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Hearing Protection Selection Tools and Resources


passive hearing protection introduction

Passive hearing protection can do more than protect from hazardous noise levels.  When selecting devices, the hearing protection devices (HPDs) should

  • Provide adequate protection against noise;
  • Be comfortable for the person to wear; and
  • Allow the wearer to hear critical sounds.

The descriptions below provide information on the various types of passive hearing protection. For questions on which device is most appropriate, consult with your Hearing Conservation Program manager, an audiologist, industrial hygienist/bioenvironmental engineer, or safety officer.

Disposable foam earplugs are widely available and can have the highest level of noise protection.

     Advantages of disposable earplugs:

  • High levels of noise attenuation
    • Noise attenuation refers to the amount of sound being blocked or reduced.Higher levels of attenuation means more sound prevented from reaching noise sensitive areas of the ear
  • Comfortable for extended wear
  • Inexpensive
  • Multiple sizes available

  • Difficult to consistently fit resulting in lower levels of attenuation
    • People wearing these devices may think they are achieving adequate protection but improper insertion can decrease the amount of attenuation
  • One size does not fit all
  • Extra training to insert properly and consistently
  • Takes extra time to insert if going in and out of noise environments


Preformed or pre-molded earplugs provide a consistent fit and are reusable. They come in different sizes.  Trained technicians at hearing conservation clinics can fit service members and civilians with the right size.


  • Reusable
  • Washable with warm soapy water
  • Provide consistent fit
  • Multiple sizes
  • Comfortable when sized and fitted correctly
  • Provide good levels of noise attenuation when fitted and inserted properly
  • Economical for people who work in consistent noise hazardous environments
  • Easy to insert if going in and out of noise environments


  • Correct sizing is critical
  • Becomes loose from jaw movements such as talking or chewing or a slight bum to the earplug


Filtered earplugs preserve sound quality. They are great for musicians as they reduce noise, lowering the volume, while not affecting sound quality. Filtered earplugs are also known as flat attenuation, linear attenuation, uniform attenuation, or musician’s earplugs. The names reflect how the earplug reduces noise equally across frequencies.  Sounds are more natural sounding with an added benefit of protecting hearing.


  • Preserve sound quality
  • Low attenuation levels enable people to hear critical sounds easier


  • Correct sizing is critical
  • Not suitable for higher noise environments
  • Becomes loose from jaw movements such as talking or chewing or a slight bump to the earplug


Level-dependent earplugs are passive earplugs that block sounds in either a closed (shown on left) or open (shown on right) position.  Level-dependent earplugs are designed for a tactical environment. A ground troop can use these devices in a closed position when riding in a transport vehicle, protecting them from the continuous noise.  While on the ground as part of a foot patrol, the same devices can be worn in the open position preserving the ability to listen for critical sounds and still protecting the individuals from sudden impulsive noise.

 Level-dependent earplugs are also known as nonlinear earplugs, amplitude-sensitive earplugs, tactical earplugs, 
                   shooter’s earplugs, and vented earplug


  • Critical sounds can be heard while protecting your ears from damaging impulsive noise
  • Two positions – open and closed
    • Closed for continuous noise
    • Open for impulsive noise
    • Disadvantages:

      The open position offers little protection against continuous noise
    • Correct sizing is critical
    • Closed position impairs ability to hear critical sounds
    • Becomes loose from jaw movements such as talking or chewing or a slight bump to the earplug


     Ear muffs, provide good protection from continuous noise environments.  They are easy to put on and take off so are great for intermittent noise exposure.  Because they cover the pinna or the outer ear, determining the direction of a sound is more difficult. Most ear muffs have a correct way to wear them. The headband should fit snugly over the top of your head.  A loose headband will cause the earcups to slide and not provide a proper seal. To get a good seal around the earcups, the material must be pliable, undamaged, and properly sized. Some ear muffs are available in multiple sizes even for small children.  When worn improperly, the ear muffs will block less noise and not provide the expected protection. 


    • Easy to don and doff, making them good for intermittent noise exposure


    • Cues to localizing sounds are blocked by ear muffs

Hearing-Critical Tasks (HCT's)

Hearing-critical tasks (HCTs) are those tasks in which the only sense that can perform the task is hearing.  In the military, HCTs are often related to the speed and safety of an action.  HCTs can be categorized as

(1)    sound detection

(2)    sound identification

(3)    localization

(4)    speech intelligibility

Noise can mask the critical sounds. Also, HPDs can interfere with HCTs by blocking the sounds, however, some HPDs are designed to pick up hearing critical sounds while protecting from hazardous noise.  The HPD EPL provides information on how listed HPDs attenuate (reduce) noise and enable the wearer to localize sounds (locate the direction of sounds).  Currently, the list has a limited number of passive HPDs, but HCE is working to expand the list to include more passive HPDs as well as active and communication devices.  Passive HPDs are earplugs or muffs that have no electronics.  Active HPDs have electronics to reduce noise levels.  Those electronics may also enhance other, desirable sounds that a Service member needs to hear.  Communication HPDs may reduce noise passively or actively, but are able to connect into a radio or communication system.  Communication HPDs are tested for speech intelligibility.  

noise environment

Noise environment for the military varies greatly from industry.  Flight decks, artillery fire, and tracked vehicles are more noise hazardous than most noise sources found in industry.  Noise is categorized as either continuous or impulsive.  Continuous noise can be found with any engines or machinery, while impulsive sounds are from gun and artillery fire.  At high levels and increased exposure, they are hazardous to hearing.



Localization is the ability to determine the direction and distance, direction alone, or distance alone of a sound.  Localizing is important for safety and detecting danger.  For example, being able to determine where the truck with the back-up alarm is coming from is important in preventing accidents. The outer ear plays an important role in localizing sounds.  When the ear is covered by an earmuff, it is harder to localize sounds. An earplug can distort the frequency of a sound making it difficult to identify the direction of a sound. For Service members, the direction and distance to gunfire is also critical in detecting the location of enemies.  HPDs and other equipment such as helmets may interfere with cues that help with localization.  Some HPDs are designed to allow for localization. Selecting HPDs based on localizing as well as noise attenuation capabilities may be mission critical.

For devices on the HPD EPL, we compare the ability to localize with the open ear, to how well those same people are able to localize with HPDs being tested.  Three measures are used:

(1)    Front-back reversals

(2)    Percent angular error

(3)    Aurally-guided search

Front-back reversals occurs when a person confuses the direction of a sound by 180o. Most people can easily distinguish between a noise in front of them versus one behind them.  A normal hearing person who is not wearing hearing protection will confuse sounds in front of them for a sound behind them less than 5% of the time.

Percent angular error is the percent of angle off from the direction of a sound. Percent angular error is a measure of how precise a person can localize.  Normal hearing people with the open ear will have a percent angular error of less than 5%.  As the angular error increases, a person may take longer to find a target or mistake the direction of a sound

Aurally Guided Visual Search (AGVS) measures the time required to find a visual target that is co-located with a sound source in the presence of other visual targets. Response time is important because it measures the functional impact HPDs have on localization capabilities.  Without a sound, people will take an average of 12 seconds to find the visual target.  With the sound paired with the visual target, people with normal hearing will take less than two seconds to find the target.  We use the term spatial awareness to describe localization on the HPD EPL.  The below rating system is used for spatial awareness.  Note the smaller the number, the better the device will help the wearer to localize a sound. Further explanation is available in the guidebook.

localizing sound in different environments

Localization, or the ability to determine the direction of a sound, is a critical skill for service members, and vital to situational awareness, safety, and mission effectiveness. 

These animations show two different scenarios that demonstrate how the environment, and any barriers to sound, can affect how quickly you locate the direction of a sound. The first video shows a person being able to locate the direction of a sound mainly through listening because there are limited sound barriers getting in the way of detection.  The second video demonstrates the effect of barriers on sound localization, and how the eyes and ears work together to determine the direction of the sound. In this second scene, a car obstructs and changes the sound (much like some hearing protectors can do), making localization more difficult.

VIDEOS: Sound Localization With and Without Barriers

Speech intelligibility

Communication is essential in military operations.  When working in a noisy environment, understanding communication can be difficult.  When communication is considered essential in a noise hazardous environment, HPDs with communication capabilities are used.  These devices are tested in conjunction with the entire communication series to ensure speech is at an acceptable level of intelligibility without interference from any one part of the system.  For military systems, speech intelligibility must score greater than 80% in a defined noise environment.  In general, the louder the environment, the harder it is to understand speech.

The below rating system is used as a guide to select devices for speech intelligibility.  The higher the number, the better speech is understood at 85 decibels (dBA).

Speech Intelligibility at 85 dBA

High (90-100%)

High Moderate (80-89.9%)

Low Moderate (70-79.9%)

Low (< 70%)

hce miluniversity classroom

HCE milUniversity Classroom

Training courses supporting the HPD EPL and hearing conservation program are available through milUniversity.  The Hearing Health Education course satisfies the annual hearing conservation training requirement.  The Hearing Conservation for Leaders course is appropriate for leaders at all levels. The HPD EPL courses are designed for safety, industrial hygiene, and hearing conservation managers.  It provides intermediate level information about different types of hearing protection and when they should be used.

Instructions on how to access the CAC-enabled training links

milUniversity is a CAC-enabled website.  

evaluated hearing device page references


American National Standards Institute/Acoustical Society of America

ANSI/ASA S12.6-2016 Methods For Measuring the Real-Ear Attenuation of Hearing Protectors

ANSI/ASA S12.68-2007 Methods For Estimating Effective A-Weighted Sound Pressure Levels When Hearing Protectors Are Worn

ANSI/ASA S12.42-2010 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

ANSI/ASA S3.71-2019 Measuring The Effect Of Head-Worn Devices On Directional Sound Localization In The Horizontal Plane

ANSI/ASA S3.2-2009 (R2014) Method For Measuring The Intelligibility Of Speech Over Communication Systems


Military Standards

MIL-STD-1474E std 15APR2015 Noise Limits


Testing Data

Gallagher, H.L., McKinley, R.L., Theis, M.A., Swayne, B.J., Thompson, E.R. Performance Assessment of Passive Hearing Protection Devices. AFRL-RH-WR-TR-2014-0148, October 2014.

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