In reality, a 40 dB sound is 100 times as loud as a 20 dB sound, but it seems twice as loud. The decibel scale is actually a pretty accurate representation of how the human auditory system perceives sound. Conversational speech is at about 60-70 dB a whisper is around 20 dBĤ. A sound of 30 dB is ten times as loud as 20 dB, and 100 times as loud as 10 dB.ģ. Every increase of 10 dB is a tenfold increase. A sound of 23 dB is twice as much energy as a sound of 20 dB.Ģ. Every increase of 3 dB is a doubling of the sound pressure level (twice as many micropascals). After that, there's way more math than I'm interested in writing about (you can find it quite easily with a Google search), but you'll be fine as long as you remember a few basic ideas:ġ. The level at which a sound becomes audible to a young, average, healthy ear is designated as zero decibels (0dB). The solution to these problems is the decibel scale. Once numbers get that big, they pretty much lose their meaning to most of us. For example, a jet airliner taking off is around 145 dB that's more than one hundred trillion times as loud as the quietest sound an average young person with no hearing loss can hear. Finally, the range from the quietest audible sound we can hear to the kind of really super-loud sound that would destroy your hearing instantly is so huge as to be incomprehensible if expressed in linear terms (like number of micropascals). For some reason, that's just not the way our auditory system works. In addition, doubling the strength of a sound in micropascals results in a sound that we perceive as being noticeably louder, but not twice as loud. For one thing, the number of micropascals at which a sound is audible differs according to frequency. We can also measure sound pressure (the force exerted by a sound wave) in micropascals, but that gets tricky. This is where the decibel scale comes in. However, since sound waves are not visible, we measure and describe them in terms of the force they exert rather than their physical size. The amplitude of ocean waves is measured in the distance from peak to trough. If the amplitude is low enough, it does not move the ear drum enough for us to notice it. Sound waves of higher amplitude exert more force on your ear drum, and are perceived as louder, while low amplitude sound waves exert less force and are perceived as quiet sounds. If you stand on the North Shore of Hawai'i in the winter, you are likely to witness waves large enough, and strong enough, to push a person on a surfboard-or to slam a clueless graduate student from Indiana onto the beach so hard that he spends what feels like an eternity writhing on the sand, convinced he'll never breathe again, while nearby teenage girls in bikinis laugh at him. These waves will be quite a bit bigger, and if you dangle your hand in the water as they arrive, you'll definitely feel them, and they may even push your hand back and forth. Now, instead of tossing a pebble, visualize yourself setting up a large, medieval-style trebuchet on the shore and tossing a Volkswagen into the middle of the pond (visualize removing the battery first, and draining all the gasoline, oil, and brake fluid-we don't want to visualize poisoning the fish). If you put your finger into the water as the ripples from the pebble arrive at the bank, you'll barely feel them. The bigger a wave is, the more force it exerts on whatever it hits. The size of a wave is called its amplitude. In the world of sound, frequency corresponds with pitch we perceive a high frequency sound as having a high pitch, and a low frequency sound as having a low pitch.Īnother thing you'll notice is that the waves are fairly small. The number of waves that hit a fixed point (like the bank) within a given time period is called the frequency. One of the things you might notice is that the distance between the waves is pretty regular, and that they're all traveling at the same speed, so the time from the arrival of one wave on the bank where you're standing to the arrival of the next is fairly predictable. You toss a pebble into the middle of the pond and watch the waves ripple outward from the place the pebble strikes the surface. You are standing on the bank of a calm pond. The human auditory system is well-adapted to detect sound waves in air, but to understand how sound waves work, it may be helpful to think of wave action in water, since that's something most of us have had a chance to watch with our eyes. If you want to be an audiologist, then instead of reading my web site, you need to enroll in a graduate program in audiology. Unless you want to be an audiologist, that is. There's a lot more to it than I'm presenting here, but this should be enough for you to understand what you need to know about the decibel scale in relation to hearing loss. It's a logarithmic scale, so it's a little tricky to understand sometimes. The decibel scale is what we use to measure how loud a sound is.
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