An external rearview mirror assembly is fixedly secured to a motor vehicle. According to the invention there is provided a method and apparatus for combining a precise knowledge about the relative positions of the loudspeakers that were intended and a precise knowledge about the actual placement of listening loudspeakers into a vector space that enables calculation of running corrections to the signals used in order to simulate the presence of the virtual loudspeakers. A second foldable flap extends from the second side at a second distance beneath the upper side. A switching circuit is provided to selectively bypasses individual ones of the n resistors during a test sequence to determine a trip temperature of the sensor. In one mode of operation, a reference is made to the first memory to retrieve the data. In order to arrange the valve stroke and valve opening as free as possible in the simplest possible way the control chamber is connectable with a high pressure level preferably by means of the control valve.