Research On Technology Of Measuring Airborne Sound Insulation In Buildings And Of Building Elements

There are some deficiencies in the conventional sound pressure method measuringsound insulation in buildings and of building elements, such as being unable to identify thesound propagation path, being greatly affected by the flanking transmission sound, lowsignal-to-noise ratio and low precision in low frequency. Another sound insulationmeasurement method is based on sound intensity technique and overcome the aboveshortcomings. It is expected to provide easier and more reliable means of measurement toevaluate green building sound environment. In this dissertation, the measuring principle of theairborne sound reduction index is discussed and the measuring methods of sound reductionindex in buildings and of building elements are studied in details. The main researches arelisted as follows:1. The requirements of the response characteristic of measurement of sound insulation onthe spectrum of sound source in motivated sound field are analyzed, and then a newpre-equalization technique employing digital signal processor is introduced. Moreover, byexperiments, it is proved that the method can help to obtain a relatively flat frequencyresponse and meet the requirements of measuring sound insulation.2. Through an analysis on sound insulation evaluation technique using impulse methodwith multichannel system, a new method is proposed to correct the sensitivity differenceamong the channels by exchanging the channels in the sound source room and receivingroom.and then is applied to experiments to be testified. The results of the experiments showthat the channel-exchange method for correction can lower the requirements for themicrophone and pre-amplifier and able to achieve a reliable result when there is inconsistentsensitivity among the channels.3. There is still certain deviation in the precision estimation and bias of sound pressuremethod and sound intensity method. And the precision estimation and bias are different fromdifferent laboratories. Therefore, in order to prove data and experiment verification for themeasuring sound insulation in buildings and of building elements using sound intensity, it isnecessary to launch the study on the precision estimation and bias of airborne soundinsulation using sound intensity method in domestic laboratories. The sound insulations offour specimens are measured by the methods mentioned above in a laboratory and the resultof the experiments is analyzed to find out the causes of precision estimation and bias. The experiments show that these two methods have the same results in the whole frequency rangebasically, but still have some deviations in the specific low frequency band. It is pointed outthat the low-frequency deviations are caused mainly by the uniformity sound field ofreceiving room. From the perspective of modal density calculation, the size differencesbetween the abbreviated term and complete term of Waterhouse Correction in ordinary roomsize is discussed to find out the comparatively big difference of them in the low frequencyrange. Therefore, when applying the Waterhouse Correction, the complete term isrecommended. This dissertation also pointed out that the Waterhouse Correction term shouldbe subtracted from the results of the sound pressure method, instead of adding it to the resultsof the sound intensity method, so as to be more in line with the physical meaning of the soundreduction index, when the sound pressure method with the sound intensity method beingcompared.4．Through the calculation of the sound reduction index of Gompert’s rectangular slits,The sound reduction index of the same wide slits located at a partition edge is maximumwhere source room has a diffuse field. The second maximum is the slits at the middle of apartition where source room has a diffuse field. The minimum is the slits at the partition edgefor a normal incidence wave on it. The sound reduction index has been measured using soundintensity. In comparison, the experimental results are consistent with the theoretical value ofthe total sound reduction index. It is proved that the sound intensity method is effective inmeasuring the sound insulation in situ.5. The sound intensity contour can be plotted after measuring the building elementswith slits using sound intensity method. The weaknesses of sound insulation could be detected.However, there are the possible differences among the weaknesses of sound insulationindicated by the contours of the sound intensity in different frequency bands, ancomprehensive analysis on the index charts of the sound intensity in different frequencybands should be taken into consideration, when using the sound intensity method to detect theweaknesses of sound insulation, so as to determinate the sound leakages more accurately andimprove the sound insulation in building and of building elements in more targeted way.