Аннотация:A method is proposed for calculating the coefficients of the operator of transparentboundary conditions (TBC) for the wave equation in a circular channel with boundary conditions ofthe third kind. The method can be applied in the case of a variable speed of sound. The dependenceof the accuracy of approximating the convolution kernel of the TBC on the approximation accuracyof its image is investigated. An example of the set of coefficients of the TBC operator is given.