The main aim of this paper is to present recent knowledge about the assessment and evaluation of low frequency noise and infrasound close to the threshold of hearing and the potential effects on human health. Low frequency noise generated by air flowing over a moving car with the open window is chosen as a source of noise. The noise within the interior of the car and its effects on a driver’s comfort at different velocities is analyzed. An open window at high velocity behaves as a source of specifically strong tonal low frequency noise which is annoying. The interior noise of a passenger car was measured under different conditions; while driving on normal highway and roadways. First, an octave-band analysis was used to assess the noise level and its impact on the driver’s comfort. Second, a Fast Fourier Transform (FFT) analysis was used for the detection of tonal low frequency noise. Finally, the paper suggests possibilities for scientifically assessing and evaluating low frequency noise but not only for the presented source of the sound.

Transmission of vibroacoustic energy from an internal combustion engine (ICE) to its surroundings largely depends on how it is mounted, on available transmission paths and on the construction of the vehicle body and/or its surrounding structures. This is especially true in low speed engines in enclosed areas which generate perceptually weak noise, but strong low-frequency waves which energy has a negative impact on human health, comfort and driving safety especially in prolonged exposure to the source. The primary aim of the article was to analyse components of the ICE unit which had a determining impact on the reduction of low-frequency waves. Thus, the structurally transmitted noise from the ICE to its surrounding structure (body of the passenger vehicle) was analysed. The results of the vibroacoustic measurements were compared to modal analysis in order to determine possible resonance sources in the vehicle body and/or for assessing the influence of the vehicles safety gear on the generated vibroacoustic energy transfer into the cabin area of the passenger vehicle. Measurements were made for a passenger vehicle at rest and operating in its most common operational speed as well as for the stationary ICE of a cogenerate unit (CGU). Measurements and FFT analysis were used for the detection of the vibroacoustic energy sound pressure level (noise) and mechanical vibration. Firstly, the low-frequency noise sources were determined and their direct effects on the human body were investigated. Finally, this paper suggests some measures which may contribute to the reduction of undesirable vibroacoustic energy in enclosed areas.

Implementation of European directives is closely related to the quality of production and the associated operational safety, maintenance of machines and mechanical systems, both mobile or stationary, in order to reduce the dynamic load (vibration and noise) on the working environment, not only during their operating state but also during their design, production, and setting of the vibration isolation components. Reducing the dynamic load of mechanical systems and their components is reflected in the working environment by reduced emissions and immissions of noise and vibration. The presented paper investigates the methods and conditions for noise and vibration control, focusing mainly on increasing the quality of rotating machine components, such as bearings by means of effective vibration isolation of the machines. The solution of this problem requires theoretical analysis and methodology for the measurement of the mechanical systems involved. The results of the vibroacoustic measurements were analysed in terms of the low frequency vibration and noise level (quality) of bearings and conditions for effective vibration isolation of the machines using vibroacoustic diagnostic method. Furthermore, the impact on the working environment was also analysed. Finally, the paper suggests some actions to be taken to effectively reduce the unwanted vibrosound energy in working places, also using recycled material as a vibration isolation element.