Developments in Ceramic Materials Research

168
Dimitris Skarlatos, Tilemachos Zakinthinos and Ioanis Koumanoudis
Measurements of absorption by Carvalho et al showed that the absorption increases at
low frequencies when the pots are located at the corners of the room. Acording to Carvalho
this conclusion confirms the relevance of the tradition that often involves the laying out of the
acoustic pots in the churches especially near the angles.
Figure 23 shows the change of Clarity and Definition in 1/1 octave band analysis due to
resonators. It is clear that there is a decrease of both indexes in the low frequency region with
the presence of resonators. The effect of resonators in the mid and high frequency region is
mixed.
x100%
0.8
0.7
0.6
0.5
Definition (D50)
0_bottles
480_bottles
0.4
63 125 250 500 1000 2000 4000
dB
8
7
6
5
4
3
2
Clarity (C80)
0_ bott
480 _bott
1
63 125 250 500 1000 2000 4000
(a) 1/1 octave band center frequency (Hz) (b) 1/1 octave band center frequency (Hz)
Figure 23. Effects of resonators on Definition and Clarity.
X100%dB
0.3
0.25
0.2
0.15
0.1
Lateral fraction (LF)
0_bottles
480_bottles
0.05
63 125 250 500 1000 2000 4000
(a)
1/1 octave band center frequency (Hz)
Figure 24. Of resonators on LF and IACC.
1
0.9
0.8
Interaural cross correlation (IACC)
0_ bott
480 _bott
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
63 125 250 500 1000 2000 4000
(b)
1/1 octave band center frequency (Hz)
For the third octave band that contains the resonant frequency, using a varying number of
resonators D50 can be expressed by the following regression equation (R-squared=0.96) is:
D50 = 0.533+ 0.139bv
(18)
where bv is the number of resonators per unit volume.
Similarly C80 can be written (R-squared=0.9).