What Is the Quietest Sound a Human Can Hear?

What's the Quietest Sound a Human Can Hear
June 05, 2020

Have you ever been sitting on the couch with your dog or cat, watching a movie comfortably, when their ears perk up? What could they have possibly heard that captured their attention? They probably heard something outside that you just weren’t physically able to pick up.

Just as we humans can only see the “visible” wavelengths of light in the vast electromagnetic spectrum, we can only hear a small portion in the auditory spectrum.

So what is the quietest sound a human can hear? First, let’s take a look at how we measure sound intensity — decibels.

What Is a Decibel?

Scientists at Bell Telephone Laboratories coined the word decibel in honor of their namesake, inventor Alexander Graham Bell. As a unit of measurement, though, decibels mean nothing on their own. They’re a ratio used as a reference point. For example, it’s some current quantity we wish to define, or “x,” as it relates to our predefined “R” quantity. So then, we must know what R is. But, in this case, it’s the smallest sound the average adult can detect at 1 kilohertz, which can change from person to person.

Typically, zero decibels sound pressure level (SPL) corresponds to 0.000002 Pascals — a measure of vibration or pressure waves that we really hear. So then, zero decibels is the smallest level of sound our ears can detect!

So there’s our answer, in its simplest form. Right?

Wrong. Well, Sort Of

The quietest sound a person can hear is not always 0 dSPL. This absolute threshold of the human hearing range is an average — some people may hear much quieter sounds, while others may be harder of hearing.

Plus, this 0 threshold only applies to tones measured at 1 kHz. This is problematic because our ability to hear doesn’t only derive from the intensity of the sound, but also with the sound’s frequency, or pitch. Human hearing becomes much less sensitive at frequencies below 1 kHz, making the sound pressure we can hear increase 1,000 times. However, for frequencies just above 1 kHz, our hearing threshold can be -9 dbSPL.

So the quietest sound a human can hear, while officially 0 decibels, is actually dependent on the sound’s pitch and the person’s ability to hear.

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No matter the level of decibels or herds… er, hertz, we won’t steer you wrong. Contact us today with any questions you may have about our products.