Much effort has been spent to increase the attenuation of lined ducts at low frequencies with only a minor increase of the blocking of the duct by thick silencers, in order to keep the stationary flow resistance of the silencer at low values. There exists a similar problem at high frequenices, where the attenuation goes down at about the square of the inverse frequency as soon as the frequency limit of ray formation is exceeded at which the free duct is about half a wavelength wide. The principal remedy of the problem, to choose narrow ducts, would increase the aerodynamic resistance. The ray-acoustical background of the low attenuation at high frequencies suggests using the existing corners of the ductwork into which the silencer is inserted for the generation of high-frequency attenuation. A naΔ±Β¨ve idea is to assume that the exciting sound ray of the inlet duct should be absorbed by an absorber on the corner wall opposite this duct, thereby avoiding the excitation of the outlet branch of the duct. Such a corner absorber could be applied in wide ducts also. This paper presents theories of joints of acoustically lined ducts with separate sound absorbers at the corner walls. The numerical results will show that high transmission losses can indeed be achieved at high frequencies, but the mechanism of the corner attenuation is not so much the absorption by the corner absorber, but more the (cut-off) attenuation of higher modes in the lined outlet branch of the duct.