Hearing-critical tasks, known as HCTs, require good hearing. Military HCTs often link with speed, safety, and communication. You can categorize HCTs as:
- Detecting sound
- Identifying sound
- Locating sound
- Understanding speech
Noise can mask your ability to hear important sounds. Hearing protection devices can interfere with HCTs by blocking sounds. Certain HPDs pick up important sounds while protecting from loud noise.
Noise Intelligence
The noise environment in the military is unique. Military noise includes flight decks, artillery fire, and tracked vehicles. These are more hazardous than most noise sources found in industry. Noise is either continuous or impulsive like a blast. Continuous noise includes any noise that lasts for over one second, such as running engines or loud machinery. Impulsive sounds are noises that last for less than one second, such as gunfire and explosions. The louder the noise and the longer the exposure, the more dangerous it is to your hearing.
Localization
Localization is being able to know where sound is coming from and how far away it is. Localizing is important for safety and detecting danger. For example, being able to tell where the truck with the back-up alarm is coming from is important in preventing accidents. The outer ear plays a key role in localizing sounds. Localization is harder when an earmuff covers your ear. An earplug can change the pitch of a sound making it hard to tell the direction of a sound. For service members, the direction and distance to gunfire is important in spotting the enemy. HPDs, and other gear such as helmets, may interfere with signs that help with localization. Some HPDs enable better localization. Selecting HPDs based on localizing as well as blocking noise may be mission critical.
Localizing in Different Environments
The ability to tell the direction of a sound is important for situational awareness, safety, and mission effectiveness.
Speech Intelligibility
Understanding speech is important in the military. Noise can make understanding speech difficult. Sometimes communication is important even in noise, like talking on a radio in a helicopter or on a ship. In general, the louder the noise, the harder it is to understand speech. HPDs with special electronics built in provide hearing protection and the ability to hear speech.
Labs test these hearing protectors to rate the speech understanding known as intelligibility. For military radio systems, speech intelligibility must score at least 80% in loud noise.
This speech intelligibility rating system is a guide to pick hearing protection. The higher the number, the better speech understanding at 85 decibels (dBA), the sound level at which noise may begin to hurt your hearing.
