Flatline Design 175 loudspeaker

Balanced performance isn't the be-all and end-all of product design. A person can listen to a product which balances the highs with the lows, detail with forgiveness, delicacy with dynamics, and still feel unmoved. Such a product might sound "proper," but it won't produce the illusion of a live performance. It takes a special window or two on reality to convince you you're listening to live music. Such a loudspeaker may have other deficiencies which keep it from being a universally appealing product, but it keeps reminding you of the live experience. It may appeal only to a small number of audiophiles, but their experience may well be more intense.

Each of us prefers a different window on reality. Some are moved by the soundstaging abilities of minimonitors; for some, it is the open, box-free sound of bi- or dipolars; for others, it is the detail of a fast tweeter. Which one is most important is individual: You'll react emotionally when you hear a product that does it for you.

Retrieving the most delicate details of the performance and the timbre of the instruments—ie, mimicking the presence of musicians in the room—can do it for me. Throw in a bi-directional radiating pattern for an open, box-free sound, and you've got my attention. Audiophiles who value these qualities will enjoy the Flatline Design Model 175s, which possess them in spades. Like every loudspeaker, the Flatline has a shortcoming—its unusual design required atypical placement in my room—but this can be worked with to achieve superior sound. Read on.

The tall, slim Flatline 175—71" tall by only 14" wide—consists of a columnar "box" housing a side-firing 10" bass driver and a front-firing 5" lower-midrange/upper-bass driver. This box is 8.25" wide and 12.5" deep. The upper midrange and treble regions are handled by a ribbon that runs the full height of the cabinet on a projecting "wing," which itself is almost flush with the front of the cabinet's inside edge. This narrow front offers an advantage to audiophiles with smaller rooms.

The tall, slim 175 has a graceful Danish-modern look. The black fabric covering the thin ribbon assembly sets off the cabinet's natural wood finish; the front-firing midrange and side-firing woofer are also covered with small, black, fabric grillecloths. On the rear of the speaker are two sets of large, well-spaced terminals for bi-wiring, bi-amping, or single-wiring, with jumpers between the terminals. If you loosen the screws on the small panel holding the input terminals, you'll find the crossover hard-wired to a handy L-shaped pullout tray, which subjects the stiff wires attached to the inside of the speaker terminals to whatever stress is applied to the plate they're mounted on. The tray could use some reinforcing braces.

The crossover and all internal wiring is of solid-core, 99.9999%-pure copper wire. After testing many types of wire, Flatline designers Lewis Muratori (footnote 1) and Otis Perkins chose copper because they felt it provided the most refined sound. The crossover uses high-quality parts: Solen and MIT MultiCap capacitors, an air-core inductor for the upper-bass/midrange unit, and a steel-core, low–DC-resistance type for better damping of the woofer. The slopes are 6dB/octave centered at 350Hz and 100Hz. The midrange and bass drive-units are shunted by RC Zobel networks, while the ribbon has a parallel resistor/capacitor/inductor in its feed, presumably to add some gentle equalization.

Low crossover points mean that the most of the audio signal is handled by the ribbon—which is all to the good. The traditional problem with mating a ribbon to a dynamic midrange driver or woofer has been the disparity in the drivers' outputs. Dynamic drivers impart a different timbre to the sound. Instead of the music sounding as if radiating from a single source, the demarcation between drivers is usually audible. By running the ribbon down to 350Hz, Flatline Design has minimized this problem.

The gentle, 6dB/octave slope further smooths the integration of the drivers. Flatline states that the 5" polypropylene driver, enclosed in its own compartment within the main speaker box, is capable of linear output up to 5kHz, though it's down well over 18dB by that point. The small grille cloth covering the 5" driver serves no sonic function—it's useful only for decorative reasons. In fact, it probably adds a bit of diffraction, since the grille frame extends in front of the cabinet and driver. I listened with the grille cloth removed.

While desirable for phase coherency, 6dB/octave crossover slopes can be problematic: the slow rolloff keeps the woofer cone active well up into the midrange, thus imparting a muddy sound in many systems. If you're going to use these gentle slopes, you need to peg the crossover point very low to allow enough rolloff to get the woofer out of the way by the lower midrange point. That's the case here: –18dB by 400Hz. The cabinet is a sealed-box design, because Flatline's engineers think that a sealed box imparts greater definition and control in the bass region than does a vented box.

A woofer firing sideways to the center of the room is a bit unusual. Side-panel mounting was chosen to allow a narrow cabinet front, and to give imaging characteristics superior to those of a wide-fronted speaker. Since low frequencies are omnidirectional (due to the wavelengths involved being very much larger than the cabinet dimensions) no anomalies should be heard; though the 175's woofers are active above 100Hz, I couldn't peg specific problems to this arrangement.

Footnote 1: Sadly, Lewis Muratori passed away in early 2010.—John Atkinson

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