How Do Noise-Canceling Headphones Work?

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ThinkStock

Noise-canceling headphones seem like an oxymoron: a piece of audio technology that creates silence, rather than noise. They’re useful on planes, in crowded offices, and for light sleepers trying to catch some shut-eye in a thin-walled apartment, but how can a pair of headphones make sound disappear?

The first component of noise-canceling headphones’ formula for success is passive noise control, or the slightly more sophisticated technological equivalent of putting your hands over your ears to block out incoming noise. Certain ear buds or headphones are shaped specifically for the purpose of physically preventing sound waves from reaching your ears; these are the types generally marketed as “noise-isolating.” Whether by creating a closer external seal around your ears and using sound-absorbing material like high-density foam, as in the case of headphones, or simply fitting better into the shape of your ear canal, as in-ear buds do, noise-isolating accessories can block up to 20 decibels of background sound.

When 20 decibels of quiet won’t quite cut it, noise-canceling headphones step in with active noise control, or ANC. Pioneered by MIT graduate and Bose Corporation founder Amar Bose and inspired by the intolerable loudness of jet engines on a transatlantic flight, ANC technology is what distinguishes noise-canceling headphones from noise-isolating headphones. Rather than simply preventing unwanted outside sound from reaching a listener’s ear, ANC uses “destructive interference” to cancel out ambient noise. The process involves placing a microphone as close as possible to where sound will be entering the ear, which will pick up on the frequencies of the incoming noise; the headphones will then generate a frequency exactly 180 degrees out of phase with the unwanted noise—an “anti-noise” output that directly cancels out the input. While ANC is most effective at lower frequencies, noise-canceling headphones can reduce overall noise by up to 80 decibels—just about the amount of irritating background racket produced by commercial jet engines, so you can get at least some peace and quiet on your long-haul flight to wherever.

What's the Difference Between Tequila and Mezcal?

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iStock.com/mediaphotos

Aside from tacos, enchiladas, and other tasty tortilla-wrapped treats, tequila and mezcal are among some of Mexico’s best-known offerings in the food and beverage category. These tipples, made from the agave plant, are so embedded in the country’s culture that Mexico City even has a museum dedicated to the two drinks, and Jose Cuervo operates a "tequila train" to none other than the city of Tequila. These beverages can be used to make a variety of cocktails, from the tequila sunrise to the mezcalita, but unless you’re a bartender or a connoisseur of spirits, you might not know the difference between the two. Is mezcal just fancier tequila?

Not exactly. Tequila is a type of mezcal, but the reverse isn’t always true. It’s similar to the distinction between champagne and sparkling wine, in which the name of the beverage depends on whether it was produced in the Champagne region of France or elsewhere. While mezcal can be produced anywhere in Mexico, tequila is made in the Mexican state of Jalisco (though a few exceptions do apply).

Tequila and mezcal also differ in the ingredients from which they are derived. Mezcal can come from any of the dozens of agave plants—a type of desert succulent—that are grown throughout Mexico. Tequila is made specifically from blue agave and, depending on the variety and brand, a bottle will contain between 51 percent and 100 percent of the plant-based nectar. According to The Tierra Group, a wholesaler of agave products, blue agave nectar is especially sweet because it’s 80 percent fructose, per Mexico’s regulations.

Lastly, tequila and mezcal taste different because of the ways in which they are prepared. Mezcal tends to have a savory, smoky, earthy flavor because the agave hearts (or piñas) are left cooking for several days in a fire pit that has been lined with volcanic rock and covered with agave leaves and earth. The piñas destined to end up in tequila, on the other hand, are often cooked in a brick oven, then crushed up to extract the juice.

If you ever feel adventurous at the liquor store and decide to bring home a bottle of mezcal, just keep in mind that there’s a particular way to drink it. “The first mistake many people make is pouring mezcal in a shot glass and pouring it down their throat,” Chris Reyes, a mixologist at New York City’s Temerario bar and restaurant told Liquor.com. Instead, the spirit is best sipped in a clay cup known as a jicarita.

Some words of advice if you do go shopping for mezcal: If you ever see a worm at the bottom of the bottle, that means it’s probably not a very good mezcal, according to Reyes. By contrast, tequila bottles should never have worms in them (despite the common misconception). So if you’re looking to avoid invertebrate-infused concoctions at all costs, tequila is your best bet.

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Presidents Day vs. President's Day vs. Presidents' Day: Which One Is It?

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iStock

Happy Presidents’ Day! Or is it President’s Day? Or Presidents Day? What you call the national holiday depends on where you are, who you’re honoring, and how you think we’re celebrating.

Saying "President’s Day" implies that the day belongs to a singular president, such as George Washington or Abraham Lincoln, whose birthdays are the basis for the holiday. On the other hand, referring to it as "Presidents’ Day" means that the day belongs to all of the presidents—that it’s their day collectively. Finally, calling the day "Presidents Day"—plural with no apostrophe—would indicate that we’re honoring all POTUSes past and present (yes, even Andrew Johnson), but that no one president actually owns the day.

You would think that in the 140 years since "Washington’s Birthday" was declared a holiday in 1879, someone would have officially declared a way to spell the day. But in fact, even the White House itself hasn’t chosen a single variation for its style guide. They spelled it “President’s Day” here and “Presidents’ Day” here.


Wikimedia Commons // Public Domain

Maybe that indecision comes from the fact that Presidents Day isn’t even a federal holiday. The federal holiday is technically still called “Washington’s Birthday,” and states can choose to call it whatever they want. Some states, like Iowa, don’t officially acknowledge the day at all. And the location of the punctuation mark is a moot point when individual states choose to call it something else entirely, like “George Washington’s Birthday and Daisy Gatson Bates Day” in Arkansas, or “Birthdays of George Washington and Thomas Jefferson” in Alabama. (Alabama loves to split birthday celebrations, by the way; the third Monday in January celebrates both Martin Luther King Jr. and Robert E. Lee.)

You can look to official grammar sources to declare the right way, but even they don’t agree. The AP Stylebook prefers “Presidents Day,” while Chicago Style uses “Presidents’ Day.”

The bottom line: There’s no rhyme or reason to any of it. Go with what feels right. And even then, if you’re in one of those states that has chosen to spell it “President’s Day”—Washington, for example—and you use one of the grammar book stylings instead, you’re still technically wrong.

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