A study of Space Launch System acoustics, Space Launch System acoustics: Far-field noise measurements of the Artemis-I launch by Kent L. Gee and collaborators, reports post-liftoff noise levels up to 136 dB and an average maximum one-third-octave spectral peak at 20 Hz.
These measurements matter because the launch acoustic environment influences launch-pad, vehicle, and payload design. Better characterization also supports the assessment of community and environmental impacts.
For the technical details, see the referenced study via DOI.