Abstract: Apparatus for damping a sound field propagating in a fluid propagation medium within a channel (1) having a closed cross-section periphery, including at least one but preferably a plurality of lattice members (2) spaced within the channel (1), each of the lattice members have partition walls subdividing the free channel cross-section into a plurality of partial channels (3) which have a length which is larger than the width of the channels, each lattice member is open at both ends, the length of the partial channels runs parallel the main channel and wherein adjacent partial channels (3) have different length for the sound oscillation state, whereby in the adjacent partial channels local sound pressure differences are produced over their length, which are at least partly compensated by having said partition walls permeable for the propagation medium to permit a local sound pressure transmission from one partial channel into the other.