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Joseph Audio Prism

Back in 2010, when I reviewed the Joseph Audio Pulsar loudspeakers, I concluded, “If I were forced to move into a smaller domicile, one with a modestly sized room for my system, the first speaker and most likely last speaker I’d consider would be the Joseph Audio Pulsar.” Since then I’ve moved into a smaller home and just as my thoughts turned to the Pulsar, Jeff Joseph sent me an announcement about his newest monitor, the Prism. Priced at $3699 per pair, the Prism is Joseph’s attempt to capture the magic of the Pulsar in a less expensive package. As you might expect, I was only too happy to find out how well he had succeeded.

Prism Tech Tour
All Joseph Audio speakers employ the “Infinite Slope” crossover, which ex-McIntosh product designer and senior engineer Richard Modafferi patented back in 1988. During the intervening years, Jeff Joseph has made substantial modifications to Modafferi’s design. The Prism speaker includes Joseph’s latest refinements on the Infinite Slope crossover.

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

The original Infinite crossover design was symmetrical, meaning that both the tweeter and the midrange driver had the same crossover slope. But the design has evolved—the Infinite Slope filter system currently employed isn’t the same as the one Joseph Audio started with more than twenty years ago. Now the company uses a steeper slope on the woofer than on the tweeter. According to Joseph, “This gives us a more seamless crossover and improves the quickness of the entire system because the decay is cleaner.”

A first-order crossover has a 6dB-per-octave roll-off between drivers. In comparison, the Prism uses a 100dB-per-octave crossover for the low pass and 18dB third order for the tweeter’s roll-off. The low-pass filter drops much faster than 24dB per octave 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. The Infinite Slope crossover allows the two drivers to mesh in a more coherent fashion than most conventional crossovers. This method confines the overlap to where the wavelengths are longer, so the lobing artifacts you see in conventional designs do not occur.

Proponents of first-order crossovers often point to the extreme phase shifts that accompany steeper crossovers as one of the reasons for using a simpler filter. But in the case of the Infinite Slope, phase shifts are not an issue. The Infinite Slope is actually “phase-matched,” because it introduces a full 360-degree phase rotation. But as the actual frequency region of the crossover is narrow and the 360-degree shift puts the two drivers back into linear phase (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 would hear on a conventional multi-driver first- or second-order-crossover loudspeakers. According to Joseph, “when you use a ‘wrapped-phase measurement’ scheme 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 off-axis frequency and power response curves of both the tweeter and midrange are far more similar than they are on speakers 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 Pulsars’ power response and phase accuracy both on- and off-axis, is more like an acoustic instrument in a real-world space than most loudspeakers.

Now that I’ve covered the overriding technological raison d’être of the all Joseph Audio loudspeakers, let’s look at the Prism’s particulars. It is a two-way, ported, stand-mounted loudspeaker with a 1″ Sonotex dome tweeter and 5.5″ aluminum-cone midrange/woofer. The crossover point for the Prism is 2.5kHz, which would be on the high side for a conventionally crossed over loudspeaker, but ideal with the Infinite Slope crossover since the midrange/woofer handles most of the “heavy lifting,” while the tweeter has far less in the way of extreme dynamic demands due to the higher crossover point. Published frequency response for the Prism is 45Hz to 20kHz, which rivals many floorstanding “full-range” loudspeakers.

Joseph Audio, as a matter of preference, does not list a sensitivity rating for the Prism or any of its loudspeakers. According to Joseph, “When I try to explain about impedance and a well behaved load to prospective owners, their eyes glaze over and they buy a ‘94dB efficient’ speaker that’s actually 87dB with a 4-ohm impedance and wicked phase angles, and then they wonder why their SET tube amp is distorting. But anyone who tries our speakers on their tube amps are often pleasantly surprised to find they play at a very satisfying levels without strain.”

 

The Prism’s cabinet design borrows heavily from the Pulsar. But the Prism is lighter weight with less internal bracing, and it lacks the Pulsar’s added wood side panels. Instead the Prism relies more on its physical shape to reduce diffraction and internal standing waves. Although the cabinet looks rectangular at first glance, it’s actually a more complex shape—the front panel is slightly wider than the back panel and the sides are made up of four separate planes instead of a pair of parallel ones. Only the top and the bottom of the speaker are parallel to each other.

Unlike the Pulsar, which has a hardwood veneer finish, the Prism employs a less-expensive-to-produce painted finish. You have a choice of white, black, or a dark reddish color that is very similar in hue to a dark cherry. The finish itself is a satin rather than gloss or flat surface. The back of the Prism has a single pair of high-quality, five-way, Cardas rhodium-and-silver binding posts. The Prism’s speaker grilles use invisible magnets attachments so there are no unsightly holes in the front baffle.

Another detail that made the Prism different from the Pulsar (and nearly all previous Joseph Audio models) was the design process Joseph used. Joseph previously worked from the crossover outwards—that point was selected first. Starting with the Pearl3 and continuing with the Prism and Profile, however, Joseph optimized the crossover’s low-pass filter and mid/woofer driver together as a system, and then brought in the tweeter and the crossover’s high-pass section. Joseph believes this methodology enabled him to realize the system’s natural coherence and seamlessness.

The Setups
At first, as I do with all monitor-sized speakers, I set up the Prisms in my nearfield desktop system. During their time in this setup, I powered the Prisms with an assortment of amplifiers including the NuPrime ST-10, April Music S-1, Dynaco Stereo 70, and Accuphase P-300. All these amps, including the Stereo 70 delivered way more power than I needed for normal listening levels nearfield. With the April Music S-1 and NuPrime ST-10, the Prisms were silent when no music was playing except for the very faintest low-level hiss from the tweeter (if I put my ear within an inch of the driver surface).

On my desktop I used a pair of IsoAcoustics speaker stands under the Prisms, which placed them so my ears were parallel with the top of the midrange/woofer’s surround. Usually with a small two-way monitor I prefer a setup in which the tweeter is on the same horizontal plane as my ears. But with the Prisms I preferred having the tweeter higher than usual. Then I mated the Prisms with an Origin SUB8 subwoofer, allowing the Prisms to roll-off naturally and adding the subwoofer at 60Hz and lower.

In my main listening room, I set up the Prisms on 24″-high Target metal, sand-filled speaker stands. Here I used the NuForce ST-10 and April Music S-1 amplifiers and a pair of JL Audio f112 subwoofers. I also used a 70Hz roll-off point, controlled by the crossover built into the Parasound P-7 preamplifier.

Sonic Impressions
One of the first things I did with the Prisms once they were set up in my nearfield system was run test tones through them—specifically sinewave sweeps between 1kHz and 4kHz—to see if I could detect any anomalies in the crossover region. I discovered that despite my best efforts I could not identify any nonlinearities or sonic anomalies from 1kHz to 4kHz despite the facts that: a) this is the region where the human ear is most sensitive; and b) 2.5kHz is where the Prism’s crossover is situated.

Going from the speakers that have been spending the most time on my desktop, the Audience 1+1, to the Joseph Audio Prism should have been more of a shock than it was. After all, the Audience loudspeaker is a full-range-driver design without any crossover, while the Prism has its crossover right at 2.5kHz. But both designs had similarly seamless frequency responses. They also had similar soundstaging characteristics. I suspect that these similarities in soundstaging and imaging resulted, in part, from the fact that both speakers feature midrange drivers that cover a wider bandwidth than is common in other loudspeakers. Because the Prism’s midrange/woofer extends to 2.5kHz, it handles a majority of the work, while the tweeter has an easier job, filling in the top octaves but never having to produce high excursion.

Because of their rear-facing ports, the Prisms can acquire too much midbass energy from room-generated bass reinforcement if they’re placed too close to a wall. To mitigate midbass room gain, I needed to position the Prisms at least two feet away from the wall. For some nearfield desktop setups, you may find that you do not have enough distance from the back of your desktop to the wall. Using a foam port plug can reduce this problem, but I found that the plug overdamped the midrange/woofer driver in a way that reduced dynamic drive and extension. Obviously, proper placement is a better solution.

 

On my desktop, I found the midbass to be somewhat warmer than neutral, primarily because I could not move the Prisms far enough away from the front wall without running out of desktop. I had a similar issue with the Pulsars, but they were even more difficult to place. Since they are larger, I had fewer placement options. In the room-based setup, I found the Prism’s harmonic balance was more neutral, and blending them with subwoofers was easier than in the desktop setup.

While it would have been instructive if I had a pair Joseph Audio Pulsars for a direct comparison (the review pair from 2010 had been returned to Joseph Audio years ago), I had to rely on aural memory (and previous listening notes). The new Prisms certainly have the Joseph Audio “house sound,” which I would characterize as easier-to-listen-into than most loudspeakers I’ve heard over the years. There is a lack of low-level buzz and hash on the Prisms. There is also a noticeable absence of additive colorations from crossover anomalies.

Although the Audience 1+1 and Joseph Audio Prisms had a similarly cohesive sound, the Prisms were far better at dealing with higher SPLs. Again, because the midrange/woofer handles a majority of the speaker’s output, the Prism can cope with being driven hard with no signs of distress. After blowing up two sets of drivers in the Audience 1+1 (both times due to user error), I try to handle the Audiences with some care. With the Joseph Audio Prisms I could be less circumspect. Although no loudspeaker is bulletproof (or oscillation-proof), the Prisms proved to be as resilient as any small or mid-sized two-way monitor I’ve used.

Obviously, if you place a small monitor speaker in a large enough room you will eventually turn it up to the point where you will hear it strain. In my medium-sized room, where the distance from listener to speaker is approximately 8 feet, the Prisms, with the assistance of two JL Audio f112 woofers, could play up to and past my own personal maximum loudness level without any audible signs of distress. Even the lower midrange and upper bass—what I refer to as “the meat and potatoes region”—remained satisfyingly full but still controlled when the Prisms were pushed hard. On my recording of Brahms’ German Requiem recorded directly to DSD 5.6, the Prisms handled the grand crescendos without showing any signs of effort.

The Prism’s port is claimed to extend its low-frequency response to 45Hz. I did some sinewave sweeps from 200Hz to 40Hz in the nearfield setup (where there would be very little room-induced group delay) and found the Prisms retain bass output with only a bit of attenuation to around 55Hz. It’s no wonder that I found integrating a subwoofer so easy.

Nowadays it’s hard to find a good loudspeaker that doesn’t image well, but some image better than others. The Prisms certainly displayed precise, well-defined images that didn’t suffer from cabinet diffraction. Even when used in the nearfield, the Prisms disappeared almost as completely as the Audience 1+1 loudspeakers, which are still my reigning nearfield imaging champions. On my own recordings, the Prisms placed each instrument exactly where it should have been. The principal difference between the Prism’s imaging and the Audience 1+1’s was that the Audience loudspeakers produced a slightly larger listening window, which allowed for more boogie-space in the nearfield.

Neutral is a much-abused term in our little audiophile world. Perhaps harmonically transparent would be a more descriptive term when applied to the Prisms. On bass-heavy pop mixes, such as the superb album from Bleachers’ Terrible Thrills Vol. II, the Prisms allowed me to hear all the way into the complex mix easily.

Conclusion
Six years ago, after I reviewed the Joseph Audio Pulsars, I ran into a number of audiophiles at the 2011 RMAF who were very interested in owning a pair. Their only hesitation was coming up with the $7700. The Prisms should shake a good portion of those fence-sitters from their roosts. While I can’t and won’t try to give you a numerical percentage of the Pulsar’s performance that is equaled by the Prisms, as in “They deliver 85% of the Pulsars’ performance,” I will go on record that the Prisms have similar sonic qualities with an overall performance level that ranks up with the best small monitors I’ve heard. No, the Prisms aren’t as visually prepossessing as the Pulsars. But in many domestic and professional listening environments the Prisms’ less blingy exterior may be a considered a positive attribute. After all, once you close your eyes, it’s all about the music, not how closely a speaker’s cabinet veneers are book-matched.

Put the Prisms in a midsized or smaller room, mate them with decent electronics and a good subwoofer, and they will deliver the musical goods in that natural and articulate way that Joseph Audio loudspeakers are known for, but at a more affordable price than ever before.

SPECS & PRICING

Type: Two-way, ported, stand-mounted loudspeaker
Drive units: 1″ Sonotex dome tweeter, 5.5″ aluminum super-duty woofer
Crossover frequency: 2.5kHz
Frequency range: 45Hz–20kHz
Nominal impedance: 8 ohms
Power handling: 15–250W undistorted power
Dimensions: 14″ x 7″ x 12″
Weight: 21 lbs. each
Price: $3699

JOSEPH AUDIO, INC.
P.O. Box 1529

Melville, NY 11747
(800) 474-4434
josephaudio.com

Associated Equipment
Source Devices:
Late 2013 MacPro model 3.7 GHz quad-core computer with 16 GB of memory with OS 10.11.1, running iTunes 12.3.1 and Amarra Symphony 3.0, Pure Music 3.0.1, and Audirvana+ 2.24, Roon, Tidal 1.1, a 2010 Mac Mini with 8GB of memory and OS 10.11.1, and similar apps
Analog Sources: VPI TNT III w/Graham 1.1 tonearm and ClearAudio Victory II cartridge, VPI HW-19 with Souther SLA-3 ’arm and Denon 103/VanDenHul cartridge. Vendetta 2B and Lio phono module preamps
DACS: NuForce DAC-10H, Emotiva Big Ego, Grace 9xx, PS Audio NuWave DSD DAC, Moon by Simaudio Neo 230 HAD
Amplifiers: April Music Eximus S-1, Accuphase P-300, and NuPrime ST-10, Dynaco Stereo 70
Speakers: Aerial Acoustics 5B, Role Audio Kayak, Audience 1+1, ATC SC-7 II, Origin SUB8 subwoofer, 2 JL Audio f112 subwoofers
Cables and Accessories: Wireworld USB cable, AudioQuest Carbon USB cables. AudioQuest Colorado single-ended RCA interconnect, Kimber KCAG interconnect, Audience Speaker AU24e speaker cable, PS Audio Quintet, Dectet, and Premier power conditioners

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