Vibroacoustics

The human ear comes into direct interaction with acoustic waves in the air, thanks to which we can hear. However, often waves propagating in the air (sounds) result directly from the presence of waves propagating in solid bodies (vibrations). For example, if you hit the anvil with a hammer, both the hammer and the anvil will start to vibrate. The resulting structural waves are directly coupled to the medium that surrounds them (air), that is why part of their energy is radiated and heard in the form of sound (or disturbing noise). In addition, vibrations in themselves can be burdensome, for example: when they are transferred to objects in direct contact with the human body (eg a car seat) or to objects that are sensitive to vibrations (eg sensitive measuring equipment). In addition, structural vibrations effectively impair the resultant acoustic insulation of partitions in buildings and ships, even when using partitions that effectively block direct sound. Therefore, limiting structural vibrations is an important aspect in improving the comfort of life and work.

From the point of view of vibroacoustics, it is important to consider such issues as:

• excitation of the structure by the source
• transmission of vibrations from one structure to another
• sound radiation

One can approach the theoretical as well as the measurement aspect for each of the above problems. These are one of my main tasks at KFB Acoustics.

In the theoretical approach, numerous models are used that capture (or approximate) observed phenomena in a strict form. The numerical method in which I specialize is Statistical Energy Analysis (SEA), which allows to solve the presented issues (excitation, transmission and radiation) in the mid and high frequencies for complex vibroacoustic structures.

In the measurement approach, devices such as accelerometers (evaluation of existing vibrations) and vibration exciters connected with the impedance head (excitation of structures with simultaneous information about the occurring force and acceleration) are used to assess the quality of the models, generate input data to numerical methods and check the effectiveness of the anti-vibration solutions (for example, by comparing the vibration levels present on the structure before and after the application of the damping mat). In addition to determining the vibration levels, we also perform more advanced measurements of mechanical admittance, structural reverberation time and use the PIM (Power Injection Method) to determine the input data to the SEA model.

I also carry out research and development works in my team that focus on improving the predictive capabilities of the models used (eg by taking into account more complex junctions between structures) and on estimating the uncertainty of the obtained results.