Developments in Ceramic Materials Research

where σ res is the scattering cross-section
σ
res
The Use of Ceramic Pots in Old Worship Places 161
2 2
λ g 4
=
2 π (1 )
2 ⎡ 1 ⎤ + μ
1+
Qres ⎢g− g
⎥
⎣ ⎦
2 2
6. THE EFFECT OF VASES ON THE ACOUSTIC QUALITY
OF THE CHURCHES
6.1. The Effect of Distance from the Pots
As it has been mentioned before, the two major problems all researchers had faced in
churches were the small number of resonators in the interior and the low resonant frequency.
In order to probably overcome these problems and to explore the effectiveness of resonators
more sufficiently, an experiment was carried out in a church. Proper resonators were chosen,
checking their resonant frequency and ensuring the relative great number of them. The
experiment was carried out in a new Byzantine church (Agia Paraskeyi of Platani) located in
Patras, Greece. For the experiment 31 ceramic pots were used (see figure 15). The resonators
were placed mainly on the floor at a distance between them of 0.7m (greater than that
predicted by equation 4) and some of them at the corners where it had been noticed that there
may be greater sound absorption. Each time, the impulse response was measured and
analyzed. For the measurement and analysis of impulse responses, the BandK Dirac v 3.1
software installed on a laptop was used.
Using the formula of Alster [43], the resonant frequency of the resonator was calculated
to be 325 Hz. To confirm this frequency the following experiment was done. Two ½ inch
similar microphones were used. One was placed inside the resonant volume through a small
hole on the bottom of the vase and one outside of it. The microphones were connected to a
dual channel RTA (Norsonic 840 RTA). The measurements were made in the field that is in
the church being tested.
Figure 15. Vases under test.
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