All gases, liquids and solids can transmit sound, and these substances that transmit sound are always called media. Sound travels at different speeds in different media. Generally speaking, it is the fastest in solid, slower in liquid and slowest in gas. The speed of sound propagation in air at 15 degrees Celsius is 340m/s.
Echo: Echo is formed when sound meets an obstacle and is reflected back.
The purpose of echo: echo strengthens the original sound and measures the distance and depth by echo.
The vibration of a string, a drumhead or a vocal cord makes the nearby air particles produce the same vibration, and these particles transfer the vibration to other particles, and so on until the initial energy is gradually exhausted. The process of pressure spreading to the adjacent air produces what we call sound waves. Sound waves are different from water waves produced by water movement. Sound waves do not move forward, but the vibration of air particles produces alternating pressure, which is transmitted to human or animal eardrums in turn to produce the same effect (that is, vibration), resulting in our subjective "sound" effect.
Judging different pitches or intervals, people's hearing follows a sensory law called Weber-Fechner Law. This law states that the increase of sensation is equal to the proportion of stimulation. The octave of pitch is the frequency ratio of 2: 1. There are two "limit points" to judge the loudness of sound: auditory valve and pain valve. If the sound intensity is considered as 1 at the limit point of auditory valve, it is 1 trillion at the limit point of pain valve. According to Weber-Fechner law, the loudness level used by vocalists is logarithmic, based on the intensity ratio of 10: 1, which is known as 1 Bell. The perceived range of loudness is divided into 12 large units, and the increment of 10 decibel is divided into 10 smaller increments, that is, 10 decibel. The loudness difference of 1 dB is about the smallest change that the human ear can feel to our hearing in the midrange.
When we listen to two sounds with similar vibration frequencies at the same time, their vibrations will inevitably appear in the form of overlapping in a fixed interval, and the sounds will strengthen each other in feeling, so this time is called a beat. In the process of adjusting the pitch of one string to the pitch of another string, Piano tuner will hear the frequency of the vibration difference decrease until it gradually disappears with the correct tuning. When the rate of vibration difference exceeds 20 times per second, a soft bass will be heard.
When we listen to two loud sounds at the same time, we will produce a third sound, that is, a combination sound or a synthetic sound. This bass is equivalent to the difference in the number of vibrations of two sounds, which is called the difference sound. It can also produce a fourth sound (weak high synthesis sound), which is equivalent to the sum of the vibration numbers of the two sounds, and is called a harmony sound.
Just as light can be reflected, so can sound, such as the echo we have all heard. Similarly, if there is an obstacle blocking the passage of sound vibration, it will produce sound shadow. However, unlike optical vibration, acoustic vibration often "diffracts" around obstacles, and not any solid can produce a complete sound shadow. Most solids propagate acoustic vibration to varying degrees, while only a few solids (such as glass) propagate optical vibration.
The word resonance refers to the reaction of an object to a specific sound, that is, the object vibrates because of that sound. If two tuning forks with the same tuning are placed close to each other, one of them will make a sound, and the other will make a corresponding vibration, which will also make this sound. At this time, the tuning fork that sounds first is the sounder, and then the resonant tuning fork is the resonator. We often find that a window in a church vibrates in response to a certain sound of the organ; Metal or glass objects in a room will have a similar reaction to the sound of a particular human voice or instrument.
In the strict scientific sense of the word * * * Ming, this phenomenon is truly * * * Ming ("disyllabic"). This word also has a less strict usage. It sometimes refers to the response of floors, walls and hall ceilings to any sound played or sung, not limited to a certain sound. Auditoriums with high noise or sound absorption ("too dry") will make performers and audience feel uncomfortable (echo halls are often described as "noisy", but there is a clear difference between simple sound reflection and vibration enhancement). For each sound attenuation, the reverberation time should be limited to 60 decibels (one millionth of the original radiation intensity).
Walls and ceilings should be made of materials that are neither reverberant nor sound-absorbing. Acoustics engineers have calculated the comprehensive efficiency coefficient of sound absorption of building materials, but the sound absorption capacity is rarely unified in the whole pitch range. Only wood or some acoustic materials have basically equal sound absorption capacity in the whole frequency range. Amplifiers and speakers can be used (often used today) to overcome the problems caused by the imperfect original design of buildings. Most modern auditorium buildings can be electronically tuned and prepared.
There are movable panels, movable ceilings and reverberation rooms to adapt to any type of music performance.
Acoustics is a science that studies the generation, propagation, reception and properties of sound waves in media and their interaction with other substances.
Acoustics, a branch of classical physics, has the longest history and is still at the forefront. Therefore, it is both ancient and quite young.
Acoustics is a subject that has developed for a long time in physics. Sound is a very common and intuitive phenomenon in nature, which has long been recognized by people. Both China and ancient Greece had considerable research on sound, especially in the aspect of temperament. Our country had rich knowledge of musical instrument manufacturing and musicology in Shang Dynasty more than 3400 years ago. Later, there were many rich experiences and outstanding discoveries and inventions in the production and dissemination of sound, musical instrument manufacturing, musicology and the application of sound effects in architecture and production technology. The study of sound abroad has also started very early. As early as 500 BC, Pythagoras studied scales and harmonic progression, and the systematic study of acoustics began with Galileo's study of the period of a simple pendulum and the vibration of an object at the beginning of17th century. Newtonian mechanics was formed in17th century, which unified acoustic phenomena and mechanical movements and promoted the development of acoustics. The basic theory of acoustics was quite perfect as early as the middle of19th century, when many outstanding mathematicians and physicists made outstanding contributions to it. 1877, the British physicist Lord john williams Rayleigh (1842 ~ 19 19) published his magnum opus Principles of Acoustics, which made acoustics a rigorous and relatively independent branch of physics, and thus opened the curtain of modern acoustics.