Digital Crossovers

Crossovers, Active speakers, passive/digital.. All these terms can quickly become confusing! Here is our attempt to summarize speaker processing for multi-way crossover applications in few lines.

Passive crossovers

Passive speaker crossovers are typically located between the amplifier and the loudspeaker. They provide filtering at the amplified level (i.e. one amplifier channel per speaker) and have the advantage of potentially being low cost to manufacture. 

On the down side, from the filter simulations to prototyping, few revisions & good electronic knowledge will be required to build a passive crossover that is well tune/matched with your speaker/amplifier configuration. The acoustic modeling of an enclosure + driver + crossover combo as a model (i.e. an estimation based on math equations) is only the first stage. Once in the real world comes the realization that "model" can only be "real" up to some extend. An extensive trial & error process will therefore be required to match your passive crossover to your enclosure. Add to this equation the knowledge required (electronic) and what sounded like an easy project with a couple of coils, caps will quickly turn in more than you can chew. 

Digital crossovers

Digital DSP processed crossovers are on the other hand located between your source and the amplifier. They provide filtering at the "line level" and you will require one amplification channel per processed speaker. (i.e. 2way stereo speaker requires 4 channel). l

On the plus side, DSP crossovers such as a miniDSP are controlled from the click of a mouse and allow much great flexibility & accuracy. What used to require a Master in Electronics for passive crossovers is now a child's play with DSP crossovers. Forget about electronic design or PCB prototyping. A miniDSP platform will provide all the processing you need for all your most common speaker filtering application. Time alignment, phase control, equalization, steep filter slopes.. you name it!

Screenshot of miniDSP 2way Crossover control panel

Here is a diagram of a typical stereo 2 way configuration where a single miniDSP 2x4 platform provides all the processing required for the 4 drivers. 

miniDSP + 2way plug-in configuration for Stereo 2 way system

Time alignment

Another obvious advantage of DSP processed speakers is the ability to "time align" a speaker, an important step to provide proper wavefront reconstruction and align the accoustic centers of multiple drivers in the enclosure.

Imagine a tweeter and woofer, both mounted to the front of your enclosure. Due to their physical constraints, their respective acoustic center(i.e. when the sound originates) is offset in space, therefore in time. For a same signal played in both, the wavefront from the tweeter will typically be "ahead in time" compared to the wavefront from the woofer. Comb-filtering among other things will result in a non-uniform frequency response affecting your listening experience.

By combining time alignment along with the phase relationship from the crossovers, miniDSP kits can make acoustical outputs of adjacent loudspeakers to become coherent.One can easily prototype many configurations by modifying delay and crossover settings with a few mouse clicks.

Where to next? 

If you'd like to learn of the components required to build your multi-way crossover application, here are two valuable links:

- For a 2 way configuration,  please have a look here.

- For a 3 or 4way configuration, please have a look here.