Name: このノイズは私を殺す！ (All This Noise Is KILLING Me!)
Uploaded: 2021-01-14T10:29:24.000Z
Duration: 13 min 20 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

転換語

Thanks to Brilliant for supporting this whole week of SciShow!

Go to Brilliant.org/SciShow to learn more.

Take a moment and listen carefully to all the noises around you.

If you hear your neighbor's music, the hum of a nearby highway, or the clatter of a passing train,

that's a sound that could be killing you.

Ok, not right away, and not all by itself,

but the sounds we hear every day  really do have effects on our health.

Not just our ears, but our hearts and even our brains.

So what we hear as sound is actually pressure waves traveling through the air around us.

We usually talk about that energy in a unit called the decibel,

but what decibels actually are is a little complicated.

Every decibel is actually one-tenth of a bel, named for the inventor of the telephone, Alexander Graham Bell.

And for weird historical reasons, the bel exists mainly in your physics textbook.

The decibel scale isn't linear, it's logarithmic.

As the number of decibels increases, the amount of sound energy goes up exponentially,

That means twice as many decibels isn't twice as noisy,

it's the difference between a loud conversation and the deck of an aircraft carrier.

Because of the way our brains process sound,

10 times more sound energy means we hear something as being only twice as loud.

So yeah, decibels are weird, but so are our brains.

Our ears also aren't equally sensitive to all frequencies,

so you might hear two sounds with the same power at totally different volumes.

So to correct for that and make loudness values more intuitive,

scientists use the A-weighted decibel scale.

Today, we're going to focus entirely on sounds that we can actually hear,

but we're also constantly hit with frequencies above and below that range.

Scientists know less about how these other kinds of sound affect us,

but it's still out there and still has energy, so we probably interact with it on some level.

For example there's some evidence that infrasound, below the range of our hearing,

might be part of what leads people to think they've seen stuff like ghosts.

Now, we all know that loud abrupt noises like firecrackers can damage our hearing.

But exposure to lower-level noise is still dangerous.

Even if it's not enough to make you go “ow, my ears.”

And it's not your eardrum that gets hurt.

That is, the tiny hair-like sensors called hair cells inside your ear.

The process that turns pressure waves in the air into the sounds in your brain is not simple.

It starts with your eardrum, which vibrates as each wave hits it.

Those vibrations shake three tiny bones inside your ear, which in turn shake the cochlea,

a pocket of fluid shaped kind of like a snail's shell.

And now comes the key part, embedded inside the cochlea are around 16,000 tiny hair cells.

As they move with the fluid, some hair cells generate electrical signals

that are carried by the auditory nerve to your brain.

The louder the noise, the more those hair cells move and the stronger the signals they produce.

But if there's too much movement, as in a sound that is too loud,

We can lose 30-50% of them before noticing our hearing start to decline.

Hair cells can bounce back to some degree, but too much damage will destroy them.

They don't regrow, and no treatment currently in use can bring them back.

Sometimes that hearing loss manifests itself as just being harder to hear.

Other times, you can get tinnitus, which sounds like a ringing in the ears that just won't go away.

15-20% of people will get at least mild tinnitus in their lives, often as a result of old age.

But persistent loud noises can bring on tinnitus more strongly and earlier in your life.

Like for example, if you were to tour in a rock band ever.

Fortunately, the CDC and the World Health Organization have figured out what sound levels are safe,

Basically, anything below about 85 decibels is safe for an eight-hour work day.

As we've explained, decibels aren't terribly intuitive.

But a good rule of thumb is that if you've got to raise your voice to talk to someone an arm's length away,

your environment is louder than eighty-five decibels.

A hockey game at 95 decibels is safe for only 47 minutes, a 100 decibel nightclub just 15,

and a 120 decibel drum set is okay for just 9 seconds a day.

So being a drummer definitionally is an unsafe work environment, so bless them all.

Of course, these values are averaged across lots of people in many different circumstances,

but every time you cross the threshold, you're taking a chance with your ear hairs.

One risky behavior many of us do every day is listening to music through our headphones.

At max volume, an iPhone puts out around 100 decibels,

which, again, is safe for only a few minutes a day.

To listen safely eight hours a day, you want to keep that slider around 70% or less.

Of course, we can't always avoid loud noises so easily.

Many critical jobs take place in loud environments or use noisy equipment,

And farmers and factory workers need jobs, and everybody needs the stuff they make.

So it's not like just avoiding that noise is an option.

And losing your hearing can have a big effect on your life, not just your ears.

Like, one study in 1999 found that people with some hearing loss and no hearing aids

were 50% more likely to be depressed than those who used aids to restore some hearing.

The sensory loss and social isolation caused by impaired hearing may also be a risk factor

for dementia and other cognitive disorders.

The thing is, even if you keep your music down and work somewhere quiet,

noise exposure is probably still affecting your life in ways you don't even realize.

Most people who live in cities are frequently exposed to noise levels above 50 decibels,

and even a background level of 60 is not unusual.

Cars, trains, and planes are the most common sources of these sounds.

50 or 60 decibels has no effect on your hearing,

but it does lead to a range of psychological responses, like getting annoyed.

Don't dismiss annoyance as a health consequence, by the way.

Noise annoyance has been linked with a range of physical, mental, and behavioral responses,

Annoyance is especially common when our expectations for the noise level are out of sync

For example, you probably wouldn't think twice about people chatting in the park,

but if it's happening in the library, that can drive you up the wall.

Some studies have shown that up to 40% of office workers are irritated by noise of 55 to 60 decibels,

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このノイズは私を殺す！ (All This Noise Is KILLING Me!)

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