A recently developed theory by Tolstoy [IEEE J. Ocean Eng.14, 4–16 (1989); J. Acoust. Soc. Am.85, 661–669 (1989)], which exactly calculates the attenuation produced by a truncated wedge barrier, has been adapted to assume a line source parallel to the barrier. The theoretical results are compared with experimental measurements obtained using acoustic impulses and rectangular barriers up to 0.45 m wide. The results are also compared with other wide‐barrier prediction techniques. It is shown that the refinement to include multiple scattering between the vertices is generally unimportant and can lead to erroneous results if the necessary series are not summed over hundreds of terms. The phase information provided by the theory is evaluated by comparing predicted and measured impulse waveforms obtained behind the barrier.