May 1, 1999 5:39 PM, By George Petersen

Although Sundholm may not be a familiar name in pro audio, Conrad Sundholm, the company’s president/chief designer, is hardly a newcomer to the industry. He founded Sunn Musical Equipment in the mid-1960s and later started Biamp Systems. Several years ago, Sundholm’s son began a recording studio and asked his father to help him pick out some studio monitors. They auditioned a wide variety of market offerings and, disappointed in what they heard, Sundholm took on the task of designing a pair of affordable, yet high-quality, studio monitors. The SL6.5w and SL10/s are the result.

The system is based around the SL6.5w, a two-way, full-range monitor with a 6.5-inch polypropylene cone LF/MF driver and a 1-inch-dome tweeter set back into a conical waveguide. The latter provides wide dispersion with the added benefit of placing the voice coils of the two drivers into acoustical alignment. The 25-pound, 15.5x10.5x11.5-inch cabinet is front-ported, and the drivers are arranged in mirror-imaged pairs. Retail is $795 a pair.

Complementing the SL6.5w monitors is a pair of SL10/s subwoofers, each featuring a front-firing 10-inch LF driver in a 32x11.5x15-inch (HxWxD) enclosure with dual front ports and an internal crossover for driving the system using a single stereo power amp. The passive subs are priced at $1,295 a pair. (Also available is the SL10/ps, the 200W powered version, retailing at $1,795 a pair.) It should be noted that the SL6.5w’s are full-range monitors and can be used either alone or with the subs, allowing the owner to start out with the mains and add the subs as necessary.

The Sundholm system provides several nice touches. The subwoofers’ 32-inch-high enclosures double as stands for the SL6.5w monitors, placing the acoustic center of the top cabinet at approximately 44 inches from the floor, a near-optimal height for seated listening in the near-field. The subs include four padded feet for each SL6.5w, designed to acoustically decouple the top monitor from the sub. Each SL6.5w monitor also includes a soft, dense-foam plug that is inserted to block the port when the monitor is used with the subwoofer. This allows the SL6.5w/SL10/s combination to do double-duty as an extended-range system in the studio or used separately—perhaps with the top units filling in as a portable near-field set when the engineer travels to another studio.

The rear panels of all the speakers include recessed cups with gold-plated, five-way binding posts and large-diameter holes to accommodate (10/12 AWG) heavy gauge wire. And speaking of wire, the SL6.5w monitors are equipped with removable straps and an extra set of inputs to handle bi- or tri-wiring applications. Setup requires little more than connecting the subs to your power amp and the monitors to the subs. However, the speakers are not magnetically shielded and should be kept at least 15 to 18 inches away from computer and video displays. (Sundholm informs us that a shielded version of the SL6.5w will be available soon.)

The Sundholm monitors do require a fair amount of power (150 to 250 watts recommended), and while not overly sensitive to the amp used, will quickly spotlight the flaws in a low-quality amp. I began with the SL6.5w speakers alone, sans sub, powered by a Bryston 4B amp, which offered plenty of punch and ample headroom. Listening to a CD I produced of a brass quintet (plus trap drummer) playing 19th-century dance pieces, the quality of the Sundholm monitors was easily discernible, from the midrange smoothness of the trombone and French horn, the snap of the trumpet and piccolo trumpet, to the crisp reproduction of the snare and cymbals. The low-end balance (in this case, mostly tuba and double-headed kick drum) was even and right, extending well below 60 b. At no time were the highs shrill, overextended or brittle.

The tweeter waveguides create a fairly wide dispersion pattern with a comfortably wide sweet spot. The HF reproduction remains constant to about 20° off-axis, after which the top end rolls off sharply. The imaging was excellent, providing a clear impression of the soundstage, allowing the engineer to hear changes in stereo mic placements and techniques clearly.

Attaching the optional subwoofers to the system opened up a new dimension, bring the LF response down to a thumping -3dB down point in the 38Hz range. The subs’ cabinet volume is in excellent proportion to the 10-inch woofer’s requirement, and placing the LF driver toward the top of the enclosure allows for proper coupling with the drivers in the top box and helps prevent standing waves between the floor and the ceiling. And although bass energy tends to be nondirectional in nature, a dual subwoofer system goes a long way toward eliminating hot spots and providing even LF coverage, even in a smaller control room.

In studio sessions on rock, jazz and pop material, mixes made on the SL6.5w’s monitors translated very well to playback on a variety of other speakers, ranging from top-end audiophile systems to cheap boom boxes and just about everything in between.

The response was natural and unhyped, which is a marked difference from many low-cost monitors that may add a couple “marketing” bumps to make them sound “better” in the extreme frequency ranges. Retailing at $795 a pair, the SL6.5w monitors are an excellent value; add in the subwoofers and you have a system that can hold its own against monitors costing much more. Anyone seeking a versatile monitor system with realistic reproduction should check these out. Sundholm Acoustics, www.sundholm_acoustics.com.

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Lab Analysis: Sundholm Acoustics SL6.5w Monitors
By John Schaffer and Rob Baum

Physical Characteristics
The Sundholm SL6.5w cabinet is a bass-reflex design with a flared 2-inch-diameter port on the baffle. The cabinet is constructed of 3/4-inch-thick MDF with a speckled granite paint finish. The woofer is recessed and flush-mounted onto the baffle with T-nuts. The tweeter is recessed an inch into the baffle, secured by wood screws and topped off by an MDF waveguide, which acoustically aligns the two drivers. There is an MDF cross-brace inside the cabinet between the woofer and tweeter. Fiberglas insulation is on five of the six internal surfaces, but not completely covering each surface (which may explain the minor spikes in the tail end of the time response at approximately 4.2 and 5.1 milliseconds on the impulse response graph).

The 61/2-inch woofer appears to be sourced from Vifa. It includes a 11/4-inch-diameter voice coil. The formed curvilinear polypropylene cone has a half-roll rubber surround, which is more environmentally stable than a typical paper cone with a foam surround, and is topped off with a soft rubber dust cap. The 3.5-inch-diameter flat spider is mounted to a black cast-aluminum frame, which, in turn, is secured onto a 0.22-inch-thick top plate. This unshielded design uses a 3.56-inch-diameter, .67-inch-thick ceramic magnet. Male terminals allow for both 0.205-inch and 0.110-inch connectors.

The Vifa tweeter has a 1-inch-diameter soft-dome diaphragm made from treated polyester cloth mounted onto a 4-inch-diameter plastic faceplate, which is covered by an MDF waveguide. The conventional motor structure (top plate, magnet, back plate/pole piece) is unshielded, but the pole piece is vented into a damped, sealed plastic enclosure to lower the tweeter’s resonant frequency, reduce reflections and cavity resonances. Terminations are dual-male 0.110-inch connectors.

The crossover features two pairs of gold-plated, five-way binding posts with straps, allowing full-range or bi-amp operation. The binding posts are mounted onto a plastic terminal cup. Inside the enclosure, the crossover components are soldered point-to-point, arranged neatly onto a Masonite board.

Acoustical Characteristics
This monitor possesses a fairly flat frequency response. Aside from a 1/2-octave-wide peak centered at 700 Hz, the frequency response varies only ±1.5 dB from 100 to 20k Hz. During the last octave, 10 to 20 kHz, there appears to be some comb filtering, probably attributed to the minor discontinuities of the MDF waveguide and tweeter faceplate. The off-axis response is surprisingly smooth. From 700 to 20k Hz, the sensitivity rolls off 10 dB at a nearly constant slope.

The Sundholm’s impulse response is fairly well damped, except for the two minor spikes spaced about 0.9 milliseconds apart, probably due to internal cabinet reflections. The woofer and tweeter appear to align in time due to the physical offset of the tweeter.

Due to the quality of the Vifa transducers, the distortion response is fairly low. The distortion measurement was taken around 85 dB and shows that the system maintains below 1%, with just a few data points over 0.5%. The spectral contamination reveals that the self-noise of the speaker is around 50 to 55 dB down from the input signal.