Boston Acoustics Lynnfield 500L loudspeaker Page 2

The tweeter AMD is injection-molded from high-temperature, glass-filled nylon. This technique assures the closer tolerances (±0.001") necessary for accurate tuning of the tubes to much shorter wavelengths. This is a novel approach to loudspeaker design—rather than try to suppress cone ringing, the AMDs simply attenuate it before it can reach the listener.

While this is a clever idea, I was concerned about diffraction from the large structures in front of the midrange and so close to the tweeter. Most designs avoid protrusions from the baffle, sometimes even flush-mounting the heads of driver-mounting bolts.

The designed-from-scratch driver complement comprises two 6.5" woofers, a 5.25" midrange, and a 1" aluminum-dome tweeter. The midrange and tweeter are mounted in a single-cast chassis to bring the drivers as close together as possible. This arrangement is said to better mimic a point source. The midrange/tweeter chassis is a massive unit with heatsinking fins. A large bolt secures the midrange/tweeter chassis from the rear, leaving no exposed hardware on the front panel.

The 5.25" midrange is made almost entirely from aluminum, including the cone, chassis, dustcap, and voice-coil former. The company says this results in better heat-sinking and high power handling. The tweeter diaphragm is a 1" aluminum dome mounted in a unique magnet structure. The small but powerful neodymium magnet is inside the voice-coil. A perforated steel grille and tiny AMD cover the dome.

The two 6.5" woofers have fiber rather than aluminum cones. Lynnfield claims the fiber cones have a smoother rolloff and less midband ringing. Unusually, the woofers each use two spiders.

The bass enclosure is a bandpass design, with the two 6.5" woofers mounted internally. The woofers fire into the ported lower section, and the enclosure's upper 80% is a sealed chamber. This dual-chamber approach reportedly results in the control of a sealed box but the extension of a ported design.

Both the bass unit and midrange/tweeter cabinets are made of 1"-thick MDF. The midrange/tweeter enclosure has two internal braces and is filled with polyester-fiber damping material. The bass enclosure uses three figure-of-eight braces in addition to the horizontal panel on which the woofers are mounted.

The crossover features a fourth-order high-pass slope on the tweeter, a second-order high-pass and low-pass on the midrange, and a second-order low-pass in the woofer network. The tweeter circuit has an additional capacitor to steepen the conventional fourth-order rolloff. Electrolytic capacitors are used in the woofer and midrange circuits, and Mylar types in the tweeter network. Internal wiring is 14-gauge oxygen-free copper. After assembly, each 500L is measured to ensure that its response is within ±0.5dB of the reference.

Incidentally, one of the midrange drivers started buzzing after being subjected to pink noise during break-in. Boston Acoustics sent me another pair of midrange/tweeter modules which worked fine, even after more strenuous break-in.

Overall, I was impressed by the level of engineering effort and manufacturing execution in the 500L. This is obviously an innovative, ambitious, and beautifully executed loudspeaker. I was eager to hear how it sounded.

Setup
My listening room has recently been host to two loudspeakers priced somewhat near the Lynnfield 500L's $5000: the $3900/pair Thiel CS3.6 and the $6200/pair Genesis III (reviewed in Vol.16 No.5, p.94 and this issue, respectively). I thus had a good basis for judging the 500L's relative merits.

I found the 500L sounded best when the internal wiring was bypassed. This requires, at a minimum, bi-wiring the 500Ls, with best results obtained by tri-wiring them. I ended up using 8' tri-wired runs of AudioQuest Midnight and Sterling.

Although the owner's manual suggests that the 500Ls can be placed very near the wall behind them (3"), I found them to boom if less than about 2' away. Further, soundstage depth was restricted at this distance. The best place in my room was with their rear panels about 52" from the rear wall. A slight toe-in snapped the center image into tight focus, but at the expense of a brighter overall balance. My listening height was 36", just below the tweeter axis. (I found very little difference in tonal balance between 30" and 40" listening heights.)

As suggested by the manual, the asymmetric satellites were positioned with the tweeters to the inside edges. Two ASC Studio Traps were mounted absorptive-side-out between each 500L and the sidewall, greatly attenuating the primary sidewall reflection. Finally, I broke-in the 500Ls by running pink noise into them for several days with the loudspeakers facing each other and wired out of phase.

The supplied spikes are so short (½") that the 500Ls rested mostly on the thick carpet. Moreover, some of the leveling knobs were so tight that they were nearly impossible to turn by hand. These factors, coupled with the impractical terminal posts, made setting up the 500Ls difficult at best. I ended up using longer spikes from another pair of loudspeakers and Monster Cable's X-Terminators for attaching spade lugs to the posts.



Footnote 2: Both Tom Norton and I also thought the 500Ls sounded too bright during our auditioning, both in Robert Harley's room and in Stereophile's dedicated listening room.—John Atkinson
COMPANY INFO
Boston Acoustics
300 Jubilee Drive
Peabody, MA 01960
(508) 538-9000
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