Re: B&C Sub designs
How does B&C calculate the Xmax (excursion) specification, and what is Xvar?
- Evolution is a process that affects not only products, but also their technical specifications. Constant advances in research provide more and more precise methods to measure the performance of loudspeakers, and describe their features. Thiele – Small parameters have become the universal language for describing loudspeaker behaviour in the small signal domain. Nevertheless, they comment little on the working limits of loudspeakers in the large signal regime. These limits are customarily indicated by Xmax, the maximum linear excursion. This value, measured in our catalogue according to AES2-1984 standard, corresponds to a maximum of 10% total harmonic distortion (THD) with a sinusoidal signal. 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 magnetic field seen by the voice coil, or the total suspension compliance, or both, drops to less than 50% of their small signal value, producing high distortion levels, strong variations from small signal behaviour and power compression. The new technique yields different results from the standard measurement based on THD.
