Crossover Design S/W

Generally speaking crossover design software combines loudspeaker SPL responses (that we have previously measured) with filter circuit data (also defined by us, the designers). This allows for the prediction (simulation) of overall speaker SPL responses which -in turn- verify whether design targets have been achieved or not.

The designer is expected to change filter component values in a repetitive manner and in a way that gets simulated responses closer to design targets. Obviously it is an exhaustive process.

Most crossover network software include an automatic optimization procedure which delivers the 'best' set of component values for a given set of design targets and circuit topology. In that sense no differences are expected to exist between different software implementations. However this optimization process may easily fail either if our design targets are impossible to fulfil or our circuit topology is too simple to realize them. In most cases we have to change our circuitry by adding extra components. This usually helps the optimization procedure find the proper components' 'solution'. Therefore successful crossover design often depends on human factor only. A detailed discussion of this issue is given in one of our tutorial articles on crossover design.

On the other hand we must be aware of the fact that crossover design is subject to one major flaw which is elaborated below:

Most woofers with low-to-medium sized diameters, exhibit a significant SPL step in the 100-500Hz frequency range due to baffle diffraction. Passive crossover filters can not 'adjust' the woofer's SPL response below 200-300 Hz. What they can do is to manipulate its mid-frequency range above 200-300Hz. A speaker to sound well must have a sort of balance between its 100Hz and 400Hz sound pressure levels. If the sound pressure dB level at 400Hz is 5 or 6 dB above the sound pressure level at 100Hz the speaker will sound 'empty'; music 'body' will be absent. So what crossover filters are expected to do is to suppress the sound pressure level above 400Hz so that it maintains a relatively small (or none at all) difference with respect to the 100Hz level.

For this task a designer must have an accurate woofer SPL response illustrating the baffle diffraction step in order to import it into the crossover design software. As we have already explained in the tutorials' section, reflections in our lab environment make SPL response measurement inaccurate below approximately 300Hz-400Hz. Typical measurement software removes SPL response values below this limit. As a consequence crossover design becomes 'blind' at very low frequencies and our speaker's sound balance gets compromised. Only sound engineers have access to large spaces (or anechoic chambers) for measuring purposes.

From a DIYer point of view crossover design software should be combined to a 'Baffle Diffraction Step' module. Capable of accepting enclosure data and woofer parameters, this module would simulate (predict) the missing low frequency SPL response up to 500-600Hz.