"Sound Waves!" focuses on how we hear. Artifacts include a 1925 carbon hearing aid, a whale ear bone, and a working oscilloscope.

All sound is produced by vibrations, or sound waves, created by air pressure. The source of pressure pushes the air next to it, and then releases the pressure. These pressure variations cause waves, and our ear drums vibrate in response. The brain perceives these vibrations as sound.

How loud those sounds are depends on the strength of the vibration and how far away it is from the listener. The speed of the vibrations determines the pitch: fast vibrations produce high-pitched sounds and slow vibrations produce low pitches. Humans can hear frequencies of 16 vibrations per second to 20,000 vibrations per second (16 hertz - 20,000 hertz).

Because different parts of objects vibrate somewhat differently, few sounds are pure notes of one frequency. Extra frequencies or overtones explain why a piano and a flute playing the same note don't sound exactly alike.

Whale Ear Bone
Akutan Island, Alaska
Circa 1935

In humans, sound waves travel down the ear canal to vibrate a membrane (the ear drum) and hence the small bones of the inner ear. In whales, sound waves traveling through water cause small vibrations in the jawbone. An adjacent fat pad accentuates these vibrations and transmits the sound waves to the small bones of the inner ear. There is no external opening.

Electric Hearing Aid
Western Electric Company
1925

Before the discovery of electricity, the hard-of-hearing used ear trumpets, or large horns, to amplify sound. This first-generation electric hearing aid replaced the "ear trumpet". This model 6033A was powered by three D batteries.

Anatomy of the carbon microphone hearing aid:
Battery pack - The square box contains three D batteries.
Receiver - small round part (goes in ear). The receiver projects the sound.
Amplifier - This model is controlled by an in-line volume/power control.
Microphone - Large round part with the clip on the back (looks like a small speaker). It collects the sound. It would have been clipped to the shirt or to a set of straps under the shirt for more discretion.

Oscillograph
Allen Dumont Laboratories
Circa 1950

I can see what you're saying!

The Oregon State University chemistry department used this cathode ray oscillograph for several decades.

An oscilloscope allows us to observe the shape of electrical signals. The display is a plot of the signal amplitude versus time. A graph of Y versus X results. Both the time and amplitude scales are adjustable over a wide range of values. In this example a microphone converted sound waves to electrical waves, which we can observe on the screen.

Dr. Smithline Three-Tone Stethoscope
U.S.A.
Pat'd 1942

Dr. James Riley, one of the founders of Corvallis Clinic in Corvallis, Oregon, used this stethoscope in his practice from 1949-1984.

French physician R.T.H. Laennec invented the stethoscope in 1816. He used a paper tube to listen to his patients' heart and lungs.