CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
230
It is also to be underlined that, even if the qualitative course of
the measured curve could be estimated, a theoretical model of
this system is still lacking.
Moreover, the measured data showed discrepancies with the
data formerly available and this confirmed the need of such
measurement campaigns in order to better understand the
acoustics of mosques.
5. THE TRANSITION OF ACOUSTICS FROM THE
BYZANTINE CHURCH TO THE MOSQUE
With the available data it was possible also to investigate the
transition of the acoustical characteristics from byzantine
churches to mosques. This happened for example when St.
Sergius and St. Bacchus (SB) was converted into a mosque. The
SB church is quite similar to the Basilica of S.Vitale in
Ravenna, Italy (SV) since both churches are byzantine-style and
date of the first half of the VI century. They have a central plan
and are characterized by a principal volume covered by a dome
and surrounded by an ambulacre, which is surmounted by a
balcony. But, while SV is conserved in its original state with
mostly a sound-reflecting floor, SB is today used as a mosque
and includes typical sound-absorbing carpets covering the floor
structure.
... - *
—*- SV measured
* *.
- -o- • SB' predicted
'*»
—*— SB measured
I
T"n^.
f ~ +
125 250 500 1000 2000 4000
Hz
Figure 9. Experimental reverberation time curves for SV and SV and
thearetical predictions for SB’.
On the other hand in the higher frequency range, where the
effect of the carpets is paramount, the insertion of a sound
absorbing floor completely alters the sound field and this can be
predicted with good accuracy.
6. CONCLUDING REMARKS
Church
V [m 3 ] s.
r [m 2 ] S K
[m 2 ]
V/Sr
V/Sp
SV
25800
11400
980
226
2633
SB
14900
6700
750
222
19.87
SV/SB
ratio
1.73
1.70
1.31
1.02
1.33
Table 2. Basic geometrical data of the rooms.
Table 2 reports the main geometrical data regarding the two
churches: volume (V), total surface (S-p), floor surface (Sp),
and the ratios V/Sj and V/Sp. Finally, also the ratios between
respective quantities in the two rooms are included (SV/SB).
While V and Sy have the same ratios (with SV being the largest
in absolute extensive terms), the floor surface is proportionally
more extense in SB.
The effect of the floor was studied by calculating the theoretical
curve for reverberation time and comparing it with the
experimental results. The theoretical curve was obtained with
the geometrical data of SB after introducing the modification
according to the ratios in Tab. 1. A room equivalent to SV was
obtained (called SB') but, differently from SB, the floor in SB'
was considered sound reflective. The consistency of the
theoretical predictions with the data collected in SB and SV was
tested.
Fig. 9 shows the reverberation time data measured in SB and
SV and compares them with theoretical predictions for SB'. It
can be noted that, for RT, the values of the prediction for SB' in
the lower frequency ranges are overestimated. This evidence is
in line with former findings (Marsilio, Prodi, Pompoli, 2001)
where the difficulty in predicting RT correctly for mosques in
the lower frequency range had been pointed out. This
inconsistency is not due to the carpets but to other architectural
details. In particular the articulation of the spaces into many
niches, half domes and finally the presence of huge domes
could have an impact on the reverberation time (Prodi, Marsilio
2003).
The systematic collection of acoustical data of ancient byzantine
churches and mosques gave the possibility of a scientific
qualification and comparison of the acoustics of those two types
of buildings for worship. The data, taken in the unoccupied
rooms, show that the values of reverberation are very high,
providing the room with a unique feeling of majesty. The rooms
are generally poorly suited for musical performance and the
delivering of speech messages suffers from the excess of
reverberation, even though inside mosques the situation seems
somehow mitigated by the sound absorbing effect of the floor
surface. The result is that better speech communication can be
established, at least in the short range. Finally, most of the
spaces tested are inserted in a noisy city environment. Since no
specific sound insulation was projected, they all suffer from
noise intrusion which reduces even more the signal to noise
ratio.
7. REFERENCES
ISO 3382, 1997, Acoustics - Measurement of reverberation
time with reference to other acosutical parameters.
Karabiber, Z., 2000, A new approach to an ancient subject:
CAHRISMA project, Proceedings of the 7 th ICSV Conference.
Marsilio, M., Prodi, N., Pompoli, R., 2001, On the prediction of
reverberation time and strength in mosques, Proceedings of the
Conference ICA2001
Prodi, N., Marsilio, M., Pompoli, R., 2001, On the effect of
floor inside mosques, Proceedings of the Conference ICA200I.
Prodi, N., Marsilio, M., 2003, On the effect of domed ceiling in
worship spaces: a scale model study of a mosque. Building
Acoustics, 10(2), in print.
