Slit-shaped gaps included in building elements such as doors or windows are apt to deteriorate the sound insulation performance of the wall system. In order to reduce sound energy transmitted through these parts, one of the practical measures is to place sound absorption materials inside the gaps. In this study, the effect of such an absorption treatment was examined through numerical and experimental studies. In the numerical study, the effect of sound absorption treatment inside the gaps existing around doors/windows was examined by applying the finite-difference time-domain (FDTD) method. To examine the results of the numerical study, a full-scale model experiment was performed with the sound intensity measurement method. In addition, a case study was performed to confirm the effect of absorption treatment of the peripheral gap of a door set in a real office space, and the effect was also confirmed by numerical study and measurement. As a result, it was found that sound insulation degradation caused by sound transmission through the gaps can be improved by sound absorption treatment inside the gaps.
A method for sharp directive beamforming using a reflector is proposed. The method involves physically varying the transfer functions and the spatial correlation matrix by placing a planar reflector near a linear microphone array. We confirmed through experiments that the proposed method was effective for increasing the spatial nulls and minimizing the power of interference in the beamforming output and consequently achieving sharp directivity.
In this study, we investigated how the temporal envelopes contribute to the recognition of isolated syllables, words, and sentences in noise-vocoded speech, under comparison with the influence of spectral resolution. The spectral and temporal resolutions of speech materials were systematically manipulated by a noise-vocoding technique. Japanese monomoraic syllables, meaningful and meaningless words, and sentences were used as test speech materials. The original speech sound was spectrally separated by a filter bank, and each spectral band was replaced with band noise, preserving its original temporal envelope. Spectral resolution was controlled by varying the number of spectral bands as 4, 8, or 16 bands. Temporal resolution was altered by smoothing the amplitude envelope using a low-pass filter with cut-off frequencies at 4, 8, or 16 Hz. Results demonstrated an increased dependence on temporal resolution in comparison with spectral resolution for the recognition of speech materials at higher structural levels (i.e., monosyllables, words, and sentences). This increased temporal dependence suggests that the temporal envelope in noise-vocoded sentences contained a greater amount of suprasegmental information, such as coarticulations, prosodies, and rhythms, in the original speech sound.
A new tensorial model is herein established for a special multidimensional array of vector sensors composed of a pressure part and orthogonal velocity parts, under which a multi-linear algebra based source number estimation algorithm is proposed. The estimation projects the covariance tensor into the signal subspace. Owing to the orthogonality between the newly defined tensor signal subspace and tensor noise subspace, it is easy to differentiate the contribution of the signal and noise by using the decision value in a compact tensorial fashion, which is the magnitude of projections from twofold mode signal subspaces. To reduce computer burden, meanwhile, the real-valued preprocessing method is applied to the covariance tensor for simplicity. Simulation and experiment results exhibit the superiority of the proposed algorithm over the conventional ones based on the matrix method.
Diffraction-reducing efficiency of a T-profile noise barrier is discussed using boundary element analyses considering a point source against an infinitely long barrier. The efficiency against a fixed point source includes both an increased thickness effect due to the T-profile cap and an interference effect due to phase difference between propagation paths around cranked edges of the cap. The latter interference effect depends on the relationship between wavelength and geometries; the effect disappears for incoherent point sources moving parallel to the barrier. For incoherent line sources such as road traffic noise, the efficiency of the T-profile barrier is almost equivalent to that of a thick barrier, and difference between them is almost less than 1 dB when the T-cap depth is equal to or less than 1 m. As a result, reduction in road traffic noise by a T-profile barrier is approximately calculated using a kind of engineering prediction models based on geometrical acoustics.
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