Reception plate method for characterisation of structure-borne sound sources in buildings: Installed power and sound pressure from laboratory data

In a companion paper, a laboratory method is described to obtain the structure-borne sound power of machines before they are installed in heavy-weight buildings. The laboratory method is based on the concept of the reception plate. In this paper, the method is shown to provide appropriate input data for the prediction of the installed structure-borne power, and thence the resultant sound pressure level in rooms removed from the room containing the machine. Case studies of two common sources are described: a whirlpool bath and a water cistern. It is shown that the method can be incorporated into recently proposed standard prediction models and that sound pressure levels in buildings can be predicted.     

Approximate method for obtaining source quantities for calculation of structure-borne sound transmission into lightweight buildings

An approximate approach is described, for obtaining the source quantities required for the calculation of structure-borne sound power from machines into supporting lightweight building elements. The approach is in two stages, which are based on existing international Standards for measurement. The first stage involves direct measurement of the source free velocity at each contact, to give the sum of the square velocities. The second stage is based on the reception plate method and yields the single equivalent blocked force, which approximates the sum of the square blocked forces. The applicability of the source data obtained has been investigated in a case study of a fan unit on a timber joist floor. The approach contains several significant simplifying assumptions and the uncertainties associated with them are considered. For the case considered, the power transmitted into the floor is estimated by the approximate method to within 5 dB of the true value, on average.     

Effect of acoustical damping with a porous absorptive layer in the cavity to reduce the structure-borne sound radiation from a double-leaf structure

Structure-borne sound radiation from a double-leaf structure with a porous absorptive layer in the cavity is studied theoretically as well as experimentally. The study is for establishing a countermeasure to reduce the structure-borne noise radiated from an interior leaf into rooms and for clarifying its reduction effect. The sound field radiated from a double-leaf elastic plate with layers of arbitrary media in the cavity set into vibration by a point force excitation is theoretically analyzed. The effect of the bulk vibration of an absorptive layer is also considered by a simple model into the present theory. Radiation reduction of an inner-layer derived from the theory is experimentally validated. Parametric studies reveal that increasing the ratio of an absorptive layer thickness to the cavity depth is effective to reduce the structure-borne sound radiation but high flow resistivity of the absorbent material is not necessarily required. A practical equation to predict the mass-air-mass resonance frequency for absorbent cavity case is given in a simple form.     

In situ radiation measurement and estimation of U/Th ratio to reflect on the uranium bearing potential zone in metamorphic rocks of Mahendragarh district, Haryana

Gross gamma radiation survey was carried out using Nal(Tl) scintillator based portable gamma ray spectrometer (PGRS) around areas of Gaonri, Dholera, Pachnota and Meghot in Mahendragarh district, Haryana. Geologically the area forms part of north Delhi fold belt comprising calc-silicate, quartz biotite schist, impure marble, quartzite and pegmatite rocks. Equivalent uranium (eU₃O₈) concentration in ppm was estimated in situ on a regular grid pattern of 500 m (E-W) × 1000 m (N-S) and grab samples were collected at grid locations for analyzing in the laboratory for estimating the contents of eU₃O_s Ra_eq, ThO₂ and %K. A comparison with the laboratory analysed grab samples for eU₃0₈ data and in situ radiation measurements shows a good match of the two sets of data. The in situ measurements indicate higher concentration of eU₃O₈ in Chapra Bibipur in northeastern most corners, Maghot area in central part, Gaonri in western part and Pachnota in southwestern part of the study area. As index to uranium favorability, U(Ra_eq)-Th contour map (prepared using Surfer software with Krieging interpolation method for this grid size) based on the data on grab samples was generated which show three major clusters of relatively high U-Th ratio. The blocks delineated are enriched in sodic mineral albite which support albite hosted uranium mineralization potential in metamorphic rocks in Haryana.