The Rountree OmniMon Loudspeaker

Summarising the story so far, what we have here is a two-way floorstanding design. Two top quality drivers are mounted very close together, providing near point-source integrity with good time-alignment. Probably uniquely and certainly interestingly, sound output is omni-directional below 2kHz but directional above. Probably uniquely too, the transmission line enclosure weighs next to nothing, avoiding energy storage and augmenting the main driver output in a carefully controlled manner. Given all the above strangeness and unique-nesses, it’s no surprise to encounter a few oddities when attempting to measure the OmniMon 1. Sensitivity is a relatively low 85dB, partly because the main driver output is omnidirectional rather than being primarily directed towards listeners. By way of compensation, however, and thanks to the extra assistance from the line/port, the bass extension is thoroughly impressive for a twoway, registering -3dB at 20Hz under far-field in-room conditions. And the impedance is very benign from an amplifier’s perspective, staying above 5 Ohms throughout.

Although the impedance traces of our samples show pretty good pair matching, the low frequency region (above 20Hz) doesn’t show the double peak normally found with transmission line (and reflex) designs; instead there’s just a single peak (sealed-box style) centred on 53Hz. According to Burton this is because the lower peak is both subsonic (c16Hz) and very well damped, while the line itself is broadly tuned to 28Hz. While the trace is mostly smooth and progressive, mild resonance effects are visible around 800Hz–1kHz.

Judged by my usual far-field in-room averaging technique, the mid and treble frequency balance is smooth and beautifully judged, but I did encounter some problems over the bass alignment: output is quite generous in the 30-60Hz low bass octave, but correspondingly a little weak in the mid and upper bass between 60Hz and 200Hz. This consistently proved to be the case in spite of trying the speakers in a number of likely and less likely locations. It’s difficult to say whether this is a ‘real’ effect or an unavoidable consequence of room reflection cancellations. Best results were obtained with the speakers as far from room walls as was practically feasible.

If the measurements were a little strange, the sound quality of the OmniMon 1 was quite shocking – in an entirely positive way, I hasten to add. Hearing this speaker immediately makes one aware of the considerable negative impact that wooden boxes have on the sound quality of nearly every other monopole speaker on the planet. The OmniMon’s super-light box is probably not actually inaudible, but its activities are certainly undetectable in practical terms, simply because its inability to store energy means that any contribution is effectively combined with the sound output of the drivers.

In a very real sense one is reminded of the wonderful freedom from boxy effects encountered with panel speakers like Quad’s electrostatics, but the OmniMon 1 sounds very different from a dipole panel in other respects, so the parallels don’t extend any further. Panel speakers are anything but omnidirectional, and dipoles don’t have deep bass, so the OmniMon has a very different character than its freedom from box coloration leads one to expect.

In fact this speaker’s ability to confound the usual stereotypes is perhaps its most obvious characteristic, and this can lead to some confusion when first confronted with such an unusual combination of qualities. We’re simply not used to hearing genuinely deep bass alongside a panel-like freedom from boxiness; we’re unaccustomed to the mix of omni midrange with tightly focused treble. You could almost say that Burton had re-invented the hi-fi loudspeaker. Certainly he’s come up with something that sounds as unique as its build and appearance might suggest.

As with all loudspeakers, an element of compromise is involved, and I’m not going so far as to say that the OmniMon 1 is perfect or that it makes all other speakers redundant. Such claims were made for the original Quad Electrostatic when it first appeared in 1957, and while it quickly established itself as an all time classic with a reputation that persists to this day, I doubt whether companies like Tannoy and JBL were adversely affected commercially. Like that Electrostatic, the OmniMon is wonderfully free from boxy character; like the Electrostatic it has limited power handling, low sensitivity and loudness capability. Unlike the Electrostatic, however, it has genuinely deep bass and omnidirectionality, so the overall character ends up sounding very different.

Omnis have been aminority interest for many years, and a notably controversial topic here in Britain since the early days of Bose and Sonab. The sound reaching a listener from a pair of speakers will always involve a mixture of direct and roomreflected sound, a mixture that depends on the characteristics of both speakers and room. Hi-fi speakers can be plotted on a ‘direct/ reflected ratio’ spectrum, with the omni design at the ‘high reflectivity’ end, and the full-range dipolar panel somewhere near the opposite end (just above the Stax ‘Earspeaker’); most conventional speakers fall somewhere in between. It’s pretty obvious that the greater the ratio of direct to reflected sound, the less you hear the listening room and the more you hear the recording. The vice versa is that the sonic signature of the listening room becomes significantly more obvious, which tends to increase the illusion of musicians actually performing in the room. Which is not to say that one or other approach is superior. After listening to hundreds of speakers over the years, I can hear the difference between the two extremes easily enough, but don’t believe it’s possible to state that one is ‘right’ and the other ‘wrong’. Ultimately, I reckon it comes down to personal preference. However, there is one caveat: because the omni involves a much greater contribution from the room, the performance of the room will play a significant role, and that of course adds some unpredictability.