Hilary L Gallagher

Acoustic Emissions from F-35 Aircraft during Ground Run-Up

A multi-organizational effort led by the Air Force Research Laboratory conducted acoustic emissions measurements on the F-35A and F-35B aircraft at Edwards Air Force Base, California in September 2013. These measurements followed American National Standards Institute/Acoustical Society of America S12.75-2012 to collect noise data to support community noise modeling and ground personnel noise exposure assessments. This field study utilized the most spatially extensive measurements of a military jet aircraft to date. In total, the microphone array was composed of 235 unique locations. These locations ranged from radial distances of 3 m outside the shear layer to 1,220 m from the aircraft with angular positions ranging from 0° (aircraft nose) to 160° (edge of the exhaust flow field). The acoustic emissions of the F-35 are presented for engine powers from idle to full augmented power (maximum afterburner). The acoustic emissions are characterized with spatial maps and are discussed in terms of overall and spectral band levels as well as statistical skewness measures. The directivity of the F-35 is described in general and in terms of variations in radial distances and individual spectral bands. Additionally, nonlinear propagation effects are identified and described along the peak radiation region for the range of engine powers.

Using impulsive peak insertion loss of hearing protectors with impulsive damage risk criteria

Impulsive noise presents special challenges for hearing conservation. The scientific community continues to search for an impulsive noise exposure criterion which accurately assesses the hearing damage risk for both short and long duration impulses. Other factors, such as the use of hearing protectors, earmuffs and earplugs, also affect the hearing damage risk but the current criteria do not address methods for using the attenuation of hearing protectors in impulsive noise. The relatively new ANSIS12.42-2010 “Methods for the Measurement of Insertion Loss of Hearing Protection Devices in Continuous or Impulsive Noise using Microphone-in-Real-Ear or Acoustic Test Fixture Procedures” describes methods for measuring the peak insertion loss of a hearing protector in impulsive noise. This paper will describe a method to apply the peak insertion loss data to impulsive noise damage risk criteria for an estimate of allowable impulsive noise exposure when using hearing protection.

Proposed Standard 3-D Aircraft Flyover Noise Measurement and Analysis Methods

Noise from high performance military fighter aircraft impacts the hearing and performance of personnel working near these aircraft and can be a source of annoyance to people living near airbases, airports 1 , and ranges where these aircraft are operated. Developers and operators of these aircraft must report the noise produced in communities as part of the NEPA (National Environmental Policy Act of 1974) process. Additionally, overexposure of personnel to high levels/durations of noise can result in permanent hearing loss, the number one veteran disability in the United States, and negatively impact voice communication capability. Additionally, the widely varying techniques used to acquire aircraft noise data make comparisons of aircraft noise and noise reduction technology performance more difficult.

Standard methods for measuring the effects of special hearing protectors on auditory performance

Traditional hearing protectors attenuate noise via passive and or active technology. The advent of special hearing protectors, i.e., those that provide communications capability, ambient listening/situation awareness function, and/or level dependent attenuation of continuous and/or impulsive noise, has generated additional needs for performance measurement and characterization. ANSI Standards, representing the consensus of the U.S. scientific community, provide accurate, reliable, and repeatable methods for measuring performance. Current standards address the measurement of passive noise attenuation, active and level dependent insertion loss, impulsive peak insertion loss, and speech intelligibility. However, a need exists for a standard measurement method/s to characterize sound localization ability and auditory situation awareness. The presentation will address the application of current standards as well as a framework for a new standard describing three possible methods to measure sound localization p...

Noise reduction ratings of active noise cancellation headsets

The recent promulgation of the MIL-STD 1474 E, “Design Criteria Standard Noise Limits,” combines data from the Real Ear Attenuation at Threshold (REAT) and the Microphone in Real Ear (MIRE) measurements to estimate the noise reduction rating of active noise cancellation (ANC) hearing protection devices. This paper will examine the American National Standards Institute standards, S12.6, S12.42, and S12.68 to assess the performance of four aviation headsets measured with REAT and MIRE methods. We will compare the protection estimates for different noises with the Noise Reduction Statistic for A-weighting (NRSA), Noise Reduction Statistic for Graphical (NRSG), and Octave Band rating methods. The NRSG method provides an efficient and accurate alternative to the Octave Band rating method. In the International Standards Organization, the ISO 4869 standard part 6 is under development to measure the attenuation of ANC protectors. Comparison with the proposed ISO 4869-6 standard will be conducted.

Assessing the performance capabilities of tactical hearing protection and communication devices

Military personnel work in unpredictable noise environments, which require flexible types of hearing protection (i.e., tactical hearing protection systems) in order to maintain mission effectiveness and situation awareness while reducing the risk of hearing loss. Acquisition decisions need to be made relative to accurate and complete measures of the total performance capabilities of tactical hearing protection systems and their effect on the user. Understanding the noise attenuation performance of tactical hearing protection systems has been a priority in order to protect the user from excessive noise exposure. However, active electronic tactical hearing protection systems have been designed to allow for enhanced communication and situation awareness, while at the same time protecting the auditory system from both impulsive and continuous noise. The Air Force Research Laboratory conducted a multifactorial assessment on currently available tactical hearing protection systems to determine the overall impact...

Personal attenuation ratings reported using Fit Check Solo™: Is background noise a concern?

It is well known that some personnel, especially Service Members, operate in hazardous noise-environments. To reduce the risk of hearing loss and hearing related disabilities, hearing protection devices (HPDs) are worn to decrease the level of noise at the ear. Noise attenuation provided by HPDs can vary greatly depending on user fit. Fit test systems were developed to measure the noise attenuation performance of HPDs and to report a personal attenuation rating (PAR) based on that particular fit. Elevated levels of background noise in a typical office-type setting (in comparison to a laboratory) could however affect PAR results. A study completed by the Air Force Research Laboratory compared PAR results of 3M EAR Classic earplugs and Howard Leight Airsoft earplugs from data collected using ANSI S12.6 methodology in the laboratory and data collected using Fit-Check Solo™ in an office environment, a controlled noise office environment, and the laboratory. Results demonstrated that PARs were affected by incr...

Noise exposure criteria for continuous noise: A case for reducing the 8 hour open ear exposure level

Personnel working in hazardous noise environments can be protected from noise induced hearing loss (NIHL) or other hearing related disabilities when their exposures are limited. Limiting noise exposures can be accomplished by engineering controls, administrative controls, and/or with the use of personal protective equipment. Damage risk criteria (DRC) were developed as a guide to limit personnel noise exposure in order to reduce the risk of NIHL. With the exception of the US Occupational Safety and Health Administration (OSHA), the US and many European countries accepted the DRC of 85 dB for 8 hours with a 3 dB per doubling exchange rate. Recent studies of the auditory response to noise dose, conducted at the Air Force Research Laboratory, found that A-weighted open ear exposures may be more hazardous (i.e., have a higher effective noise dose) than equal A-weighted level protected ear exposures. A potential conclusion of these studies is that hearing protectors are more effective than previously thought and reducing the open ear exposure criteria may be needed in order to minimize NIHL. This presentation will describe the pros and cons of reducing the 85 dBA DRC.

Modeling of fighter jet cockpit noise

Military fighter jet cockpit noise may pose a hearing loss risk to pilots and can disrupt communications. The current study is an attempt to model the noise levels in the cockpit of F-35 aircraft as a function of aircraft operation parameters. Levels are based on a complex interplay of parameters such as airspeed, altitude, dynamic pressure, and the flow rate of the in-cockpit environmental control system. Full population of an operational envelope from point-by-point measurements would require an excessive number of flights. In the current work, in-cockpit noise levels were measured during sampled flight conditions. Correlations between levels and flight parameters were investigated. A preliminary parameter-based model is presented, and the ability to predict levels within the operational flight envelope is addressed. [Work supported by USAFRL through ORISE.]

Acoustic emissions from flyover measurements of F-35A and F-35B aircraft

Acoustic emissions of F-35A and F-35B aircraft flyovers were measured in September 2013, in a multi-organizational effort led by the Air Force Research Laboratory. These measurements followed American National Standards Institute/Acoustical Society of America S12.75-2012 guidance on aircraft flyover noise measurements. Measurements were made from locations directly under the flight path to 12,000 ft away with microphones on the ground, 5 ft, and 30 ft high. Vertical microphone arrays suspended from cranes measured noise from on the ground up to 300 ft above the ground. A linear ground-based microphone array measured noise directly along the flight path. In total, data were collected at more than 100 unique locations. Measurements were repeated six times for each flyover condition. Preliminary results are presented to demonstrate the repeatability of noise data over measurement repetitions, assess data quality, and quantify community noise exposure models.