Developments in Ceramic Materials Research

162
Dimitris Skarlatos, Tilemachos Zakinthinos and Ioanis Koumanoudis
Figure 16 shows the output of the two microphones using FFT analysis. The gray line
(Ch1) corresponds to the microphone outside the pot and the black line (Ch2) to the
microphone inside the pot. As one can see from this figure, in the frequency response of the
pot, there are three dominant peaks: one at a frequency of 336 Hz which corresponds to the
resonant frequency, and two higher overtones at 2617 Hz and 3367 Hz. The observed
overtones, as stated above, are not harmonically related to the fundamental since they have a
different source of origin [46].
Figure 17 shows the output of the two microphones using narrow band (1/3 octave)
analysis, for the same measuring setup. The light gray bars (Ch1) correspond to the
microphone outside the pot and the dark gray bars (Ch2) to the microphone inside. The black
bar corresponds to the 1/3 octave band that contains the resonant frequency. The
corresponding band level for the microphone inside the pot is 18.1 dB higher than the
corresponding outside. It is clear in figure 17 that the resonance is quite wide and affects four
1/3 octave bands with center frequencies 200, 250, 315 and 400 Hz. The overtone of 2617 Hz
affects slightly the 1/3 octave band of 2500 Hz. These 1/3 octave bands are the bands of
interest.
Level (dB)
100
90
80
70
60
50
40
336 Hz
Frequency response of resonators
2617Hz 3367Hz
Ch1 Ch2
30
0 1000 2000 3000 4000 5000 6000
Figure 16. Frequency response of resonators using FFT analysis.
Band level (dB)
100
90
80
70
60
50
40
30
20
10
0
63
80
100
Figure 17. Third octave band spectrum of pots.
125
160
200
250
1/3 octave band spectrum
315
400
500
630
800
1000
Frequency (Hz)
1250
1600
2000
Center frequency (Hz)
2500
3150
4000
Ch1
Ch2
5000
6300