v7.0, 20040922, me

Sunday, October 31, 11:00 am – 12:30 pm
Session Q AUTOMOTIVE AUDIO

Chair: Richard Stroud, Stroud Audio, Inc., Kokomo, IN, USA

11:00 am
Q-1 Construction of a Car Stereo Audio Quality Index— Andrea Azzali, University of Parma, Parma, Italy; Angelo Farina, University of Parma, Parma, Italy; Guido Rovai, Fiat Auto, Orbassano – Torino, Italy; Giovanni Boreanaz, Vehicle - NVH, CRF (Fiat Research Center), Orbassano – Torino, Italy; Giorgio Irato, Vehicle - NVH, CRF (Fiat Research Center), Orbassano – Torino, Italy
A measurable index (IQSB) quantifying perceived quality of car stereos has been developed to forecast aural appreciation. Results of panel interviews and listening tests (in a special “auralization room”) have been correlated with the analysis of corresponding binaural recordings. Two outputs were obtained. First, a model of the subjectively most relevant features was identified in terms of statistically significant “verbal descriptors.” Second, a single-figure index was constructed, function of objective measurable quantities related with audio performance, and well correlating with the average verbal evaluation (both of “naïve” and “expert” listeners). This tool is of great importance for the automotive industry because it allows for the direct quantification of the audio system performance, a significant part of the perceived quality of the product.
Convention Paper 6306

11:30 am
Q-2 Measurement of Speech Transmission Index Inside Cars Using Throat-Activated Microphone and Its Correlation with Drivers’ Impressions—Fabio Bozzoli, Angelo Farina, University of Parma, Parma, Italy
One of the most used intelligibility parameters is the Speech Transmission Index. The techniques for determining it employs an artificial speaker and listener. Inside cars, where signal to noise ratio is particularly low, the value of STI is mainly influenced by this ratio. Determining the sound power of real speakers is the only way for piloting correctly the artificial mouth. We have implemented a technique that is based on a throat-activated microphone, and it is able to find the level of real speaker’s voice inside noisy spaces in the effective conditions. We have primarily studied the speech inside cars and have discovered how the value defined by typical configurations may be extremely different from real ones. In this way, we have been able to produce more reliable excitation signals. Using this “raised signal” we have tested one car and have tried to find a good correlation between drivers’ impressions and objective values.
Convention Paper 6307

12:00 noon
Q-3 High Power Step-Up Converter for Car Subwoofers— Giovanni Franceschini, Alberto Bellini, Emilio Lorenzani, Matteo Cavatorta, University of Parma, Parma, Italy; Francesco Violi, ASK Industries, Reggio Emilia, Italy
This paper presents an original DC/DC step-up converter topology for high power car audio applications with a battery supply. A prototype was realized and tested for the power supply of a TANDEM subwoofer box. Audio signals are characterized by high dynamic variations, thus they can be amplified only relying on power supplies with high dynamic capabilities and low output ripple. The latter constraint can be achieved only using closed-loop switch-mode DC/DC converters at high switching frequency. So doing converter efficiency is reduced, and EMC problems arise. In summary, power supply efficiency and supply voltage quality are key features of the converter design. In this paper the above mentioned issued were tackled relying on an open loop topology. The original solution is the adoption of a three-phase transformer within a full-bridge converter topology. The proposed architecture will be referred to as 3boost power supply. Experimental results confirm that the 3boost power supply topology allows achievement of higher efficiency, a lower ripple factor, and a unitary transformer utilization factor. It turns out that it is an efficient power supply for a car audio subwoofer system, specifically for a digital output stage, where the quality of the supply level is a key element. The proposed architecture is patent pending.
Convention Paper 6308