1.3 Introduction
1.3.1 Characteristics of Sound - Pressure Variations
1.3.2 Characteristics of Sound - Speed of Sound
1.3,3 Characteristics of Sound - Pitch Loudness and Timbre
1.3.4 Characteristics of Sound - Intensity
1.3.5 Doppler Effect
Unit 2.1 Multiple Choice Extended Questions - Waves
Unit 2.1 Multiple Choice Extended Answers-Waves
Unit 1.3 Multiple Choice Questions - Sound
Unit 1.3 Multiple Choice Answers - Sound

Unit 1.3 Sound Waves

Characteristics of Sound

1.3.4 Pitch

The fundamental frequency, measured in Hertz is main determinant in the perception of the pitch. The piano note middle C has a frequency of 261.63 Hz in the modern musical scale. Different musical instruments sounds are usually composed of many harmonic frequencies but the fundamental frequency gives us the basic quality we perceive as pitch and the characteristic sound of the instrument.

A normal ear can hear frequencies as low as 20Hz and as high as 20,000Hz. But very few people today can hear this range of frequencies as normal aging and exposure to normal sounds in everyday modern life tends to do at least some damage to most peoples hearing.

Distinguishing between frequency is better at low frequencies so musical instruments tend to have low fundamental frequencies.


In a general way the loudness of a sound is a reflection of the amplitude of the sound wave, as louder sounds tend to show larger variations in pressure generally . The energy carried by any wave is proportional to amplitude squared. So if the amplitude is doubled then the power increases by a factor of four (22). Sound intensity is defined to be the power per second reaching a unit area. Normal conversation has an intensity of about 10-6 Wm-2.

Perception of sound depends on the amount of energy reaching your ear but amplitude is affected by other factors like frequency since with a higher frequency wave the same amplitude hits your eardrum more often. 

The human ear can detect intensities as low as 10-12 Wm-2and as high as 103 Wm-2 (although this is loud enough to cause damage to the ear). This is a huge range so the logrithmic scale of loudness was created called the sound intensity level, measured in decibels (dB). This is explained further in the next section.


We can tell which instrument is playing a musical selection as the actual sound is a combination of harmonics and the final wave form depends on the interference of these. Similarily we can tell the difference between the voices of people.

Our perception of loudness is mainly determined by the intensity of the sound which is the power per square meter. Frequency and waveform of the sound influence the perception of loudness.

Our perception of pitch is mainly determined by the fundamental frequency Frequency and waveform of the sound influence the perception of pitch.

Timbre is determined by waveform of the modified fundamental frequency after the interference from other frequencies present and their phases as influence by intensity.

1. Comment on the statement "To be heard, a sound wave must cause a relatively large displacement of air (for instance, at least a cm or more) around an observer's ear."

(a) Answer = .....

Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.