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Science Series Part 3: What is Frequency?

Dr. Emily Martinson, Au.D., Ph.D.

Just when you thought it was safe to start reading the blog again, we jump back into physics!  Today we will be discussing frequency, which is a very important property of sound that has a major impact on our hearing.

As discussed in Sciences Series Part 1 and Science Series Part 2, sound is a physical vibration through a substance (such as air or water) that produces a wave.  That wave has three main properties: frequency, intensity, and wavelength.  Today we will be discussing frequency.

Most of us think of frequency as “how often something happens.”  For example, the frequency with which I skip dessert is zero times per day.  The scientific definition of frequency is very similar.  Frequency can be defined as the rate at which a vibration occurs, or the number of times the wave completes one full cycle in a given time period (usually one second). 

For example, if the wave completes two full cycles in one second, the frequency is two cycles per second.  Frequency is typically measured in a unit called Hertz, which (in addition to being a rental car agency) is defined as cycles per second.  One Hertz is one cycle per second, and is abbreviated as Hz.

Knowing the definition of frequency is all well and good, and will certainly impress your friends at fancy dinner parties, but how does frequency relate to what we actually hear?  Human beings who do not have any hearing loss can hear sounds from 20-20,000 Hz.  Dogs, cats, and other animals can hear a much larger range.

Understanding frequency is important because when we hear a sound, we interpret frequency as pitch.  Sounds with a high frequency are heard as high pitch (like a violin), while sounds with a low frequency are heard as low pitch (like a string bass).  This is important because when our hearing is tested by an audiologist or hearing care provider, a full range of frequencies (or pitches) will be tested to paint a full picture of our hearing ability. 

Typically, when we lose our hearing due to the natural aging process, we lose high frequency sounds first.  Stay tuned to the Science Series for more on the differences between high frequency and low frequency sounds!