Siemens Industry Software NV
Question
Asked 9th Sep, 2015
What is relation between structure borne noise and Airborne noise (in terms of Frequency / intensity)as heard by the car passangers?
Hello All,
I wanted to know if there are any studies relating sound emitted from a structure to what is heard by the passenger in car.
The intensity of sound or sound power will decrease due to raditation loss factor. How is it with frequency, the sound treamitted from surface of a structure to the Human ear , would it have higher frequency as it travel through less denser medium (Air)?
Popular answers (1)
The best way to look into this problem is to consider it from a source-system-receiver point of view. The receiver in your case is the human occupant (driver or passenger) of the vehicle. ultimately, the sound comes to this receiver by airborne components and is influenced by the car interior (shape, damping, absorption) as well as by the own shape and characteristics of the occupant. This relates to the discipline of sound quality which deals with the subjective and objective perception aspects related to human sound perception.
The source on the other hand can be both airborne or structure borne (also depending on the point of view taken to identify what one calls a source). For example the tyre/road interface causes airborne sound radiation from the contact zone as well as from the surfaces of the vibrating tyre. It also causes structure borne source transmitted as forces from the wheel into the suspension. The car engine also has both source components. The engine surfaces radiate sound which is emitted as an airborne source, at the connection points with the rest of the car (engine mounts, connection to driveline...) also vibration is generated and injected as a force in the rest of the car, corresponding to structure borne components.
Finally, everything which is between the source and the receiver is the transmission system. This transmission can be purely airborne (e.g. the airborne path between engine surfaces and occupant, only attenuated by acoustic isolation such as offered by the firewall, or the airborne path between the wheel/road contact zone and the car interior. The shape, dimensions and materials in this transfer path define the degree of noise reduction (or enhancement, e.g. by acoustic resonance effects). Alternatively, the transmission can be structure borne, e.g. between wheel suspension and the car interior panels or between the engine mounts and the car interior panels. Structural dynamics, stiffness and damping properties govern this transmission. At the interior car surfaces (panels, roof, windows...), this vibration is again transformed into sound so that in the end the occupant receives airborne sound from multiple transfer paths.
Sound transmission is hence a very complex problem with multiple aspects and of mixed air- and structure borne nature. It is hard to make a general split in frequency ranges between air- and structure borne transmission, it depends very much on the concrete application, but for car interior noise, the transmission path below 500Hz is dominantly structure borne and above 800Hz it is mainly airborne (but small components may vibrate and radiate at higher frequencies and large cavities may have important airborne components at lower frequencies.
As to your last question concerning the media effect: it affects the wavelength as the speed of sound is different, but the frequency remains the same.
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All Answers (1)
Siemens Industry Software NV
The best way to look into this problem is to consider it from a source-system-receiver point of view. The receiver in your case is the human occupant (driver or passenger) of the vehicle. ultimately, the sound comes to this receiver by airborne components and is influenced by the car interior (shape, damping, absorption) as well as by the own shape and characteristics of the occupant. This relates to the discipline of sound quality which deals with the subjective and objective perception aspects related to human sound perception.
The source on the other hand can be both airborne or structure borne (also depending on the point of view taken to identify what one calls a source). For example the tyre/road interface causes airborne sound radiation from the contact zone as well as from the surfaces of the vibrating tyre. It also causes structure borne source transmitted as forces from the wheel into the suspension. The car engine also has both source components. The engine surfaces radiate sound which is emitted as an airborne source, at the connection points with the rest of the car (engine mounts, connection to driveline...) also vibration is generated and injected as a force in the rest of the car, corresponding to structure borne components.
Finally, everything which is between the source and the receiver is the transmission system. This transmission can be purely airborne (e.g. the airborne path between engine surfaces and occupant, only attenuated by acoustic isolation such as offered by the firewall, or the airborne path between the wheel/road contact zone and the car interior. The shape, dimensions and materials in this transfer path define the degree of noise reduction (or enhancement, e.g. by acoustic resonance effects). Alternatively, the transmission can be structure borne, e.g. between wheel suspension and the car interior panels or between the engine mounts and the car interior panels. Structural dynamics, stiffness and damping properties govern this transmission. At the interior car surfaces (panels, roof, windows...), this vibration is again transformed into sound so that in the end the occupant receives airborne sound from multiple transfer paths.
Sound transmission is hence a very complex problem with multiple aspects and of mixed air- and structure borne nature. It is hard to make a general split in frequency ranges between air- and structure borne transmission, it depends very much on the concrete application, but for car interior noise, the transmission path below 500Hz is dominantly structure borne and above 800Hz it is mainly airborne (but small components may vibrate and radiate at higher frequencies and large cavities may have important airborne components at lower frequencies.
As to your last question concerning the media effect: it affects the wavelength as the speed of sound is different, but the frequency remains the same.
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