Design Goals: Sonist loudspeakers are designed to work well with low-powered directly heated triode single-ended amplifiers (SET's), using output tubes such as 2A3, 45, 300B, EL34 (in triode mode), PX25, 6C33B, GM70, and 845. The Concerto 2 and Concerto 3 are 2-way designs with 95dB sensitivity and tube-friendly benign impedance curves, nominal 7 ohms, not going below 6 ohms. Both models feature polypropylene capacitors, air-core inductors, non-inductive resistors, silver solder, and rhodium-plated 5-way binding posts. Both models are bi-wireable and bi-ampable.
Extended Bass Shelf: Extended Bass Shelf (EBS) bass alignment lowers the frequency response by 1-2dB below 200Hz, to improve the quality of the bass response when being driven by SET's, which typically produce a warmer bass than solid state amps, due to their lower damping factor. According to Dick Olsher, noted audio reviewer, "Such an alignment [EBS] is best suited for medium to small listening rooms where excessive midbass response may be a problem. The EBS alignment achieves lower bass extension at the cost of reduced response in the midbass. However, typical room gain below 150 Hz usually fills in the missing bass at the listening seat." All models feature adjustable bass tuning ports to alter the bass response to work well with solid state amplifiers, and to help match the bass output to the characteristics of the listening room.
Crossover Design: In order to compensate for the midrange emphasis of SET amplifiers, and to provide a more linear system frequency response, a Zeta of 1.3 is used in the Concerto 2 crossover, and a Zeta of 1.2 is used in the Concerto 3 crossover. The tweeter leg of the crossover is second order at 2500Hz for both the Concerto 2 and the Concerto 3. The woofer leg of the Concerto 2 crossover is first order at 750Hz, that of the Concerto 3 is first order at 900Hz, to compensate for the increased bass output and maintain the proper balance between bass and midrange. The spread between the tweeter crossover frequency and woofer crossover frequency provides a built-in Fletcher-Munson compensation at low levels (the human ear doesn’t perceive bass and treble as well as midrange at low levels), and since SET amps have more midrange output at higher levels relative to the bass and treble, the system frequency response is normalized at both low and high levels. The result is an involving and lifelike presentation at both low and high levels, improved low-level dynamics and resolution, and enhanced nuance and subtlety.
Tweeter Response Characteristics: In both the Concerto 2 and Concerto 3, the Fountek JP3.0 ribbon tweeter has a 15 ohm non-inductive resistor, and the tweeter waveguide provides 3-4 dB of gain between 2500Hz and 8000Hz, which provides the proper balance between bass, midrange, and treble at low and high levels. Also, dynamic transients in the tweeter frequency range are thus more immediate and provide a greater sense of presence. The frequency range between 2500Hz and 8000Hz contains the harmonic overtones, formants, spatialization cues, and timbral characteristics of acoustic instruments and voice, so the subtleties and nuances of the performance are reproduced in a compelling and immediate manner. Since the tweeter output is acoustically amplified by the waveguide, there is much lower distortion at both low and high levels. This reduced distortion from 2500Hz on up provides a smoother, silkier treble response unobtainable without the use of the waveguide. An additional benefit of the reduced distortion and increased dynamic range is improved soundstage depth and transparency.
Constant Directivity Waveguides: The constant directivity waveguides for the tweeter and woofer are formed in the 2” thick solid Poplar front baffle, which reduce horizontal and vertical early reflections and room effects, produce a timbrally accurate and dynamic wavefront, and help reduce baffle diffraction effects. In addition to providing directional focus, the tweeter waveguide provides between 3 - 4dB of gain between 2500Hz and 8000Hz, so the signal level to the ribbon tweeter can be reduced, reducing distortion, since the ribbon tweeter diaphragm doesn't have to move as far for a given SPL level. This improves soundstaging and transparency, and provides very low distortion at high SPL levels. The woofer waveguide narrows the midrange wavefront of the 8" woofer between 1000Hz and 1400Hz, which makes room placement easier by reducing sidewall and floor bounce early reflections, thereby reducing notch filter effects caused by the out-of-phase reflections arriving at the ear later than the original wavefront. The 8" woofer naturally narrows the frequency response starting around 1200Hz, where the dispersion angle is around 60 degrees, narrowing with increased frequency above 1200Hz. The woofer waveguide also provides 1-2dB of gain between 1100Hz and 1400Hz, providing increased liveliness and dynamics. The woofer crossover is designed to compensate for the increased output in the operating range of the woofer waveguide, providing a flat frequency response.
Poplar Front Baffle: The front baffles are made from 2" thick single billets of solid Poplar, highly regarded for its low resonance. Acoustically, Poplar highlights the treble and lightens the lower midrange and bass, with a slight emphasis in the lower treble and the middle midrange. Poplar is the wood of choice for several well-known horn loudspeaker manufacturers, in addition to Sonist. The 2" thickness of the baffle provides mass loading to reduce baffle resonance, and the crossovers are tuned to balance the frequency response. The front baffle has a 3/4 roundover on all sides, contoured to eliminate baffle diffraction effects. The constant directivity waveguides are formed into the baffle itself, minimizing alignment anomalies and mechanical resonance associated with separately formed elements. The bass tuning ports are also formed in the baffle, flared to prevent "chuffing" with high energy bass content.
Cabinet Construction: The cabinets are made with ¾” Medite, a high-density type of MDF, mitered panels, with a front baffle made from 2” thick solid Poplar, providing a mass-loaded platform for mounting the drivers. The front baffle is glued to the cabinet face using a tongue and groove design, and corner glue blocks are used throughout to stiffen the cabinet. The tweeter waveguide is formed in the solid Poplar front baffle, using three passes of a pin router with custom templates to provide a smooth and uniform surface. The woofer waveguide is formed with a single pass with a pin router, again using a custom template. The inside circumference of the woofer opening is chamfered to prevent cylindrical reflections. The rear-mounted bi-wire terminal cup is inset into the cabinet to provide a flush-mount with the rear cabinet wall.
Cabinet Finishing: The front baffles, flared bass ports, and tweeter and woofer waveguides are hand-sanded with coarse, medium, and fine grades of sandpaper, and the front edges of the waveguides are also hand-sanded to round off the transition between the waveguides and the front plane of the front baffle. The cabinets are hand-sanded on the edges and corners. The cabinets have one undercoat, two coats of textured paint, and a clear semi-gloss lacquer topcoat. The front baffles have one sealer coat, two coats of stain, and a clear semi-gloss lacquer topcoat.
H-Brace Cabinet Bracing: A ½” thick H-brace is dadoed into the rear inside panel, front baffle, and both sides of the cabinet to stiffen the cabinet. The H-brace is located 3/5 of the distance from the bottom of the cabinet, 2/5 from the top of the cabinet, so that there are no coincident resonances, reducing common standing wave frequencies and sympathetic panel resonances.
Constrained Layer Cabinet Damping: Multiple layers of foam and viscous elastomer are bonded to the interior surfaces of the cabinet with a viscous elastomer sound dampening adhesive to reduce internal resonances and absorb acoustic energy that would otherwise radiate from the outside surfaces of the cabinet. This reduces both bass “boominess” and male and female vocal “chestiness”, so the cabinet doesn’t introduce its own colorations to the presentation.
Driver and Terminal Cup Mounting: Soft rubber grommets are used for mounting the tweeter and woofer, in order to provide air-tight seals, using threaded inserts and Allen bolts. A soft rubber grommet is used to seal the terminal cup mounting flange with the cabinet.
Hard-wired Isolation-Mounted Crossovers: The crossovers are hand-made and hard-wired, no printed circuit boards, using silver content solder and OFC copper wiring. The crossover board is mounted on rubber grommets with threaded inserts and Allen-bolts, to mechanically isolate the crossover components from the cabinet, and to de-couple the crossover board and components from mechanical coupling with the cabinet. The crossover components are further isolated from the circuit board with silicone gasket material, and held in place with elastomer binding straps, snugged down to prevent component vibration during play. The crossover board is mounted on the rear panel behind the tweeter, to prevent airborne vibrations from being transmitted to the crossover from the backwave of the woofer. Silver content solder is used for all connections, and air-core inductors, polypropylene capacitors, and non-inductive resistors are used exclusively in all crossovers.
Grills: The grill frames have outside and inside chamfers to conform to the woofer waveguide angle, covered with black stretchy cloth, mounted with four small disk magnets inset into the grill frame, so there are no mounting pegs or holes. The disk magnets adhere to the metal frame of the woofer.
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