An in-situ measurement technique of a material surface normal impedance is proposed. It includes a concept of "ensemble averaged" surface normal impedance that extends the usage of obtained values to various applications such as architectural acoustics and computational simulations, especially those based on the wave theory. The measurement technique itself is a refinement of a method using a two-microphone technique and environmental anonymous noise, or diffused ambient noise, as proposed by Takahashi et al. [Appl. Acoust. 66, 845-865 (2005)]. Measured impedance can be regarded as time-space averaged normal impedance at the material surface. As a preliminary study using numerical simulations based on the boundary element method, normal incidence and random incidence measurements are compared numerically: results clarify that ensemble averaging is an effective mode of measuring sound absorption characteristics of materials with practical sizes in the lower frequency range of 100-1000 Hz, as confirmed by practical measurements.

Water is considered an everlasting free source that can be acquired naturally. Demand for processed supply water is growing higher due to an increasing population. Sustainable use of water could maintain a balance between its demand and supply. Rainwater harvesting (RWH) is the most traditional and sustainable method, which could be easily used for potable and nonpotable purposes both in residential and commercial buildings. This could reduce the pressure on processed supply water which enhances the green living. This paper ensures the sustainability of this system through assessing several water-quality parameters of collected rainwater with respect to allowable limits. A number of parameters were included in the analysis: pH, fecal coliform, total coliform, total dissolved solids, turbidity, NH3–N, lead, BOD5, and so forth. The study reveals that the overall quality of water is quite satisfactory as per Bangladesh standards. RWH system offers sufficient amount of water and energy savings through lower consumption. Moreover, considering the cost for installation and maintenance expenses, the system is effective and economical.

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In an earlier paper [T. Otsuru et al., J. Acoust. Soc. Am., 125, 3784-3791 (2009)], the theoretical development and concept of ''ensemble averaged'' surface normal impedance were summarized by some of the authors using the math-physical model based on the boundary element method (BEM). This paper elaborates further on past discussions of the measuring method of the surface impedance of materials. First, three materials, namely, 50-mm-thick glass wool, 25-mm-thick glass wool, and 10-mm-thick needle felt, were measured in a reverberation room to compare the absorption characteristics measured using sensors of different types. Measured data show good agreement between the sensor types in the absorption coefficients, while some discrepancies are seen in the impedances. Next, the feasibility of our method in terms of sound absorption characteristics was confirmed using a series of measurements in comparison with the impedance tube method. Finally, the effects of sample size and receiver-to-sample distance are presented both in simulation and measurement for investigating the level of utility in various applications. The resulting absorption characteristics are examined to elucidate an appropriate measurement setting and demonstrate the general utility of the method.

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IntroductionWhile numerous methods have been proposed to measure material absorption characteristics [1][2][3], to date, the available impedance databases have generally been inadequate. In order to measure the surface normal impedance of a material, which may be used for absorption modeling in a numerical analysis of room acoustics on the basis of the wave equation, the authors previously proposed a method in which two microphones (a pp-sensor) and ambient noise [4] are used. Considering that the strong point of numerical analysis based on the wave equation is generally high accuracy in the lower frequency range, the target frequency range of the method was tentatively set to between 100 Hz and 1,500 Hz.Several measurements were conducted in various environments (an office, a corridor, a cafeteria and a terrace) to measure the normal surface impedances of glass wool and rock wool. The results showed good repeatability and wide applicability. Moreover, preliminary investigations [5] using the boundary element method (BEM) proved that the measurement is based on the concept of ensemble averaging, and that such averaging makes the measurement efficient and appropriate for sound absorption measurements. However, there are only a limited number of experiments in which the results obtained by this method were compared with those obtained by conventional methods.In the first section of this paper, we briefly review the new measurement approach in which a particle velocity sensor attached to a microphone (the pu-sensor) [5] is used. Although the original measurement method was designed for in-situ applications, the revised method described here is applied for use in a reverberation room to simplify measurement conditions and to make the system relevant for new applications. In the next section, a series of measurements made using both the original and revised methods are presented to clarify the agreement between the results obtained using the two sets of apparatus. Finally, the plausibility of the proposed method for the measurement of sound absorption characteristics as evidenced by comparing the output with the results obtained by two other conventional methods, namely the reverberation room method and the tube method, is discussed.

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This paper presents the results of a study in which the performance of palm oil clinker (POC) sandas an alternative acoustic material for controlling noise problems was investigated. The specimens were prepared using the basic mortar mixture of cement-to-river sand ratio of 1:4. The five mixtures used in the study containedPOC sand at the amounts of 0%, 25%, 50%, 75% and 100% of the total weight of the sand. Hardened mortar properties of density and compressive strength as well asacousticperformance were measured. The results show that the specimens containing POC sand gave an average noise reduction coefficient of 0.30, which is larger than the corresponding value of 0.25 for the specimens withriver sand only. The combination of 50% POC and 50%river sand achieved the highest sound absorption coefficient of 0.5 at 315 Hz and 0.4 at 1000Hz. It was also found that although POC sand reduced the compressive strength of specimens, the values obtained was still within the strength limit of non-load bearing structures. The findings suggest that POC sand has the potential to be used in the construction of non-structural wall in reducing the noise pollution.