The Radio Shack Optimus LX-4 Loudspeaker

News Flash: According to a faithfulAudio Mecca denizen, Radio Shack is closing out the LX-4s for $49.95 (in some markets) which makes this speaker an even bigger bargain!

No, you're not in the Twilight Zone, and no I'm not writing this from inside an insane asylum. Being of sound mind and body, I  hereby declare the  Radio Shack Optimus LX-4 loudspeaker to be the sonic bargain of the Century.

It's not often that I stick my nose in audio's mass market arena; I'm accustomed to audiophile price tags in the kilobuck range. So  if it weren't for Pierre Sprey of Mapleshade/Insound, I'd still be oblivious to what is ounce for ounce the most cost effective audio purchase of my life.

Pierre calls me (about a week before Thanksgiving 95) to chat about cable, and during  the conversation he casually asks if I'd  heard the Radio Shack LX-4. Well, no Pierre, actually it's like being at McDonald's - you don't spend more time than you have too at a fast... I've auditioned the whole line carefully he says, and the LX-4, but not the bigger  LX-5, is a great little speaker. No, he's not kidding; he actually prefers it to the BBC spec LS3/5a minimonitor which costs around $900/pr! Better imaging and that Linaeum tweeter is responsible for excellent treble clarity,  he opines. But Pierre,... It's on sale until Thanksgiving at $60 a speaker (regularly $100) he advises me. Now I'm really curious. Could it be possibly be true? Good sound for $120/pr?

So I call my home town Radio Shack, and sure enough there's one pair left - just for me. And so it was that the Pro LX-4s entered  my listening room, under my arm, packaged in two yellow cardboard boxes, each about the size of a shoe box.

I was familiar with Linaeum, a loudspeaker company in Portland, Oregon, whose products I'd seen and heard at past Consumer  Electronics Shows. My first action, therefore, was to investigate their  ties with Tandy/Radio Shack. My call was routed to Steve Geist, who turns out to be the LX-4's designer. According to Steve, the speaker was conceptually  laid out and commissioned by Tandy. The tweeter (model ET5) is apparently being manufactured in Japan under a license from Linaeum. Final assembly of the speaker is in Malaysia for obvious cost cutting reasons.

I asked Steve several other questions about the filter network and about any simple after market tweeks he thought would be  worthwhile. The network he designed turns out to be the height of simplicity: first order electrical slopes consisting of a single cap for the tweeter and a small ferrite-cored  coil for the woofer. And as far as mods, he felt  that changing out the coil was the best bet.

It was time to unpack the speakers and give'em a critical listen. I take the grills off, and take a look at the drivers:  there's  the Linaeum tweeter, and believe it or not a 4-inch Kevlar-domed midrange/woofer! Most unusual at this price point. Stand-mounted, the tonal balance is most definitely minimonitor like, which is to say lean. Not enough upper  bass to properly flesh out cello, double bass, or piano. Although I didn't try it bookshelf or wall mounted, this speaker would definitely benefit from any room-boundary bass augmentation. The treble character  catches my  attention immediately: natural and nicely detailed. It's just incredible to find a tweeter at this price point that sounds as civilized as the ET5. No one should be made to listen to the trash that passes for a  tweeter on other  $100 speakers! To be perfectly honest, I have wished for treble so refined in much more expensive speakers. Hell, some ultra-expensive speakers (eg, the Thiel CS7 at $9,000/pr) could benefit by taking a page out of the LX-4's  book. Considering the inexpensive electronics this speaker will likely be mated with, its treble quality represents a major blessing.

Don't expect much dynamics from a 4-inch woofer; there are physical  limitations on the amount of air a small woofer can displace.  Beware, a four-banger is no V-8. There's plenty of volume, however, to fill a moderately sized room all right, but the LX-4 is unable to scale the dynamic range  from soft to loud without some compression. Also, be careful not  to push this speaker with more muscle than about 50 watts into 8 ohms, or you could fry a voice coil.

Imaging precision and focus are competitive with speakers costing hundreds more. The soundstage was painted with surprising  transparency. The feeling of being able to see far into the inner recesses of the original acoustic was quite compelling. This is certainly a speaker  that will satisfy folks who place imaging high on their list of sonic  priorities.

The upper mids were on the grainy side, which impacted female voice and violin overtones. Textures here lacked the smoothness of  more  expensive designs. I had a feeling that this sonic aspect could be improved through tweeking of the crossover network, and so I tore into the innards of the LX-4.

Structurally, the cabinet is held together by hot glue alone. The  only screws I could find were those holding the drivers onto the  front baffle. The real surprise came when I popped out the woofer and peeked at the filter. There was a mylar cap soldered to the back of the terminal cup in  series with the tweeter, but no coil was in sight. I checked the  other channel with the same result. Apparently, the woofer is allowed to run wide open. Was this done to save a few pennies? The effect on the frequency  response is minor, but listening to the woofer's breakup modes can't be  too pleasant an experience.

I quickly popped in a 0.47 mH air-cored coil in series with the the woofer (probably a $2 item in 19 or 20 gauge copper)  and gave a  listen. Smoothness in the upper mid/presence regions improved dramatically.

In the end I incorporated three inexpensive mods that elevate the LX-4 sonic report card from a C to a B. I'll describe these for  those of you out there who aren't intimidated by a soldering iron.

(1) 0.47 mH air coil in series with the woofer. Pop out the woofer and terminal cup. Pull off the woofer's clip-on connectors and  set it aside. De-solder the woofer's yellow lead wire at the terminal cup. Solder the coil leads between the lead wire and terminal cup. Locate the coil under the padding material, which is inside the box.
(2) Bypass the  stock cap with a 0.1 microfarad high-grade cap (eg, Kimber or MIT). Solder the bypass cap in parallel with the existing cap.
(3) Insert a small square of acoustic-grade foam into the enclosure directly under the woofer.  Reconnect the woofer's  lead wires and re-screw the woofer and terminal cup.

That's it. Of course, I don't have to tell you that these mods void the warranty. But at $60 a side, I can afford to take that  risk.

The bass alignment is a standard bass reflex, with the small port positioned anatomically-correct on the back baffle. The box is  tuned to 55 Hz, which makes the design prone to infrasonics as in sub 20 Hz garbage from vinyl playback. So plan to use these  speakers with tape, FM radio, and CD only. The impedance magnitude is quite amplifier friendly: 8  ohms minimum in the power range of the orchestra at 250 Hz, with an overall minimum of 6 ohms at 20 kHz. Hence, the LX-4 should  do well with non-exotic amps.

As my daughter (Dahlia), has put in a strong request for these speakers, they're about to end up in her room. I can't think of a  more cost effective starter speaker for a student, or as a foundation for a second system for a bedroom or an office, than the Radio Shack LX-4. Check it out!