Getting Started with Sound
Use the microphone to investigate the sound around you.
1. Press the Microphone icon (shown here) to open the Sound Intensity card.
2. Locate your microphone; it’s usually on the lower portion of your phone. Speak softly into the microphone, then loudly. Make observations in both meter and graph modes. The sound sensor is measuring the intensity, or loudness, of the sound in decibels (dB).
3. Now start a new project and try these experiments:
In addition to speaking into the phone, try clapping, stomping, singing, and whistling. Record each sound. How do the different runs of each sound compare to one another?
In graph mode, quietly hum a tune into the phone, gradually increasing the volume for 30 seconds. How does the graph change over time?
If you have access to multiple phones, try laying them along a long walkway in equal distances. Then speak from one end while recording. See how the volume changes across phones based on distance.
Explore the environment—where do you find the highest and lowest measurements?
Confused about loudness and frequency? Experiment with the sounds while viewing both the meter and graph modes.
What’s Going On?
Sounds are made by vibration. Your voice, for example, comes from vibrations in your throat’s vocal chords. These vibrations create alternating zones of high and low air pressure that travel outward—much like the expanding circular ripple made by a pebble thrown into a pond.
All sounds can be described in terms of their frequency and intensity.
Intensity is what you measure here with the Science Journal, in units of decibels (dB). Intensity, or loudness, depends on the distance that a vibrating object moves each time it vibrates; we hear greater intensity as increased loudness.
The frequency (also, pitch or tone) of a sound wave is equivalent to its rate of vibration. The faster an object vibrates, the higher the pitch of the resulting sound. The Science Journal does not measure frequency—only loudness.
The quietest sound that the average human ear can detect is defined as 0 dB. Ordinary conversation corresponds to about 60 dB, and sounds above about 140 dB are painful to the human ear. But sounds don't have to be painful to be harmful. Continued exposure to sounds of 90 dB—about the loudness of a vacuum cleaner—can eventually cause hearing loss.
The decibel scale is logarithmic, which makes for some trickiness: A sound source of 40 dB isn’t twice as intense as one with 20 dB—it’s 100 times more intense. Meanwhile, if one ringing alarm clock produces 70 dB, two ringing alarm clocks produce not 140 dB, but 73 dB. Like we said, it’s a strange scale.
- 10 dB rustling leaves
- 20 dB whispering at 5 feet
- 30 dB soft whisper
- 50 dB rainfall
- 60 dB normal conversation
- 90 dB blender
- 100 dB car without muffler
- 110 dB shouting in ear
- 120 dB thunder
- 130 dB jackhammer
- 140 dB airplane taking off
Here are a few of the many experiments you can do with your sound sensor.
Take a sound safari: Bring your sound sensor to especially quiet, noisy, or unusual places—a busy street, a park, the library, a concert hall. What do you notice? Or try sitting still somewhere for an extended period of time; how does the changing soundscape register on the decibel meter?
As sound travels, its intensity or loudness gradually weakens as the energy of a sound wave gets spread over a larger and larger area. Test this principle by doubling, then tripling your distance from a single, constant sound source, such as a buzzer in an otherwise quiet room. How does your measurement change?
(Note: Mathematically, we expect the dwindling of a sound’s intensity with distance to follow the inverse square law: If distance is doubled, loudness should drop to ¼ of its initial value. Does the law seem to hold true?)