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Audible Range and Beyond

Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz.

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Student-friendly explanation

Sounds below 20 Hz are called infrasound, and sounds above 20,000 Hz are called ultrasound. Humans normally cannot hear infrasound or ultrasound, but some animals can detect frequencies outside the human hearing range. Ultrasound is useful because it can travel in a directed way and reflect from small objects.

How to write this in exams

  1. 1

    Start with the exact idea

    Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz.

  2. 2

    Then show how to use it

    Compare the given frequency with 20 Hz and 20,000 Hz. Below 20 Hz means infrasound, within the range means audible, and above 20,000 Hz means ultrasound.

  3. 3

    Add one concrete example

    Bats use ultrasound for navigation, while elephants can communicate using low-frequency infrasound over long distances.

  4. 4

    Avoid this incomplete answer

    Wrong answer: 25,000 Hz is very loud sound. This is wrong because loudness depends on amplitude, while ultrasound is based on frequency.

Definition

Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz.

Example

Bats use ultrasound for navigation, while elephants can communicate using low-frequency infrasound over long distances.

Rule to remember

Human audible range: approximately 20 Hz to 20,000 Hz. Below 20 Hz is infrasound; above 20,000 Hz is ultrasound.

Memory hook

Under 20 is infra; over 20,000 is ultra.

Examples and method

Worked example

A frequency of 15 Hz is below the human audible range, so it is infrasound. A frequency of 30,000 Hz is above the range, so it is ultrasound.

Method to apply

Compare the given frequency with 20 Hz and 20,000 Hz. Below 20 Hz means infrasound, within the range means audible, and above 20,000 Hz means ultrasound.

Diagram support

A number-line diagram from below 20 Hz to above 20,000 Hz can show infrasound, audible sound, and ultrasound.

How CBSE asks it

Exams may ask classification of given frequencies or examples of animals and devices using infrasound or ultrasound.

Avoid common mistakes

Common confusion

Students often think ultrasound means very loud sound. It actually means sound with frequency above 20,000 Hz.

Common wrong answer

Wrong answer: 25,000 Hz is very loud sound. This is wrong because loudness depends on amplitude, while ultrasound is based on frequency.

Exam tip

Write the numerical range with units: 20 Hz to 20,000 Hz. Then classify below as infrasound and above as ultrasound.

Quick check

A sound has frequency 25,000 Hz. Can an average human hear it, and what is it called?

An average human cannot hear 25,000 Hz because it is above 20,000 Hz, so it is called ultrasound.

Study the audible range and beyond diagram carefully

Use the labelled diagram to keep audible range and beyond clear in short answers and revision.

What this diagram makes clear

This diagram keeps the labels and direction of audible range and beyond in the right order.

Where this helps in exams

Use this for labelled diagram work and short exam answers on audible range and beyond.

Revision cue

Revise audible range and beyond through the labels before writing the answer.

Answer writing and exam use

1-mark answer

Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz.

2-mark answer

Audible range is the range of frequencies that humans can normally hear, about 20 Hz to 20,000 Hz. Human audible range: approximately 20 Hz to 20,000 Hz. Below 20 Hz is infrasound; above 20,000 Hz is ultrasound. Bats use ultrasound for navigation, while elephants can communicate using low-frequency infrasound over long distances.

3-mark answer

Sounds below 20 Hz are called infrasound, and sounds above 20,000 Hz are called ultrasound. Humans normally cannot hear infrasound or ultrasound, but some animals can detect frequencies outside the human hearing range. Ultrasound is useful because it can travel in a directed way and reflect from small objects. Human audible range: approximately 20 Hz to 20,000 Hz. Below 20 Hz is infrasound; above 20,000 Hz is ultrasound. A frequency of 15 Hz is below the human audible range, so it is infrasound. A frequency of 30,000 Hz is above the range, so it is ultrasound. Exams may ask classification of given frequencies or examples of animals and devices using infrasound or ultrasound. Wrong answer: 25,000 Hz is very loud sound. This is wrong because loudness depends on amplitude, while ultrasound is based on frequency.
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