The active control method was used to suppress the sound diffracted by an outdoor barrier. This m... more The active control method was used to suppress the sound diffracted by an outdoor barrier. This method operated by the cancellation of the sound pressure at the diffraction edge of the barrier, which normally behaves like the virtual source of the diffracted field. The results of two experiments are shown in this paper. In the first experiment, we employed two independent controllers that utilized multi-channel adaptive signal processing to minimize the sum of the mean square of the sound pressure at four and six points along the diffraction edge. Measurement of sound pressure levels at various distances from the barrier showed effective sound suppression, with about 6-dB excess attenuation over the barrier's insertion loss at the receiver at a distance of 50 m. A practically realistic noise source, a fan blower, was used as a primary source in the second experiment and the moderate attenuation could be achieved at almost all the receiver points. The results obtained in these two experiments provided the experimental verification of the strategy for the active suppression of sound diffracted by a noise barrier.
Boundary surface control (BoSC) is a useful method of reproducing the sound field physically. How... more Boundary surface control (BoSC) is a useful method of reproducing the sound field physically. However, it is challenging in the case of real-time operation. This is mainly due to the calculation cost of a lot of inverse filter convolutions to obtain reproduction signals. This paper proposes a method for reducing of number of inverse filters and implements it in 24-channel narrow directivity (shotgun) microphone array and 24-channel circularly arranged loudspeaker array. Moreover, it provides an experimental evaluation of the reproduction accuracy according to measurement of reproduced wavefront. The accuracy of the reproduced wavefront by the filters, whose number was reduced to less than 1/5 by proposed method, was comparable with the case of full number of filters. Finally, a system aiming at sound field reproduction in a wide frequency range was constructed by a hybrid method of reproducing with an inverse filter in the low range and directly outputting from the speaker in the direction corresponding to the microphone in the high frequency range. We confirmed that real-time processing is possible for this hybrid method by using a convolution plug-in of digital audio workstation software.
Journal of the Acoustical Society of America, Sep 1, 1997
The active control method was used to suppress the sound diffracted by an outdoor barrier. This m... more The active control method was used to suppress the sound diffracted by an outdoor barrier. This method operated by the cancellation of the sound pressure at the diffraction edge of the barrier, which normally behaves like the virtual source of the diffracted field. The results of two experiments are shown in this paper. In the first experiment, we employed two independent controllers that utilized multi-channel adaptive signal processing to minimize the sum of the mean square of the sound pressure at four and six points along the diffraction edge. Measurement of sound pressure levels at various distances from the barrier showed effective sound suppression, with about 6-dB excess attenuation over the barrier's insertion loss at the receiver at a distance of 50 m. A practically realistic noise source, a fan blower, was used as a primary source in the second experiment and the moderate attenuation could be achieved at almost all the receiver points. The results obtained in these two experiments provided the experimental verification of the strategy for the active suppression of sound diffracted by a noise barrier.
Journal of the Acoustical Society of America, Oct 1, 2016
Sound field reproduction system can be categorized roughly into two types. The first is physicall... more Sound field reproduction system can be categorized roughly into two types. The first is physically assured system which reproduce the wavefront or another physical parameters by engineering means. Typical examples are the boundary surface control system, the wave field synthesis, the ambisonics, and so on. The second type is a psychological system that reproduces phantom images one sound at any desired position by artificial manipulation with rather simple technique such as volume based amplitude panning. Examples are the two channel stereo system and the surround system using 5.1 or more loudspeakers. The latter can be recognized as somewhat “artistic” method, because it requires norms based on artistic sense. The present study aims to fuse the engineering and artistic systems mentioned above. The boundary surface control system, which consists of 24-channel narrow directional microphones and 24 channel loudspeakers, was used as the platform of research. Based on the conventional control technique using inverse filtering, additional manipulation such as simple reproduction scheme for high frequency was introduced. Also, the concept of variable reflection acoustic wall system, which adds the artificial reverberation to the sounds that listener makes, was involved in the reproduction system for the direction of the presence.
Journal of the Acoustical Society of America, Oct 1, 1996
Because of the rapid progress of DSP hardware performance, the application of active noise contro... more Because of the rapid progress of DSP hardware performance, the application of active noise control to a moving noise source has become a much more realistic problem. This study describes the preliminary investigations concerning the behavior of a multichannel adaptive algorithm with a moving primary source. The steepest descent algorithms, such as multiple error filtered-x LMS, are often used in practical feedforward active control applications. A previous study showed that the stability and the performance of this algorithm strongly depend on the estimation errors of the transfer responses of the acoustic plant being controlled. The effect of the primary signal variations including the Doppler effect, however, had hardly been investigated. In this study, the convergence properties of the algorithms with the moving sound source were examined by numerical simulations. To simplify the problems and clarify the substantial limitations of the system, a pure tone and a simple free field was assumed as the primary signal and the sound field, respectively. Results showed that the system could converge, and the possible attenuation was varied corresponding to the positions of the primary source.
Journal of the Acoustical Society of America, Nov 1, 2006
For acoustic design of special spaces such as studios, it might be necessary to realize a diffuse... more For acoustic design of special spaces such as studios, it might be necessary to realize a diffuse reflection from the specific wall surface. Moreover, this requirement often changes according to the time or situation. In this study, a new acoustic wall system is examined; it is a variable reflection acoustic wall system that can address such strict requirements. This system fundamentally comprises a loudspeaker, a pick-up microphone, and absorbent material. Varying the amplitude of the radiation sound that is picked up by the microphone and reradiated by the loudspeaker mounted behind the absorbing material therefore corresponds to varying the reflection performance of the wall system. Several models are proposed. The measurement results show that the proposed models can realize various absorption characteristics. Additionally, these models can realize various radiation characteristics: diffuse reflection and inclined reflection to a desired direction. Furthermore, the frequency characteristic of simulated radiation is changed, so the proposed system can generate reflection coefficient with intended frequency characteristics. The design of an effective feedback canceller between the pick-up microphones is the subject of ongoing research toward practical use of this proposed system.
To examine the relationship between surface scattering and the properties of a sound field, a vis... more To examine the relationship between surface scattering and the properties of a sound field, a visualization technique based on the sound intensity measurement is introduced. Measurement of the impulse responses at four closely located points yields the intensity response in three orthogonal directions. Dominant peaks in the intensity response could be recognized as the dominant reflections from the certain room surface. Our method projects such information onto the spherical panoramic photo of the field. In addition to such qualitative visualization, quantitative examination is also tried. We have introduced here the index called uniformity of arrival directions, UAD, as one measure of sound field. The UAD is defined by the temporal changes of uniformity of arriving directions of reflections and is calculated by the intensity levels observed at equally divided solid angles on the surface of an imaginary sphere around the measurement point.
Mixing consoles, which are usually of large dimensions, are essential equipment in a mixing room ... more Mixing consoles, which are usually of large dimensions, are essential equipment in a mixing room of a production studio. This large obstacle always has to be placed nearby the listening position in a mixing room. A significant dip at around 100 Hz is often observed on the monitoring response, the transfer function from the loudspeaker to the listening position, in a small/medium sized mixing room. This paper studies the relationship between the dip at around 100 Hz and the effect of the presence of the mixing console. The generating mechanism of the dip is investigated by numerical simulations and experimental measurements. The results show that the reflection sound from the floor and the behavior of the mixing console as a cross over filter are important when considering the dip. Examples of trials for improvement of the dip are also examined.
Journal of Physiological Anthropology and Applied Human Science, 2004
Recent development of sound reproduction systems such as 5.1 surround produces artificial sound f... more Recent development of sound reproduction systems such as 5.1 surround produces artificial sound field inside the enclosure. The acoustic characteristic of the enclosure is an important factor which determines the quality of the sound field reproduction. This paper provides a useful method for evaluating the characteristics of the sound field in the enclosed space. The proposed method is based on the visualization of the measured sound intensity. In this research, the sound intensity is obtained by measuring the impulse responses from the sound source to the receiving points. The direction and the strength of the intensity can be interpreted as having a strong correlation with the reflected sound from the corresponding direction. The proposed method thus projects that information, i.e., the arriving direction and the strength of the intensity, as the circle having appropriate radius onto the surface of the rectangular wire-frame box. This visualization makes it easy to grasp the fundamental characteristics of the reflections in the enclosure.
Nippon Onkyo Gakkaishi/Acoustical science and technology/Nihon Onkyo Gakkaishi, Mar 1, 2024
Acoustic intensity estimation is an important research topic in the field of architectural acoust... more Acoustic intensity estimation is an important research topic in the field of architectural acoustics. Various point-based intensity estimation methods using microphone probes have been proposed so far. On the other hand, research has also been conducted on average acoustic intensity field estimation methods using microphone arrays. This study proposes a method for estimating instantaneous sound intensity fields that can be applied to arbitrary spatial dimensions and array configurations. The proposed method is based on representing the instantaneous sound field using the reproducing kernel of a space of spherically band-limited functions. One of the key advantages of the proposed is its ability to analytically handle the spatial differentiation involved in the calculation of particle velocities, allowing for more accurate intensity estimation compared to the p-p method. Numerical simulations were conducted to validate the effectiveness of the proposed method, using a three-dimensional plane wave sound field.
The active control method was used to suppress the sound diffracted by an outdoor barrier. This m... more The active control method was used to suppress the sound diffracted by an outdoor barrier. This method operated by the cancellation of the sound pressure at the diffraction edge of the barrier, which normally behaves like the virtual source of the diffracted field. The results of two experiments are shown in this paper. In the first experiment, we employed two independent controllers that utilized multi-channel adaptive signal processing to minimize the sum of the mean square of the sound pressure at four and six points along the diffraction edge. Measurement of sound pressure levels at various distances from the barrier showed effective sound suppression, with about 6-dB excess attenuation over the barrier's insertion loss at the receiver at a distance of 50 m. A practically realistic noise source, a fan blower, was used as a primary source in the second experiment and the moderate attenuation could be achieved at almost all the receiver points. The results obtained in these two experiments provided the experimental verification of the strategy for the active suppression of sound diffracted by a noise barrier.
Boundary surface control (BoSC) is a useful method of reproducing the sound field physically. How... more Boundary surface control (BoSC) is a useful method of reproducing the sound field physically. However, it is challenging in the case of real-time operation. This is mainly due to the calculation cost of a lot of inverse filter convolutions to obtain reproduction signals. This paper proposes a method for reducing of number of inverse filters and implements it in 24-channel narrow directivity (shotgun) microphone array and 24-channel circularly arranged loudspeaker array. Moreover, it provides an experimental evaluation of the reproduction accuracy according to measurement of reproduced wavefront. The accuracy of the reproduced wavefront by the filters, whose number was reduced to less than 1/5 by proposed method, was comparable with the case of full number of filters. Finally, a system aiming at sound field reproduction in a wide frequency range was constructed by a hybrid method of reproducing with an inverse filter in the low range and directly outputting from the speaker in the direction corresponding to the microphone in the high frequency range. We confirmed that real-time processing is possible for this hybrid method by using a convolution plug-in of digital audio workstation software.
Journal of the Acoustical Society of America, Sep 1, 1997
The active control method was used to suppress the sound diffracted by an outdoor barrier. This m... more The active control method was used to suppress the sound diffracted by an outdoor barrier. This method operated by the cancellation of the sound pressure at the diffraction edge of the barrier, which normally behaves like the virtual source of the diffracted field. The results of two experiments are shown in this paper. In the first experiment, we employed two independent controllers that utilized multi-channel adaptive signal processing to minimize the sum of the mean square of the sound pressure at four and six points along the diffraction edge. Measurement of sound pressure levels at various distances from the barrier showed effective sound suppression, with about 6-dB excess attenuation over the barrier's insertion loss at the receiver at a distance of 50 m. A practically realistic noise source, a fan blower, was used as a primary source in the second experiment and the moderate attenuation could be achieved at almost all the receiver points. The results obtained in these two experiments provided the experimental verification of the strategy for the active suppression of sound diffracted by a noise barrier.
Journal of the Acoustical Society of America, Oct 1, 2016
Sound field reproduction system can be categorized roughly into two types. The first is physicall... more Sound field reproduction system can be categorized roughly into two types. The first is physically assured system which reproduce the wavefront or another physical parameters by engineering means. Typical examples are the boundary surface control system, the wave field synthesis, the ambisonics, and so on. The second type is a psychological system that reproduces phantom images one sound at any desired position by artificial manipulation with rather simple technique such as volume based amplitude panning. Examples are the two channel stereo system and the surround system using 5.1 or more loudspeakers. The latter can be recognized as somewhat “artistic” method, because it requires norms based on artistic sense. The present study aims to fuse the engineering and artistic systems mentioned above. The boundary surface control system, which consists of 24-channel narrow directional microphones and 24 channel loudspeakers, was used as the platform of research. Based on the conventional control technique using inverse filtering, additional manipulation such as simple reproduction scheme for high frequency was introduced. Also, the concept of variable reflection acoustic wall system, which adds the artificial reverberation to the sounds that listener makes, was involved in the reproduction system for the direction of the presence.
Journal of the Acoustical Society of America, Oct 1, 1996
Because of the rapid progress of DSP hardware performance, the application of active noise contro... more Because of the rapid progress of DSP hardware performance, the application of active noise control to a moving noise source has become a much more realistic problem. This study describes the preliminary investigations concerning the behavior of a multichannel adaptive algorithm with a moving primary source. The steepest descent algorithms, such as multiple error filtered-x LMS, are often used in practical feedforward active control applications. A previous study showed that the stability and the performance of this algorithm strongly depend on the estimation errors of the transfer responses of the acoustic plant being controlled. The effect of the primary signal variations including the Doppler effect, however, had hardly been investigated. In this study, the convergence properties of the algorithms with the moving sound source were examined by numerical simulations. To simplify the problems and clarify the substantial limitations of the system, a pure tone and a simple free field was assumed as the primary signal and the sound field, respectively. Results showed that the system could converge, and the possible attenuation was varied corresponding to the positions of the primary source.
Journal of the Acoustical Society of America, Nov 1, 2006
For acoustic design of special spaces such as studios, it might be necessary to realize a diffuse... more For acoustic design of special spaces such as studios, it might be necessary to realize a diffuse reflection from the specific wall surface. Moreover, this requirement often changes according to the time or situation. In this study, a new acoustic wall system is examined; it is a variable reflection acoustic wall system that can address such strict requirements. This system fundamentally comprises a loudspeaker, a pick-up microphone, and absorbent material. Varying the amplitude of the radiation sound that is picked up by the microphone and reradiated by the loudspeaker mounted behind the absorbing material therefore corresponds to varying the reflection performance of the wall system. Several models are proposed. The measurement results show that the proposed models can realize various absorption characteristics. Additionally, these models can realize various radiation characteristics: diffuse reflection and inclined reflection to a desired direction. Furthermore, the frequency characteristic of simulated radiation is changed, so the proposed system can generate reflection coefficient with intended frequency characteristics. The design of an effective feedback canceller between the pick-up microphones is the subject of ongoing research toward practical use of this proposed system.
To examine the relationship between surface scattering and the properties of a sound field, a vis... more To examine the relationship between surface scattering and the properties of a sound field, a visualization technique based on the sound intensity measurement is introduced. Measurement of the impulse responses at four closely located points yields the intensity response in three orthogonal directions. Dominant peaks in the intensity response could be recognized as the dominant reflections from the certain room surface. Our method projects such information onto the spherical panoramic photo of the field. In addition to such qualitative visualization, quantitative examination is also tried. We have introduced here the index called uniformity of arrival directions, UAD, as one measure of sound field. The UAD is defined by the temporal changes of uniformity of arriving directions of reflections and is calculated by the intensity levels observed at equally divided solid angles on the surface of an imaginary sphere around the measurement point.
Mixing consoles, which are usually of large dimensions, are essential equipment in a mixing room ... more Mixing consoles, which are usually of large dimensions, are essential equipment in a mixing room of a production studio. This large obstacle always has to be placed nearby the listening position in a mixing room. A significant dip at around 100 Hz is often observed on the monitoring response, the transfer function from the loudspeaker to the listening position, in a small/medium sized mixing room. This paper studies the relationship between the dip at around 100 Hz and the effect of the presence of the mixing console. The generating mechanism of the dip is investigated by numerical simulations and experimental measurements. The results show that the reflection sound from the floor and the behavior of the mixing console as a cross over filter are important when considering the dip. Examples of trials for improvement of the dip are also examined.
Journal of Physiological Anthropology and Applied Human Science, 2004
Recent development of sound reproduction systems such as 5.1 surround produces artificial sound f... more Recent development of sound reproduction systems such as 5.1 surround produces artificial sound field inside the enclosure. The acoustic characteristic of the enclosure is an important factor which determines the quality of the sound field reproduction. This paper provides a useful method for evaluating the characteristics of the sound field in the enclosed space. The proposed method is based on the visualization of the measured sound intensity. In this research, the sound intensity is obtained by measuring the impulse responses from the sound source to the receiving points. The direction and the strength of the intensity can be interpreted as having a strong correlation with the reflected sound from the corresponding direction. The proposed method thus projects that information, i.e., the arriving direction and the strength of the intensity, as the circle having appropriate radius onto the surface of the rectangular wire-frame box. This visualization makes it easy to grasp the fundamental characteristics of the reflections in the enclosure.
Nippon Onkyo Gakkaishi/Acoustical science and technology/Nihon Onkyo Gakkaishi, Mar 1, 2024
Acoustic intensity estimation is an important research topic in the field of architectural acoust... more Acoustic intensity estimation is an important research topic in the field of architectural acoustics. Various point-based intensity estimation methods using microphone probes have been proposed so far. On the other hand, research has also been conducted on average acoustic intensity field estimation methods using microphone arrays. This study proposes a method for estimating instantaneous sound intensity fields that can be applied to arbitrary spatial dimensions and array configurations. The proposed method is based on representing the instantaneous sound field using the reproducing kernel of a space of spherically band-limited functions. One of the key advantages of the proposed is its ability to analytically handle the spatial differentiation involved in the calculation of particle velocities, allowing for more accurate intensity estimation compared to the p-p method. Numerical simulations were conducted to validate the effectiveness of the proposed method, using a three-dimensional plane wave sound field.
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Papers by Akira Omoto