Start by getting to know your decibel meter app. For a more detailed explanation, see the links in the More to Explore section. Human perception of “loudness” roughly corresponds to the sound pressure level, although it also depends on the sound’s frequency. All of these quantities can be expressed in decibels, and you might see a subscript after the “dB” indicating which one is being measured (like dB SPL). There are different physical quantities related to sound that can be measured, like sound pressure level (measured in pascals), sound intensity (measured in watts per square meter), or the electronic signal used to generate sound in a speaker (measured in volts). *The complete explanation is a little more complicated than this. So if you want to explore the sounds of the world around you – all you need is your phone! However, modern smartphones (which already contain built-in microphones) have apps available that will display the sound reading in dB directly on your phone’s screen. What does all this have to do with your phone? Previously, if you wanted to measure sound levels, you would need to buy a standalone decibel meter – a device with a microphone and a screen that would display the sound level in dB. Note that the loudness of a sound also depends on your distance from the source of the sound (it will get quieter as you get farther away) – so to do a direct comparison of different sounds, you have to keep this distance constant. That’s why hearing protection is recommended for people using equipment like lawnmowers. Sound levels above 80 dB can cause hearing damage over long periods of time, and sound levels above 120 dB can cause immediate damage. Sound confusing? Don’t worry – here’s a list of reference sounds and their approximate decibel levels: 0 dB doesn’t mean there is no sound at all – rather, 0 dB is chosen as a reference level at the threshold of human hearing. A 40 dB sound is twice as loud as a 30 dB sound, and four times as loud as a 20 dB sound, etc. For example, a 30 dB sound is twice as loud as a 20 dB sound. What does that mean? For every increase of 10 dB, the loudness of the sound doubles. The decibel scale is a little unusual because it is logarithmic, not linear. We measure the loudness of sound in decibels, abbreviated dB *. Sound is measured using a unit you’re probably a little less familiar with. But how do we measure sound? You might describe a sound as “quiet as a whisper” or “louder than a jet engine,” but you probably don’t use a number. 
You wouldn’t bat an eye at someone saying they are 6 feet tall or that it’s 70 degrees outside. You’re probably familiar with the units we use to measure everyday quantities like length or temperature.
To find a science fair project that is just right for you, browse our library of over 1,200 Science Fair Project Ideas or use the Topic Selection Wizard to get a personalized project recommendation. Good science fair projects have a stronger focus on controlling variables, taking accurate measurements, and analyzing data. This activity is not recommended for use as a science fair project.
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