Technology · Level 3 · 176 words

The Microphone That Listens Through Wood

Original passage © Studio AM, written for Fluency.

An ordinary microphone mainly responds to pressure changes traveling through the air. A contact microphone takes another route. Fastened to a wooden panel, metal rail, or instrument body, it responds directly to vibration in that surface. A light tap on the far end can therefore become a strong electrical signal, while nearby conversation may sound faint.

Many contact microphones contain a thin piezoelectric element. When the surface bends or shakes, it strains this material. The material produces a small electric charge that follows the motion. An amplifier strengthens that changing signal, and a speaker turns it back into audible sound.

Placement matters because a surface does not vibrate equally everywhere. Near a rigid support, movement may be small; near a flexible section, it may be larger. Wood, glass, and steel also favor different patterns of vibration. Sound artists use this difference to reveal hidden textures, from a bridge cable's hum to the scratch of a pencil across a table. The device does not merely hear an object. Its attachment makes the object part of the microphone.

Comprehension questions

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4 questions
1. What is the main idea of the passage?

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D. A contact microphone converts an attached surface's vibrations into an electrical signal, making material and placement part of what it hears.
The passage traces surface motion through a piezoelectric element and emphasizes how attachment location and material shape the result.

2. Why might a flexible section produce a stronger contact-microphone signal than a point near a rigid support?

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A. The flexible section may move more and place greater changing strain on the sensing element.
The text links larger surface movement with strain in the piezoelectric material, which produces the electrical signal.

3. What does “rigid” mean in the phrase “Near a rigid support”?

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B. stiff and not easily bent
The passage contrasts the rigid support’s small movement with a flexible section’s larger movement, indicating stiffness.

4. What strengthens the small changing electrical signal?

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C. an amplifier
The second paragraph states that an amplifier strengthens the changing signal before a speaker makes it audible.

Source: Written for Fluency. Original passage © Studio AM, written for Fluency.