\n experiiiicritid study of self-excited ion acoustic wLves with wavelengths greater tllrin the riidius of the discharge tube in i i dc-low pressure column is presented. The propagat,ion of this type of waves \vxi observed over a pressnre range of 5 . lo-' torr 5 p 5 10-I torr and ciirrerits of 0.02 -4 5 i 0.15 A in various gnses (iirgon, neon, helium, and hydrogen) in cylindrical glass tubes tvith diiimeters of d = 2; 4 and 6 cni.The Dispersion behaviour and the existence range were measured in dependence of the internal partimeters of the discharge (characteristic velocities und collision frequencies) arid the geometry of the discharge tube. I t is shown, that the existence range depends not only on gns pressure and current but is influenced iilso hy the geometry of the discharge tube. The minimum wnvelengt.hs which belong to the upper cut-off frequencies correlate with the radius of the discharge tiihe ;it ciirrents higher than i l y 0,2 . I and increasing pressure.