Numerical simulation of impulse responses is an important task for room acoustic design and prediction. Since an impulse response is a concept in the time domain, time-domain simulation methods are popular for this task. At the same time, frequency-domain simulation methods are also used for simulating a room impulse response by computing frequency responses and applying the inverse discrete Fourier transform (IDFT). In this case, well-established frequency-domain solvers, including finite element method (FEM) and boundary element method (BEM), can be used. However, IDFT generates some artifacts that are undesirable for room acoustic evaluation. If such artifacts can be attenuated, then the frequency-domain methods become more attractive for simulating room impulse responses. In this paper, we propose a post-processing method to attenuate the artifacts from the impulse responses computed by the combination of frequency-domain simulation and IDFT. It is formulated as a convex optimization problem, and the alternating direction method of multipliers (ADMM) is applied to obtain the solution. Numerical experiments confirmed that the proposed method can effectively reduce the undesirable artifacts from the reconstructed impulse responses. An example implementation of the proposed method in MATLAB is provided at https://doi.org/g9h5.

On Hashima Island (commonly known as Gunkanjima) in Nagasaki, Japan, where Hashima Coal Mine was formally approved as a part of the World Heritage Site, there are many reinforced concrete (RC) structures constructed several decades to a century ago. Continuous evaluation of their deterioration properties generates data regarding historic buildings and helps understand the progress of deterioration in RC buildings. A visual inspection (VI) is generally used for deterioration surveys however, determining the internal deterioration using this method alone is difficult. In this study, the hammering method is used, which analyzes the acoustic characteristics of impact echoes to determine the deterioration condition. The impact sound on the concrete surface is analyzed and compared with the VI results to improve the deterioration investigation accuracy. A steel ball impacts the columns of RC buildings, and the radiated sound from the concrete surface is recorded using a microphone. Next, the sound pressure level at the maximum amplitude of the impact sound is obtained. The above levels are compared with the VI results in general, the worse the visual results, the louder are the levels. On the other hand, although visual results are suitable, some data have higher sound pressure levels. According to a 1/3 octave band analysis, the data having similar sound pressure levels show similar frequency characteristics regardless of the visual results, indicating that such data have similar deterioration properties. These results show that the hammering method can provide information regarding the deterioration of the RC buildings on Hashima that cannot be obtained via the VI alone.

The use of open-plan offices is increasing as they are effective in improving intellectual productivity by fostering communication among workers. Previous research on the relationship between the indoor sound environment and intellectual productivity has mostly reported the impact of the sound environment on the tasks that individuals work on. However, there has been little research on the impact of sound environments on office spaces where multiple workers are actually working. In this research, we developed a system that can analyze the individual characteristics of workers concerning the sound environment by simultaneously measuring their impression evaluation against the sound environment and the sound environment in the office. The system collects workers' impression evaluation against the sound environment through a regular questionnaire using the experience sampling method. At the same time, it measures the sound environment in the office with multiple small measurement devices. The obtained sound environment evaluation data and the acoustic data in the office were uploaded onto the Web server as a single database.

The sounds from childcare facilities are often a cause of noise problems with neighbors. However since the sound power levels of children's play and other sounds in child-care facilities have not become clear, evaluation methods have not been established, making countermeasures difficult. In order to evaluate the noise, it is necessary to model the location of the sound source and the sound power level. We have been developing a sound source identification system that uses multiple Raspberry Pi-based recording devices to estimate the location of a sound source and sound power levels. By using GPS for time synchronization, the system can be distributed and placed without connecting cables, which is expected to expand the measurement area significantly. As a method of estimation, the arrival time difference is calculated by cross-correlation from the signals input to each recording device, and the sound source location is estimated from the calculated arrival time difference and the location information of the device. The effectiveness of this system was verified in an anechoic chamber and outdoor fields.

When measuring the acoustic properties of architectural materials in a free field or in situ, reflections from the surroundings of the target material and diffraction from the sample edges often generate significant measurement errors. In this paper, a method for measuring acoustic properties by using a parametric loudspeaker, which is superdirective due to the nonlinearity of superhigh-pressure ultrasound, is proposed to overcome this problem: its strong directivity can reduce undesired waves by focusing the sound onto a narrow spatial range. However, such a superstrong ultrasound generates pseudo sound on the microphone surface and increases the measurement errors. Hence, two different strategies, acoustic filtering via phononic crystals and phase-cancellation excitation of the ultrasound, are experimentally investigated to reduce such induced errors. They are also used to evaluate the surface impedance of glass-wool boards at oblique incidence is measured in a free field and in situ. The results show that the proposed method can efficiently measure the surface impedance at frequencies higher than 800 Hz. (C) 2019 Elsevier Ltd. All rights reserved.

Acoustic measurements of an architectural material in a free field or in-situ are influenced by diffraction from sample edges and reflections from other room boundaries. These undesired waves may cause a measurement error. Especially, a measurement at oblique incidence is quite difficult as the incident angle is larger or the sample size is smaller. In this study, a parametric loudspeaker, which is super-directive by utilizing the nonlinearity of ultrasound, is used to overcome the difficulty. The parametric loudspeaker can reduce the undesired waves by focusing the incident sound onto a small spatial range and will be used as a simple and accurate measurement method. However, the super strong ultrasound used as the source signal causes the nonlinear distortion called "pseudo sound" on the microphone surface and increases the measurement errors. In order to minimize such induced errors, two methods are investigated experimentally: acoustic filtering via phononic crystals and the phase-cancellation excitation of the ultrasound. In our previous work, acoustic impedance of a glass-wool board at oblique incidence is measured using these two methods in an anechoic chamber. The results show that the proposed method is effective at frequencies above 800 Hz in a free field. Based on this, in the presented study, in-situ measurements are conducted in a conference room. This investigation shows that the proposed method can efficiently estimate the acoustic impedance at oblique incidence in-situ at frequencies above 800 Hz

Most railway stations of Japan finished with materials of good durability and fire resistance, causing insufficient sound absorption. This implies that background noise is loud and announcements are unclear. We conducted a field survey and a subjective experiment focusing on listening difficulty From the result, the background noise ranged 65"/0 dB and the announcements were higher than background noise. However the difference did not exceed 10 dB at most measurement points. When the level difference of the announcement and the background noise was +10 dB, about 29 % of subjects reported the female announcement difficult to hear and 50% reported the male announcement difficult to hear.

When measuring surface acoustic impedance and/or absorption coefficient of architectural materials in-situ, interference between the reflection from the target area and the undesired waves, such as reflection from other boundaries and diffraction from sample edge, often causes serious measurement error. The authors have investigated a measurement method of these properties using a parametric loudspeaker, which produces a sharp audible sound beam by the nonlinear-interaction of ultrasound, to minimize such harmful effects. Its strong directivity may reduce the undesired waves by making the sound incident onto the small spatial range. However, the super high sound pressure ultrasound causes “pseudo sound” on the microphone surface, and increases error in the results, especially in lower frequency range. In this study, two methods, phase-cancellation method and application of acoustic filter with phononic crystals, were verified experimentally to eliminate the pseudo sound. As a fundamental investigation, the reduction effect of the two methods against the pseudo sound was verified in a free field measurement. Regarding acoustical property measurement, surface impedance and absorption coefficient of glass-wool boards were measured applying the two methods in an ordinary room. The results showed good agreement with those measured by the impedance tube method for frequencies higher than 1 kHz.

The air-cooled packaged air-conditioner, widely used in small and medium buildings, needs the large number of outdoor units to apply various room conditions. Its operating efficiency can be changed by the high distribution density of the units and some other installations. This study aims to propose an optimum configuration of building installation at the rooftop by providing a better wind environmental condition for the energy saving. Thus, it is necessary to predict the airflow field around the rooftop. First, the airflow field around the rooftop was investigated by the Particle Image Velocimetry using scale models. The positional relation between the devices showed a sensible effect on the airflow characteristics. Moreover, the experimental data was compared with that of the Computational Fluid Dynamics (CFD) analysis to evaluate the accuracy of the calculation. They are similar to be said that CFD can represent the real situation approximately.

The acoustic properties of architectural materials, such as the absorption coefficient and the acoustic impedance, are the important elements when considering the acoustic performances of rooms. Measured results of these parameters in a free field and in-situ situation are often affected by undesired waves due to the diffraction from sample edge and reflection from other boundaries. A parametric loudspeaker, which produces a sharp audible sound beam by the nonlinear interaction of ultrasound beams, was used to minimize such influences in this study. At first, the radiation directivity of a parametric loudspeaker was measured and its strong directivity was confirmed. To verify this method for in-situ measurement, the proposed method was applied to a measurement in a conference room. The parametric loudspeaker could reduce the effect of the diffraction from the sample edge and reflection from other boundaries, although the measurement accuracy was decreased in the low frequency range less than 1.5 kHz. The measurements using a parametric loudspeaker might be affected by a pseudo sound, which is a spurious signal generated by the nonlinearity of the ultrasound. Then, two methods were investigated to reduce this effect and to propose a suitable measurement method using the parametric loudspeaker. The measurement accuracy of the absorption coefficient at normal incidence was improved with the method in an anechoic chamber.

本研究では，所望の吸音特性をもつ音響メタマテリアルを3Dプリンターを用いて作成し，健康・衛生面の問題，耐久性，耐水性，強度といった従来一般的に用いられた多孔質吸音材の課題を解決した，次世代吸音材として提案することを目的とする．研究は(1)理論・数値解析による音響メタマテリアルの設計，(2)3Dプリンタを用いた音響メタマテリアルの作成と性能検証，(3)特性のデータベース化と最適設計手法の確立，という3つの目標に従い進める．令和2年度は，物質の結晶構造を模した"硬くて衛生的で耐水性に優れた"多孔質吸音材の開発を目的として研究を進めた．(1)数値解析によるパラメトリックスタディを行い，(2)の途中段階までが進捗である．ある周期構造に対し，ミクロなユニットセル内での音の浸透性や流れの特性からマクロな音響特性である等価密度や等価体積弾性率を導き，そこから吸音率を算出するというZielinskiら(J Sound and Vibration, 2020)の数値解析手法を有限要素法解析ソフトに実装し，ダイヤモンド構造や単純立方格子といった基本的な結晶構造を対象に数値解析を行った．ユニットセルのサイズや空隙率等が吸音特性に及ぼす影響を加味し，実用的な範囲のサイズで優れた吸音特性をもつ構造を検討した．また，静適応力解析により，従来の多孔質吸音材に比べ本構造の強度が向上していることを確認した．加えて，これらの検討結果を基に，3Dプリンタを用いて実際に周期構造を作成した．セラミック入り樹脂材料を用いて作成した本構造は，"硬くて衛生的で耐水性に優れ"ており，従来の多孔質吸音材がもつ課題をクリアした構造となりうる．現在，作成した構造の吸音効果を実験的に検討する(実施目標(2))ための機材として，音響管を制作している．

本研究は、建築材料の音響特性を高精度に計測し、3次元の音響シミュレーションシステムを開発するという最終目標に向けて、鋭い放射指向性をもつパラメトリックスピー カを音源として用いた吸音特性の測定法の開発を行うものである。その狭指向性により音波を材料に局所的に入射することで、不要な反射や回折の影響を低減し、従来の測定法で困難であった条件でも計測が可能となる、汎用的な測定法となることが期待される。 パラメトリックスピーカを用いて可聴音を計測するためには、音源信号として用いる高音圧な超音波が受音系統で引き起こす、擬音とよばれる局所歪、およびそれに起因する計測誤差を低減する必要がある。そこで、受音点付近での超音波の音圧を低減することを考えた。まず、音源信号として位相反転信号を用いる信号処理的な制御、及びフォノニック結晶と呼ばれる物理フィルタを用いた構造的な制御により、この課題を解決した。 次に、吸音材料として一般的に用いられる多孔質吸音材を対象に、垂直入射吸音特性の計測を行ったところ、2つの手法を用いることで、擬音の影響による計測誤差が低減できた。 また、位相反転駆動方式では、超音波の低減領域が非常に狭く、特に入射角が大きい場合で受音点をその領域内に設置することが困難であった。しかし、その駆動方式に更なる改良を加えた結果、どの角度においても精度よく測定を行うことができた。 以上の検討より、音源信号の位相反転駆動、またはフォノニック結晶をパラメトリックスピーカの狭指向性に組み合わせることで、不要な反射や回折、擬音の影響を低減し、従来困難であった入射角が大きい場合や試料サイズが比較的小さい場合にも、計測が可能となることを確認した。