Health & Safety

Sound Basics

We live at the bottom of an ocean of air that constantly exerts a pressure on us. We experience the sensation of sound when our eardrums are stimulated by sound waves in the air around us. Sound waves are vibrations created when an object—such as a car engine, a loudspeaker, our vocal cords, or a tuning fork—causes a disturbance or change in the air pressure around it. Acoustic experts measure sound waves in a variety of ways, but sound waves are commonly described in terms of frequency and amplitude. Most of the sounds we hear are a complex mix of different and overlapping frequencies and amplitudes.

Each sound wave increases and decreases the background air pressure many times per second. The number of wave cycles per second is the sound wave’s frequency or pitch, which is typically measured in Hertz (Hz). Each Hz represents one wave cycle per second. If our ears are working perfectly, we can hear frequencies from about 20 Hz (for example, the largest organ pipe) to 20,000 Hz (for example, some dog whistles). As we move away from the source of a sound, the pressure drops approximately in proportion to the distance. As the distance from the sound source doubles in length, the sound pressure level is reduced by half.

The height and depth of sound waves is referred to as amplitude or loudness. As the amplitude increases, the volume increases. Our ears can detect sound over a very wide range of amplitudes, which are often measured and described in terms of decibels (dB). The softest sound humans can hear is approximately 0 dB.

Sound and Hearing

Sound waves collected by the Pinna (outer ear) are funneled down the ear canal and set the ear drum in corresponding motion. The malleus, incus and stapes (also known as the hammer, anvil, and stirrup) transfer these vibrations to the spiral shaped structure called the cochlea. The cochlea is a fluid filled chamber lined with minute hair cells that are sensitive to different frequencies. When exposed to the vibrations caused by various sound waves, the hair cells send nerve impulses to the brain and the brain interprets those nerve impulses as the variety of sounds we hear.

Exposure to loud sounds may cause temporary or permanent damage to the hair cells in our ears and, accordingly, damage our hearing because the hair cells cannot transmit sound to our brain. A single, very loud sound—such as a gunshot or an explosion—could cause immediate hearing loss. Prolonged exposure to other loud sounds over an extended period of time could also cause hearing loss.

Protect Your Hearing

Given the potential risk of temporary or permanent hearing loss associated with exposure to loud sounds, it is wise to be conservative and use common sense in your listening habits. For example, you should use earplugs when operating noisy machinery or firearms. Keep your distance from heavy construction equipment or jet engines. When listening to music or other audio (with or without a headset or headphones), keep the volume at moderate levels and limit the amount of time you listen.

Although there is no single volume setting that is appropriate for everyone, you should always use your headset or headphones with the volume set at moderate levels and avoid prolonged exposure to high volume sound levels. The louder the volume, the less time is required before your hearing could be affected. You may experience different sound levels when using your headset or headphones with different devices. The device you use and its settings affect the level of sound you hear. If you experience hearing discomfort, you should stop listening to the device through your headset or headphones. To protect your hearing, some hearing experts suggest that you:

  1. Set the volume control in a low position before putting the headset or headphones on your ears.
  2. Limit the amount of time you use headsets or headphones at high volume.
  3. Avoid turning up the volume to block out noisy surroundings.
  4. Turn the volume down if you can’t hear people speaking near you.