It must have been during the early 80s when Bruce Edgar was struck with horn fever. The basic symptom of this affliction is manifested in the belief that high-efficiency, horn-loaded, loudspeakers are paramount for musical realism. For the last 15 years or so Bruce has been infecting many other music lovers with a similar passion for horns.
Horn loading represents a worldview that sees high efficiency as a gateway through which the full dynamic and emotional palette of reproduced music may be experienced. In contrast, the typical audiophile loudspeaker with a sensitivity in the range of 86 to 88 dB, or a factor of a hundred lower relative to 98 dB, routinely runs into power compression and significant distortion as it attempts to scale the full dynamic range form soft to very loud. Much of the music’s emotional content is encoded in the recording’s dynamics. And it seems to me that high-efficiency designs are clearly superior in articulating a startlingly real illusion of the power and majesty of musical instruments, from the evocative simplicity of a solo voice to the complexity of a full ensemble. For example, most audiophile speakers fail the Lesley Test. I’m referring here to David Manley’s 1992 live-to-two-track recording of Lesley Olsher. Recorded without compression or Dolby noise reduction onto an analog tape master at 30 inches per second, the Lesley album gives Lesley full, unadulterated, dynamic scope. Even those ultra high-end audiophile box wonders that cost as much as a BMW are embarrassed when Lesley strides into full voice. You’ve got to love it, how a 5-foot tall soprano can bend such towers of power. They can’t cut it in the midrange. Oh, there’s plenty of bass punch, but the critical mids don’t have sufficient headroom. The Slimline, on the other hand, sails through the Lesley Test without a hint of dynamic distress.
Horn passion can take on serious proportions. In the mid 80s, Bruce was building large, 40 to 50 Hz, horns with volumes on the order of 20 cubic feet. That’s double the size of a standard refrigerator. In his defense, let me state that such large horn sizes and volumes are required by the underlying physics. And it’s certain that full-bass horns will remain very large in the future, because as Paul Klipsch once quipped, no one has figured out how to miniaturize a 32-foot long sound wave. However, with a wife acceptance factor of zero, large horns had no commercial viability. Bruce concluded, quite correctly, that he should be making higher frequency horns using a smaller woofer. By the late 80s he had designed several 100 Hz, one-fourth sized, bass horns using a Pyle 5-inch woofer. In 1995, the basic concept evolved into the System 80, which utilized a single 5-inch JBL woofer. On the suggestion of several dealers, he redesigned and enhanced the System 80 into a narrower profile, smaller footprint package, and thus the Slimline was borne.
Sporting a sensitivity of 100 dB and a price tag of $1,800/pr, the Slimline clearly fills a much-needed void in affordable high-efficiency loudspeakers. The recent popularity of low-power single-ended triode amplifiers has intensified the search for suitable speaker loads and has highlighted the commercial rarity and cost of high-efficiency designs. It therefore gives me great pleasure to introduce the Slimline to a wider audience. When you consider the woodworking and driver costs involved in executing a three-way horn-loaded design of this size, the Slimline’s asking price represents a minor miracle. This is a three-way design with an 80-Hz hyperbolic-exponential bass horn, which uses two 5-inch JBL woofers. The woofers are housed in an optimized compression chamber so as to cancel the bass horn’s throat reactance and maintain a flat response to the cutoff frequency. The bass horn is folded with the mouth exhausting at the bottom of the front baffle. A 300 Hz rectangular Tractrix midrange horn loads a 5-inch JBL driver. The size of the midrange horn was settled on after experimentation with 250, 300, 400, and 500 Hz horns. The 300 Hz horn was selected on the basis of the best overall image presentation. The Tractrix midrange horn type, rediscovered and popularized by Dr. Edgar, is a key element in all of his recent designs and distinguishes them from classic 40s and 50s horn systems that rely exclusively on exponential horns. The ear is quite sensitive to horn colorations in the midrange, and it’s now clear that even text-book perfect exponential midrange horns produce mouth reflections and standing waves that give such horns a megaphone like character. The Tractrix flare sounds quite natural and has recently been accepted by several manufacturers as the most appropriate choice for high-end music reproduction. Finally, a round Fostex pro-horn tweeter is used to fill in the range from several kHz to about 18 kHz. The tweeter is positioned directly above the midrange horn to allow for the slimmest profile possible.
Let me start off with tonal balance considerations. The Slimline’s range I like the most is the upper bass and lower midrange. The frequency range from about 100 Hz to 500 Hz represents a significant sweet spot. It is clean, full-bodied, and nicely textured. Rostropovich on cello with the Saint Paul chamber Orchestra (Teldec D101707) was an absolute pleasure to behold. The majesty of the cello was well served, as was the orchestral foundation. This after all is the power range of the orchestra. Most folks, who complain about lack of bass, as with lean balanced minimonitors, are really missing out on upper bass and lower midrange. This is the range, which is most often affected by room modes to the tune of large peaks and dips (10 dB or more) at the listening seat. No matter how flat the anechoic response of stand-mounted speakers may be, once they are positioned away from room boundaries to optimize imaging, the mid and upper bass octaves (80 Hz to 320 Hz) inevitably sound grossly uneven at the listening seat. These same folks are often moved to purchase subwoofers in order to fix the problem, and are understandably left unsatisfied because they are augmenting deep bass response without really addressing the upper bass issues. In my experience, properly executed bass horns maintain a more uniform in room response due to the directional characteristics of the bass, which tends to be less omindirectional relative to conventional direct-radiator bass. Take a look at the big picture shown in Figure 1 below. This shows the Slimline’s frequency response measurement at the listening seat, pretty much where my ears happen to be. The bass is flat to about 90 Hz at a position yielding optimum soundstaging (about 6 feet from the rear wall). Of course, mid bass punch is diminished in the range from 60 to 80 Hz. As you can imagine, double bass sounds relatively weak, which interferes with my enjoyment of classic jazz. I could do a bit better here by moving the speaker closer to the corners of the listening room, but at the cost of losing imaging specificity and soundstage depth. I want to call your attention, however, to the range from 100Hz to 500Hz. Keep in mind that this is an in-room measurement. What you’re seeing here is a remarkable level of performance. There is evidence of room modes and boundary reflections, but on the whole this is much smoother than what I normally see out in the real world. The Slimline possesses the same sort of magic in this range that I’ve previously experienced from large planar speakers. The plane wave launch from such a large diaphragm has minimal interaction with the sidewalls, floor and ceiling, which acts to minimize room effects. The Slimline’s bass directionality appears to endow it with similar in-room behavior, and is something worth writing home about. If you really want deeper bass, please note that he Slimline is designed to work with a powered subwoofer, and Dr. Edgar specifically recommends the Hsu and Carver systems as ideal for augmenting the range below 100Hz.
Figure 2, is similar to Figure 1 in all respects, except that it zooms in on the midrange to show its balance relative to the upper bass and treble. Male voice is well served by such a balance, though it tends to sound a bit too chesty. However, female voice as well as violin timbre were lacking in sheen and brilliance. In general, the midrange while clean and dynamic sounds a bit polite, much like the old QUAD electrostatics. No in-your-face excitement here. If you crave a hot balance, the Slimline is bound to disappoint you. The treble is extended to about 15 kHz and is of high quality. In particular, the presence region (5 –6 kHz) is well behaved without the nasty resonances that plague some full-range drivers. However, the transition between the midrange and tweeter horns could have been better engineered. I can accept the midrange balance, which is akin to a back of the hall perspective, but the character of the upper mids (3 kHz) bothers me the most. Harmonic textures sound a bit rough through here. The tactile analog of what I hear is equivalent to running my hand across a piece of fine-mesh sand paper. Of course, what every self-respecting music lover is after here is the feeling of a velvety smooth harmonic tapestry. The degree of this effect was amplifier dependent, being the least obvious with single-ended designs and the most obvious with push-pull types.
The Slimline represents an easy amplifier load. Its impedance magnitude is shown in Figure 3, and as you can see it does not dip below 6 ohms.
The fact that the Slimline is easy to drive with as little as two to three watts isn’t meant to imply that it isn’t particular about the partnering amp. Amps whose tonal character is also recessed in the midrange exacerbate the Slimline’s laid back tonality to the point of boredom. I obtained good results with the Cyrus Brenneman 15 wpc Cavalier integrated amp. As always, be sure to audition the Slimline or any potential speaker purchase with your own power amplifier to ensure compatibility.
The vertical alignment of the horns really pays off, as the Slimline throws a surprisingly spacious soundstage with good focus and spatial resolution. Its imaging capabilities are far superior to many other multi-way systems, though it lacks the coherency of a full-range design.
This is a speaker that will not appeal to the typical audiophile listener whose priorities are more aligned with the trivial pursuits of bass extension and presence. This is not a spectacular speaker that will impress friends and neighbors during a casual listen. But if you’re committed to musical values, the Slimline will pay handsome long-term dividends. It is supremely listenable while painting a believable orchestral foundation. Music lovers will love the Slimline for the same reasons they find live music so compelling: clarity, effortless dynamics, and lack of distortion. It deciphers the music’s emotional content, the nuances buried between the notes, far better than any average sensitivity speaker design.
Sensitivity: 100 dB 1W/1m
Weight: 95 pounds
Dimensions: 51” H x 14.5” W x 21” D