RadioShack Optimus Pro LX5 loudspeaker By John Atkinson   •   June, 1995 It was a classic American tale: hearing that the head honcho of RadioShack was in town, the principals of Oregon-based high-end loudspeaker manufacturer Linaeum found out where he was staying and called him to see if RadioShack would be interested in marketing their speakers. They were rewarded for their daring by being given an introduction to the right RadioShack department head, and before you could say time-coherent, a deal was struck for RadioShack to manufacture a new line of three "audiophile" loudspeakers featuring a version of the unique Linaeum tweeter. The less-expensive Optimus Pro X77 and LX4 models use a baffle-mounted tweeter that radiates just to the front; the top-of-the-line Optimus Pro LX5 reviewed here mounts a bi-directional tweeter on the top of a diecast aluminum enclosure.

Although the LX5 is list-priced at $149.99, I actually bought the review pair of speakers on impulse for just $99.99 each in one of the regular RadioShack sales. If the speaker sounded even half as good as the gossip in cyberspace had indicated, it would be an audiophile bargain.

What's so special about the Linaeum tweeter? In a conventional tweeter, a coil of wire suspended between the circular poles of a ring-shaped magnet moves backward and forward according to the dictates of the electrical signal, driving a dome or cone diaphragm to excite the air. In the Linaeum tweeter, there's still a voice-coil, but this time it's flattened into a vertical shape and suspended between opposed rectangular magnet poles. It still moves backward and forward, but instead of driving a diaphragm, it pushes and pulls the vertical joining point of two semi-cylindrical 3"-long sheets of stiff plastic film, each of which is fixed at its other end. Imagine two (empty) beer cans side by side: the point where they touch is where the voice-coil is attached. Under the influence of the electrical signal, the two semi-cylinders rotate back and forth, the resultant traveling waves producing sound.

The advantages over a conventional tweeter are a uniformly wide horizontal dispersion pattern and good linearity, both of which lend the tweeter some of the attributes of a good planar drive-unit. If, as in the LX5, two sets of diaphragms are placed back to back with a common magnet structure, sharing a common voice-coil, those at the rear pull when the front ones push: the radiation pattern is that of a dipole. The radiation to the rear should produce an enhanced feeling of "airiness" to the speakers's sound in all but the very deadest rooms.

According to Linaeum's Ben Stutz, Linaeum assembles the tweeter subassemblies for RadioShack, shipping them to the Far East to be incorporated into the speakers. (The LX5, for example, is made in Malaysia.) The tweeter used in the LX5 differs from that used in Linaeum's own models in using a thicker diaphragm, the result being reduced sensitivity.

The Optimus LX5's enclosure is diecast from aluminum and finished in matte-gray Nextel. The tweeter, with a white "Linaeum" logo painted on its black top plate, is mounted atop the cabinet. It actually sits in a molded plastic tray (which presents some reflective surfaces in the path of the sound) and is covered with a wire-mesh grille, this held in place with four bolts. The small woofer—its radiating diameter is just 3.6"—is mounted on the front baffle, with a slight flare surrounding the polypropylene cone. The woofer dustcap is actually a small disc of some kind of damping material. Two vents of unequal length are placed on the front baffle to reflex-load the woofer.

A plastic panel on the speaker's rear carries reasonable-quality binding posts—hooray!—with the minimal crossover glued to its inside. An iron-cored series inductor rolls off the highs in the woofer feed with a 6dB/octave electrical slope, while a 6.2µF plastic-film series capacitor keeps LF from the tweeter.

Sound
After moderate break-in, I fired the Optimi up with some music. I started out with them about 26" into the room. Mid- and low bass, of course, were completely absent. There was usable output down to 70Hz or so, but the ports produced chuffing sounds at frequencies below 70Hz at anything like satisfying levels. Moving the speakers closer to the room boundarie didn't add much in the grunt department, but exaggerated the already exaggerated upper bass to the point that I really didn't want to listen further. I guess no one ever went broke selling a speaker with too much bass—or at least, in the LX5's case, too much upper bass. The 120–180Hz region was just too boomy, too ill-defined for me to want to spend much time with the LX5. The big ol' bass fiddle on Ella Fitzgerald's "Fascinatin' Rhythm," from The Songbooks collection (Verve 823 445-2), was just a boomy blur, not offering much in the way of pitch differentiation.

Okay, I moved the speakers back out into the room. Less boom, but still enough to annoy. What to do? Luckily, a few months back I had downloaded from The Audiophile Network some threads about how to get the best from the LX5 (footnote 1). One David Cairns had suggested filling the speaker's ports with drinking straws. This would provide a degree of resistive damping which would both knock down the upper-bass peak a bit and tighten up the quality of the low frequencies. Accordingly, I cut some drinking straws to the right length—I used red straws, but I don't really think the color is significant (unless you think everything makes a difference)—and managed to stuff nine into each port.

With the ports so modified, the balance still sounded ripe, but not unpleasantly so. Pitch definition was better, but this little speaker will always be a bit of a boombox. But at least now I could live with the balance. Which is why I broke the magazine's rule about modifying review samples. The LX5 sounded so promising in the high frequencies that I had to do something.

The LX5's tonal balance was mellow, smooth, even polite, which is quite a feat for a loudspeaker designed for the undiscriminating mass market. The LX5's highs were shelved down, but not unpleasantly so. Its treble was actually of astonishingly good quality for a speaker in this price region. However, what would otherwise be an inoffensive presentation suffered from a muffled quality. I tried removing the mesh covers for the tweeters, which helped a little, at the expense of the speaker's aesthetics. But the shelved-down high treble was not the problem. Something wrong was happening in the midrange. Yes, there was a slight nasal coloration, a little bit of an "aww" formant noticeable in the upper midrange, but the lower mids significantly lacked clarity.

This muffled quality was very much music-dependent. The Optimus is almost the antithesis of the Canon S-35 that I also review this month, in that, while I preferred the Japanese/English speaker on rock music, finding its upper midrange a bit too colored to be pleasing on classical, the American/Malaysian design was generally pleasing on classical orchestral and chamber music. Dorian's superbly natural-sounding recording of secular cantatas by Bach (DOR-90199), which was Stereophile's "Recording of the Month" in March (Vol.18 No.3), sang forth from the LX5s with the music unscathed. But play a typical rock track, with high-level kickdrum and bass guitar, and the music mushed up.

Bass guitar particularly suffered at the hands of the LX5. While the fundamentals are suppressed, the second and third harmonics, which do much to define the instrument's pitch centers—see my essay in the Stereophile Test CD 2 booklet—were smeared with resonant overhang. Coupled with the mellow high frequencies, the LX5's presentation on rock program became quite uninvolving. For example, Bonnie Raitt's great "Nick of Time" cut, from the CD of the same name (Capitol CDP 7 91268 2), sounded pleasant but boring. And Ms. Raitt should be anything but boring!

The Optimuses' soundstaging was good, but not as well-defined laterally as I was expecting. Central images were a little too diffuse in absolute terms, with high frequencies pulled a bit to one side. (Why this was so will be explained in the "Measurements" section.) Image depth was only so-so, but these speakers are not really aimed at soundstage freaks, who would be better advised to get a pair of NHT SuperZeros at $230/pair.

It will be no surprise to learn that the Optimus's dynamics are limited. Sound-pressure levels in about the mid-80s were all that I could realistically expect from the speakers before the upper midrange/low treble started to harden. But again, I have to say that I quite enjoyed the sound on well-recorded classical pieces. That Linaeum tweeter does seem to be a class act.

I did try the LX5s with my multimedia PC, driven by my secondhand Advent 300 receiver, to play Myst (footnote 2). Nice. Very nice. But the Optimuses don't appear to be magnetically shielded, which makes setup near a computer a bit hairy.

Conclusion
At full price, the Optimus LX5 comes under serious pressure from such star performers as the PSB Alpha and the NHT SuperZero. Mellower-balanced than either, it misses out too much of the music in comparison, even though its high frequencies sound really fine. But purchased in one of RadioShack's never-ending series of sales (footnote 3), the LX5 is a great value for an audiophile who prefers classical music. Its balance will work better there than on typical rock, where the ubiquitous bass drum and bass guitar will exacerbate the speaker's failings. It should also make a good surround speaker.

To sum up, I offer Larry Archibald's words when he heard the RadioShack Optimus LX5s in my system over the Easter weekend: "Uninvolving, but unreasonably pleasant-sounding at the price."

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Footnote 1: Other mainly reversible tweaks for the LX5 suggested on The Audiophile Network bulletin board are: replacing the crossover capacitor with a premium-quality type, or at least bypassing it with a 0.1µF audiophile type; (carefully) removing the plastic tray on which the tweeter sits; adding damping/bracing to the aluminum cabinet; and increasing the amount of internal fiber stuffing.

Footnote 2: Myst is the first computer game that I've heard discussed as though it were a book or a movie—or a piece of music! And unlike Doom, Mortal Kombat, and other thrash adventure games, it doesn't involve blood, chainsaws, or severed limbs. With production values and depth of detail to rival the Back to the Future movies, it's the most complete computer game I've yet played.

Footnote 3: I have this idea for a truly heretical $400 high-end system consisting of a pair of LX5s bought on sale, a secondhand Advent 300 receiver (mine cost $75), and an Optimus CD-3400 portable CD player. Of course, audiophile cable and interconnect, and good stands such as the lead-shot–filled Celestions, would double that figure! And, if you really wanted to go all-out for quality and liven up the Optimus's balance, you could add an Audio Alchemy DAC-in-the-Box ($259) or a Parts Connection Assemblage D/A processor ($449) and a $40 HAVE Canare S/PDIF cable. And if you couldn't find a secondhand Advent, you could always spring for an Arcam Alpha 5 integrated amplifier ($399). But that would be a fun office system, wouldn't it?