33 C.F.R. § 86.01 Frequencies and range of audibility.
Title 33 - Navigation and Navigable Waters
The fundamental frequency of the signal shall lie within the range 70–525 Hz. The range of audibility of the signal from a whistle shall be determined by those frequencies, which may include the fundamental and/or one or more higher frequencies, which lie within the frequency ranges and provide the sound pressure levels specified in §86.05.
Title 33: Navigation and Navigable Waters
PART 86—ANNEX III: TECHNICAL DETAILS OF SOUND SIGNAL APPLIANCES
Subpart A—Whistles
§ 86.01 Frequencies and range of audibility.
