Its amplitude response would be absolutely flat and its roll-off characteristics would be the proverbial brick wall. It would have no phase shift or time delay. The frequency dividing network would be, in reality, a frequency gate. Each driver would be fed only the frequencies it is capable of reproducing. Third best, and this is where we really begin, are multiple drivers mounted one above the other with no time shift, i.e., non-coincident drivers adjusted front-to-rear to compensate for their different points of sound propagation. This gets closer to being possible, but still is elusive. Since we cannot have that, second best would be multiple speakers, along the same axis, with sound being emitted from the same point, i.e., a coaxial speaker that has no time shift between drivers. It would be one driver that could reproduce all frequencies equally well. And what we have is the physics of sound, and of electromagnetic transformation systems that obey these physics.Ī perfect crossover, in essence, is no crossover at all. But we exist here and must make the best of what we have. Another universe, another system of physics, and the quest for a perfect crossover might not be so difficult. In 1983, a 4th-order state variable active filter was developed by Rane to implement the Linkwitz-Riley alignment for crossover coefficients and now forms the heart of many analog active crossover designs. Over the years active crossovers proliferated at a rate equal to the proverbial lucky charm. It is seldom whether to cross over, but rather, how to cross over. Typical of truly useful technical papers, it is very straightforward and unassuming: a product of careful analytical attention to details, with a wonderfully simple solution. Largely ignored (or unread) for several years, it eventually received the attention it deserved. Siegfried Linkwitz and Russ Riley, then two Hewlett-Packard R&D engineers, wrote the aforementioned paper describing a better mousetrap in crossover design. And many DSP crossovers offer an 8th-order Linkwitz-Riley (LR-8) option.īefore exploring the math and electronics of LR designs, it is instructional to review just what Linkwitz-Riley alignments are, and how they differ from traditional Butterworth designs. Offering in-phase outputs and steep 24 dB/octave slopes, the LR-4 alignment gives users the necessary tool to scale the next step toward the elusive goal of perfect sound. Today, the de facto standard for professional audio active crossovers is the 4th-order Linkwitz-Riley (LR-4) design. In 1983, the first commercially available Linkwitz-Riley active crossovers appeared from Sundholm and Rane. Their efforts became known as the Linkwitz-Riley (LR) crossover alignment. In it, he credited Russ Riley (a co-worker and friend) with contributing the idea that cascaded Butterworth filters met all Linkwitz's crossover requirements. In 1976, Siegfried Linkwitz published his famous paper on active crossovers for non-coincident drivers. Linkwitz-Riley Crossovers 2nd to 8th-Order.Butterworth Crossovers 2nd to 4th-Order.Linkwitz-Riley Crossovers: A Primer Dennis Bohn, Rane RaneNote 160, written October 2005
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