Hearing damage and risk threshold · no pain does not mean safe

The ringing that went away

0:00After a night of loud music your ear keeps ringing. The next morning that ringing is gone, so it has recovered. Most people think so. It isn't true.

Where the damage sits

0:15In your inner ear there are thousands of hair cells that turn sound into signals for your brain. Sound that is too loud damages those hair cells. They do not grow back. A broken bone heals, a wound closes, but these hair cells do not come back.

0:31What is gone is gone. And you do not feel it happening. There are no pain nerves in them. That ringing is not the damage itself, it is your ear being briefly overloaded. But in that same night connections to your auditory nerve are lost too, and those do not come back.

0:50An ordinary hearing test does not see that, and that is why the next morning it feels as if nothing happened.

Eighty and one hundred and twenty

0:58Now two numbers, and the point is that they are two different numbers. The first is one hundred and twenty decibels: the threshold of pain. Above it sound hurts, and then you know. The second is eighty decibels: the risk threshold. From there on sound can damage your hearing.

1:16Between them lie forty decibels, and in that whole range sound does damage without letting you notice anything. No pain, no warning, impossible to repair afterwards. "It did not hurt" tells you nothing about whether it was safe. At eighty decibels you may stay in it for eight hours a day.

1:37What do you think: how long at eighty-three?

Why three decibels halves the time

1:44Four hours. And you can work that out yourself. Three decibels more means twice as much sound. What damages your ear is not the loudness alone and not the time alone, but the two together: how much sound energy has gone through in total. If it becomes twice as strong, it may last only half as long to end up at the same amount.

2:06Three decibels more, time divided by two.

Eighty-nine decibels

2:10Say you measure eighty-nine decibels in the sports hall during a tournament. You start at eighty, and that goes with eight hours. Eighty-three is one step: four hours. Eighty-six, two hours. Eighty-nine, one hour. Eighty-nine decibels, one hour.

2:27If you get two hours, you have counted two steps of three decibels instead of three.

How loud it may be at a party

2:33In the Netherlands it is agreed how loud amplified music at an event may be: one hundred and three decibels, averaged over a quarter hour. From eighty to one hundred and three is twenty-three decibels more, so halving almost eight times. Of those eight hours about two and a half minutes remain.

2:54That is a different rule from the eight hours per working day. But it does tell you where you stand if you stand at the front.

How you see that something is gone

3:02What is left of your hearing, you can measure. In a hearing test you get beep after beep, each at its own frequency, and each tone gets louder until you only just notice it. That way it is recorded per frequency how loud it had to be. What you get is a graph of your own threshold of hearing.

3:21For someone who hears well that line runs neatly along the top. With damage it drops, and not equally everywhere: there is often a dip in it, somewhere around a few thousand hertz. That is exactly where your ear is most sensitive, so that is where the sound arrives hardest and the hair cells break first.

3:42Getting older does something else: it nibbles at the highest tones, from the right. A dip in the middle comes from somewhere else. Here are two of those graphs. Which of the two would make you think of headphones, and which of age?

Fifteen decibels is a factor of thirty-two

4:02What can you do about it? Turning it down helps most, because you tackle the source. Standing further away helps too. Good hearing protection takes about fifteen decibels off, and that sounds like little. Fifteen decibels is five steps of three.

4:19Each step doubles the time, so doubling five times is a factor of thirty-two. That sports hall goes from one hour to thirty-two hours. The other way round gives the same: eighty-nine minus fifteen is seventy-four, and that is below the risk threshold of eighty.

4:37Two routes, the same answer. If you get five hours, you have multiplied by five instead of doubling five times.

Summary

4:47Four things. One: hearing damage sits in the hair cells in your inner ear, they do not grow back, and you feel nothing while it happens. Two: the threshold of pain is around one hundred and twenty decibels, the risk threshold at eighty. Between them lie forty decibels in which sound does damage without warning.

5:06Three: at eighty decibels you may stay in it for eight hours a day, and every three decibels more halves that time. Four: in an audiogram you see that damage again, as a dip in the middle. Dropping on the right-hand side goes with getting older.

The two questions

5:24Two questions. First question: at ninety-five decibels, how long may you stand there by this rule? Second question: someone says it can do no harm as long as it does not hurt. Is that right?

The answers

5:39The first: from eighty to ninety-five is fifteen decibels, so five steps of three. Starting from eight hours, halve five times: four, two, one, a half, a quarter. A quarter of an hour. The second: no. Pain only starts around one hundred and twenty decibels, damage already at eighty.

5:57Everything in between does its work in silence, so your ear does not warn you.

Closing

6:03You can now work out how long you may stay somewhere, and you know why the ringing goes away while the damage stays. On the channel there is a separate video about why a sound that is twice as strong does not sound twice as loud.