Joseph Audio Pulsar (TAS 203)

A Small Speaker with a Big Sound

Country star Minnie Pearl always opened her performances with a big ‘ol “Howdy!” (Actually, it was more like “Howwdeeeee,” with the end of the phrase escalating in pitch when she hit the “d.”) The Joseph Audio Pulsar deserves a similarly effusive welcome. When I asked Jeff Joseph why he created the Pulsar speaker he replied, “I’ve always wanted to make a really excellent mini-monitor speaker. The midrange/woofer I developed for the Pulsar was the missing link.
Finally, I had all the parts.“ So, in essence, the new Pulsar is a mini-Pearl that fits into small spaces where the Pearl can’t. It also costs only one-third the price.

Pulsar Tech Tour

The Pulsar speakers look a lot like the top section of a Pearl, but with a slightly smaller enclosure. The Pulsar employs the same tweeter, which has a special design using a hexadym magnet system. Instead of a big spheroid donut magnet behind the dome that reflects energy, there are six small yet powerful neodymium magnet structures. Since they take up less space there’s more room for absorptive material to damp the tweeter’s rear wave. According to Jeff, “There’s as much energy coming off the rear of a dome tweeter as off the front. The problem with most tweeters is the large reflective surface of a magnet right behind the dome. With our tweeter we can adequately damp the tweeter’s back wave.”

All Joseph Audio speakers employ the Infinite Slope Crossover. Ex-McIntosh product designer, Richard Modafferi, patented it back in 1988. During the intervening years licensee Jeff Joseph has made substantial modifications to Modafferi’s design. The Pulsar speaker includes Joseph’s latest refinements on the Infinite Slope crossover design.

As you might infer from its name, the Infinite Slope crossover has a much steeper slope than a conventional crossover. Conventional speakers with regular crossovers are more likely to exhibit audible (off-axis) discontinuities between drivers because the much wider span where the two driver’s frequency ranges overlap. With the Infinite Slope crossover the hand-off from tweeter to midrange/woofer occurs over a much narrower span of frequency ranges.

A first-order crossover has a 6dB-per-octave roll-off between drivers. In comparison the Pulsar uses an extremely steep crossover for the low pass and an 18dB-per-octave third-order for the tweeter’s roll-off. Jeff told me, “The lowpass filter drops extremely fast until it hits about -41dB at which point the attenuation tapers off. This is the benefit of the Infinite Slope technique—it has a very steep initial drop, and reduces wave interference much more effectively than a standard 24dB-per-octave network does. It allows the two drivers to mesh in a more coherent fashion than a conventional crossover.”

The original Infinite Crossover design was completely symmetrical, meaning that both the tweeter and the midrange driver had the same crossover slope. Jeff adds, “The Infinite Slope filter system we use now isn’t like the one we started with eighteen years ago. Now we use a steeper slope on the woofer than we do on the tweeter. This gives us a more seamless crossover and improves the quickness of the entire system because the decay is cleaner.”

Proponents of first-order crossovers often point to the more extreme phase shifts that accompany steeper crossover schemes as one of the reasons they prefer simpler crossover methodologies. The Infinite Slope crossover is actually “phase-matched” since it introduces a full 360-degree phase rotation in its crossover. But since the actual frequency region of the crossover is so narrow and the 360-degree shift puts the two drivers back into phase coherence (except for the fact that the woofer is one full cycle behind the tweeter), the audible effect of this phase shift is less than you will hear on a conventional multi-driver first- or second-order crossover. According to Jeff, “When you use a ‘wrapped phase’ measurement like we do with the Infinite Slope, you overlay the phase shifts from both drivers so they can be adjusted to sum together nicely. The final result is the phase shift occurs over too narrow a frequency range to be audible.”

Another advantage of an Infinite Slope crossover design is that the on and off-axis response curves of the speaker can be far more similar to each other than with conventional crossovers. Jeff explains, “When you listen to live acoustic music you aren’t confined to a narrow and artificial window. You can move around and the sound doesn’t change much. That’s because the power response of live acoustic instruments in a room is more even without the irritating artifacts and incoherencies of speakers with conventional crossover designs.” In theory and practice the Pulsar behaves more like an acoustic instrument in a real-world space than most loudspeakers.