Waveform Research Mach 17 loudspeaker
The loudspeakers I heard that day sounded very dynamic, delivering the frequency extremes with definition and power while providing a wide, deep soundstage and superb imaging. I requested a pair for review.
Readers familiar with Larry Archibald's statement of Stereophile's "firm ground rules" ("The Final Word," December 1994, Vol.17 No.12, p.306) know that a manufacturer must have a minimum of five US dealers before a review of one of their products can appear in this magazine. Why, then, am I reviewing the mostly mail-order Mach 17? Wes Phillips and John Atkinson gave me the go-ahead for several reasons. First, the speaker is a widely advertised (in magazines and on the Internet) mail-order product with a 30-day money-back guarantee—a sales approach the manufacturer claims keeps the product's cost down to $7k. Second, various versions of the 17 have been in production for more than seven years. Third, the street buzz, as well as informal raves from magazine staff who stopped by room 602 during HI-FI '96, is that the new Mach 17 is worth a serious audition. Fourth, the Mach 17 has been adopted as a recording monitor by the Telarc, Delos, and Dorian record labels.
Waveform only makes one product, the Mach 17, which represents the 11th version of the company's basic floorstanding, full-range dynamic speaker. It differs greatly from the much earlier version (roughly a Mach 3) that LA reviewed for Stereophile back in 1989 (footnote 1). Compared to that earlier model, the Mach 17 has two 12" woofers (rather than a single 15"), one midrange (rather than the earlier version's D'Appolito-style double-midrange surrounding the tweeter), and one dome tweeter rather than a dome tweeter plus a ribbon supertweeter. The previous version was bi-, not tri-amplified like the Mach 17. The outboard electronic crossover is now made by Bryston, a leading electronics manufacture, rather than produced in-house. The 17's pyramidal enclosures are four-, not eight-sided. Finally, each Mach 17 enclosure is 55 lbs lighter, and the whole system $2800 cheaper, than the earlier version.
These design changes are the result of a collaboration between: John Ötvös, a master cabinetmaker and audio enthusiast; Claude Fortier, acoustic designer; and the team of Bryston engineers who created the external electronic crossover. However, the continued existence of this product is primarily due to the vision, perseverance, hard labor, and craftsmanship of one man, John Ötvös, who single-handedly spends 75 hours to create each Mach 17 system. This one-man production team can build only 30 such systems each year.
Ötvös's design goals for the Mach 17 are very ambitious. The speaker is claimed to have a flat (±2dB) measured response over the audio bandpass, a smooth vertical response within a 0–30° envelope, and a smooth off-axis response up to 60° horizontally. The Mach 17's dispersion was made the first priority over other design considerations, such as time alignment, or the ability to reproduce a squarewave or step pulse. The 30° and 60° off-axis response curves were honed and refined during many trips to Canada's National Research Council (NRC) Acoustic Testing Laboratories in Ottawa. The Mach 17 was designed to have high power-handling and high sensitivity (over 90dB/1W/1m), while being an easy impedance for amplifiers (no lower than 4 ohms). At the same time, total harmonic distortion was not to exceed 1% for continuous 85dB levels.
The Mach 17's crossover is a special version of the Bryston 10B LR electronic crossover. The front panel features an adjustable level control for each of the three speaker-driver sections. Separate mute switches are placed on the front panel for each driver in both channels, to enable the owner to identify buzzing drivers or poor, noisy connections. It uses all discrete components (which accounts for its 1500 part count) for its 14 discrete class-A op-amp buffer and filter stages per channel (twice as many as the stock Bryston 10B). This provides a complete three-way, 24dB/octave Linkwitz-Riley design.
Waveform calls the Mach 17's external electronic crossover an "active filter." It is argued that there are several advantages to an outboard electronic crossover. Amplifiers driven by an electronic crossover are only required to work within a restricted signal range, so that midrange response can be isolated from the large power demands that might occur from bass transients. This should be evident for instruments like the pipe organ, whose heavy deep-bass notes can make significant power-supply demands on an amplifier. The outboard crossover also means the absence of inductors and impedance-matching circuits from the signal path. The amplifier can then directly control the back electromotive force of the cone driver, which can result in superior transient behavior. Individual loudspeaker driver level controls can aid in room-response smoothing. Furthermore, the manufacturer claims that the design results in reduced intermodulation distortion, and distortion produced by high current-flow within passive crossover components.
The crossover is fully balanced, input to output, to prevent hum or other noise sources from affecting the intricate cabling required for the Mach 17 system. Yes, this means three pairs of high-quality balanced output cables to the amplifiers are needed, in addition to the pair of balanced interconnects from the preamplifier feed. All connections are gold-to-gold to prevent signal degradation from corrosion or oxidized contacts. The manufacturer claims the Linkwitz-Riley alignment used in this crossover corrects phase alignment for all crossover points, and provides a uniform power response.
The disadvantage of the Mach 17's tri-amplification design is the cost of the six channels of similar-gain amplification needed to drive it. John Ötvös, an authorized Bryston dealer, drives the Mach 17 at trade shows with a pair of Bryston 5B-STs, this a three-channel solid-state amplifier with 120Wpc continuous output. The 5B's multiple channels yield savings by enclosing the needed six channels in only two amplifier chassis.
The Mach 17's specified wide dispersion results from mounting the tweeter and midrange drivers in an adjustable, 37-lb, egg-shaped "head module." "The magic is in the egg," Ötvös claims, due to the egg's relative point-source dispersion characteristics. To provide optimal imaging, the egg can be turned or tilted up to 45° left or right, and 13° up or down, to provide exact on-axis response for the listener's seated position. The upper frequencies are handled by a 1" Vifa silk-dome tweeter, the same driver used in the Snell Type A. The midrange unit is a 6" Audax with a vacuum-formed plastic TPX cone, flat surround, vented pole-piece plug, and cast aluminum basket. The vented phase plug improves dispersion at the driver's higher frequencies. The metal baskets of each driver are cut so they can be mounted in overlapping fashion, bringing their acoustic centers closer together.
The egg itself is template-cut on a bandsaw to make the cabinet cavity, with the resulting 16 layers of MDF glued together in a vacuum bag, hand-turned on a lathe, and then further template-worked by jig and router on a bench. The egg is then finished with a silver-pearl glaze over black mini-textured, acid-cured paint. It is then filled with off-cuts of foam and fiberglass to damp back-radiation, and mounted on a base (2.5" of acoustic foam, 3/4" of MDF) called the "transition molding." This base is designed as an absorbent pad to prevent acoustic bounce-back off the top of the woofer cabinet, which would produce a comb-filter effect in the midrange's output. The head module is isolated from spurious bass vibrations by four ¾" rubber dowels and a sheet of 1/16" Neoprene rubber. Electrical connection is made via a 4-pin, gold-plated Neutrik XLR connector. The removable grille is of acoustically transparent cloth on a cage of 1/8" by ¼" bar steel, and weighs exactly 2.83 lbs—"an important number in speaker measurement," John Ötvös reminds us.
The 88-lb woofer cabinet is constructed from ¾" MDF with nine internal braces, has a front baffle constructed of double layers of ¾" MDF, and an internal volume of 4.8 cubic feet. This section's top, on which the head module rests, has a tote handle of black nylon rope; this allows the user to pick up the unit and move it with ease, and folds back to disappear under the head module's transition molding. The cabinet sits on rubber-insulated nylon furniture guides; spikes are not provided. Black-oxide line inlay is provided for the vacuum-formed radius-mitered cabinet edges. The two 12" treated paper-cone Philips woofers are reflex-loaded with two 3" ports, one on each side of the woofer array.
Footnote 1: Back in 1989, Larry Archibald reviewed the four-way, $9800/pair Waveform Loudspeaker (November 1989, Vol.12 No.11, pp.122–132). He praised its dynamics, but criticized the high-frequency boost from its ribbon supertweeter (now gone from the design). This review elicited a 12-page manufacturer's comment (December 1989, pp.237–249) from designer John Ötvös.