Our perception of the pitch of a sound and its other properties is determined by the characteristics of the acoustic wave. These are the same characteristics that are inherent in any mechanical wave, namely the period, frequency, amplitude of oscillations. The subjective sensations of sound do not depend on the length and speed of the wave. In the article we will analyze the physics of sound. Pitch and timbre - how are they determined? Why do we perceive some sounds as loud and others as quiet? The answers to these and other questions will be given in the article.
Pitch
What determines the height? To understand this, let's do a simple experiment. Let's take a flexible long ruler, preferably aluminum.
Let's press it to the table, pushing the edge strongly. Let's hit the free edge of the ruler with your finger - it will tremble, but its movement will be silent. Now let's move the ruler closer to us, so that its smaller part protrudes beyond the edge of the countertop. Let's hit againruler. Its edge will vibrate much faster and with a smaller amplitude, and we will hear a characteristic sound. We conclude that in order for sound to occur, the oscillation frequency must be at least a certain value. The lower limit of the audio frequency range is 20 Hz, and the upper limit is 20,000 Hz.
Let's continue the experiment. Shorten the free edge of the ruler even more, set it in motion again. It is noticeable that the sound has changed, it has become higher. What does the experiment show? He proves the dependence of the pitch of the sound on the frequency and amplitude of the oscillations of its source.
Sound volume
To study loudness, we will use a tuning fork - a special tool for studying the properties of sound. There are tuning forks with different leg lengths. They vibrate when struck with a hammer. Large tuning forks oscillate more slowly and produce a low sound. The small ones vibrate frequently and differ in pitch.
Let's hit the tuning fork and listen. The sound weakens over time. Why is this happening? The volume of the sound is attenuated due to a decrease in the amplitude of the oscillation of the legs of the device. They do not vibrate so strongly, which means that the amplitude of vibrations of air molecules also decreases. The lower it is, the quieter the sound will be. This statement is true for sounds of the same frequency. It turns out that both the pitch and the volume of the sound depend on the amplitude of the wave.
Perception of sounds of different volumes
From the above, it seems that the louder the sound, the clearer wewe hear, the more subtle changes we can perceive. This is not true. If the body is made to oscillate with a very large amplitude, but a 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. Warning signals, sirens are tuned exactly to 1 kHz.
Volume level of different sounds
The table shows common sounds and their loudness in decibels.
| Type of noise | Volume level, dB |
| Calm breathing | 0 |
| Whisper, rustle of leaves | 10 |
| Ticking of a clock 1 m away | 30 |
| Regular conversation | 45 |
| Noise in the store, conversation in the office | 55 |
| Sound of the street | 60 |
| Loud talk | 65 |
| Print Shop Noise | 74 |
| Car | 77 |
| Bus | 80 |
| Engineering machine tool | 80 |
| Loud scream | 85 |
| Motorcycle with silencer | 85 |
| Lathe | 90 |
| Metallurgical plant | 99 |
| Orchestra, subway car | 100 |
| Compressor station | 100 |
| Chainsaw | 105 |
| Helicopter | 110 |
| Thunder | 120 |
| Jet engine | 120 |
| Riveting, cutting of steel (this volume is equal to the pain threshold) | 130 |
| Airplane at launch | 130 |
| Rocket launch (causes shell shock) | 145 |
| Sound of a medium caliber shotgun near the muzzle (causes injury) | 150 |
| Supersonic aircraft (this volume leads to injury and pain shock) | 160 |
Timbre
The pitch and loudness of the sound are determined, as we found out, by the frequency and amplitude of the wave. Timbre is independent of these characteristics. Let's take two sound sources 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 the note for the first octave), the second - a flute, the third - 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 vibrations of the sound wave. The movement that an acoustic wave of complex sounds makes is called a non-harmonic oscillation. The wave in different areas oscillates with different strength and frequency. These additional overtones that differ in volume and pitch are called overtones.
Don't confuse pitch and timbre. The physics of sound is such that if“mix” additional, higher ones to the main sound, we get what is called a timbre. It is determined by the volume and the number of overtones. The frequency of the overtones is a multiple of the frequency of the lowest tone, i.e. it is an integer number of times greater - 2, 3, 4, etc. The lowest tone is called the main tone, it is it that determines the pitch, and the overtones affect the timbre.
There are sounds that do not contain overtones at all, such as a tuning fork. If you depict the movement of its sound wave on a graph, you get a sine wave. Such vibrations are called harmonic. The tuning fork emits only the fundamental tone. This sound is often called boring, colorless.
When a sound has a lot of high-frequency overtones, it gets harsh. 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, endows the sound with a certain timbre.
