Realistic Optimus Pro LX5

 

Realistic Optimus LX5From time to time we see interesting new variations on the loudspeaker theme; sometimes manufacturers come up with better cone materials for their mid/bass units, and occasionally interesting tweeters pop up. Recently, there has been a renewed interest in ribbons, but other types have come and gone too. For yours truly, one of the most interesting was the unique Linaeum ‘figure of eight’ dipole design, which the British hi-fi market saw in the rather odd looking Realistic Optimus Pro LX5 in 1995. Blink, and you would have missed it – but there are still quite a few around it it’s one of the most interesting loudspeakers of its day; all the more so because it was a budget design.

Conventional dome tweeters use a coil of wire through which the electrical signal carrying the audio passes, and this is suspended between the circular poles of a ring-shaped magnet. As the current alternates, it moves the dome or cone forward or backward to move the air, thus producing sound. The Linaeum tweeter’s voice coil is flattened vertically and suspended between opposed rectangular permanent magnets placed on either side which push or pull two semi-cylindrical sheets of mylar film, fixed at the other end. These excite the air by rotating back and forth, making sound. Effectively they work as a dipole, radiating both front and back, the result being a very different listening experience to a conventional dome tweeter – as is very clear to hear as soon as you set ears on them!

Impressive stuff, but that’s not the end of the story. The Realistic’s Optimus Pro LX5 speaker was made by Tandy Corporation (Realistic was the speaker brand of that company, which sold in the US via Radio Shack stores, and in the UK exclusively via Tandy). Its fiendishly clever tweeter subassemblies were bought from Oregon-based high end speaker maker Linaeum, and shipped to Malaysia where it was incorporated into the speaker box and mated to a rather generic mid/bass driver. It was made alongside the less-expensive Optimus Pro X77 and LX4 which used a less desirable front baffle-mounted tweeter, with the LX5 sporting the top mounted bi-directional tweeter fitted to a baseplate. Just to confuse matters, the Realistic Optimus Pro LX5 also sold as the Genexxa Pro LX5, which was to all intents and purposes identical. Linaeum also made its own range of loudspeakers of course, using its unique tweeter – but in this guise it is said to have a thinner, more sensitive, better sounding but arguably less durable diaphragm.

The LX5 is a small loudspeaker, measuring 267x162x165mm (HxWxD) and weighing in at 3.4kg apiece. The 50x110m Linaeum dipole driver sits on top, protected by a wire mesh grille; directly underneath is a moulded plastic top plate which is affixed to a rather unglamorous, matte grey finished metal box which houses the crossover and the 130mm mid/bass driver. This uses a polypropylene cone, which was pretty passé even for the nineteen nineties, although some variants of the speaker later used Kevlar. The crossover point is 4.5kHz, and the claimed frequency response of the speaker is 85Hz to 20kHz. Nominal impedance is said to be 8 ohms, and the manufacturer stated that the power handling was 100W RMS.

Not only is the LX5 a very small speaker, but its internal cabinet volume is even less than a conventionally designed loudspeaker of the same size. This doesn’t help sensitivity, and nor does the fact that the mid/bass unit has a smaller cone than you might expect from its overall diameter. Two front-firing reflex ports attempt to jolly things along, but again are very small and cannot move much air. The one thing that does make a difference is the crossover, which is very minimalist with a single iron-cored series inductor rolling off the woofer at 6dB per octave, and a 6.2µF plastic-film series capacitor protecting the tweeter from having to reproduce bass notes! Still, not even this can rescue the LX5’s sensitivity from being a dire 83dB/1w/1m. In fairness, any very small box will struggle to do much better, but the LX5 is still right at the bottom of the limits of acceptability. Most modern solid-state power amplifiers put out at least 50W RMS these days, which should drive the LX5 to reasonable levels – but don’t expect to partner this little loudspeaker to your 3W single-ended tube amp, or power a party the like of which Studio 54 would be proud!

This is the story of happiness and misery in differing measures. Rarely does one get to hear such a charismatic speaker these days – one that is highly accomplished in the treble and yet really rather flawed in the bass. As a result, it means the LX5 will either succeed or fail depending on your choice of music, and also at what volumes and in which room you listen to it. It’s safe to say that this is not your average bland, generic sounding modern loudspeaker; it’s almost as if it’s the last gasp of the mad sounding things we used to see in the nineteen seventies. In some respects – such as the sense of air and space in the treble, and its general sweetness – it embarrasses speakers which are way more expensive. Yet in others you’re wondering how it was ever signed off and approved for sale. When correctly placed on a rigid stand at least 30cm away from a rear wall, the LX5 works okay but anywhere else and you get obvious upper bass boom, allied to some serious chuffing from the bass ports on occasion!

Cue up Scritti Politti’s The Word Girl, and you’re greeted by an uncannily spacious sound – one that despite the diminutive dimensions of the LX5 fills the whole room with light, breezy sound. The upper registers really are very good, sounding open and unfettered in a way that shames even some £5,000 standmounters that I’ve heard. The glistening harmonics from that Roland D50 keyboard shimmer all around, and singer Green Gartside’s voice sounds silky and ethereal. For such small speakers, they’re remarkably open and unrestricted, really making a nice noise. The trouble is that the bass is lighter than it should be, yet seems to boom over a narrow range in the lower midband, giving a boxy sound to the proceedings. This is odd, because the last thing that the treble is, is boxy. It means your ears need to take a few minutes to acclimatise. but when you have then things seem a little easier to listen to.

The trick is to position the LX5 just right, then not provoke its bass into misbehaving. This means you can’t take the volume up very high with music that has strong basslines, lest it begin to compress them and/or make the cabinet resonate too much or work the ports too hard. Gentle, largely acoustic soul numbers, such as Randy Crawford’s Rainy Night in Georgia, are ideal – whereas Goldie’s intense drum and bass track Terminator is not! Get the measure of the LX5, don’t drive it too hard and feed it sweet, gentle music – including classical, and it’s great. A real joy is my favourite rendition of Beethoven’s Pastoral Symphony, which served up an effortlessly spacious and expansive sound, had well placed images within the recorded acoustic, and excellent depth perspective. Only on the crescendos with massed strings do you begin to ‘hear’ the mid/bass unit’s constrained feel, and slight tendency to give a ‘one-note’ bass. All the same, when in the zone the Linaeum tweeter is capable of a delightful sound, given half a chance.

Anyone who has lived with a Realistic Optimus Pro LX5 will know its low frequency performance is a problem area; its tendency to boom in the upper bass isn’t endearing, but steps can be taken to help. Some people recommend stuffing the bass ports with drinking straws to provide resistive damping(!), others simply cut foam bungs and insert those with greater success. Removing the mesh grilles on the tweeters also helps with the treble, giving a slightly brighter and crisper sound. Others have modified the crossover capacitor with a high end audiophile-grade one, and increasing the amount of damping in the aluminium cabinet.

Not for headbangers, the Realistic Optimus Pro LX5 is nevertheless an extremely interesting and fun little ‘curio’ from the nineteen nineties, one that slipped between the cracks and has been largely forgotten. All the same, pretty decent examples do occasionally pop up in the classifieds and online auction sites, and are well worth playing with – especially in a second or even third system where space is limited. The one that got away is well worth grabbing back, and with prices ranging from £50 for a well campaigned pair to £150 for minters, you have no excuse not to!

One comment

  1. Donald

    Very interesting diversion from the norm.
    Would have loved to see a diagram of tweeter.

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