[en] In this work, anomalies of acoustic phonons are studied in the elemental superconductors Nb and Pb and in lead-thallium and lead-bismuth. By using high-resolution spin-echo neutron spectroscopy, energy resolutions in the range of μeV were reached, which corresponds to an improvement of several orders of magnitude compared to conventional neutron spectroscopy. Several renormalization effects and anomalies appear at phonon energies near the energy gap 2Δ and at temperatures above and below the superconducting transition temperature T_c. Whereas the relative changes of the linewidths and energies agree well with predictions based on BCS theory, the absolute values differ significantly. Surprisingly, Kohn anomalies coincide with the 2Δ (T = 0 K) both in Nb and Pb. By means of neutron spectroscopy on several Pb_1_-_xBi_x and Pb_1_-_xTl_x alloys, it could be demonstrated that the saturated energy gap 2Δ (T = 0 K) follows the energy of the Kohn anomaly as it changes in the alloys.