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New perspectives to save cultural heritage
Altan, M. Orhan

CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
Figure 2. The relationship between the measured reverberation times
and the volumes of mosques and churches:all pass values.
Figure 4. The dependence of reverberation time with frequency for the
byzantine churches.
V [m3)
Figure 3. The relationship between the measured reverberation times
and the volumes of mosques and churches: averaged values of 500Hz,
1kHz and 2kHz octave bands. Dashed lines indicate the occupied and
unoccupied concert halls.
In fact while the mosques show the maximum of reverberation
in the lower frequency range the byzantine churches have
generally the maximum in the medium frequrency range. This
finding has an immediate link with the impression of a listener.
The acosutic field in byzantine churches is extremely
reverberant and the sounds overlap in time with little possibility
of being separated. This applies also to spoken of sung phrases,
whose intelligibility is greatly affected by the excess of
reverberation. Such conditions of reverbeartion are also at the
upper linit of acceptability for typical lyturgical music played
with an organ. As regards the mosques the reverberation curves
are easily grouped into two sub-groups of “large” spaces like
Suleymanie and Selymie and the “small” ones like Sokullu and
St. Sergius and St. Bacchus. For the former group the
reverbeation time halves when passing from 500 Hz to 2 kHz
causing a peculiar timbric effect in the spaces: the same
phenomenon is observed also in the latter group but it is not so
marked. In particular the frequency range of the singing
formants (2 - 3 kHz) has a shorter reverberation time than the
lower frequencies. This fact contributes in improving the oral
unaided communication in the mosques since the masking due
to the reverberation is controlled by the sound absorption in the
higher frequency range.
3.2 The sound level
The sound level is investigated by means of the parameter
called strentgth (G) reported in Fig. 6. The plot includes the
overall values measured inside each space after averaging of all
source and receiver positions.
Lin 125 250 500 1K 2K 4K
Figure 5. The dependence of reverberation time with frequency for the
Each point has the bars related to one standard deviation of the
mean values. The first and clearest observation is that the sound
level both in byzantine churches and in mosques has a
decreasing trend with increasing of the volume. The logarithmic
fit lines have quite a good regression coefficient.
The values are good just for the smaller mosques and allow in
general only a fair degree of communication over a small
distance without the aid of electroacoustic devices. Then the
sound level inside the byzantine churches is higher than that in
the mosques with a comparable volume. This is true on average
but the values in the different positions are not constant, and in
both cases they decrease when moving away from the sound
source. This means that there is a sort of overlap between the
data as also shown in Fig. 6. Typically the lower levels for a
smaller mosque (or church) can be compared with the higher
levels measured inside a large one. In other words what happens
is that, given a mosque and a byzantine church of comparable
volume, the sound level measured at the same distance from the
sound source will differ by a fairly constant amount depending
on the volume. The churches show a higher sound level for
most of the volumes tested. For larger volumes the difference
tend to vanish since in both types of enclosures the shielding
effects of architectural elements and also the air absorption
become quite relevant.
3.3 The clarity
The attributes of the sound field concerning clarity and the
definition of the message delivered in the spaces for worship
have been measured according to suitable parameters like
clarity (C50 and C80) and definition (D).