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Thermophone

Thermophone is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Thermophone rather than just read about it. In short: A thermophone is a type of transducer that converts an electrical signal into heat, which then becomes sound. It can be thought of as a type of loudspeaker that uses heat fluctuations to produce sound, instead of mechanical vibration.

Thermophone — main illustration
Thermophone — illustration

Key takeaways

  • Thermophone belongs to engineering; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Thermophone to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Thermophone from memory before moving on to harder problems.

Reference excerpt

A thermophone is a type of transducer that converts an electrical signal into heat, which then becomes sound. It can be thought of as a type of loudspeaker that uses heat fluctuations to produce sound, instead of mechanical vibration. The basic principle of the thermophone has been known since the 19th century. Thermophones have been used to calibrate acoustical apparatus (like microphones) since the 20th century. In recent years, the name thermoacoustic speaker has also been used.

Beginnings

Thermoacoustics is the study of the interaction between heat and sound. It is the basis of the thermophone. Byron Higgins in 1802 reported "singing flames" which occurred when the necks of jars were put over a hydrogen gas flame. Sondhauss (1850) and Rijke (1859) performed further experiments. A theory of thermoacoustics was produced by Lord Rayleigh in 1878. The theory and practice of creating sound with electric heat emerged in the late 19th century. In 1880, William Henry Preece observed that, upon connecting a microphone transmitter to a platinum wire, sounds were produced:

...the sonorous effects were most marked and encouraging, when the microphone transmitter M was spoken into. The articluation, though muffled, was clear, and words could easily be heard. In 1917, Harold D. Arnold and Irving B. Crandall of Bell Labs developed a quantitative theory for the thermophone. Since then, thermophones have been used as a precision device for microphone calibration. However, they did not see widespread use elsewhere due to their poor efficiency.

Description When alternating current is passed through a thin conductor, that conductor periodically heats up and cools down following the variations in current strength. This periodic heating and cooling creates temperature waves which the conductor propagates into the surroundings. As the temperature waves propagate away from the conductor, the thermal expansion and contraction of the transmission medium (e.g. air) produces corresponding sound waves. An optimal thermophone is made of a conductor which is very thin and has a small heat capacity.

Modern thermophones In 1999, Shinouda and others presented a porous doped sillicon thermophone for ultrasonic emission. In 2008, Xiao et al. reported a thermophone made of carbon nanotubes. Since then, there has been a resurgence of research into thermophones and thermoacoustics. New materials for thermophones are being explored, and thermophones have been created using VLSI processes (like integrated circuits are).

References

Illustrations

Thermophone: A diagram of a simple thermophone, from a 1917 Bell Labs paper
A diagram of a simple thermophone, from a 1917 Bell Labs paper
Thermophone: E.C Wente, a researcher of thermophones in the 20th century[2]
E.C Wente, a researcher of thermophones in the 20th century[2]

Worked examples

Example 1 — a first encounter with Thermophone

Start with the simplest possible case. Write down what Thermophone claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Thermophone before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Thermophone ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Thermophone

In research
Thermophone appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Thermophone in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Thermophone is common in secondary-school and first-year university syllabi. It links to neighbouring topics 19th-century inventions, Electrical components, Solid state engineering, so understanding it makes those chapters shorter.
In everyday life
Look for Thermophone outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Thermophone in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Thermophone means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Thermophone out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Thermophone in simple terms?

A thermophone is a type of transducer that converts an electrical signal into heat, which then becomes sound. It can be thought of as a type of loudspeaker that uses heat fluctuations to produce sound, instead of mechanical vibration.

Why does Thermophone matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Thermophone?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Thermophone.

Tags

  • 19th-century inventions
  • Electrical components
  • Solid state engineering
  • Transducers

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