That part of the acoustic impedance due to the effective mass of the medium, that is, to the inertia and elasticity of the medium through which the sound travels. The imaginary component of acoustic impedance, expressed in acoustic ohms.
"When my wife was young, her parents played two albums of recorded bird songs for her at bedtime, as a way of lulling her to sleep. For all of our married life (32 years now and counting) my wife has told me about these LPs, which were published in the late 50s I believe. Well, not too long ago she managed to purchase rare copies of the LPs that ..."