Linear Sound Pressure Level Research Articles

Sound amplitude of discrete bubbles entrained by an impacting water stream.

Experiments were undertaken to develop a relationship between bubble size and acoustic-emission amplitude for a vertical stream of water impacting a water pool. A particular focus is the formation of the discrete bubbles. Although the relationship between bubble diameter and the natural frequency of sound emissions has been established through Minnaert's work, a comprehensive investigation into the amplitude of sound emissions is missing. Air bubbles were generated from the impact of falling-water streams of varying diameters on an underlying water pool and their acoustic emissions were recorded using a nearby hydrophone. Sound amplitude was found to increase monotonically with bubble size. A second-order polynomial relationship between logarithmic acoustic sound pressure level (L) and bubble diameter (Db) was found, L=-0.0401Db2+1.5781Db+110.7225 within the ±3 dB margin of error. The relationship between linear sound pressure level (P) and bubble diameter (Db) is expressed by the equation P=0.0059Db2+0.0505Db+0.3591, within the ±3 dB margin of error. Results demonstrate that larger bubbles (D > 4 mm) exhibit noise emissions similar to bubbles produced by other mechanisms, such as the underwater nozzle, while smaller diameters tend to produce higher noise levels compared to the same mechanism.

Identification of operating mode of a petrol chainsaw based on short-time parametrization and analysis of vibro-acoustic signals

Petrol chainsaws during operation, regardless of the type of their drive and power, generate vibrations and noise that usually exceed the permissible values which are specified in standards and/or regulations. The values of vibration accelerations and emitted noise levels declared by the manufacturers are determined in standardized conditions and they may significantly differ from the values affecting operators. In order to determine the actual impact on operators of chainsaws under nominal operating conditions (in situ) one have to identify the percentages of the chainsaw's operating modes: Idle – ID, Full load – FL, Racing – RA. The article presents the methodology of identifying the operating modes of petrol chainsaws based on recorded vibroacoustic signals. Moreover, a method of identifying these states based on a tachometric signal has been proposed. Different approaches were considered to the identification of operating modes. Basic method is based on tracking of changes of the instantaneous values of vector sums of frequency-weighted values of RMS vibration accelerations – ahv and linear sound pressure levels – Lp. Advanced methods are based on short-time analysis and parametrization in frequency bands of the acoustic signal, as well as the time–frequency maps of vibration and acoustic signals. Discriminants of vibroacoustic signal were determined that allowed us to identify the operating mode of the chainsaw.

Nonlinear modeling and prediction of forklift acoustic annoyance based on the improved neural networks

Aiming at the characteristics of high decibels and multiple samples for forklift noise, a subjective evaluation method of rank score comparison (RSC) based on annoyance is presented. After pre-evaluation, comprehensive evaluation and data tests on collected 50 noise samples, the annoyance grades of all noise samples were obtained, and seven psycho-acoustic parameters including linear sound pressure level (LSPL), A-weighted sound pressure level (ASPL), loudness, sharpness, roughness, impulsiveness and articulation index (AI) were determined by correlation calculation. Considering the nonlinear characteristics of human ear subjective perception, objective parameters, and annoyance were used as input and output variables correspondingly and then three nonlinear mathematical models of forklift acoustic annoyance were established using traditional artificial neural network (ANN), genetic-algorithm neural network (GANN), and particle-swarm-optimization neural network (PSONN). Moreover, the prediction accuracy of the three models was tested and compared by sample data. The results indicate that the average relative error (ARE) between the experimental and predicted values of acoustic annoyance based on PSONN model is 3.893%, which provides an effective technical support for further optimization and subjective evaluation.

Efficiency of an ANC system in the tractor cabin under controlled engine workload

The noise at the driver seat of an agricultural tractor is produced mostly by the engine. Its characteristic broadband noise spectrum varies considerably with engine workload. The passive noise control techniques adopted in tractor cabins, based on the application of sound-absorbing and sound-proofing materials, are effective against medium-high frequencies noise components. The residual noise in sound-proof cabins is characterized by tonal emissions with low frequency components (< 500 Hz) but regarded as responsible for various disorders and diseases following long-term exposure. In addition to the "A" weighting filter adopted to evaluate occupational exposure to noise, other approaches are reported in the scientific literature considered more appropriate to evaluate low frequency noise (LFN), as well as studies testifying the effectiveness of active noise control (ANC) technologies in the low frequency range. In this article, the performance of an ANC system is evaluated in its ability to reduce noise levels inside the soundproof cabin of an agricultural tractor. To test this system, spectro-phonometric measurements of the equivalent linear sound pressure level were conducted under controlled and repeatable engine workloads, obtained by connecting the tractor to a dynamometric brake, while simultaneously acquiring the related engine performance curves. Altogether, three different couples of loudspeakers were tested. Frequency analysis in one-third octave band showed that the ANC system was mainly effective against LFN components (below 120 Hz) with peaks of reduction up to 20 dB. Then, on the basis of indications from previous studies, the data of linear sound pressure levels were processed applying the "A", "B", and "C" weighting filters, to show the different emphasis given to the effects of the system. Eventually, a point-by-point composition of the equivalent levels of sound pressure was drawn over the whole range of the engine, to highlight the conditions in which the ANC system was more effective.

Field Study of the Interior Noise and Vibration of a Metro Vehicle Running on a Viaduct: A Case Study in Guangzhou.

The interior noise and vibration of metro vehicles have been the subject of increasing concern in recent years with the development of the urban metro systems. However, there still is a lack of experimental studies regarding the interior noise and vibration of metro vehicles. Therefore, overnight field experiments of the interior noise and vibration of a standard B-type metro train running on a viaduct were conducted on metro line 14 of Guangzhou (China). Both the A-weighted sound pressure level and linear sound pressure level were used to evaluate the interior noise signals in order to revel the underestimation of the low-frequency noise components. The results show that the interior noise concentrates in the low-to-middle frequency range. Increasing train speeds have significant effects on the sound pressure level inside the vehicle. However, two obvious frequency ranges (125–250 Hz and 400–1000 Hz) with respective corresponding center frequencies (160 Hz and 800 Hz) of the interior noise are nearly independent of train speed. The spectrum analysis of the vehicle body vibration shows that the frequency peak of the floor corresponds to the first frequency peak of the interior noise spectrum. There are two frequency peaks around 40 Hz and 160 Hz of the sidewall’s acceleration level. The frequency peaks of the acceleration level are also independent of the train speeds. It hopes that the field measurements in this paper can provide a data set for researchers for further investigations and can contribute to the countermeasures for reducing interior noise and vibration of a metro vehicle.

Sound Quantity and Quality of Sampo 3065 Combine Harvester

ABSTRACT- Noise is considered as one of the most debilitating conditions in farming operations. In this study, a number of factors affecting the noise generated by Sampo 3065 combine harvesters were evaluated. Factors were engine speed and gear ratio for combines with and without original cabins. A factorial experiment arranged as a completely randomized design with four replicates was used. Results indicated that loudness level correlated strongly with A-weighted sound pressure level (R2=0.99) but had a weak relationship with linear sound pressure level (R2 = 0.60). Other results showed that original cabins decreased 30.5, 22.8 and 5.4 percent of the loudness level, A-weighted and linear sound pressure levels, respectively. Mean value averages for loudness level, A-weighted and linear sound pressure levels for high engine speed were 6.9, 9.1 and 11.1 percent higher than those at low engine speed.

R-weighting provides better estimation for rat hearing sensitivity.

Since sounds may induce physiological and behavioural changes in animals, it is necessary to assess and define the acoustic environment in laboratory animal facilities. Sound studies usually express sound levels as unweighted linear sound pressure levels. However, because a linear scale does not take account of hearing sensitivity-which may differ widely both between and within species at various frequencies-the results may be spurious. In this study a novel sound pressure level weighting for rats, R-weighting, was calculated according to a rat's hearing sensitivity. The sound level of a white noise signal was assessed using R-weighting, with H-weighting tailored for humans, A-weighting and linear sound pressure level combined with the response curves of two different loudspeakers. The sound signal resulted in different sound levels depending on the weighting and the type of loudspeaker. With a tweeter speaker reproducing sounds at high frequencies audible to a rat, R- and A-weightings gave similar results, but the H-weighted sound levels were lower. With a middle-range loudspeaker, unable to reproduce high frequencies, R-weighted sound showed the lowest sound levels. In conclusion, without a correct weighting system and proper equipment, the final sound level of an exposure stimulus can differ by several decibels from that intended. To achieve reliable and comparable results, standardization of sound experiments and assessment of the environment in animal facilities is a necessity. Hence, the use of appropriate species-specific sound pressure level weighting is essential. R-weighting for rats in sound studies is recommended.

Unsteady Isentropic Flow through Ducts with Prescribed Sound Pressure Level Distribution

An analytical method for the determination of the required shape of a duct for a prescribed sound pressure level distribution is presented in this paper. The physical model involves a sound wave propagating in an unsteady flow of compressible fluids through ducts. Two cases are considered. In the first case, the channel shape, F(X), is given as either an exponential function or a linear function of the distance along the axis with an unknown parameter in the expression for F(X). The unknown parameter is determined by the prescribed ratio of the sound pressure level at the exit section of the duct to that at the entrance. In the second case, the sound pressure level is specified at every point along the length of the duct, and the duct shape, F(X), is sought. The governing differential equations of the model are presented. The method of complex superposition is used to separate the real and the imaginary parts of the perturbation quantities. The results show that the cross-sectional area is sensitive to the flow speed and the frequency of the sound source. Furthermore, a convergent/divergent duct has to be used to achieve a linear sound pressure level distribution.

Noise in heavy goods vehicles

Data are given of noise spectra obtained in the cabs of new, and in-service, heavy goods vehicles having gross vehicle weights up to 40 tons. Comparisons are made between dB(A) and linear sound pressure levels under motorway conditions at 30, 40 and 50 mile/h. The emphasis has been on the collection of data, particularly in the infrasonic region, which lies in the octave bands between 2–20 Hz. The results confirm that high levels of infrasound exist in the cabs and these levels are, possibly, influenced by the ventilation of the cab and the road speed. The data obtained are discussed from the points of view of hearing hazard, impaired vigilance, and possible dangers arising from infrasound. It is concluded that in the noisier vehicles there is certainly a danger to hearing, and from available data on the effects of noise in the laboratory and in industry, there is probably some effect on vigilance. The extent of the possible hazard of infrasound is less well established and a need for further research is pointed out.