Capt John Hall, USAF
48MDOS/RAF, Lakenheath
A new custom Hearing Protection Device (HPD) ear plug has recently been tested at RAF Lakenheath and RAF Mildenhall which utilizes a venturi to limit sound pressure reaching the eardrum. Preliminary real world tests of this technology with 48th Fighter Wing F-15 pilots and 352nd Special Operations Combat Controllers have demonstrated significant benefits which will be studied further at the Air Force Research Laboratory at Wright-Patterson AFB.
The venturi principle has been used in gasoline engine carburetors for over 50 years, but a designer in Holland has creatively applied the principle to hearing protection. A venturi is a narrow opening designed to create aerodynamic turbulence as air pressure increases. Since sound is oscillating air pressure, it makes since that this technology can be used to restrict hazardous noise.
The venturi on board the "Sound Censors" custom earplug restricts sound pressures progressively more in the high frequencies where noise is most harmful. The attenuation characteristics pass enough low and mid frequency information (at safe levels) to enable the wearer to understand speech (as well as environmental auditory cues) in noise significantly better than other HPDs currently on the market. The plugs meet all International Standards Organization (ISO) requirements for hearing protection in hazardous noise and are low profile enough to fit comfortably under all DoD headgear, helmets, and communication headsets.
Several pairs of Sound Censors were tested this year. An 493rd Fighter Squadron F-15E pilot who recently mission tested a pair reports "marked improvement of radio and intercockpit voice communications." Likewise, Combat Controllers at the 352nd Special Operations Group (SOG) report the devices "greatly enhance mission effectiveness" aboard SOG airframes and during tactical operations on the ground.
A complete summary of the venturi HPD principle, real world performance in the USAF, effective Noise Reduction Rating (NRR), and directions for further study at the Air Force Research Lab for possible Air Force wide approval will be discussed.