Performance Notes

Nevertheless, they comment little on the working limits of loudspeakers in the large signal domain. These limits are customarily indicated by Xmax, the maximum linear excursion. In a typical measurement, this value corresponds to a maximum of 10% total harmonic distortion (THD) with a sinusoidal signal (though most manufacturers, including B&C, now typically provide data for Linear Mathematical Xmax, not measured Xmax). Recent research shows that this method can yield ambiguous results, and even different numerical values for the same loudspeaker. The main limit of this measurement is that it looks at the output signal instead of the physical features of the driver itself. On the contrary, the most up-to-date instruments for distortion analysis can measure the variations in loudspeaker parameters when they are fed with high-level signals. In this way, an excursion limit can be fixed beyond which the parameter’s variation becomes excessive. The “Xvar” value reported in our data (generally after the traditional “Xmax” value) is measured this way. Beyond this excursion limit, the loudspeaker force factor (Bl), or the total suspension compliance (Cms), or both, drops to less than 50% of their small signal value, producing high distortion levels and strong variations from small signal behavior. This new technique yields different results from the standard Xmax measurement. B&C Speakers believes that this added information gives a more accurate and reliable description of loudspeaker capabilities in actual operating conditions.