The theoretical basis for the protection of autosome

Any person in their daily life is faced with manifestations of noise: on city streets, stadiums, public buildings, production. An ordinary car is no exception, in which you have to spend a lot of time and feel the whole gamut of extraneous negative factors. To understand the physical essence of this phenomenon, its effect on a living organism and the organization of the system of protection against it, let us try to understand the concept and nature of noise.

The essence of noise and its types

Noise is nothing more than a combination of sounds of varying intensity and frequency, creating an additional psycho-emotional stress and having a detrimental effect on a person. Thus, it is in the undesirability and harmfulness for the object of influence that its main difference from ordinary sound lies. In a car, subject to increased noise, the driver and passengers get tired faster and this can lead to an emergency. In this regard, the need arises to combat this undesirable phenomenon. And in order to know the enemy by sight, lets figure out what kind of noise is.

In everyday life, it is most often characterized by the words "strong" and "weak". But far from many people know what lies behind them. They are based on two parameters that determine the degree of perception and the strength of the minds influence - the level of sound (its intensity) and the level of sound pressure. We change them by adjusting the sound volume of the speaker system. The generally accepted scale for measuring these indicators is a logarithmic scale with a unit of measurement in decibels (dBA). The critical value of the sound level for a person is 130 dBA, at which it causes a painful effect. According to the location of the maximum sound pressure level in the frequency spectrum, noise can be conditionally divided into:

• low-frequency (LF) - up to 300 Hz;
• mid-frequency (MF) - from 300 to 800 Hz;
• high-frequency (HF) - more than 800 Hz.

Taking into account the amplitude oscillations of the sound wave during time intervals, the noise is divided into constant, intermittent and impulsive. Constant noise is characterized by a change in amplitude within 5 dBa within 8 hours. Constant noise includes structure-borne noise transmitted from the engine, transmission, shock absorbers, and vehicle wheels. Intermittent has a discrete structure of changes, impulse form jumps of duration about 1 sec. Intermittent can be attributed to the hum of the included heating system. The squeaks of plastic parts are impulsive. Human hearing adjusts to the "background" level and, as it were, gets used to it. At the same time, it does not notice sounds that are quieter than this level, but sensitively picks up "sharp" noises that exceed the "background" in amplitude. The "sharper" the sound, the more noticeable it is to the human ear.

Ways of generating a noise field in a car

Sound vibrations from primary sources penetrate into the interior of the vehicle through insufficient density of door and window openings, air ducts and technological openings along the body. In the process of limiting the cabin from the action of such acoustic vibrations, there are two main components. This is the suppression and limitation of the appearance of background noise in the sources themselves, that is, by improving the operation of the power unit, the design of the chassis, and the exhaust system. The height and texture of the tread of the tire are of great importance in this regard. On the other hand, the degree of sound insulation of the car directly depends on the thickness of the glass, cladding and panels.

Structure-borne noise propagates from a source of noise and vibration through the body of the machine by means of associated fasteners and rotation transfer mechanisms such as suspension, transmission, and steering. The resulting mechanical vibrations drive other body parts, which create a secondary background noise. Reflected sounds play an important role in the formation of the latter. Acoustic waves arising in the process of operation tend to both bend around an obstacle and be reflected from various surfaces, which creates an additional load on the surrounding space. For example, sound vibrations are reflected off the road surface and back towards the bottom of the car. Additional vibration in the floor is also caused by the energies accompanying the exhaust of the exhaust gases. All of this is combined into a general cacophony of sounds, defined by our hearing organs as noise.

System rigidity and why is it needed

As already mentioned, vibrations make a significant contribution to the overall structure of noise exposure. It should be borne in mind here that the constant movement of particles of solids not only causes sound, but can also lead to more significant results, coinciding with other waves in a certain part of space. With harmonic vibrations, the stiffness of the vibrating system determines the possibility of resonance in a certain frequency range. As the stiffness increases, its probability decreases at high frequencies with the same amplitude of the input action. In addition, for resonance at low frequencies, an increase in the input action is necessary.

You can comment on this with the following example. A person rocks a tree with a diameter of 10 cm. At the same time, he easily “finds” resonance, and even more than one. If he rocks a tree with a diameter of 20 cm, then the "search" for the point of coincidence of the vibrations will take away more strength from him. And these forces will not be enough at all when the tree is swinging 40 cm. From this it can be seen that with the same amplitude of the input action, an increase in the rigidity of the system reduces the likelihood of the system entering resonance. As applied to a car, high stiffness makes it possible to “ignore” the small values of structural and airborne noise, since they will not be enough for this phenomenon to appear in various parts of the car body.

In order to increase the rigidity of the body and the trim elements of the vehicle, the DD Tuning online store offers all kinds of sealing and vibration-absorbing materials. In addition, the range includes traditional and innovative noise protection products as well as thermal insulation products.