INTERNAL AND EXTERNAL NOICES REQUIREMENTS

Vibroacoustic comfort includes mandatory legal requirements:

• internal noise
• external noise

Currently, in the Russian Federation, the maximum level allowed for internal noise in a passenger car is 77dBA at the level of the hearing organs of the driver and all passengers. At the same time, the maximum noise is estimated when the car accelerates to a speed of 120 km/h, as well as at constant speeds in the range from 60 to 120 km/h.

The external noise of a car with an internal combustion engine accelerating intensively at a speed of 50 km/ h should not exceed 74 dBA, according to current requirements. These driving modes are chosen based on the principle of passing intersections with traffic lights, where there are usually a lot of pedestrians. For new and developed vehicles, the external noise should be lower and not exceed 72 dBA, and in the future - 70 dBA – there is a tendency to reduce the sound effect on pedestrians. These requirements are already in force in many countries.

Electric vehicles are additionally required not to be quieter than 66 dBA in urban modes. Such electric vehicles or "hybrid" vehicles undergo additional tests at low speeds and when moving backwards. Based on these tests, decisions are made on equipping with special audible warning devices. This is due to the quiet operation of electric motors at low loads and is necessary so that pedestrians accustomed to the noise of cars with internal combustion engines are warned about the approach of an electric vehicle.

The internal noise of a car depends on several key factors:

• noise transfer function of the body
• the noise level associated with the power unit
• the noise level from the road
• the noise level from the chassis
• and the level of aerodynamic noise.

Noise transfer function (NTF) of the body is a characteristic that describes how sound pressure and vibrations are transmitted and propagated inside the car from external noise sources to the interior. It shows the relationship between the input sound effect (for example, engine, road, or wind noise) and the noise level perceived inside the cabin.

The transfer function reflects the acoustic and vibration response of the car body and interior, taking into account resonances, standing waves and the influence of the car's design.

This function is important in the design of sound insulation, interior acoustics and sound comfort of the car, helps to optimize materials and structures to reduce noise and vibrations in the cabin.

NTF of a car body depends on several key factors:

• the size and geometry of the body affect standing waves and resonances that change the amplitude-frequency response (frequency response) of noise inside the cabin
• body stiffness — "membrane" vibrations of body panels lead to distortion of noise transmission, especially at low frequencies
• panel materials and construction — their vibroacoustic properties determine the level of noise absorption or reflection.