Joseph Audio RM33si Signature loudspeaker Page 2
"The [RM33si's] cabinet construction is quite a bit more sophisticated than the RM22si's," Jeff Joseph explained. "It has a sealed separate subenclosure for the midrange and tweeter, and isolates them from the sound pressure of the woofer. The narrow, trapezoidal front baffle is also different from past designs, as is the use of a side-firing woofer. We employed that trapezoidal shape to stagger the frequency at which diffractions occur, and it really improves the imaging—it also gives you a little better off-axis response. We still employ a downward-firing port like that in the RM22si, but that port is rectangular; the RM33's is cylindrical, with a little bit of a flare on the bottom of it. The cabinet is very solidly built, and there is also a good deal of bracing inside. Of course, the bolt-on side panels add stiffness and mass to the structure of the cabinet, as well as offering the aesthetic benefit of being detachable, should you need to tidy up a nick or change the wood finish to fit a new décor. More important, they allow us to make the cabinet much thinner."
Even with its wood-veneered side panels (on the review samples, a lushly grained rosewood), the RM33si is barely over 3' tall and only 8" wide, but a full 16" deep. On its custom-built, sand-filled Sound Anchor tripod, which allows for a subtle backtilt, the RM33si rises to a little over 41?" tall. "A lot of times, when people were looking at these speakers during [Home Entertainment 2001] this past spring in Manhattan, they were convinced they were listening to a 5" two-way," Joseph recalled, "until some large transient came along and scared them. And then they'd ask, 'Are there subwoofers here?'"
For all practical purposes, the RM33si fulfills the ideal of a coherent two-way minimonitor atop an exceptionally fast, articulate, dynamic subwoofer. With its special motor system and a four-layer voice-coil wound on a long aluminum former, the 8" aluminum-cone woofer is said to offer exceptional excursion and power-handling. Yet with a low crossover point—at 125Hz, or midway through the upper bass—the RM33si's woofer effectively operates just below the lowest fundamental tones of the soprano, alto, and tenor voices. So voices aren't wallowing about in the subsonic resonances of the big driver's larger, ported box.
"Much of what you're hearing in the RM33si in the frequency range from around 125Hz on up to just below 2kHz, where the tweeter kicks in, is all that 5" midrange driver..." Joseph enthused. "The 5" midrange has a magnesium cone that is extremely stiff and light, and is mounted in a new basket design that is really acoustically transparent. The fingers of the basket are narrower, and there are larger windows of air behind the cone, so the sound comes off the cone unimpeded by any reflections in the rear. We've mated this midrange with a really fancy tweeter with a pure silver voice-coil. In the Sonatex process, they pre-coat the fabric four times with a damping and sealing material, which gives it superb acoustic properties. This tweeter also employs a double-magnet system, which makes it a lot more sensitive and provides better control of the voice-coil."
However, the RM33si's most significant advance over previous Joseph Audio designs is in the implementation of Joseph's patented Infinite Slope crossover design. "Actually, there are two different circuits implemented in the RM33si," Joseph explained. "In the original Infinite Slope, we had a sharp cutoff for both the tweeter and the midrange or woofer. Thinking in terms of a two-way system, both the woofer and the tweeter would roll off very quickly. The difference in this is that while the woofer still rolls off quickly, the tweeter comes on gradually.
"The low-pass to the woofer is an Infinite Slope, and it is wired in series with the midrange and tweeter crossovers. So that is a whole new animal: it has the Infinite Slope but it is also a series configuration. Technically, it's an asymmetrical Infinite Slope crossover. The benefits of the series configuration are that it improves the phase through [the] crossover and improves the fill between the woofer and the midrange. Very tricky to get it right. The crossover is also different in the transition between the midrange and tweeter, using a steep cutoff on top of the midrange, which effectively suppresses any ringing that would occur from a metal cone, but also keeps the midrange driver from interacting with the tweeter above the crossover, so that you don't have the cancellation and lobing pattern that you would see if it were a conventional crossover."
"Allowing the tweeter to roll off slower provides a more transparent match between the drivers, where the crossover is harder to identify. It also results in improved transient response. The waterfall plot of stored energy around the crossover is substantially reduced, which generally correlates to a very clean, detailed, grain-free presentation—but at the same time, a more relaxed sound. There's a different character to the sound; it sounds very natural, and it retains the clarity and definition of the original Infinite Slope, perhaps even improving on it in some respects. But it has a fuller, more throaty quality to it, and at the same time, a more natural and relaxed representation that sounds more like live music and less like the mechanical facsimile thereof. And because we felt the sonic benefits using a series connection were more significant than a biwiring option, we employ a single set of the patented Cardas binding posts—which grip the spades like a vise for a really firm connection. Nor do they accept banana posts, so the RM33si is in fact CE-compliant for the European market."