What’s the best way to block the sound of a voice?

Atif asked:

My neighbor talks loudly on the phone and I can’t sleep. What is the best method to block his voice noise?

Great question Atif! There are few things more distracting than hearing someone else’s conversation, and only hearing one side of a phone conversation is even worse. Even if you don’t want it to, your brain is trying to fill in the gaps and that can definitely keep you awake. So what’s the best way to avoid hearing your neighbor? Well, probably the very best way is to try talking to them. Failing that, though, you have three main options: isolation, damping and masking.

Ruído Noise 041113GFDL
So what’s the difference between them and what’s the best option for you? Before we get down to the nitty gritty I think it’s worth a quick reminder of what sound actually is: sound waves are just that–waves. Just like waves in a lake or ocean. Imagine you and a neighbor share a small pond and you like to go swimming every morning. Your neighbor, on the other hand, has a motorboat that they drive around on thier side. The waves the motorboat makes keep hitting you as you try to swim and you want to avoid them.  This is very similar to your situation: your neighbor’s voice is making waves and you want to avoid being hit by them.

Isolation: So one way to avoid feeling the effects of waves in a pond, to use our example, is to build a wall down the center of the pond. As long as there no holes in the wall for the waves to diffract through, you should be able to avoid feeling the effects of the waves. Noise isolation works much the same way. You can use earplugs that are firmly mounted in your ears to form a seal and that should prevent any sound waves from reaching your eardrums, right? Well, not quite. The wrinkle is that sound can travel through solids as well. It’s like we built our wall in our pond out of something flexible, like rubber, instead of something solid, like brick. As waves hit the wall the wall itself will move with the wave and then transmit it to your side. So you may still end up hearing some noises, even with well-fitted headphones.

Techniques: earplugs/earbuds, noise isolating headphone or earbuds, noise-isolating architecture,

Damping: So in our pond example we might imagine doing something that makes it harder for waves to move through the water. If you replaced all the water with molasses or honey, for example, it would take a lot more energy for the sound waves to move through it and they’d dissipate more quickly.

Techniques: acoustic tiles, covering the intervening wall (with a fabric wall-hanging, foam, empty egg cartons, etc.), covering vents, placing a rolled-up towel under any doors, hanging heavy curtains over windows, putting down carpeting

Masking: Another way to avoid noticing our neighbor’s waves is to start making our own waves. We can either make waves that are exactly the same size as our neighbor’s but out of phase (so when theirs are at their highest peak, ours is at our lowest) so they end up cancelling each other out. That’s basically what noise-cancelling headphones do. Or we can make a lot of own waves that all feel enough like our neighbor’s that when thier wave arrives we don’t even notice it. Of course, if the point it to hear no sound that won’t work quite as well. But if the point is to avoid abrupt, distracting changes in sound then this can work quite nicely.

Techniques: Listening to white noise or music, using noise-cancelling headphones or earbuds


So what would I do? Well, first I’d take as many steps as I could to sound-proof my environment. Try to cover as many of the surfaces in your bedroom as in absorbent, ideally fluffy, surfaces as you can. (If it can absorb water it will probably help absorb sound.) Wall hangings, curtains and a throw rug can all help a great deal.

Then you have a couple options for masking. A fan help to provide both a bit of acoustic masking and a nice breeze. Personally, though, I like a white noise machine that gives you some control over the frequency (how high or low the pitch is) and intensity (loudness) of the sounds it makes. That lets you tailor it so that it best masks the sounds that are bothering you. I also prefer the ones with the fans rather than those that loop recorded sounds, since I often find the loop jarring. If you don’t want to or can’t buy one, though, myNoise has a number of free generators that let you tailor the frequency and intensity of a variety of sounds and don’t have annoying loops. (There are a bunch of additional features available that you can access for a small donation as well.)

If you can wear earbuds in bed, try playing a non-distracting noise at around 200-1000 Hertz, which will cover a lot of the speech sounds you can’t easily dampen. Make sure your earbuds are well-fitted in the ear canal so that as much noise is isolated as possible. In addition, limiting the amount of exposed hard surface on them will also increase noise isolation. You can knit little cozies, try to find earbuds with a nice thick silicon/rubber coating or even try coating your own.

By using many different strategies together you can really reduce unwanted noises. I hope this helps and good luck!

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What’s the loudest / softest / highest / lowest sound humans can hear?

Humans can’t hear all sounds. Actually, not even most, in the grand scheme of things. Like how we can only see a narrow band of all wavelengths–hence “visible” light–we can also only hear some of the possible wavelengths. And wave heights. You might remember this from physics, but there are two measurements that are really important on a diagram of a wave: wave length and intensity. Like so:

CPT-sound-physical-manifestation
This should be bringing back flashbacks of asking if you were going to be able to use a formula sheet and a calculator.
So you’ve got the wavelength, which is the distance between two peaks or two troughs, and the amplitude, which is the distance between the mid-point of the wave and the tip of a peak. Which is all very well, but it doesn’t tell you much in the grand scheme of things, since most waves aren’t kind enough to present themselves to you as labelled diagrams. You actually have a pretty good intuitive grasp of the wavelength and amplitude of sound waves, though. The first is pitch and the second is what I like to refer to as “loudness”. (Technically, “loudness” is a perceptual measurement, not a… you know, this is starting to be boring.)

So there’s a limit in how loud and how soft a sound can be and a limit of how high and low a sound can  be. I’ll deal with loudness first, because it’s less fun.

Loudness

So we measure loudness using the decibel scale, which is based on human perception. Since 0 decibels is, by definition, the lower perceptual limit of sound for humans, the quietest sound humans can hear is just above that, which is around 20 micro-pascals of pressure. Of course, that’s healthy young humans. The older you get, the more your hearing range decreases, which is why your grandmother asks you to repeat yourself a lot. The loudest is just under 160 decibels, since exposure to a sound at 160 decibels will literally rip your eardrum. That’s things like being right under a cannon when it fires, standing next to a rocket when it launches or standing right next to a jet engine during take off, all of which tend to have other problems associated with them. So… avoid that.

Pitch

Pitch is a bit more interesting. Normal human hearing is generally between 20 hertz and 20 kilohertz–compare that to 15 to 200 kilohertz for dolphins and bats! (Because they both rely on sonar and echo-locution for hunting.) Just like hearing range for loudness, though, this gets narrower as you get older, particularly at the higher end of the range. Here’s a video that runs the gamut of the human hearing range (warning: you might want to turn your speakers down).

If you’re older than 25 (which is when hearing loss usually starts in the upper ranges) you probably couldn’t hear the whole thing. If you did, congratulations! You’ve got the hearing of a normal, young human.