Hales Audio System Two Signature loudspeaker

When a loudspeaker designer produces a world-class product, it is usually the result of years, perhaps decades, of experience gained from designing less ambitious products. To review a particular designer's product history is to witness the learning curve in action as both his skill and technology advance. Successfully battling the laws of physics to produce a truly exceptional loudspeaker is thus thought of as the domain of the seasoned veteran whose vast knowledge and experience culminate in the pinnacle of his career—a world-class loudspeaker. Moreover, it is just these designers, working their way up to their masterpiece, who are the most successful at getting an ambitious design right. The high-end loudspeaker business is littered with the remains of companies that attempted to build a first product far too lofty for their skills.

Having said all that, is it possible that the Hales System Two Signature loudspeaker, the first product from a new company and a 22-year-old designer (footnote 1) can be a real contender in the highly competitive $5000 loudspeaker market? The answer, surprisingly, is yes. Without getting too far ahead of myself, I will say that the Hales System Two Signature is a remarkable achievement in dynamic loudspeaker design.

Hales Audio was founded by designer Paul Hales and two partners in 1988 to build the original Hales System Two. An audiophile and speaker designer since his early teens, Paul Hales started building loudspeakers for friends while at college studying mechanical engineering. During his senior year, he worked on the design of the System Two. As graduation approached, he had to make the choice between getting a real job or pursuing his dream of building a commercially successful loudspeaker business. The System Two was introduced at the 1989 Winter CES in Las Vegas. Shortly afterward, Paul decided to make a no-compromise version of the System Two that kept the same design principles, but took them to their ultimate realization. The result is the System Two Signature reviewed here.

Technical description
The System Two Signature is unusual in appearance, yet strikingly beautiful. The very narrow and deep enclosure (11" by 21") gives the appearance of a small cabinet when seen on axis, and a very large enclosure when seen from the side. The cabinet is finished in stained walnut, giving it an exotic, rosewood-looking color. Solid walnut is used on cabinet edges, adding to the Signature's elegant appearance.

Moving on to the technical details, the Signature is a two-way system employing dual 7" Dynaudio woofer/midrange drive-units wired in parallel and a single MB titanium-dome tweeter crossed over at 2kHz. The drivers are mounted toward the top of the enclosure and configured in a D'Appolito arrangement. The tweeter is located between the woofers so that it coincides with their acoustic center to simulate a point-source radiation characteristic. In addition, variations in vertical radiation pattern—the lobing effect—are reduced, resulting in a smooth dispersion and less sensitivity to listening height.

The Dynaudio 17W75EXT woofers were chosen for bass performance as well as midrange characteristics since they must reproduce a fairly large portion of the spectrum. These drivers are somewhat unusual in that the magnet is inside the voice-coil, resulting in greater concentration of magnetic flux. In addition, the voice-coil is 3" in diameter, which is generous for a 7" driver. Woofer loading is said to be a balance between LF extension and transient performance. The popular MB Electronics MCD25 titanium-dome tweeter has a smooth response and a very high "oil-can" resonant frequency.

Rather than mount the crossover inside the cabinet, it is enclosed in an external unit designed to lie just behind the loudspeaker. The crossover, which appears to be made of cast iron, is sand-filled and has threaded inserts for spikes. Between the cast iron, sand, and electronics, the crossovers weigh in at 24 lbs each. Two pairs of Edison-Price Music Posts protrude from the crossover enclosure for bi-wire connection to a power amplifier. Jumpers are supplied for single-wire operation. Connection between crossover and speaker terminals is made by two pairs of Cardas Hexlink 5 cables that are an integral part of the crossover. The rather short (12") cable dictates that the crossover be located right behind the loudspeaker. Like the crossover, the loudspeaker cabinet holds two pairs of Music Posts that receive the Hexlink. To reduce the chance of miswiring between crossover and loudspeaker, the cable pairs and speaker terminals are color-coded. In addition, the vertical alignment between the two pairs indicates correct connection. Getting these cables backwards would low-pass filter the tweeter and high-pass filter the woofer, sending low frequencies to the tweeter and resulting in its certain death. Care should thus be exercised when making this apparently simple connection.

Mounting the crossover externally is an unusual design. The only other speaker with an external crossover that comes to mind is the Avalon Ascent. The rationale behind this expensive feature is isolating the crossover components from the mechanical vibration present inside the loudspeaker enclosure. According to Paul Hales, such vibration can induce voltages, albeit tiny ones, in crossover components and thus introduce distortion in the input signal. Filling the crossover with sand and mounting it on spikes further isolates crossover electronics from vibration. In addition, Paul Hales believes splitting the frequency spectrum as close to the amplifier as possible and providing the signals with frequency-optimized conductors is beneficial.

The crossover is a second-order filter that, combined with the acoustic rolloff of the drivers, results in an effective third-order slope. The Butterworth topology features a tweeter padding network and a diffraction loss compensation circuit in the low-pass section. Solen and Wonder Cap polypropylene capacitors and Solen 14-gauge air-core inductors are used throughout.

Perhaps the most elaborate aspect of the Hales System Two Signature is the enclosure. Rarely is such attention paid to the cabinet's mechanical characteristics and contribution to the sound. The emphasis on solid mechanical design reflects Paul Hales's mechanical engineering background and a current trend in dynamic loudspeakers.

First, the cabinet is constructed with 2"-thick MDF side walls and a 4" thick MDF front baffle. This extremely dense front baffle provides the drivers with a rigid surface that holds the driver assembly stable, preventing spurious motion between magnet and voice-coil. Inside the enclosure, five horizontal braces support the walls to reduce resonances. These plywood braces have four large holes to prevent acoustical partitioning of the cabinet. The brace positioning is designed not only to minimize resonances, but to distribute the resonant frequencies uniformly. Careful attention was paid to avoiding the coincidence of one panel's fundamental resonant frequency with another's harmonic resonance. In addition to reducing and distributing panel resonances, the braces break up acoustical resonances within the enclosure.

The theory behind this design is similar to that used in choosing listening-room dimensions. Optimal room ratios distribute room resonant modes so that, besides not having the same fundamental resonant frequency, the harmonics of one mode do not coincide with the fundamentals or harmonics of another mode. Although the modes still exist, the peaks are distributed smoothly throughout the low-frequency band, avoiding a large pileup at certain frequencies that are more audible. For example, the worst case is a box-shaped room in which all the dimensions are identical. Each pair of surfaces (length, width, height) would have the same resonant frequency, thus creating a huge peak at that frequency. The next worse case is where one dimension is double that of another dimension. The second harmonic of the longer dimension would coincide with the fundamental of the shorter dimension, again creating a pressure peak at that frequency. Good room design distributes these resonances so that, instead of overlapping, they fill in the nulls between peaks. The result is lower amplitude resonances and less audibility of them since they are surrounded by neighboring modes.

The panel section sizes between braces are similarly optimized in the System Two Signature to spread out the resonant energy. To further damp resonances, the interior is filled with 6" of rigid fiberglass behind the woofers and longhaired wool in the rest of the enclosure. Paul Hales believes that by reducing the cabinet's contribution to the reproduced sound, dynamic loudspeakers can have the openness, transparency, detail, and resolution of planar designs, without sacrificing those qualities we like in moving-coil loudspeakers: dynamics, high spls, and ease of placement. The decision to lavish such extensive design work and formidable construction on the System Two Signature was inspired by the Wilson WATT. Paul Hales, after hearing the WATT and the result of isolating the sound of the drivers from box resonances, decided to build his own loudspeaker in a no-compromise enclosure.

Cabinet resonances, in addition to coloring the spectral balance, create time smearing of the signal. The cabinet stores acoustical energy as mechanical energy, then releases it as acoustical energy slightly delayed in time with respect to the sound radiated by the driver. The result is loss of image specificity, poor soundstaging, and obscured inner detail. This time-domain dispersion can be revealed on MLSSA's cumulative spectral decay plots (though it must be noted that without access to a large room, the system's resolution in the lower midband, the frequency region where such cabinet problems are endemic, is limited).

Footnote 1: Paul Hales, now 24 years old, was 22 when the Signature's design was finished.
Hales Audio
Company no longer trading (2006)