An omnidirectional sound source is often used as a repeatable source to measure impulse responses in concert halls to obtain room acoustics metrics. The limitation of using an omnidirectional source is that real sound sources, such as musical instruments, do not exhibit omnidirectional radiation patterns. For an orchestra, many instruments with unique directional radiation patterns are distributed across the stage. To achieve more realistic auralizations, a 20-element compact spherical loudspeaker array was constructed to simulate the frequency-dependent radiation properties of instruments. This loudspeaker array is capable of achieving a truncated third-order spherical harmonics representation of an instrument’s radiation pattern. Once the source is moved to different instrument locations around stage, frequency-dependent weighting factors for each driver are controlled to match the source’s radiation pattern to that instrument. Full three-dimensional impulse response measurements of the source were made to characterize the source’s directional performance. From these measurements, frequency-dependent gains were applied to determine the accuracy and frequency range of the directional reproduction, and the results for various instruments will be presented. The implementation of this source into an existing measurement setup for future measurements of U.S. and European concert halls will also be discussed. [Work supported by NSF Award 1302741.]
Listener envelopment (LEV), the sense of being surrounded by the sound field, is a perception that has been found to be related to the overall impression of a concert hall. The purpose of this study was to investigate the relationship between the perception of LEV and the direction and arrival time of energy from spatial room impulse responses (IRs). IRs were obtained in a 2000-seat concert hall using a 32-channel spherical microphone array and analyzed using a third-order plane wave decomposition. Additionally, the IRs were convolved with anechoic music and processed for third-order Ambisonic reproductions and presented to subjects over a 30-loudspeaker array. Instances were found in which the energy in the late sound field did not correlate with LEV ratings as well as energy in a 70–100 ms time window. Follow-up listening tests were conducted with hybrid IRs containing portions of an enveloping IR and an unenveloping IR with crossover times ranging from 40 to 140 ms. Additional hybrid IRs were studied wherein portions of the spatial IRs were collapsed into all frontal energy with crossover times ranging from 40 to 120 ms. The tests confirmed that much of the important LEV information exists in the early portion of these IRs.
+1 814-863-7145 5 Key words: spherical microphone array; room acoustics; spatial measures; measurement hardware; 6 room impulse response 7 8 NOTE: Portions of this work were presented at two conferences: 9 Dick, D.A., and Vigeant, M.C., "Measurement repeatability of late lateral energy level and lateral 10 energy fraction." J. Acoust. Soc. Am., 135:2236, 2014 [Abstract only] 11
Commercially available omnidirectional loudspeakers, which are used to measure room impulse responses, typically have a limited bandwidth and are only omnidirectional below approximately 1kHz. To extend the operating bandwidth, a three-way omnidirectional source was built consisting of a subwoofer, a mid-frequency dodecahedron, and a high-frequency dodecahedron. The subwoofer contains two 10 in. drivers in a sealed box. The mid-frequency dodecahedron uses 12 4 in. mid-bass drivers. The high frequency dodecahedron was made with 12 closely spaced 3/4 in. dome tweeters, providing omnidirectional behavior up to approximately 5 kHz. The directivities of the dodecahedrons were validated by taking measurements in an anechoic chamber. The performance of the sources in a realistic setting was assessed using measurements taken in Eisenhower Auditorium, located at Penn State. Measurements were made with the three sources placed individually on the stage in the same location and compared to measurements made with the sources stacked one on top of the other. The stacked configuration yielded significantly different results than the individual configuration. Additionally, measurements were made rotating the individual sources on the stage to evaluate the effect of angular orientation on measured parameters. Parameter differences were found to be small up to the 4 kHz octave band. [Work supported by NSF Grant 1302741.]
The design of multipurpose venues typically includes variable acoustic elements which adjust the acoustics of the space to support the intended use. The most common approach to vary the acoustics of a venue is to use variable absorption, often in the form of heavy drapery and/or acoustic felt banners. These elements are often characterized by changes in reverberation time, but their position also impacts the spatial distribution of room energy. In order to study the effects of variable acoustic elements on the three-dimensional sound field at specific audience locations, spatial impulse response measurements were taken in a number of venues using a 32-element spherical microphone array. The venues ranged from a small recital hall of 400 seats to a typical multipurpose hall with 1300 seats to a 2500-seat concert hall with variable acoustics. Beamforming techniques were used to analyze the effects of the variable acoustic elements on the spatial and temporal distribution of sound energy at several receiver locations in each venue. The sound fields in these venues will be compared to those measured in dedicated concert halls, which have been measured for recent work on the topic of listener envelopment. [Work supported by NSF Award 1302741.]
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