[Code of Federal Regulations] [Title 33, Volume 1] [Revised as of July 1, 2005] From the U.S. Government Printing Office via GPO Access [CITE: 33CFR86.07] [Page 218] TITLE 33--NAVIGATION AND NAVIGABLE WATERS CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY PART 86_ANNEX III: TECHNICAL DETAILS OF SOUND SIGNAL APPLIANCES--Table of Contents Subpart A_Whistles Sec. 86.07 Directional properties. The sound pressure level of a directional whistle shall be not more than 4 dB below the sound pressure level specified in Sec. 86.05 in any direction in the horizontal plane within 45 degrees of the forward axis. The sound pressure level of the whistle in any other direction in the horizontal plane shall not be more than 10 dB less than the sound pressure level specified for the forward axis, so that the range of audibility in any direction will be at least half the range required on the forward axis. The sound pressure level shall be measured in that one-third octave band which determines the audibility range.