v7.0, 20040922, me
Saturday, October 30, 1:30 pm 5:30 pm
Session M: ROOM AND ARCHITECTURAL ACOUSTICS; SOUND REINFORCEMENT
Chair: Mendel Kleiner
M-1 Acoustic Redesign of the Danish National GalleryJan Voetmann, DELTA Acoustics & Vibration, Hørsholm, Denmark
After the inauguration of the expansion of the Danish National Gallery in 1998 a serious acoustic mishap was experienced in the new large exhibition rooms. These interconnected rooms of approx. 33,000 cubic meters (approximately 1.2 million cubic feet) were supposed to also offer a multipurpose acoustical environment for a variety of cultural events. A record-breaking reverberation time of approximately 11 seconds was measured. The acoustic redesign process included not only the necessity of finding acoustical effective solutions; these solutions also had to be invisible or near-invisible due to the architectural requirements. This paper describes how the requirements were met, resulting in a highly acceptable reverberation time of a little more than 2 seconds.
Convention Paper 6270
M-2 Systematic and Common Errors in Sound System STI and Intelligibility MeasurementsPeter Mapp, Peter Mapp Associates, Colchester, UK
STI and its derivatives (RaSTI and STIPa) have become the internationally accepted methods for acoustically measuring the potential intelligibility performance of a sound system. However, in practice, many of the measurements carried out in the field to either verify or ascertain sound system and Voice Alarm intelligibility performance are often based on flawed techniques. This paper examines a number of common problems found to affect measurement accuracy. The paper also highlights conditions under which STI and STIPa inherently appear to incorrectly predict intelligibility performance. In particular it is shown that the currently available commercial software programs and instrumentation fail to correctly predict the performance of sound systems exhibiting irregular or band limited frequency responses when they are operating in reverberant environments under quiet (i.e., high signal to noise ratio) conditions. Significant discrepancies between the various measurement platforms are also found to occur.
Convention Paper 6271
M-3 Phase Equalization for Multichannel Loudspeaker-Room ResponsesSunil Bharitkar, Audyssey Laboratories, Inc., Los Angeles, CA, USA
Given a multichannel loudspeaker system, in a typical single or multiple listener setup, the combined response of the loudspeakers will exhibit significant fluctuation around the crossover region due to noncoincident positions of any two loudspeakers. This fluctuation manifests as an undesired broad spectral notch or a peak around the crossover region. The spectral notch, for example, introduced around the crossover due to complex addition of the two loudspeaker responses, generally, cannot be compensated with only magnitude response equalization. In this paper we present a recipe for compensating the spectral notch around the crossover region by designing a digital equalization filter using a stable all-pass network.
Convention Paper 6272
M-4 Assessment of Music Audio Quality in a Sports StadiumScott Willsallen, Densil Cabrera, University of Sydney, Sydney, Australia
This paper investigates subjective and objective parameters of a sound reinforcement system in a large sports stadium. The sound at fourteen groups of three receiving positions was studied in a subjective listening test, as well as through objective system measurements. For an orchestral music sample, seventeen system tunings were subjectively assessed with fifteen scales. Objective measurements were made at each receiving position. Results showed significant variation for many of the subjective scales between tunings, as well as between receiving positions. To some extent, subjective and objective measurements were related as they describe system tuning and receiving position. Beyond its specific results, this paper highlights a range of difficulties in empirically assessing audio quality for music in a very large venue.
Convention Paper 6273
M-5 Line Array Performance at Mid and High FrequenciesHenrik Staffeldt, HS Consulting, Copenhagen, Denmark; Ambrose Thompson, Martin Audio Ltd., London, UK
This paper focuses on the direct sound frequency response of line arraysrectilinear or curvedat mid and high frequencies (1 kHz to 10 kHz), which is arguably the most important range and one that is relatively easy to measure. In this frequency range a line array may produce irregular on- and off-axis frequency responses in the audience area, which is difficult to predict using simpler models. The irregularities, which appear as frequency varying attenuation, depend in a complicated way on array configuration and air absorption. Array performance prediction software usually models a line array as a number of directive point sources placed on a line or curve. The directive point source model has been used to simulate line arrays to study the frequency response behavior of line arrays at mid and high frequencies. The results of the study are compared with frequency response predictions calculated by new software including multichannel array controller simulations and measured complex spherical polar data for a specific 3-way line array cabinet. The predictions are compared to direct sound frequency response measurements on line arrays using the same 3-way cabinet to show the degree of accuracy with which directive point source models can predict the frequency responses of line arrays.
Convention Paper 6274
M-6 Head-Tracked Auralization of Acoustical Simulation Christoph Moldrzyk, Technical University of Berlin, Berlin, Germany; Wolfgang Ahnert, ADA Acoustic Design Ahnert, Berlin, Germany; Stefan Feistel, ADA Acoustic Design Ahnert, Berlin, Germany; Tobias Lentz, Aachen University, Aachen, Germany; Stefan Weinzierl, Technical University of Berlin, Berlin, Germany
A desirable feature of modern acoustical simulation programs is the easy, fast, and reliable auralization of prediction results. To be considered as a serious tool, the auralization results should be equivalent to human perception in reality. In this paper we consider a new auralization technique based on a head-tracked headphone system with high spatial resolution and real-time convolution. We discuss the measurement of directional head-related transfer functions, the calculation of directional binaural impulse responses, and the realization as a real-time convolution software. A listening test was performed, comparing reality, measurement, and prediction results for a sample room.
Convention Paper 6275
M-7 Directional Measurement of Airborne Sound Transmission Paths Using a Spherical Microphone ArrayBradford Gover, National Research Council, Ottawa, Ontario, Canada
A spherical microphone array has been used to perform directional measurements of airborne sound transmission between rooms. With a source and array on opposite sides of a wall, omnidirectional impulse responses were measured to each of the array microphones. Beamforming resulted in a set of directional impulse responses, which were analyzed to find the distribution of arriving sound energy at the array position during various time ranges. Weak spots in the separating wall are indicated as directions of increased arriving sound energy. The system was able to identify minor defects in a test wall in between two reverberation chambers and also to identify leaks in the wall of an actual meeting room.
Convention Paper 6276
M-8 Electronic Bass TrapReza Kashani, University of Dayton, Dayton, OH, USA; James Wischmeyer, Bag End Loudspeakers, Barrington, IL, USA
Bass traps, regardless of their effectiveness in abating bass acoustic coloration in a room have two, somewhat undesirable attributes: (1) large size and (2) lack of adaptability. An alternative to the use of bass traps, discussed in this paper, is incorporating a properly devised, feedback control scheme into a powered subwoofer making the subwoofer to exhibit the same dynamics as that of a bass trap. This patent pending, active coloration control solution, which can be viewed as an electronic bass trap adds acoustic damping to the low-frequency modes of a room. In addition to a powered subwoofer, the electronic bass trap uses a microphone and an op-amp circuit. Numerical and experimental results indicate the effectiveness of the electronic bass trap in adding acoustic damping to the low-frequency standing wave(s) in a room.
Convention Paper 6277