Acoustic impedance variations of Helmholtz resonators of two plates with orifices inlet neck against the distance between the plates

Experimental examinations of acoustic impedance of complex
Helmholtz resonators of two plates with orifices inlet neck using Kundt tube
procedure were performed. Few variants of model resonators were studied
depending on the number of orifices (and their diameters) in the plates and
against variations of the distance between the plates for a constant volume of
the resonator cavity. A regular dependence of the acoustical impedance as well
as the absorption coefficient against the distance between the inlet cover
plates was observed for a given configuration of the orifices. Changes of the
configuration (number of orifices their size and plane distribution in both
plates and the relation between the lower and the upper one design) caused
evident variations in acoustical properties, however no regular dependence could
be found. Some configurations are more optimal than the others.