  Acoustic waves are those waves which travel with the speed of sound through a
medium. H. Lamb has derived a cutoff frequency for stratified and isothermal
medium for the propagation of acoustic waves. In order to find the cutoff
frequency many methods were introduced after Lamb's work. In this paper, we
have chosen the method to determine cutoff frequencies for acoustic waves
propagating in non-isothermal media. This turning point frequency method can be
applied to various atmospheres like solar atmosphere, stellar atmosphere,
earth's atmosphere etc. Here, we have analytically derived the cutoff frequency
and have graphically analyzed and compared with the Lamb's cut-off frequencyfor
earth's troposphere, lower and upper stratosphere.
