The different thermoviscous attenuation regions for the principal mode of sound propagation in a gas‐filled tube may be defined in a simple diagram, with boundaries based on discriminants containing dimensionless combinations of radius, wavelength, and mean free path. The additional condition for propagation of higher‐order modes may be placed on the same diagram. The condition is always satisfied in the ’’very wide tube’’ region, which makes experimental investigations of the principal mode more difficult in this region.