Boston Symphony Hall, several numerical guidelines had been developed and applied to the design of rooms with specific acoustic demands such as theatres, concert halls, and opera houses. Previous papers have discussed guidelines based on the following principles: voice directivity, which was employed in the design of at least 11 rooms; “echo theory”, which quantifies the perception threshold between direct sound and first order reflections in order to prevent echoes from occurring, aiding in the design of at least 7 rooms and leading to the first known use of an acoustic scale model; and notions of reverberation, which influenced the design of at least 14 rooms. This paper discusses three additional pre-Sabine numerical guidelines that were used in room acoustic design: (1) audience rake, (2) stage acoustics and proscenium design, and (3) length, width, and height ratios. The origin of these theories, as well as examples of rooms in which they were applied, are discussed and compared to current practices in room acoustic design.

Richard H. Lyon: Sound propagation, acoustic modeling, and the MIT A&V Lab

In the mid 1970s, the Acoustics and Vibration Laboratory at the Massachusetts Institute of Technology was an exciting place for any student interested in acoustics and noise control. As one of the directors of the lab, Professor Lyon had a profound influence on the activities, students, and researchers working and studying there. Among the other things that Dick is known for such as Statistical Energy Analysis, Machinery Noise Diagnosis, and Product Sound Quality, he was also overseeing research on urban sound propagation and applications of acoustical scale modeling. This presentation will discuss some of this research, the culture of the A&V Lab, and personnel interactions with Professor Lyon from one of his student's and researcher's point of view.

Using scale modelling to assess the prehistoric acoustics of Stonehenge

With social rituals usually involving sound, an archaeological understanding of a site requires the acoustics to be assessed. This paper demonstrates how this can be done with acoustic scale models. Scale modelling is an established method in architectural acoustics, but it has not previously been applied to prehistoric monuments. The Stonehenge model described here allows the acoustics in the Late Neolithic and early Bronze Age to be quantified and the effects on musical sounds and speech to be inferred. It was found that the stone reflections create an average mid-frequency reverberation time of (0.64 ± 0.03) seconds and an amplification of (4.3 ± 0.9) dB for speech. The model has a more accurate representation of the prehistoric geometry, giving a reverberation time that is significantly greater than that measured in the current ruin and a full-size concrete replica at Maryhill, USA. The amplification could have aided speech communication and the reverberation improved musical sounds. How Stonehenge was used is much debated, but these results show that sounds were improved within the circle compared to outside. Stonehenge had different configurations, especially in terms of the positions of the bluestones. However, this made inaudible changes to the acoustics, suggesting sound is unlikely to be the underlying motivation for the various arrangements.

A possible acoustic design approach for multi-purpose auditoria suitable for both speech and music

In several auditoria, it has been observed that the reverberation time is longer than expected and that the cause is a horizontal reverberant field established in the region near the ceiling, a field which is remote from the sound absorbing audience. This has been observed in the Boston Symphony Hall, Massachusetts, and the Stadthalle Göttingen, Germany. Subjective remarks on their acoustics suggest that there are no unfavourable comments linked to the secondary sound field. Two acoustic scale models are considered here. In a generic rectangular concert hall model, the walls and ceiling contained openings in which either plane or scattering panels could be placed. With plane panels, the model reverberation time (RT) was measured as 53% higher than the Sabine prediction (frequency 500/1000Hz), compared with 8% higher with scattering panels. The second model of a 300 seat lecture theatre with a 6m or 8m high ceiling had raked seating. In this case, the amount of absorption in the model was increased until the point was reached where speech had acceptable intelligibility, with the early energy fraction, D⩾0.5. For this acceptable speech condition with the 6m ceiling, the measured mid-frequency T15 was 1.47s, whereas the Sabine predicted RT was 1.06s. The sound decay was basically non-linear with T30>T15>EDT. Exploiting a high-level horizontal reverberant field offers the possibility of acoustics that are better adapted as suitable for both speech and unamplified music, without any physical change in the auditorium. Using secondary reverberation in an auditorium for a wide variety of music might also be beneficial.

Investigation on the effect of aperture sizes and receiver positions in coupled rooms

Some recent concert hall designs have incorporated coupled reverberation chambers to the main hall that have stimulated a range of research activities in architectural acoustics. The coupling apertures between two or more coupled-volume systems are of central importance for sound propagation and sound energy decays throughout the coupled-volume systems. In addition, positions of sound sources and receivers relative to the aperture also have a profound influence on the sound energy distributions and decays. This work investigates the effect of aperture size on the behavior of coupled-volume systems using both acoustic scale-models and diffusion equation models. In these physical and numerical models, the sound source and receiver positions relative to the aperture are also investigated. Through systematic comparisons between results achieved from both physical scale models and numerical models, this work reveals valid ranges and limitations of the diffusion equation model for room-acoustic modeling.

A diffusion equation model for investigations on acoustics in coupled-volume systems

Coupled-volume rooms remain as one of the most exciting and challenging research lines in room acoustics. Their benefits lie on their multiple-slope energy decay profiles, being of interest in many current concert halls. However, so far there is no consistent predictive model being able to help architects and acousticians in selecting appropriate design parameters. This work is devoted to studying effects of aperture-size and source/receiver positions on the energy decay characteristics. For this purpose, a diffusion equation model is used to model a coupled-volume system, providing an effective tool for analysis. The diffusion equation model is first validated by experimental investigations using scale models. Bayesian energy decay analysis is applied to the results of both the acoustical scale model and the diffusion-equation model to provide deeper insight in the energy decay characteristics and their dependence on the aperture sizes and the sound source/receiver positions.

New opera house in Astana: A recent opportunity to use a room acoustic scale model

The acoustic design of the New Opera House in Astana (Kazakhstan) currently under construction was carried out by Biobyte in Milan, Italy (Enrico Moretti and Maria Cairoli) assisted by Gade & Mortensen Akustik, Denmark (Anders Gade). In order to predict the acoustic consequences of the room geometry and decide on details in the design such as diffusion treatment of curved surfaces, it was decided to build a 1:20 scale model, in which several room acoustical parameters were measured. However, the scale model also provided an opportunity to compare the performance of scale model testing and room acoustic predictions by two computer simulation programs, which were also used for predictions in the design process. Therefore, besides information about the adequacy of the diffusion treatment to avoid focusing from concave surfaces (an aspect which is not well described by computer simulation) we obtained data on measurement accuracy—or rather deviations—between the results from the scale model (DIRAC) and the two different room acoustic prediction programs (CATT and ODEON). These results will be presented and discussed in the paper.

Room Acoustic Modelling Techniques: A Comparison of a Scale Model and a Computer Model for a New Opera Theatre

Today most acoustic consultants are using room acoustic computer models as a basis for their acoustic design. However, room acoustic scale modelling is still being used for the design in some major projects, although the costs and the time needed are significantly larger than those related to computer modelling. Both techniques were used by the author in a project for a new opera theatre; first the acoustical design was based on computer simulations using the Odeon software, and next a 1:20 scale model was built and tested. In the paper the results obtained with the two different modelling techniques are compared, and in general a satisfactory agreement has been found. The advantages and drawbacks related to each of the modelling techniques are discussed.

Bayesian characterization of multiple-slope sound energy decays in coupled-volume systems

Due to recent developments in concert hall design, there is an increasing interest in the analysis of sound energy decays consisting of multiple exponential decay rates. It has been considered challenging to estimate parameters associated with double-rate (slope) decay characteristics, and even more challenging when the coupled-volume systems contain more than two decay processes. To meet the need of characterizing energy decays of multiple decay processes, this work investigates coupled-volume systems using acoustic scale-models of three coupled rooms. Two Bayesian formulations are compared using the experimentally measured sound energy decay data. A fully parameterized Bayesian formulation has been found to be capable of characterization of multiple-slope decays beyond the single-slope and double-slope energy decays. Within the Bayesian framework using this fully parameterized formulation, an in-depth analysis of likelihood distributions over multiple-dimensional decay parameter space motivates the use of Bayesian information criterion, an efficient approach to solving Bayesian model selection problems that are suitable for estimating the number of exponential decays. The analysis methods are then applied to a geometric-acoustics simulation of a conceptual concert hall. Sound energy decays more complicated than single-slope and double-slope nature, such as triple-slope decays have been identified and characterized.

Acoustical design and scale model test for the opera house of Zhongshan city

The opera house of Zhongshan City in Guangdong province of China is the performing art center of the city. It was completed in Oct. 2005. It has 1400 seats including 833 stall seats and another 484 seats on two levels of balcony. The volume of the auditorium is 12000m3 and the V/N is 9.1m3 per seat. The main purpose of the building is for the performances of opera and ballet. Some music and conference events are also to be held there. Therefore, the occupied reverberation time at medium frequencies is set to be 1.6s and its background noise level has to meet NR-20. During the acoustical design, a 3D computer simulation model established with ODEON software and a 1:20 scale model was made to analyze the sound fields of the auditorium with and without a music shell on the stage. After the completion of the building, an acoustics test was taken. Several performances show that its acoustics reaches a quite high level and has won high praises.

NUMERICAL ANALYSIS AND AURALIZATION OF THE “ROARING DRAGON” PHENOMENON BY THE FDTD METHOD

The “Honji-Do” temple located in the “Nikko Toshogu” area, in Nikko City, Japan, is famous for its strange acoustic phenomenon called “Roaring Dragon”. A dragon is painted on the ceiling of this building and we can hear a strange fluttering echo when making a handclap under the head of the dragon. The temple was unfortunately destroyed by an accidental fire in 1961 and was rebuilt in 1969. In the reconstruction work, reproduction of the “Roaring Dragon” was one of the most important items and a 1/4 acoustic scale model experiment was performed to study the reason of the acoustic phenomenon and the way of its reconstruction. In this study, numerical analyses using the finite difference time domain (FDTD) method have been performed to examine the “Roaring Dragon” phenomenon by referring the results of the scale model experiment. Furthermore, the acoustic phenomenon has been simulated in an anechoic room by applying a 3-D sound field simulation technique.

Acoustic scale model experiments for room acoustical design of halls

Acoustic scale model experiments for room acoustical design of halls

Further investigations on acoustically coupled spaces using scale-model technique

Recently, architectural acousticians have been increasingly interested in halls that incorporate coupled-volume systems because of their potential for creating nonexponential sound energy decay. Effects of coupling-aperture configuration and source and receiver locations on energy decay are essential aspects of acoustically coupled spaces that have not yet been extensively investigated. In order to further understand these effects on sound fields in coupled rooms, a systematic experimental study is carried out. An acoustic scale model technique is used in collecting room impulse responses of a two-room coupled system for varying aperture configurations and surface-scattering conditions. Baseline behavior is established by varying aperture area for a fixed aperture shape and analyzing relevant energy-decay parameters at different locations. Effects of aperture shape and number are systematically investigated by varying these parameters while holding coupling area fixed. Similarly, effects of receiver location are systematically investigated by varying the distance of the receiver from the coupling aperture for a fixed aperture configuration. Schroeder decay-function decompositions by Bayesian analysis reveal sensitivities to receiver location and aperture configuration across different frequency bands.

Acoustic scale model experiments using a piezoelectric dodecahedral speaker system

Acoustic scale model experiments using a piezoelectric dodecahedral speaker system

Paul S. Veneklasen, contributions to electroacoustic system and design

Paul Veneklasen’s interest in acoustics was wide ranging. Research and development in electroacoustics occupied his endeavors in the early years. This paper will present a survey of his work. Topics to be presented include development of a series of condenser microphones and loud- speaker systems at the Altec Lansing Corporation, and development of instrumentation to measure the sound pressure level using the Western Electric 640 AA condenser microphone. Projects of a more unusual nature included the development of a Fabric Acoustimeter or ‘‘Fuzz Feeler’’ to measure by acoustic means the ‘‘handle’’ of a fabric, development of the tooth and forehead microphones for detecting and transmitting voice signals in very high-level noise enviroments and research and development of the electronic stethoscope. This instrument extended the frequency range of heart sound analysis. Paul’s interest and pioneering work in auditorium acoustics led to contributions to the development of instrumentation for use in acoustical scale modeling research.

ステージ形態のオーケストラ演奏に対する音響効果

This paper presents objective and subjective evaluations of eight types of side stage enclosures for orchestra performances. Three different methods are applied in this study; the ray tracing computer simulation, the acoustical scale model experiment, and the auditory experiment by pared comparison. Results are as follows: The acoustic characteristics of stage enclosure shapes can be determined by comparing remained and radiated energy within 80 msec. Preferred stage shapes vary interms of the playing, conducting, and listening positions.

POROUS MATERIALS FOR SCALE MODEL EXPERIMENTS IN OUTDOOR SOUND PROPAGATION

The accuracy of acoustic scale modelling strongly depends on the choice of porous absorbing materials with properties at the scale frequencies which resemble those of full size absorbers. In this paper the Attenborough impedance models are used to identify a combination of microscopic parameters, which ensures that the surface impedance is scaled correctly at the model frequencies. The theory and methodology for the selection are given. Measurements of microscopic and acoustic properties of several uniform common porous materials suggest that the theoretical assumptions are reliable.

Determination of The Scattering Parameters of Fittings in Industrial Buildings for Use in Computer Based Factory Noise Prediction Models: Part 2 – Scale Model Experiments

In a companion paper results obtained from computer simulation1 have demonstrated that the sound propagation characteristics of disproportionate rooms are determined by the product of the fitting parameters scattering cross-section (Q) and absorption coefficient (αobst) of fittings. It was also proposed that the absorption of a fitting as measured in a conventional reverberation chamber is equivalent to four times the product of those two parameters. This suggests that measurement of fitting absorption in a conventional reverberation chamber could provide the data required for input into current computer based factory noise prediction models. Since both parameters are required as inputs to computer models it would be necessary to separate them in some way from the data obtained in the reverberation chamber. In this paper two methods for determining the scattering parameters of fittings in industrial buildings based upon acoustical measurements are described. The accuracy of these is compared with that resulting from the application of a geometrical measurement method to determine the scattering cross-section (Q) of various shapes of model scatterers employed in experimental work employing 1:20 acoustic scale models. The values of Q obtained from each method were used to predict sound characteristics a model disproportionate chamber using RAYSCAT. The predicted results obtained from the computer model by inputting the values of Q determined using the acoustical measurement methods were found to be more accurate than those using the geometrical measurement method.