Developments in Ceramic Materials Research

IACC
( τ )
=
t2
∫
The Use of Ceramic Pots in Old Worship Places 157
() ( + τ )
p t p t dt
L R
t1
1
t ⎛ 2
⎞2
2 2
⎜ pL() t pR( t+ τ ) dt⎟
⎜∫⎟ t1
⎝ ⎠
where pR () t and pL () t are the sound waves that arrive at the right and left ear
respectively.
IAAC is used in architectural acoustics to determine the sense of the spatial distribution
quantitatively and the acoustic quality of the sound. Its values range from 0 to1 and if this
value is lower than 0.4, the acoustics are considered to be good.
5. OPERATION OF CERAMIC POTS
As mentioned before, the Helmholtz resonator is a simple form of sound vessel or any
cavity confined by solid walls containing a certain volume of air and bearing a narrow tubelike
– not long – neck with an aperture that communicates with the air outside. In practice
Helmholtz resonators are lumped, not distributed acoustic elements consisting of a rigid wall
cavity of volume Vres with a neck of area s and length d . It is assumed that the characteristic
dimension of resonators is much smaller than the acoustic wavelength for the frequency of
interest. However, theoretically there are other shapes of sound vases, such as: without a
neck, or having more than one aperture, or formed by continuous cavities that communicate
with each other. An interesting form of Helmholtz resonators is the quarter wavelength
resonators which simply are pipes or tubes closed at one end and opened at the other.
p
l
s
V
p
a b c
Figure 14. Simple (a) and quarter wavelength resonators (b) Mechanical analogy (c).
The ceramic pots found in worship places are actually Helmholtz resonators. The
resonators behave as a single degree of freedom mass, attached to a spring. The mass of air in
the neck of the resonator is excited by acoustic pressure at its aperture. The resonator
resonates as a mass-stiffness system resulting in a large response at its resonant frequency.
The resonant frequency of a resonator is given by [41]:
l