General information
The noise of a car when driving cannot be avoided. The goal of all efforts of developers is to reduce wind noise. The quieter the noise produced by units and components such as the engine, chain drive, tires, etc., the greater the wind noise heard when driving at high speed.
In addition to the general wind noise, there may be some noises that are heard as an annoying hissing or whistling sound. The causes of these noises may be partly due to manufacturing or repair factors. They are mainly caused by poorly installed components that need to be positioned and installed in the correct position.
The maximum noise heard in the car is wind noise. As the speed increases, the sound level in the car increases.
Normal air flow noises
At high speed, as the air flows around uniform flat surfaces such as the roof, door windows, etc., turbulent layers of air are formed in which changes in air pressure occur. Some of these pressure changes are propagated as sound waves and are transferred into the car through the door windows and seals. Here the noise is particularly loud due to the proximity of the driver's or passenger's door window. The noise is mainly expressed as a low roar, which becomes louder as the speed increases.
Noises caused in part by changes in air flow direction and air flow around individual elements
If air flows along the edge of the car, the air flow cannot completely go around the surface, and the flow breaks down at the edge. Eddies are formed, which are destroyed again after some time or after passing some distance.
Change in air flow direction
| Pos. | Spare Part No | Name |
| 1 | - | Vortex |
| 2 | - | Sound wave |
| 3 | - | Flow |
The build-up and decay of turbulence and the corresponding pressure changes lead to the creation of sound waves. A similar effect can be observed on the A-pillar of a car. Here, the area where turbulence usually forms is located directly above the door window. This facilitates the penetration of noise (roar) into the car's interior.
Vortex zone
| Pos. | Spare Part No | Name |
| 1 | - | Air flow |
| 2 | - | Increasing vortex |
The turbulence also forms underneath the car, and so the corresponding noise is created. As the air flows around small elements or passes through small gaps (such as the radiator grille), the roaring noise turns into a whistling sound that increases in frequency and becomes louder as the speed increases.
Noise caused by vibration of seals
Seals that do not have a solid contact in the window and door areas can also cause vibrations caused by pressure changes on the outside of the car, which means noise is transmitted to the car's interior. The vibrating part of the seal works here in the same way as a loudspeaker membrane.
Beginning of oscillations (diagram)
| Pos. | Spare Part No | Name |
| 1 | - | Vibrating seal |
| 2 | - | Breaking into a car |
Resulting noise
Small leaks in the vehicle's interior sealing system allow a small amount of air to pass through. This creates "free-flow noise" (air flow mixes with still air, causing turbulence). The volume of "free-flow noise" increases greatly with increasing speed, and can be heard as a whistling sound (like a tire losing air).
Noises in cavities
If the body cavity is open to the outside of the car, this can cause the volume of air in the cavity to resonate. The result depends on the volume of the cavity and the size of the opening. (For example, observed when blowing across the neck of a bottle).
Wind noise when sunroof is open
Problem:
- When the sunroof is open at approximately 60 km/h, a low frequency noise (rattling) occurs.
Cause:
- When the sunroof is fully open, noticeable variations in air pressure occur inside the vehicle due to air flow over the opening.
Corrective action:
- At speeds above 60 km/h, close the sunroof slightly until the rattling noise is no longer heard.
Wind noise through door seals
- Due to the air currents passing along the sides of the body and over the roof, the pressure outside is slightly lower. Due to the heating and ventilation system, the pressure inside the car is slightly higher. This pressure difference at certain speeds causes, for example, the doors to move away from the seals by a few millimetres. If there is also a crosswind that affects the movement of the car, this effect increases.
- The resulting differences in clearance are compensated for by means of flexible door seals (when the door seals are not damaged).
Paths through which external sound penetrates into the car's interior
| Pos. | Spare Part No | Name |
| 1 | - | Interior ventilation |
| 2 | - | Windshield seal |
| 3 | - | Window door seal |
| 4 | - | Roof hatch seal |
| 5 | - | Door seals |
| 6 | - | Trunk lid seal |
| 7 | - | Interior ventilation |
| 8 | - | Door handles |
Wind noises
| Wind noise type | Where do they arise? | |
| Ordinary | Noises of normal air flows | Roof, windows, doors |
| Noises caused in part by changes in air flow direction and air flow around individual elements | A-pillars, side mirrors, antenna, windshield wipers | |
| Strong | Noise caused by vibration of seals | Door gaps too wide, door/window seals not securely fastened |
| Air exit and passage noises | Leaks in the body sealing system | |
| Cavity noises | Unsealed body cavities | |
| Factors listed under the heading "strong" require corrective action. |
Summary
The occurrence and intensity of wind noise in a vehicle depends on the shape and design of various elements.
There are two subjective methods of assessment and service diagnostics that allow you to reduce the noise level and improve the sound quality in the car:
- Reducing the intensity of noise sources
- Reducing the length of the paths
To achieve an overall improvement in the wind noise situation in a car, both factors must be taken into account.
Sealing systems for doors, windows and the tailgate have a major impact on the acoustic comfort in a vehicle.
Problematic sources in practice
Driver's door and passenger's door seal
Diagnostics:
- Wind noise from the upper door seal area
Cause:
- Incorrect alignment of the door frame relative to the roof
Corrective action:
- Re-check the door position with the door window open
- Check the contact area between the door seal and the sealing surface. The width of the sealing area should be at least 5 mm.
Correct gap between door and A-pillar or door and roof
Adjusting the tailgate
Diagnostics:
- Wind noise coming from the junction of the roof and the top edge of the tailgate
Cause:
- The tailgate is positioned too high
Corrective action:
- Release the tailgate where it connects to the hinges and move the tailgate further down. As you do this, pay attention to the gaps relative to the adjacent elements.
- Reinstall the lock if necessary.
The tailgate is positioned too high
Adjusting the sunroof
Diagnostics:
- Wind noise from the sunroof
Cause:
- Incorrectly adjusted sunroof
Corrective action:
- Adjust the sunroof according to the following requirements:
- There should be a uniform gap around the entire perimeter of the roof hatch.
- The sunroof must be adjusted to match the roof profile.
- The front edge of the sunroof should close flush with the roof surface or slightly below.
- The seal around the perimeter of the sunroof must touch the sunroof cover evenly around the entire perimeter.
Adjusting the installation of the sunroof cover
Adjusting the right windshield wiper
Diagnostics:
- Wind noise from right windshield wiper area
Cause:
- The wiper arm is set too high
Corrective action:
- Remove the wiper arm from its shaft and adjust it so that it is positioned below the air turbulence area present on the air deflector when it is in its resting position.
Adjusting the windshield wiper arm
| Pos. | Spare Part No | Name |
| 1 | - | Too high |
| 2 | - | Right |
Wind noise diagnostics sequence (diagram)
1. Customer complaint
- What is the customer's complaint and what detailed information about the wind noise can they provide?
2. Under what conditions does wind noise occur?
- 1. Sequence A: Diagnosis is possible based on detailed information provided by the client.
- Take corrective action to eliminate wind noise.
- Road test the vehicle to ensure that the problem has been resolved. The vehicle should travel exactly the same distance it traveled previously when the wind noise was produced.
- If corrective actions based on the information provided by the customer do not produce results, further testing should be performed at a service station (see sequence B).
- 2. Sequence B: It is not possible to perform diagnostics based on detailed information provided by the client.
- Check for faults at the service station, referring to any applicable TSB (Technical Service Bulletin).
- Visually inspect the outer seals, check the gaps.
- Visual Inspection: Have any components been installed on the vehicle since manufacture or since the vehicle was repaired following a collision?
- Perform diagnostics based on a road test.
- Take corrective actions based on the diagnosis.
- Perform another road test. The car must travel exactly the same distance it traveled previously when the wind noise was reproduced.
- If this road test does not show that the result of the work was positive, additional tests should be performed, such as a powder test, a stethoscope test, or an ultrasonic test.
Diagnostics at a service station
Before repairs are made, a visual inspection of the vehicle should be performed, paying particular attention to the door alignment. When the doors are correctly adjusted, the occurrence of wind noise at high speeds can often be stopped (by raising the doors above the seals).
Checking with a stethoscope
A stethoscope is a simple and suitable device for detecting air leaks in the body. If the fan is turned on at the highest speed and all doors, windows and other openings are closed, the air pressure inside the car can be made greater than outside. Then the outside of the car is checked for air leaks.
Testing using powder
By coating the contact surface of the door seal with white powder, it is possible to identify door seals that do not make good contact. To do this, carefully close and then reopen the door. This will reveal the sealing surfaces that do not make contact.
Ultrasonic leak detector
Leaks can also be detected using an ultrasonic leak detector and a sonic generator. To do this, an ultrasonic generator is placed inside the car and the outside of the car is checked using a leak detector set to the generator. The leak detector will easily show any leaks that are present.
Road tests
The causes and onset of wind noise can often be identified by performing a road test. The following points should be noted:
- Choose a dry, flat, straight road with as little traffic as possible.
- Make sure your tire pressure is correct to avoid noise from your tires.
Movement technique
- Perform a road test in all speed ranges using the highest gears (fourth or fifth).
- The road test should be performed by two people and different seat positions should be tested.
- Prepare the vehicle if necessary (use masking tape to seal off the required areas).
- During the road test, pay special attention to the door openings and door seals.
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