Our perception of pitch and its other properties is determined by the characteristics of an acoustic wave. These are the same characteristics that are inherent in any mechanical wave, namely the period, frequency, amplitude of oscillations. Subjective sensations from sound do not depend on the length and speed of the wave. In the article we will analyze the physics of sound. Height and timbre - how are they determined? Why do we perceive some sounds loud, while others - quiet? Answers to these and other questions will be given in the article.
Pitch
What determines the height? To deal with this, we’ll conduct a simple experiment. Take a flexible long ruler, preferably aluminum.
Press it to the table, pulling out the edge. We hit with a finger on the free edge of the ruler - it will tremble, but its movement will be silent. Now we will move the ruler closer to ourselves, so that a smaller part protrudes beyond the edge of the countertop. Hit the ruler again. Its edge will vibrate much faster and with less amplitude, and we will hear a characteristic sound. We conclude: in order for sound to arise, the oscillation frequency must be no less than a certain value. The lower limit of the audio frequency range is 20 Hz, and the upper is 20,000 Hz.
Continuing the experience. We will shorten the free edge of the ruler even more, set it in motion again. It is noticeable that the sound has changed, has become higher. What does the experiment indicate? He proves the dependence of the pitch on the frequency and amplitude of the oscillations of its source.
Sound volume
To study the volume, we will use a tuning fork - a special tool for studying the properties of sound. There are tuning forks with different lengths of legs. They vibrate when hit with a hammer. Large tuning forks oscillate more slowly and make a low sound. Small ones vibrate often and differ in pitch.
Hit the tuning fork and listen. The sound weakens over time. Why is this happening? The sound volume attenuates due to a decrease in the amplitude of oscillation of the legs of the device. They vibrate not so much, which means that the amplitude of the vibration of the air molecules also decreases. The lower it is, the quieter the sound comes out. This statement is true for sounds of the same frequency. It turns out that both the height and volume of the sound depend on the amplitude of the wave.
The perception of sounds of different volumes
From the above, it seems that the louder the sound, the more clearly we hear it, the more subtle changes we can catch. This is not true. If you make the body oscillate with a very large amplitude, but low frequency, then such a sound will be poorly distinguishable. The fact is that in the entire range of audibility (20-20 thousand Hz), our ear best distinguishes sounds around 1 KHz. Human hearing is most sensitive to these frequencies. Such sounds seem to us the loudest. Alerts, sirens are tuned precisely to 1 KHz.
Volume level of different sounds
The table shows common sounds and their volume in decibels.
| Type of noise | Volume level, dB |
| Calm breathing | 0 |
| Whisper, rustle of foliage | ten |
| Ticking clock located at a distance of 1 m | thirty |
| Ordinary conversation | 45 |
| The noise in the store, talking in the office | 55 |
| Street sound | 60 |
| Loud conversation | 65 |
| The noise of the printing shop | 74 |
| A car | 77 |
| Bus | 80 |
| Machine tool | 80 |
| Shout | 85 |
| Silenced motorcycle | 85 |
| Lathe | 90 |
| Metallurgical enterprise | 99 |
| Orchestra, subway car | 100 |
| Compressor station | 100 |
| Chainsaw | 105 |
| Helicopter | 110 |
| Thunder | 120 |
| Jet engine | 120 |
| Riveting, chopping steel (such a volume is equal to the pain threshold) | 130 |
| Airplane at start | 130 |
| Rocket launch (causes shell shock) | 145 |
| Sound from firing a medium-caliber rifle near a muzzle (leading to injuries) | 150 |
| Supersonic aircraft (such a volume leads to injuries and pain shock) | 160 |
Timbre
The height and volume of sound are determined, as we found out, by the frequency and amplitude of the wave. The timbre is independent of these characteristics. Let's take two sources of sound of the same pitch to understand why they have a different timbre.
The first instrument will be a tuning fork, sounding at a frequency of 440 Hz (this is a note for the first octave), the second is a flute, and the third is a guitar. With musical instruments we reproduce the same note on which the tuning fork sounds. All three have the same pitch, but still sound different, differ in timbre. What is the reason? It's all about the features of the sound wave. The movement that an acoustic wave makes of complex sounds is called non-harmonic oscillation. The wave in different areas fluctuates with different strength and frequency. These additional sounds, which differ in volume and pitch, are called overtones.
Do not confuse pitch and timbre. The physics of sound is such that if we “mix” additional, higher ones into the main sound, we get what is called a timbre. It is determined by the volume and number of overtones. The frequency of overtones is a multiple of the frequency of the lowest tone, that is, it is more than an integer number of times - 2, 3, 4, etc. The lowest tone is called the main tone, it determines the pitch, and overtones affect the timbre.
There are sounds that do not contain overtones at all, for example a tuning fork. If you depict the movement of its sound wave on the graph, you get a sinusoid. Such oscillations are called harmonic. Tuning fork produces only the main tone. This sound is often called boring, colorless.
When a sound has a lot of high-frequency overtones, it turns out to be sharp. Low overtones give the sound softness, velvety. Each musical instrument, voice has its own set of overtones. It is the combination of the fundamental tone and overtones that gives a unique sound, gives the sound a certain timbre color.