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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.

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.

The purpose of this paper is the presentation of the main experiences of customers and users of trucks and buses regarding the electronic systems placed in these vehicles, specially in the Latin American market. Basically, in the past years the number of on-board electronic devices increased a lot and the evolution of the customer know-how concerning the new technologies is in progress. Therefore, a line between the mechanical engine and the electronic vehicle management will be traced on this paper, considering the time the customers have taken to react regarding the applied innovations.

The interior noise of automotive vehicles is basically composed by two portions. The structureborne sound through the elastic moutings, which is characterized by the low frequencies and the airbornesound through the divisory between the engine compartment and passenger compartment. This last path is mainly traveled by the high frequencies. We show the low frequencies, specially those related to the explosion order make the composition of the overall sound level, when the noise is evaluated by a weighting curve, trying to simulated the ear response, as for example the curve “A”, from which originates the well familiar dB(A). The highest frequencies, although almost ever, are neglected by the weighting curve “A”, are very important when we see the communication aspect in the passenger compartment. To solve this, we use another parameter, calculated from physical measurements and named Articulation Index (Al). We show its association with the highest frequencies.

The paper presents the concepts and applications regarding Articulation Index (AI) that is widely used in the automotive industry as a powerful parameter to qualify/quantify the middle and high frequency spectra associated to the internal noise of vehicles. We are able to show a short historical review including the today used definitions and calculations based in third octave band spectra through and idealized speech region model like our pioneer Brazilian standard. We show also other applications, where AI can be an excellent tool to evaluate vehicle acoustics. We emphasize the relation of AI to Speech Intelligibility and make considerations concerning other factors influencing Intelligibility. In addition we comment the integration we have produced with an overall noise parameter like dB(A) - (H-index) and the proposition of an AIM - Articulation Index Modified.