Developments in Ceramic Materials Research

The Use of Ceramic Pots in Old Worship Places 169
C80 = 2.07 + 1.88bv
(19)
Figure 24 shows the effect of resonators in LF and IACC. An increase of LF and IACC
was also observed.
7. CONCLUSION
For twelve to thirteen centuries, many official and popular temple builders in Greece, as
well as of other European countries, applied the sound vases in the churches. No Byzantine or
Medieval texts make any mention of the system of the sound vases. From the architect’s
viewpoint it can be concluded that: the use of vases was without any scientific knowledge and
following a tradition in an uncontrollable fashion.
Most researches of Christian monuments with walled-in sound vases, interpreted these as
sound amplifiers in keeping up with tradition. Besides, they lacked the general evidence
regarding sound vases and they were not familiar with the relative bibliography.
Probably the clergy, that had access to the libraries of monasteries, must have known of
Vitruvius’s renowned book, “De Architectura”, and perhaps someone who was interested in
good acoustics of the chanting and sermons must have imposed the sound vases. This is a
hypothesis that is verified by the great influence of Vitruvius on the West for centuries. Thus
the sound vases became to the choir masters a strong belief initially, before finally fading
away around the 18 th – 19 th centuries, both in Greece and in other European countries.
After Helmholtz and the development of building acoustics, the study of the walled-in
sound vases in churches began to be carried out in the proper way.
Generally speaking, the resonators act as a selective amplifier in a short distance from
resonators, but reduce the sound level far from them. This amplification is up to 8 dB in the
near field of them. This reduction with the distance follows a logarithmic law and in the far
field of them an attenuation of sound is observed.
A decrease of reverberation time (T30) was observed. This decrease is restricted to the
resonant frequency and in some overtones. The quality factor of pots is quite small and this
fact extends the effect of them in a wide frequency band (over one octave) mainly in the low
frequency region.
The most significant effect of resonators is on the energy ratios C80 and D50 which
seems to be linearly increasing by the number of resonators.
Another effect is that keeping the same number of resonators, a decrease of clarity and
definition in the vicinity of resonators was observed. The effect of resonators is not restricted
to the resonant frequency. In higher frequencies their effect is also observable but is less
important than in the resonant frequency.
The small number of vases found in most of the Christian churches (with some
exceptions) has an unobservable effect on the acoustic quality of them and this is an
indication that this technique was rather empirical.
Looking at the pots found, there are some points that although seems to be fortuitous, are
related to the acoustical properties of resonators. These points are: