A simple analysis shows that, when a transient plane wave in an elastic medium is reflected at a plane boundary with a lossy medium, the transient waveform of the reflection is affected by the loss parameters of the second medium. If the attenuation in the second medium is small, and if the ρcproducts of the two media are matched, then the reflected waveform is the convolution of the incident waveform, with the integral of the Fourier transform of attenuation as a function of frequency. Thus, attenuation for a lossy solid or liquid can be obtained by this external‐pulse technique. Where attenuation is some simple function of frequency, its Fourier transform is some recognized generalized function. Sample waveforms have been observed using airborne sound in specially prepared tubes; good qualitative agreement with predicted waveform was obtained.