JSE Infinity Slope Model 1 Speaker System Review

The JSE Infinite Slope Model 1 speakers outwardly resemble many other speaker systems but embody two unique design features. The most obvious one is suggested by the term “infinite slope,” which implies the use of steep crossover filters. Although not truly infinite, at about 100 dB per octave the JSE crossover slopes contrast sharply with the usual 6-, 12-, or 18-dB-per-octave slopes of other speaker systems.

The advantages of using infinite-slope crossovers, if they could be realized in practice, would include: 1) handling any specific audio frequency by only one driver, thus eliminating the response irregularities and pattern distortions that result when two or more drivers operate at the same frequency; 2) reducing intermodulation distortion by eliminating bass frequencies from high-frequency drivers; 3) increasing dynamic range and power-handling ability, since the middle- and high-frequency drivers do not have to be designed to handle the high cone excursions imposed by bass frequencies; 4) eliminating “cone breakup” and the associated response irregularities that occur when a speaker driver is driven at frequencies above its design limits. Although the JSE crossover slopes are not really infinite, the manufacturer claims that all these benefits are realized in its products.

A conventional crossover network becomes complex (and costly) when its slope exceeds the usual 6 or 12 dB per octave. In addition, phase shifts can be very large in the vicinity of the crossover frequency when a large number of reactive elements (capacitors and inductors) are used. According to JSE, the patented crossover design of the company’s speakers uses inductive coupling between some of its coils to produce “zeros” (transmission nulls) in the crossover response just outside the transmission band. These zeros are canceled by “poles” (transmission maxima) in the adjacent transmission band. The result is a uniform overall amplitude and phase characteristic said to be a good approximation to that of an ideal all-pole, minimum-phase transfer function.

The second unique element in the JSE speaker’s design is the Phase Shift Bass Loading system, which is claimed to provide enhanced low-bass response, flatter mid-bass response, and lower distortion than conventional woofer configurations. Two woofers, of different sizes, operate in a sealed space. The amplitude and phase of the signal driving the larger woofer are modified so that the two drivers operate in phase at the lower end of the bass spectrum (40 Hz), giving an augmented output at low-bass frequencies. At higher frequencies, the output of the larger woofer is attenuated and its phase is shifted so that the two woofers are driven in quadrature (90 degrees apart) at the upper end of the larger woofer’s range (about 300 Hz). The attenuation and phase shift together produce a steep crossover between the two bass drivers, leaving the smaller one to carry the middle and upper bass (as well as the midrange) without the usual response peak and resulting boominess.

The JSE Infinite Slope Model 1 is a fairly compact floor-standing system, equipped with casters for easy movement. Its wooden cabinet (available in walnut, natural-oak, or black-lacquer finishes) measures 31 inches high, 14-1/4 inches deep, and 13 inches wide at the bottom. The front panel slopes back at a 15-degree angle, reducing the depth of the speaker’s top surface to about 6-3/4 inches. Each speaker weighs about 55 pounds.

The black grille cloth’s frame unsnaps to reveal a fully finished speakerboard with three vertically aligned drivers. The 8-inch low-bass driver is just below the center of the panel, with the 6-1/2-inch mid-bass/ midrange driver above it. The 8-inch driver cone is made of reinforced polypropylene, and the 6-1/2-inch cone is formed of filled polypropylene. Both drivers are heavily damped, with Q ratings of about 0.25. Near the top of the speakerboard is the 1-inch dome tweeter, which operates above 2,000 Hz. It is damped and cooled by ferrofluid in its magnetic gap and is rated to handle over 300 watts.

The JSE Model 1 is recommended for use with amplifiers rated to deliver from 20 to 300 watts into 8-ohm loads. Its nominal impedance is 8 ohms, with a 5-ohm minimum. The system’s sensitivity (with a 2.83-volt drive level) is rated as 90 dB sound-pressure level (SPL) at 1 meter, the frequency response as 40 to 20,000 Hz ±3 dB. Price: $969 per pair.

Lab Tests

The averaged room-response curve of the JSE Model 1 speakers, measured on the axis of one cabinet and about 30 degrees off the axis of the other, was remarkably smooth and free of the usual amplitude irregularities caused by a room’s standing waves. The horizontal dispersion (confirmed by fft response measurements but also evident in the room curves) was very good for a speaker using a single 1-inch tweeter, with little difference in response on-axis and 45 degrees off-axis below 10,000 Hz and only about 8 dB difference in response at 15,000 Hz.

The close-miked woofer response was measured in two ways: separately for each woofer and at a single point midway between the two. The results were similar, showing a ± 1.5-dB variation from 60 to 1,100 Hz. The woofer curve spliced easily to the room curve, yielding a composite frequency response that varied only ± 3 dB from 56 to 20,000 Hz. The only significant departure from flatness was a slight bump between 1,000 and 2,000 Hz, apparently in the output of the 6-1/2-inch bass/midrange driver near its upper frequency limit, with an amplitude about 2.5 dB above the average response in that frequency range. The combined low-bass output fell at 12 dB per octave below 60 Hz. The 8-inch woofer’s output peaked at 90 Hz and fell off at 6 dB per octave above that frequency.

Our FFT frequency-response measurements confirmed most of the results of the room measurements, including the smoothness of the low and middle frequencies and a tweeter response that was flat within 6 dB overall from 2,000 to 18,000 Hz. These measurements also displayed the extraordinarily steep crossover slopes of the JSE speaker—at least 50 dB per octave in the first 24 dB of the cutoff slope.

Group-delay measurements also underscored the effectiveness of the Model 1’s crossover system, with a 0.2-millisecond overall variation from 3,000 to 22,000 Hz. In the combined frequency range of the two woofers, there was a delay shift of about 0.5 millisecond compared with the tweeter delay, but there was less than 0.2 millisecond variation between 500 and 3,000 Hz. This result indicates a degree of phase linearity that we have not previously seen in a multidriver dynamic speaker system. Even the best of them, which may have a very uniform group delay over most of their range, usually display large shifts in the woofer and midrange driver bands.

The impedance of the JSE Model 1 was 5 ohms at 20 and 2,750 Hz, with a maximum of 22 ohms at 56 Hz. Its first minimum above that peak was 6 ohms at 110 Hz. These measurements confirm the validity of the speaker’s 8-ohm impedance rating. We measured its sensitivity (with 2.83 volts of pink-noise input) as 88 dB SPL at 1 meter. Woofer distortion was measured with a drive level of 3.56 volts, equivalent to a 90-dB SPL. Separate measurements were made for the two woofer cones. Because of the manner in which the outputs of the drivers combine, it was not practical to combine their distortion readings, but the two curves were plotted as essentially parallel traces, with distortion readings in the range of 1 to 2 percent from 300 down to 50 Hz, increasing slowly in the lowest bass to 5 percent at 25 Hz.

Our peak-power tests with short (one- or two-cycle) tone bursts produced an audible rasp from the woofers at 100 Hz with an input of 350 watts to the speaker’s 6-ohm impedance at that frequency. At higher frequencies, we were unable to drive the speaker into obvious distortion with the available amplifier power. At 1,000 Hz, the amplifier clipped at 760 watts into the 9.5-ohm impedance of the 61/2-inch woofer. At 10,000 Hz, where the dome tweeter’s impedance was 7 ohms, the amplifier clipped at 985 watts.

Comments

When we first listened to the JSE Infinite Slope Model 1 speakers (before making any measurements), our impression was of a somewhat bright sound with little evidence of deep or strong bass. Other speakers to which we had been listening prior to that time had a relatively “warm” sound, with good but not prominent highs. The contrast with the Model 1 was striking—and surprising, since we had heard the JSE speaker a few months before and had not been aware of the characteristics that appeared in our familiar surroundings.

The message in this is simply that a sudden change from one speaker to another with different sound properties can lead to erroneous conclusions. Putting it another way, we tend to become accustomed to a particular sound quality and may be jarred somewhat by a very different one. That is what happened to us in this case. Extended listening left no doubt that real bass in a program was reproduced with full potency and a gratifying lack of distortion by these speakers. The absence of artificial midbass coloration was partially responsible for our initial reaction, since the voices of fm station announcers were reproduced without the annoying heaviness that we find objectionable in so many speakers.

As for the “brightness,” part of this impression may have been our reaction to the speaker’s slight midrange peak at 2,000 Hz, but we suspect that it was mostly a consequence of the speaker’s very flat, widely dispersed high-end response.

We were able to use the JSE Model 1’s for several weeks and found them among the most enjoyable speakers we had heard in some time. An advantage of intrinsically flat speakers is that their overall sound balance is easily altered to suit a listener’s taste (without losing the speakers’ essential good qualities) by using tone controls or an equalizer. We felt no need for such alteration, but experiments left no doubt that it was a practical procedure—unlike the usual attempts to correct deficiencies in a speaker’s sound by similar means, which hardly ever works! In any case, the JSE Infinite Slope Model 1 speakers sound just great. They are also very reasonably priced and look as good as they sound.

It was also gratifying to find a “radically different” speaker design that was just that—and which unarguably produced the claimed results! No hype was needed to present the case for the JSE system’s design, and our measurements fully confirmed the FFT test data supplied by the manufacturer, as our ears did for its claimed listening qualities. The inventor of the Phase Shift Bass Loading system and the Infinite Slope Crossover, Richard Modaferri, is a highly respected engineer— among his creations were the McIntosh MR77 and MR78 tuners—who has been concentrating on speaker design for over seven years. The results speak for themselves.

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