Air & Sound
Grade Level: 6th -8th; Type: Physical Science
In this experiment students will examine the relationship between air pressure and the perceived loudness of sounds.
- Why do we take a deep breath before yelling/screaming?
- How do you increase the loudness of an instrument?
- What is the relationship between air pressure and sound level?
- How do megaphones/speaking trumpets work to amplify sound?
Have you ever been told to turn your music or the television volume down? In most cases it is to accommodate others, but exposure to prolonged loud noises can affect our hearing. Loudness is measured in decibels (dB). The decibel is a ratio between the loudness of a sound relative to a reference point, usually the sound pressure level of air. The human hearing range, with respect to loudness, is between 0 to greater than 130dB. Breathing is around 10dB and normal conversations range from 40-60dB. At around 85dB the chances of noise induced hearing loss increases. Prolonged exposure to sounds such as a motorcycle engine or kitchen blender can affect your perceived range of loudness and frequency (pitch). Some sounds can even produce pain such as an ambulance siren, around 130dB. In this experiment students will produce sounds and measure loudness in decibels. By examining the force it requires to create sounds of varying loudness students can then find the relationship between air pressure and loudness.
- Sound-level meter (found at electronic/computer stores or a physics laboratory)
- Musical instrument – woodwind or brass
- Megaphone/ speaking trumpet – construct with poster board
- Find a quite room to perform your sound level meter readings. Setup your meter so that the microphone is free from any obstruction. Produce all your sounds approximately 2 meters from the microphone. Setup a chair or marker so you can remember that position. Record the sound pressure levels in dB for each of your sounds.
- Speak at your normal volume.
- Speak at your normal volume but use a megaphone.
- Scream with a megaphone
- Whisper with a megaphone
- Play a note on the instrument of your choice at a moderately soft loudness (mp). What kind of breath do you need to take?
- Play that same note at a loud level (f). What kind of breath do you need to take?
- From your data figure out the relationship between air pressure and sound level.
Terms/Concepts: Sound wave; Decibel; Sound pressure level; Amplitude; Musical dynamics – piano, forte, mezzo-piano, mezzo-forte, pianissimo, fortissimo.
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