Synthesis LM210 Speaker System Review

Synthesis loudspeaker systems are designed and manufactured by a subsidiary of Conrad-Johnson, a well-known manufacturer of high-end amplifiers and preamplifiers. While offering the quality and attention to detail for which Conrad-Johnson electronic components are noted, the Synthesis products are priced to meet the needs of a somewhat broader market.

The compact and attractively styled Synthesis LM210, which looks like a miniature version of the flagship Synthesis Reference System, is the smallest and least expensive speaker in the line. A two-way floor-standing system, it is only 10-1/2 inches square and 33-1/2 inches tall. Its 6-1/2-inch polypropylene-cone bass/midrange driver operates in a ported enclosure with twin vents on the front of the cabinet. All internal wiring is soldered (no clip connectors are used). The system crosses over at 1,500 Hz to a 1-inch soft-dome driver, which, like the woofer, is made in Denmark. The crossover network uses high-quality polypropylene capacitors and air-core inductors. The enclosure’s venting alignment and the crossover characteristics are designed to give the system a Bessel-type response with linear phase shift through the crossover region. The crossover slope is initially a gradual 6 dB per octave, increasing eventually to 12 dB per octave. The 1,500-Hz crossover frequency was chosen to minimize the audible breakup effects that can occur even in 6-inch drivers between 1,500 and 2,500 Hz.

The cabinet is constructed of 3/4-inch Medite (a type of particle board) veneered with oak on all sides and with 1-1/4-inch solid oak along the edges. All the corners and edges are rounded. The drivers and ports are on the upper section of the front panel, which is angled backward about 20 degrees for time-alignment of the drivers and reduced internal low-frequency standing waves. Internal padding with 1-1/2-inch-thick damping material reduces high-frequency standing waves. A black cloth grille snaps onto the front panel of the speaker.

The speakers are supplied with spikes that can be screwed into threaded inserts in their bases to make a more positive contact with the floor. Each speaker weighs about 32 pounds. Price: $1,195 per pair.

Lab Tests

The averaged room response of the pair of Synthesis LM210 speakers we tested varied only ±3 dB from 150 to 20,000 Hz. The only obvious departures from smoothness were a peak and a dip, each about 4 dB in amplitude, at 250 and 500 Hz, respectively. A room-response measurement at these frequencies (especially the lower one) is subject to boundary effects, so these anomalies in the room response cannot be clearly assigned to the speakers themselves.

Close-miked measurements of the woofer output, however, showed a similar peak and dip. The reason was apparent when we measured the low-frequency output at one of the vents—it had a 15-dB peak at 210 Hz and a minimum at 500 Hz. A similar 15-dB peak appeared at 2.000 Hz, although it did not appear distinctly in the room-response measurement. When the vent and cone outputs were combined (with allowance for the different diameters of the two sources), the resulting bass-response curve was flat within ±3 dB from 30 to 1,700 Hz.

The system’s composite frequency response was ± 3 dB from 28 to 20.000 Hz and quite smooth over that range except for a 5-dB depression, a little less than an octave wide, centered at 500 Hz. Our quasi-anechoic response measurements with the IQS FFT analyzer were in general agreement with the swept-frequency measurements. The horizontal dispersion of the tweeter was excellent, and the response curves on-axis and at 45 degrees off-axis diverged only above 10,000 Hz.

Because of the designers’ obvious efforts to achieve linear phase shift, we were especially curious to check the LM210’s group-delay characteristic. It was a pleasant surprise to find that the group delay—a measure of phase linearity—was exceptionally uniform. It varied less than ± 0.1 millisecond from about 700 to 30,000 Hz. Even in the woofer range, where group-delay variations are normally much larger (and where they generally have not been shown to be audible), the delay was constant within ±12 milliseconds.

The minimum impedance of the LM210 was 6.7 ohms at 150 Hz, and its maximum was 35 ohms at 55 Hz. The two bass resonances were at 22.5 and 55 Hz. System sensitivity was moderately low, 85.5 dB sound-pressure level (SPL) at 1 meter with an input of 2.83 volts of pink noise. The bass harmonic-distortion readings were relatively high with a constant input of 4.7 volts (equivalent to a 90-dB spl output). Distortion readings were in the range of 3 to 6 percent from 200 Hz down to 50 Hz but rose rapidly at lower frequencies. In pulse-power tests, the woofer cone rattled with a 100-Hz input of 300 watts into its 7.5-ohm impedance. At 1,000 and 10,000 Hz, the 12-ohm speaker impedance limited the maximum power our amplifier could deliver. At both frequencies the amplifier clipped, at about 600 watts, before there was any sign of distortion in the speaker’s output waveform.

Comments

From our first hearing of the Synthesis LM210’s, it was clear that their sound quality was well above average. The frequency balance (the proportion of lows, middle, and highs in the output) was excellent, and the speakers always sounded much larger than they really were. Part of the reason for their big sound was their extended sound stage, with a noticeable feeling of depth and height. We placed the speakers about 2 feet from the wall behind them and 4 feet from the side walls, and the width of the stereo stage was also somewhat greater than the actual spacing between the speakers. We did not use their mounting spikes.

After making our measurements, we tried—unsuccessfully—to detect by ear the lower-midrange irregularities that showed up in our tests. Despite their apparently extended low-frequency response, however, the LM210’s could not deliver a useful amount of bass below about 50 Hz. Any attempt to put more than a few watts into them at 30 Hz or below produced an audible fluttering of the woofer cone and accompanying rasping sounds. A good low-cut filter in the amplifier would be highly desirable in a system using these speakers.

Because of the exceptional spaciousness of their sound, we were curious to hear how the LM210’s would perform with the Carver Sonic Holography system, which requires a very linear phase response for its best effect. The results were all we could have hoped for: The already sizable sound stage the speakers produced expanded to fill the room in a most spectacular way.

We never tired of listening to these speakers, whose sound belied their size, weight, and cost. All high-fidelity sound reproduction is an illusion, of course, but the LM210’s managed to create and sustain that illusion more effectively than most speakers we have used. Doubtless this effect was enhanced by their compact dimensions. They really did not make themselves obvious, even in a small room, yet the sound managed to be as large as it should have been, whether we were listening to a solo voice or a full orchestra. The designer of these terrific little speakers obviously knew what he was about.

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