Search Results

The methodology consisted in comparing two different techniques for dynamic evaluation of vehicle’s thermal comfort, using the obtained data from a relatively simple thermal stress equipment (ISO 7243) and correlating it to the results from a complex dedicated thermal comfort equipment (ISO 7730 - ISO 14505). Therefore, it was necessary to add sensors and develop a new program using the algorithm provided by the standard. The results showed that it is possible to use this correlation with good approximation for a quick analysis, with simpler instrumentation, reduced complexity and lower cost of the measurement.

Since the Weber-Fechner Law (1860) until 1950 there was no trustful method to calculate Loudness of complex sounds. At that time, ISO proposed three weighting curves, A, B and C based on rough approximations of the isophonic curves, 40, 70 and 100 phons. It was supposed to be a temporary suggestion. Curves B and C were abandoned, but A weighting survives until today! In 1957, Stevens and Zwicker presented two independent methods to obtain Loudness in sones, based on the new Stevens' Power Law. In 1965, Kryter introduced Noisiness in noys. Stevens in 1975 presented Perceived Magnitude as an improvement of Loudness calculation. In these acoustic parameters, the sound pressure levels per frequency band are transformed into acoustic sensation levels, and through the sensation spectrum the magnitude of the overall sensation is calculated. The A, B and C curves, for low, moderate and high levels do not follow this concept.

An effective program for external noise reduction of vehicles was firstly established in Brazil by an agreement between ANFAVEA and CETESB in the beginning of last decade. IBAMA worked this proposition and published in 1993 the first CONAMA Resolution, including the pass-by noise limits and the deadlines to satisfy the new sound pressure levels. Since then, CONAMA is responsible for this subject. In 2001 lower levels were imposed, similar to those existing in Europe, with 2006 as the deadline for all vehicle families. The paper describes and gives and overview of the procedures, the acoustic technologies and improvements developed to achieve, in two steps, the new limits, mainly for commercial vehicles, like heavy trucks {from 92 dB(A) to 80 dB(A)} and passenger cars {from 84 dB(A) to 74 dB(A)}. We enumerate also the non-acoustic problems solved, for instance the thermal problems, due to the acoustic barriers applied to reduce pass-by noise.

Loudness of sounds is often assumed to be an adequate indicator of the unwantedness, for general noise control purposes, of sounds. Experiments have shown, however, that for many sounds there are differences between some physical aspects of sound, and judgements of Loudness (soft/loud) compared to judgements of Noisiness (acceptable/unacceptable), which is sometimes called Perceived Noise or Perceived Noise Level, depending on the units used. Internal sound pressure level of two sets of vehicles, commercial and passenger cars, are used to calculate the acoustic parameters: Loudness in sones, according to Stevens and Noisiness in noys according to Kryter. The calculations are similar, but Kryter's Equal Noisiness Contours emphasize the high frequencies. We look for the degree of linear correlation of these acoustic parameters, applying to the experimental data least squares curve fittings. In addition we establish a ranking for both parameters using a specific set of vehicles.

The paper looks for the degree of linear correlation of some acoustic parameters concerning Speech Intelligibility in vehicles. The Articulation Index (AI) was originally a criterion to characterize the influence of parasite noise on the Intelligibility of a conversation in the design of speech communication systems. Introduced in the automobile acoustics, it is more and more commonly used by vehicles manufacturers to estimate the middle and high frequency content of spectra noise inside various types of vehicles driven under several running conditions. The correlation with Speech Intelligibility, measured through subjective measurements is well known. Presently we have more sophisticated parameters like STI, RASTI, SII… directed mainly to architectural acoustics and sometimes used in vehicle acoustics. They require specific hardwares and softwares and are more complicated to deal with and often are called machine measures of Speech Intelligibility.

The paper looks for the degree of linear correlation of some acoustic parameters when their results are compared taking into consideration the internal noise of a set of passengers cars and another set of commercial vehicles. The acoustic parameters dealing with the overall noise (Loudness, dB(A) and dB(B)) and those related to the high frequency portion of the spectrum (Articulation Index and Sharpness) are chosen. The sound pressure levels in the passenger compartment are measured according to ISO 5128. The parameters are calculated in some specific velocities. A least square fit to a straight line to each pair of the acoustic parameters is applied. The results are discussed taking into consideration the degree of correlation trying to investigate how dependent or independent the parameters are. In addition it is possible to see the fluctuation range of these parameters concerning each set of vehicles.

The paper goes beyond the conventional way of looking at Loudness. We go into the calculation procedures taking into consideration two methods coming from the work of two researchers: Zwicker and Stevens. These methods are described in ISO 532. Instead of going to the traditional way of comparing the overall noises we penetrate in the calculation processes, step by step, getting subsidies to analyze the contributions of each frequency band. We applied the two methods using some random sound pressure spectra we generated. We are able to compare the total Loudnesses in both methods using a least-square fit with linear approximation. The spectra of contributions in sones in third-octave bands are also compared for both methods, through the development of simple mathematical expressions which are able to identify the parcel correspondent to each third-octave band.

This paper goes beyond the usual Loudness and make the introduction of a new parameter called Perceived Magnitude, developed by Stevens, as an improvement to qualify/quantify acoustic sensations. As a pioneer application we have applied it to quantify some acoustic sources associated to automotive industry. We emphasize the differences concerning Loudness and Perceived Magnitude, and show the right way to compare the results. The sound pressure level spectra of some sources in octave bands are used to calculate the overall noise in SONES associated to the above parameters as well the usual dB(A). A suggestive and innovative spectral composition weighted by the above functions is introduced to interpret the results. Finally we discuss the benefits we can achieve using the new parameter in vehicle acoustics.

This paper uses sets of experimental data, concerning commercial vehicles, to study the correlation between pass by and stationary noises through measurements executed according to external noise standards. We consider two sets of experimental data: before the new legislation (higher levels) and lower levels satisfying the new limits in Brazil. In addition we calculate the Loudness in sones, from the octave band noise spectrum, and compare the results with the usual evaluation in dB(A), with the purpose of emphasizing the qualification besides the quantification aspects and promoting conditions for people understanding. Besides the overall noise, we show the bandwidth contribution for each parameter and analyse the spectrum profile associated to the “A” weighting curve applications. The discussions, conclusions and recommendations are supported by regression curves and graphics taken from the measurements effectuated involving the chosen parameters.