Voice interfaces are of much interest for car designers: they are a safe way to operate various devices. However car compartments are very hostile environments for voice capture and emission because road noise is very loud. For every new car much time must be spent on their optimization which involves tools for quality evaluation. Comparing configurations is not practical while driving. A simple model of voice interfaces based on impulse responses makes reliable tests much easier to implement. This paper describes its practical application and shows a few objective results.