# HANDBOOK OF ACOUSTICS - online book

### A complete view of Acoustical Science & its bearings on music, for musicians & music students.

 EXAMINATION PAPERS.                        291 marked 1 will be points of rest, since they are on both sets of nodal lines. The points 2 also are nodal points, for they have equal ampli­tudes in opposite directions. A little consideration will show also that the lines 2, 1, 2 connecting these points of rest will be nodal lines. Hence the sand figure will be the square 2, 2, 2, 2. It can be obtained by clamping the plate at 2 and bowing close to one of the corners. Now (b) let fig. D represent the plate B, but vibrating in opposite phase as shown. Let E represent D superposed on A. Then the rectangles a a b b will have twice the amplitude due to each set of vibrations singly. The points 1, 1, 1, 1 are of course nodal points: the four corners 3, 3, 3, 3 and the centre 0 are also nodal points, since they have equal and opposite amplitudes. Consequently the sand figure will be the cross along the diagonals 3, 0, 3. It can be obtained by clamping the plate at the centre and bowing near the middle of one of the sides. 6. (a) What is a good form for a resonator? Explain {b) why a well-made resonator is not set into active vibration, even by a loud tone, unless the tone is accurately of the pitch to which the resonator is tuned ; (