Optimus PRO LX5 Speaker System Review

The Optimus PRO LX5 (sold through Radio Shack stores) is a compact, inexpensive loudspeaker featuring a novel wide-dispersion tweeter that radiates to the front and rear in a dipolar pattern. Designed and manufactured by Linaeum Corporation, the tweeter crosses over at approximately 2.5 kHz to a nominally 5-inch cone woofer operating in a small vented enclosure.

The PRO LX5 enclosure is made of die-cast aluminum with a dark gray, suede-like textured finish. The black grille unsnaps to reveal the woofer cone and two small ports (each about 5/8 inch in diameter). The tweeter, mounted on the top of the speaker, is covered by a perforated metal grille retained by four screws.

The externally visible portion of the Linaeum tweeter consists of two sections of thin plastic about 1-1/2 inches wide, each forming an oval loop extending about 3 inches along the speaker’s front-to-back axis. Apparently the loops act as pulsating diaphragms, driven in a manner not readily visible from the outside (even with the perforated grille removed).

It was easy to verify by listening that the tweeter radiated two lobes to the front and rear and had virtually no radiation from the sides — the classic figure-eight pattern characteristic of a dipole radiator. The broad lobes of the pattern provide a wide angle of coverage to front and rear, with the portion of the rear output that is reflected from the wall behind the speaker enhancing the sound’s spatiality.

The specifications furnished with the PRO LX5 state that its response extends from 85 Hz to 25 kHz, and a printed “typical” response curve indicates a reasonably uniform output from about 150 Hz to 35 kHz, with a sharp drop at higher frequencies and bass output decreasing at about 10 dB per octave below 150 Hz. The other specifications include a 50-watt power-handling capacity (with a maximum of 100 watts) and a nominal 8-ohm impedance rating.

We tested the Optimus PRO LX5 speakers on 30-inch stands, about 9 feet apart and 18 inches in front of a wall. The room response, averaged for the two speakers and corrected for high-frequency boundary absorption, was notably uniform from about 500 Hz to 20 kHz, with a variation of ±3 dB over that range. The close-miked woofer response closely resembled the printed curve, peaking to a maximum at 150 Hz and falling at 10 dB per octave from there to 20 Hz.

A composite response curve, created by splicing the bass and room-response curves, showed a smooth, flat output over most of the audio range, with a rise at the 20-kHz upper limit of our measurement that gave some credence to the manufacturer’s curve. But although the woofer did indeed put out a useful level at 85 Hz, the maximum output at 150 Hz exceeded that level by some 10 dB.

The Linaeum tweeter’s horizontal dispersion was excellent, with no significant change in output between on-axis and 45-degree off-axis measurements below 10 kHz and a drop of about 10 dB in the 15-kHz range. But because of the system’s unusual radiation pattern at high frequencies, our

MLS quasi-anechoic response measurements tended to be more ragged than usual. The multiple reflected outputs from the rear radiation, which tended to smooth out the room measurements, created unavoidable interference patterns in the MLS tests. Group delay (a measure of phase linearity) was unusually low.

The speaker’s impedance minimum was about 5 ohms at 70 and 250 Hz, with peaks of 35 ohms at 130 Hz and 20 ohms at 40 Hz and 1.6 kHz. The system sensitivity was 86 dB sound-pressure level (SPL) at 1 meter with an input of 2.83 volts of random noise. We measured the woofer distortion with a 4.2-volt input, equivalent to a 90-dB SPL at 1 meter. Above about 150 Hz the distortion was between 0.6 and 1 percent, but it rose to almost 5 percent at 100 Hz and to 10 percent at 80 Hz.

Despite its small woofer, the Optimus PRO LX5 was able to handle rather large inputs of single-cycle tone bursts without damage. At 100 Hz the woofer cone bottomed with an input of 95 watts, which is quite respectable for a 5-inch driver. At 1 kHz the woofer easily absorbed everything the amplifier could dish out, at 530 watts, and at 10 kHz the Linaeum tweeter had no trouble handling a 1,200-watt input.

The Optimus PRO LX5, despite its low-frequency limitations, produced a surprisingly balanced overall sound, with no obvious lack of bass. Undoubtedly this was because of its very healthy output between 100 and 500 Hz, which gives a good sense of the lower octaves without sounding boomy or unnatural. The speaker’s wide, smooth, and well-dispersed middle-and high-frequency output distinguishes it from many others of similar size and price.

In A/B comparisons against other speakers of comparable size, the PRO LX5 easily held its own. When we teamed it with a good subwoofer, the combination was thoroughly satisfying, with the PRO LX5’s own low-frequency rolloff nicely complementing the subwoofer’s frequency range. Actually, the most interesting aspect of this combination was how little the subwoofer added to the system’s sound. Only with programs containing strong, deep bass (under 50 Hz or so) was there any obvious difference in the sound when using the subwoofer.

The Optimus PRO LX5 is clearly an excellent value, and a lot of speaker for its size and price.

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