A little History

It was 1983. My search for a "high-end" speaker took me to all the local salons to result in the purchase of my first pair of Ohm Acoustics loudspeakers. The floorstanding and remarkably full-range Ohm Walsh 4 set me back $1500 and left me one happy audiophile. They were so good that I bought a pair of the smaller Walsh 1 for another room a bit later.

Fourteen years later, it's 1997, naturally. One of my first-ever review assignments? To evaluate the Ohm Walsh 300MkII. These speakers were larger than my first pair of Ohms, with a larger driver and cabinet, deeper bass and greater output capability. At $4000/pr, they were also more expensive.

Today my father-in-law owns a pair of those 300MkIIs, incidentally the very pair which was the subject for a little SoundStage! piece I wrote a couple of years ago. The intervening years have made two things clear: First, the Ohm Walsh300MkIIs hadn't been completely broken in when I wrote about them. Though many things had already impressed me, I had yet to hear what those speakers really could do - this despite several weeks of riding them hard. Because their speakers are notoriously difficult to break in, Ohm now gives the buyer not a 10- or 30-day trial but a 120-day in-home evaluation period.

Second, the perspective gained over the last six years of audio reviewing has confirmed that if you had a large -- or very large -- room and your electronics were up to the task, those speakers are, hands down, the biggest bargain I can think of. Further playing has brought out detail I hadn't dreamt this design capable of. The Ohm 300MkIIs create bass that will embarrass most so-called subwoofers. Their output capability exceeds what my ears can stand and they have a sweet spot as large as the room itself. Combine all that with natural soundstaging chops that compete with anything, and the result is a pair of speakers that's a must-hear for anybody with the requisite space, and a budget that extends that far and well beyond. In many ways, these are truly magnificent speakers.

Ohm Acoustics manufactures two very different types of loudspeakers - the usual cone'n'dome variety (certain models incorporating different ideas on dispersion) and their claim to fame, a complete line of speakers using the Walsh driver based on the work of the late Lincoln Walsh. Years of refinement have created what Ohm calls the CLS or Coherent Line Source driver. Picture a typical cone woofer elongated in depth akin to a megaphone - but not quite. Now point this driver downward so that it fires into the top of the speaker's enclosure. Sound propagates off the back of the driver rather than front, and by virtue of its open-air surroundings, in a 360-degree rather than narrow-directivity dispersion pattern.

States Ohm Acoustics on the subject: "The CLS system uses an inverted cone driver with the speaker coil driving the peak of the cone. The sound vibrations travel from the top down and out to the rim.

By using a cone material in which sound travels faster than it does in air (supersonic) and by carefully aligning the angle of the cone, the driver generates a vertical wave front, radiating sound equally in all directions like an expanding drum. Because the inverted cone driver radiates in all directions, it sounds the same in all directions." In other words, the driver is naturally time-coherent and omni-directional. But Ohm feels that, with certain circumstantial exceptions, an omni-directional response in the treble is undesirable. Rear-wall reflections at these frequencies can become confused with the original sound and consequently blur imaging. Hence, in addition to the CLS main driver, Ohm adds a "super tweeter" mounted vertically at the Walsh driver's top and angled inwards so as to cross its main axis well in front of the listener. This tweeter is reportedly pressed into service around 8 kHz which eliminates a crossover network anywhere near the critical 2-6kHz range where human hearing is most sensitive to discontinuities.

The tweeters are positioned such that they radiate high frequency energy diagonally across the listening area. This creates good stereo imaging over an extraordinarily wide listening area. It also allows fine adjustment of high-frequency balance via toe-in or toe-out as they naturally sound brightest when the tweeter fires straight at the listener.

With the exception of the Walsh 5 Mk2 (whose controls on the back would interfere), Ohm makes versions of all its Walsh models where the super tweeter is aimed at the ceiling instead, thus becoming optimized for rear/side speaker duty in home theater setups. Ohm finds that non-directive treble sounds more enveloping and therefore more convincing on movie effects such as rain and thunder.

The Micro Walsh

The speakers under review are brand-new models and far smaller than any Ohms I've ever used, thus clearly intended for primarily small rooms. With its jarmulke skullcap, today's tall version of the Micro stands just a touch over 36 inches - er, tall and measures a mere 6 x 6 inches across, parked atop an 8-inch integral square base. The diminutive short version clocks in at all of 23 inches [below]. There are no provisions for spikes of any sort. Remove the speaker's bonnet and you find a protective perforated canister that houses the driver proper. This canister is just over 5 inches in diameter, telegraphing that the driver inside must be smaller than 5 inches across. But don't let that fool you. Due to its unique geometry, the CLS driver has a greater radiating surface and therefore superior displacement capabilities than ordinary dynamic cones of equivalent diameter. Ohm is fairly closed-mouth, both about the soft- dome tweeter used and other details. The review pair was finished in a rich Rosewood veneer and is priced at $1000/pair. A cloth-covered version is available for $900. Ohm specifies a nominal impedance of 6 ohms, a frequency response of 45 to 20 kHz +/- 3.5dB and a sensitivity of 87 dB with a standard 2.8V input, making the Micros suitable for amplifiers between 20 and 150 watts.

Fit and finish were good, with only very few floor-standing speakers in this affordable category competing in real Rosewood livery. Close inspection revealed craftsmanship not quite of furniture-grade level but from a few feet away, the speaker looked remarkable. The only subject of doubt? The grill bonnets can't be firmly affixed to the speaker but simply rest on top. That's no big deal until someone brushes past them. If I owned these? I'd stow the caps away. I thought the speakers looked better without 'em.

The speakers come with a gold sticker placed at one corner underneath the bonnet. Indicating tweeter direction, this corner must point toward the center of the listening area. Those wanting to do without the grills will probably want to relocate the sticker too, perhaps underneath the base for future reference. Sticker gone, the speaker now has a remarkably distinctive yet finished appearance. At roughly 16 lbs, the Micro is lighter than a lot of monitors, though deceptively inert. The cabinet has all the rigidity you'd expect from an enclosure with a 6-inch square footprint. When you consider that the Walsh driver excursions are vertical as opposed to horizontal like your usual cone drivers, the speaker's entire height makes up the de facto thickness of its baffle. This is why larger Walsh speakers arrive with casters. There are no horizontal forces exerting on the speaker to make spikes or other coupling measures redundant.


The good news? These new Micros don't take remotely as long to break in as their hoary predecessors. About 40 hours gave Ohm's John Strohbeen and me reason to believe that they were ready for prime time, so into the listening room they went. I ended up with an equilateral triangle between speakers and listening chair which put the speakers relatively far apart but resulted in excellent soundstaging and solid center fill without toe-in. With these Ohm models, the wider you space the speakers apart, the more on-axis you sit with the tweeters. I settled on this configuration because I quite liked the overall balance, with the driver canisters' centers not quite three feet from the back wall.