The attenuation of plane compressive waves in a semiinfinite composite bar is studied. The bar is composed of a main strip and two serrated septa symmetrically bonded to the main strip by viscoelastic material. The one‐dimensional solution gives two complex wavenumbers whose values depend on the complex shear modulus of the viscoelastic material, the frequency, and the relative dimensions. It is shown that maximum attenuation occurs for an optimum value of the loss tangent of the shear modulus. For a typical practical example, this attenuation is about 20 dB in the first three wavelengths for a loss tangent of 0.32.