Infrasonic and low‐frequency flow‐noise measurements were made during laboratory tests of an H‐58 omnidirectional hydrophone. The hydrophone was tested in three configurations: bare, framed, and faired. The incident water speeds varied from 0.25 to 0.45 knot, which correspond to a Reynolds number range from 8800 to 16 000. The faired and framed configurations developed flow‐noise levels lower than the bare hydrophone, and the latter configuration developed the highest noise levels at the lowest frequencies of the 1–50−Hz band. Hydrodynamic factors which influence the acoustic measurements made during this test are discussed, and the importance of hydrophone configuration during very low‐frequency measurements is demonstrated.