Knowledge summary
Summary (1)
Usually, in electroacoustics, we consider that the wavelength is much bigger than the dimensions of the system under study: it is the lumped element hypothesis.
A short duct can be seen as an equivalent mass-spring system, thus expressing the internial and compressibility phenomena of the fluid.
The end condition (extremity of the duct) determines the behavior of the duct: a duct open at both ends behaves as an acoustic mass (the air can move without compression). A duct open only at one end acts as an acoustic spring (the air is compressed without moving).
The electrical equivalent of a tube, open at both ends, is a series inductor. The electrical equivalent of a tube, open only at one end, is a capacitor connected in parallel.
The equivalent circuits of long waveguides are T and
networks. In low frequencies, the impedance values are those obtained with lumped elements.
