It was probably all those concerts you attended when you were in your teens and early 20s. Or all the clubs, with that thumping, thumping, thumping bass. Or maybe it was the hours and hours plugged into your iPod with the volume cranked up, singing along to the bands you listened to back in the day.

Hearing loss — sorry to sound old — is real, something that happens even to those who didn't spend large chunks of their 20s in loud bars or trapped underneath the latest headphones or earbuds. It's measurable. It has a name.

Presbycusis, otherwise known as age-related hearing loss. But don't fret: A little hearing loss, especially when it comes to high-pitched sounds, shouldn’t be curl-up-in-a-ball depressing. It’s natural. It’s common.

The normal range of human hearing, from low-sounding frequencies to the high dog-whistle stuff, is about 20 hertz (cycles per second) to 20,000 hertz (or 20 kilohertz). As we grow older, we can lose the ability to hear both the lowest and the highest frequencies. The most drastic losses come, first and most often, on the high end of things.

Many teenagers can hear very close to what is considered the 20 kilohertz high-end threshold. Many people under 25 can hear up to the 14 kilohertz or 15 kilohertz tones. As you get older, though, it all starts sliding downhill.

The good news is that those high tones (and even the super-low ones) are not ones we hear every day. They're not ones we need to hear. So even though a young, healthy human can detect tones from 20 hertz to 20,000 hertz, "frequencies between 500 and 4000 hertz are most important for speech processing," according to a review conducted by the Agency for Healthcare Research and Quality of the U.S. Department of Health and Human Services.

So if you've crossed 25 and you can't hear that 17 kilohertz mosquito-y sound? No need to curl up just yet. "I think it's really natural," says audiologist Anne Oyler, the associate director for Audiology Professional Practices for the American Speech-Language-Hearing Association (ASHA). "I don't think it's cause for concern."

Take a test

A host of online hearing tests, many of them conveniently sponsored by hearing aid manufacturers, can show you just what you're missing. (A couple apparently not sponsored are here and here.)

"The good thing about [these tests] is that they’re providing access for a lot of people," Oyler says. "If you are having difficulty hearing already [...] then taking one of these tests might just confirm your suspicion, and maybe you want to follow up and have your hearing tested [with a professional]."

Warning #1: Watch your volume when you take those tests. Didn't you learn anything from those concerts?

Warning #2: If you're over 30, and you've gone through more than a couple pairs of headphones in your life, the tests can get a little depressing.

Volume, of course, is a factor in all this testing, too.

Generally, you're considered to have normal hearing if you can detect sounds from 250 hertz to 8,000 hertz at 25 decibels or lower. A whisper is about 20 decibels. That concert you heard back when you were 20? That probably came in around 80-120 decibels, depending on how close to the speaker tower you were.

Another factor: The softer the sound is, the more the ear loses the lower, bass frequencies. "[If] you are listening to a recording of an orchestra and you turn the volume down, you will find that the bass instruments are less and less prominent," says a study from the Department of Physics and Astronomy at Georgia State University. "This is the purpose of the so-called 'loudness contours' on audio amplifiers; they allow you to boost the bass frequencies when you are listening at low sound levels."

So you may not be able to hear that blackboard-screeching tone at the upper end of the scale any more and you may be losing the bass, too, especially when you turn the volume down. Blame aging. Blame all that loud music. (Anything over 85 decibels for more than a minute can potentially damage hearing, according to the Centers for Disease Control and Prevention.)

But know that you're not alone if your ears aren't what they used to be. Know that all those Beats-wearing whippersnappers aren't listening to spine-decalcifying 18,000 hertz tones anyway, even if they can hear them.

And know that if they're anything like you, they've got theirs coming, too. It happens to the best of us.

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