Oct 20, 2004 7:36 PM, By Arthur Bloom

ACTIVE NEAR-FIELD REFERENCE MONITORS

At one time, reviewers often concluded that self-powered near-field monitors costing $1,500 or less rivaled the quality of ones costing twice as much. With the $3,000 to $5,000 range undergoing its own quiet revolution, this claim can hardly be made today. For example, the BM15A—an updated, active version of Dynaudio Acoustics' TEC-nominated BM15—is a near-field self-powered monitor whose quality cannot be bought at half the price.

As one might expect from Dynaudio (a company that made its name building hi-fi speakers before entering the professional arena), the BM15As simply sound good. Although my ATC 50As are characterized by a more crystalline accuracy (at twice the price), the BM15As have a sweetness and warmth that makes musical playback an indefatigable pleasure.

With a matte-black finish, beveled edges, bass port and rigid, weighty construction, the BM15A is a professional product from tweeter to woofer. At 42 pounds, the monitor is a two-way design, with the low- and high-frequency drivers powered by 200-watt and 100W discrete MOSFET amps. The crossover is a fifth-order phase-aligned design centered at 1.7 kHz.

Front panel LEDs indicate power on, the engagement of protection circuitry and low-frequency clipping. Rear controls allow the user to trim high and low frequencies with low-Q equalizers (6 dB at 15 kHz and 50 Hz). Inputs are balanced and include toggle switches to vary sensitivity between +4 and -10 dBm.

The soft-dome tweeter is Dynaudio's high-headroom "Esotec" type, upgraded from an earlier version found on the BM15. The Esotec tweeter is a doped, soft-dome, ferrofluid-cooled design, which Dynaudio claims can handle transients of 1,000W. The monitor's 9.5-inch bass driver, however, incorporates Dynaudio's most impressive innovations. With a large dust cap integrated into the cone/dome assembly, aluminum hexagonal wire used for its high-excursion, low-mass 4-inch voice coils and magnets placed at the center of the drivers, the mechanism is simple and lightweight. The magnet's central location even provides inherent shielding. Efficiency is enhanced by the unusual placement of a second ceramic on the top plate to concentrate flux into the gap.

My use of the BM15As during an unusual recording session for Ingram Marshall's forthcoming CD (Dark Waters on New Albion Records) speaks to their versatility. The piece combines live English horn—which is simultaneously processed through a digital delay—with a pre-recorded sample collage on DAT. Rather than feed the outputs from the delay and DAT direct to tape, a single Soundfield SPS 422 Microphone System was used to record the ambient mix of the English horn swith the delay and DAT played through the BM15As in a fabulously reverberant church.

Thanks to the virtues of the BM15As, I WAS able to create an organic mix of live and reinforced sound. Although the monitors were light enough to carry and maneuver, their output filled the church's cavernous nave. Through careful positioning, I avoided feedback and the comb-filtering "Grateful Dead bootleg sound effect" artifacts, which can plague recordings of reinforced audio. Although a similar production could have been created with Pro Tools and some choice plug-ins, the result might not have equaled what I was able to achieve through the collision of real waves in real space. Few readers are looking for monitors applied simultaneously for recording live and reinforced sound, yet the success with which I was able to use the BM15As in this unconventional way indicates something of their prowess.

Though Dynaudio lists the frequency response as 40 to 20k Hz (+/-3 dB), I found the bass response more prominent than this spec might suggest. In addition, Dynaudio instructs users to position each monitor with its off-center port closest to its stereo partner (ports on the inside, tweeters on the outside) to enhance bass coupling.

Indeed, during the BM15A's extended visit to my studio, I was consistently impressed with the chocolate-y goodness of their mid to low frequencies—perfect for the piano samples I was frequently using during this period and perfect for the Sade and Tracy Chapman I would listen to during breaks. At the same time, the BM15As did not want for snap or punch, from “Gettin' Jiggy” with Will Smith, to heralding Stravinsky's “Rite of Spring.”

As with any self-respecting near-field monitor (actually, Dynaudio catalogs the BM15As as near/mid-fields), these pups can bark with SPLs maxing out at 105 dB at 1 meter. Simply put, from project studios looking for an all-purpose pair to larger studios searching for some serious near-fields, the BM15As are worthy contenders.

The BM15As list for $3,599/pair and are compatible with Dynaudio's BX30 subwoofer system (to 22 Hz), which lists for $2,999.

Dynaudio Acoustics, www.dynaudioacoustics.com.

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Lab Analysis: Dynaudio Acoustics BM15A
By Rob Baum and John Schaffer

PHYSICAL CHARACTERISTICS
The BM15A cabinet is constructed of 31/44-inch-thick, black vinyl-covered particle board, miter-folded along the sides, top and bottom. The baffle is 31/44-inch thick, black-painted MDF, which accommodates recessed cut-outs with T-nuts for the drivers, a dual-flared 2.35-inch diameter port and two operational LEDs. The recessed driver mounting avoids certain response anomalies, while the flared ports minimize port "chuffing." A look inside the cabinet reveals a separate, sealed compartment for the plate amplifier mounted on the back. This extra effort spares the amplifier components from excessive vibration. The driver's enclosure includes a cross-brace and two layers of stuffing; the outer layer is polyethylene foam, while the inner layer polyfill.

The woofer is an impressive 8-inch Dynaudio 24W100. This unique driver incorporates a one-piece, straight-wall, polypropylene cone/dust cap, a 11/42-roll rubber surround and a 6-inch-diameter spider. The stamped steel basket includes an integrated housing for the inherently shielded, neodymium motor structure. The motor structure is complemented with a 4-inch-diameter voice coil wound onto an aluminum bobbin. This speaker is capable of high linear excursion, which translates to extended bass at high sound levels. Electrical terminations are dual 11/44-inch male connectors.

The Dynaudio D-260DA tweeter uses a nearly half-sphere, treated cloth dome with a 111/48-inch diameter, underhung voice coil wound onto a vented aluminum bobbin. The deep dome increases stiffness without resorting to hard materials that are not as well-damped. The nonshielded, ferrofluid-cooled motor structure is vented into a sealed plastic cup to lower the tweeter's resonant frequency and linearize the tweeter's phase response at crossover. All of this is secured onto a cast-aluminum waveguide/faceplate. A three-legged aluminum cage is mounted onto the front of the faceplate to protect the diaphragm. Diametrically opposed voice coil lead-outs provide stability and balance and are terminated by dual 11/44-inch male connectors.

The amplifier has a balanced XLR input with a +4/-10dBm sensitivity switch. Trim pots for the woofer and the tweeter range from -3 dB to +3 dB. The amplifier's neatly arranged, double-sided, glass-epoxy circuit board has plated-through holes. All components’ construction is top-quality. A low-hum field toroidal transformer is used in the power supply.

ACOUSTICAL CHARACTERISTICS
Like the Yamaha NS-10M and Sundholm Acoustics monitor (both of which we have tested), the BM15A's sonic footprint resembles that of a consumer loudspeaker. These monitors are not flat and are not designed to be flat. They enable the recording engineer to hear the track the way much of the population hears it, as if through a home stereo, rack system, portable system or automobile. In fact, except for the decade between 500 Hz and 5,000 Hz, the response is smooth. The off-axis response isn't flat either, but it's smooth and well-controlled, tapering only -2 dB from 1,000 Hz to beyond 10,000 Hz.

The transient response reveals that the acoustic centers of woofer and tweeter are correctly aligned without any physical offset. As well as being time-coherent, the transient response is well-damped.

The distortion response, which was measured at around 95 dB SPL, indicates that the THD remains at approximately 1%, except for the tweeter's upper-response limit. The spectral contamination, a test comprising an input of multiple tones, tests the speaker's self-noise. This particular speaker system had an impressive signal-to-noise ratio of around 55 dB.