The benefits of active loudspeaker crossovers has been understood for many years. In an active loudspeaker system, each individual speaker can be driven by its own power amplifier. A band limited signal is fed into each amplifier that can have its phase and frequency response tailored individually. There is a big advantage to driving each speaker directly from a power amplifier since the current draw of a speaker can be quite non linear. If the amplifier has essentially a zero ohm output impedance, these affects a minimized. It is easy to compensate for sensitivity differences of the drivers and clipping can be confined to the output of single driver.

Passive loudspeaker components tend to be large and not very ideal. Capacitors are not really just capacitors and inductors are not really just inductors.

Historically, active crossovers were usually constructed by analog filter circuits placed in front of a set of power amplifiers in a separate enclosure. The filtering would usually be simple butterworth, bessel or linkwitz-riley implementations with limited adjustability. The loudspeaker would have separate inputs available for the tweeters, midrange and woofers. Of course, this meant lots of speaker cables and a stack of amplifiers.

DSP based crossovers can extend the active crossover idea in several important ways. First, the filters can be substantially more optimized. The same types of filtering that analog implementations relied upon are still available via IIR based DSP filtering. These filter options can be complemented by other topologies such as finite-impulse response (FIR) filters that are not available as analog filters. In a modern DSP crossover, the complexity of the filter is somewhat arbitrary, the computation power is generally available to do as much as you want. With a DSP crossover you can adjust delay, add individual look ahead limiters (to avoid warranty repairs) and even individually match the response of each production loudspeaker.

Another technology change that has made DSP crossovers much more practical is that high quality switching amplifiers are now available. Most studio monitors today, use internal amplifiers and certainly any wireless audio system would probably be self contained as a practical matter.

Perhaps, the easiest way to create a DSP crossover is to use a single chip solution such as one of Analog Devices' SigmaDSP processors. Typically a system is created using a graphical design package that simplifies the development and tuning process of creating a workable solution. This is a great way to create low cost, high volume DSP based solutions for mass market applications. With this approach you can get 15-16 bit CD quality.

Danville's dspCrossover™ technology goes much further. We generally start with a SHARC DSP which is much more powerful processor than any of the integrated parts. More importantly, we use very high performance DACs, low phase jitter clocks and low noise analog support circuits. Inputs can be digital or analog, wireless or wired. We have a power graphical design and tuning interface (DSP Concepts' Audio Weaver) that allows real time tuning with optimized code. When you are satisfied with the result, you just write to flash. The result is a fast time-to-market solution with very high performance.

Our target markets are high end home stereo, home theatre and professional audio studio monitors. Although not strictly a crossover application, we can also use this techology for high quality headphone DACs.

Almost all of our dspCrossovers are custom designed to meet the individual needs of the target speaker and customer. Working with Danville, complements the skills of your acousticians and speaker designers with a skilled audio oriented DSP technology company.



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Danville Signal Processing, Inc.
29687 82nd  Avenue Way,  Cannon Falls, MN 55009
Phone: (507) 263-5854 Fax: (877) 230-5629