The Rountree OmniMon Loudspeaker

Rountree OmniMon
The Rountree OmniMon Loudspeaker

Besides this sonic augmentation function, the well damped interior of the enclosure acts as a (rather short) transmission line, terminating an inch or so above the plinth, loading the front(!) side of the bass/mid driver (while also preventing front-to-back phase cancellation). It can do this in spite of its miniscule mass because it plays no part in supporting the drive units. Instead it’s actually ‘hung’ from the frame of the main driver, which itself is mounted on the end of a thick steel rod, rising up from a similarly massive steel plinth. This combination, totalling something like 40kg, is literally the backbone and foundation of the design: the threaded top of the rod passes right through the central polepiece and back plate of the up/downward facing main driver, which is secured by a large nut, hidden beneath a polished decorative boss. This of course means that the bass/mid diaphragm moves vertically rather than horizontally, so the direct output heard by listeners is actually radiated omni-directionally from the back of the cone. It also means that mechanical forces generated by the main driver operate vertically, so they don’t risk modulating the tweeter output, and are ‘grounded’ in the high mass plinth, with no need for spikes: Definitely very unconventional.

So where does the tweeter go? This is not an omni-directional device – indeed rather the reverse, as it’s a high quality ribbon with a 63x9mm diaphragm, based on the Aurum Cantus unit and modified by Rountree. This forward-firing device is mounted on a perforated metal collar that fits snugly against a rubber decoupling gasket fixed around the main driver’s exposed magnet, giving a measure of time-alignment between the two drivers. That classy Scandinavian main driver has a slit ’n fill paper cone diaphragm, the better to control resonances, and natural directivity means that any high frequency break-up modes are automatically directed upwards, rather than towards listeners. Faraday rings on the voice-coil former and top of the mounting post reduce distortion and inhibit over-excursion. The crossover network, operating with fairly gentle slopes at 2.2kHz (acoustically), is housed in an external metal box, which is sand-filled to prevent or damp any vibration effects. It’s equipped with two pairs high quality five-way terminals, permitting bi-wiring or bi-amping, and links to the speaker enclosure by a single Neutrik Speakon terminated umbilical. Although not in our preproduction samples, regular production will have high quality LFD internal wiring.

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 omni-directional 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.

blog comments powered by Disqus

Featured Articles