Modal Analysis ²³¹ is implemented to produce amplitude spectrums of the soundboard modes of vibration. Associate professor of physics at the University of Sydney, Rod Cross attached four piezoelectric disks, 20 mm diameter and 0.3 mm thick, to each soundboard. The disks were connected, via a 10 MegOhm voltage probe, to an ADC-212 analogue to digital convertor. The signal was monitored by PicoScope software that effectively turned the PC into a digital storage oscilloscope. The data was also analysed by Kaleida graph software in order to plot graphs and to perform an FFT (Fast Fourier Transform) to obtain the frequency spectrum.

Modal Analysis may be described as the process of describing the dynamic properties of an elastic structure in terms of its normal modes of vibration. In experimental modal testing, one excites the structure at one or more points, and determines the response at one or more points. From these sets of data, the natural frequencies (eigen frequencies) , mode shapes (eigen functions)and damping parameters are determined often by the use of multidimensional curve-fitting routines on a digital computer. ²³²

The piezo electric disks were positioned in four areas of the soundboard. Four soundboard positions were monitored for each sound. Two positions remained fixed, P1 & P2, and two positions were varied for each note, A & B. The probe positions were specific to each of the soundboards.

See Appendix 3, Part II of thesis, for complete soundboard spectras for each note.

^{231     7}Fletcher & Rossing Modal analysis may be defined as the process of describing the dynamic properties of an elastic structure interms of its normal modes of vibration. Fletcher & Rossing
^{232     8}Fletcher& Rossing,128-129.