Conduction electrons on closed orbits in pure copper single crystals at low temperatures can interact with an ultrasonic wave packet to produce replicas of the wave packet nearby. Measurements of the ratio of replica amplitude to primary amplitude for magnetic fields between 50 and 260 G are reported. The measurements are compared with the predictions of existing theoretical models. A semiquantitative model for the generation of replica wave packets is presented which explains many of the features of the magnetic field dependence of the replica amplitude and suggests new ways to calculate the electron relaxation time in metals. The use of replica wave generation in a device to produce a continuously variable signal delay is proposed, and an application of the measurements of replica-wave-packet amplitude to the theory of electromagnetic generation of ultrasound is discussed.