"Bus Cabin Interior Acoustic Environment"
- This assignment is a student thesis. For your application to be considered you should currently be a university student eligible to complete a Master thesis as part of your university program.
- Students can apply by themselves or in an already formed group.
- Below presented topics are to be defined based on existing information and suggestions by all involved parties.
We at the Verification and Validation group, are responsible to conduct tests for both the development of new products and to certificate our current line of products. We are involved in almost all phases of the development of Volvo Buses products.
Description of thesis work
A bus can be considered a unique type of vehicle from the acoustic point of view. Usually vehicles, as passenger cars and trucks, have cabins with significantly smaller volumes when compared to the total volume of a bus. The volume of a bus can be considered as similar as small rooms. So, understanding how to describe properly the acoustic environment inside the bus is of extreme importance. Within the field of room acoustics, a series of parameters were defined to describe and understand how the environment can affect the users.
One of these parameters is the reverberation time, which is defined, in general, as the time it takes the sound level to decay ca 60dB after the sound source is turned off. In general, the reverberation time represents how long it takes the sounds takes to be absorbed by the room.
The ideal reverberation time is determined according to the room usage, for example in concert hall and tv studio of similar volume, the “ideal” reverberation time would be of 1.8s and 0.8s respectively. So, it is important to determine the correct usage of a room to set a goal for the reverberation time.
Another important aspect is the room modal response. The room modal response or the room modes can be related to the room’s resonant frequencies. These resonant frequencies can have a huge impact on the users, if a certain frequency can be unpleasantly amplified. Impacting the overall sound quality of a room. The room modes are in general related to the geometry and layout of the room. Two rooms with similar volumes can present a very different modal response.
In motor vehicles there is some known noise sources and having the initial room modes matching to the most common operating frequency of the source can lead to a decreased sound quality and user comfort. So, it is important to be able to calculate and measure the room modes for the complete assessment of the acoustic environment inside the bus cabin.
The methods to investigate the modal response and reverberation time in rooms of many sizes are largely used. But usually, the measurements in small volume rooms presents challenges and the existing methods may need to be adapted.
In products different as city buses and coaches the correct approach could lead to improve acoustic comfort for the passengers. The requirements for each type of vehicle should be determined separately according to the usage.
A low sound level although always aimed for it is not sufficient to determine the proper acoustic comfort of a room or vehicle.
So, the main objectives of this proposal study are:
- Determine the rooms acoustic parameters to be assessed in a bus and its targets
- Access and optimize the acoustic environment of the current coach
- Access and optimize the acoustic environment of a current city bus
- Compare the acoustic environment in a Double Decker and Single Decker city buses and propose improvements
The ideal student(s) will possess good communications skills in English (written and verbal), show a high level of initiative, be self-driven, have good analytical capabilities and have a high interest in room acoustics.
The successful candidate should have strong technical skills and should be willing perform measurements.
The candidate should have a bachelor’s degree in civil or mechanical engineering and is now completing his/her Masters.
Any experience within the field of vehicle engineering is an advantage and relevant courses within the subject of acoustics is a merit.
Number of students
1 or 2 students
Conrado de Mello Calvet, NVH Lead Test Engineer, Verification and Validation
Phone number: +46 31 3086437
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