The final model in today’s hORNS lineup is the very different Mummy. It gets an ultra low-mass 12" woofer with a big magnet to take on everything below 1’800Hz. A SEOS wave-guided compression driver covers the bands above. This enclosure is a heavily damped 75 litres and a bass reflex, with two rear ports like the FP series. The 95dB/4Ω Mummy should be an easy load for most amplifiers. The SEOS profile appears to allow for a hybrid loading between typical horns and common domes’n’cones bass reflex solutions. The big issue with horns is that their size is determined by the low-frequency cutoff. To go low, they must be very big.

Their main benefit is controlled directivity in many variants. Wave guides can shape directionality to be wide or narrow and different in the vertical and horizontal axes. An obvious advantage of controlling this aspect is managed room interaction and reflections. The SEOS geometry was an extended community-sourced R&D effort spanning more than four years to create an optimum horn geometry for home audio. The ultimate goal was a superior horn profile to significantly improve the performance of high-sensitivity transducers. The super-elliptical shape was chosen to eliminate that on-axis response dip common to older horn profiles. A large roundover is applied to the mouth area to eliminate diffraction. Because SEOS is wider than tall, the woofer can be placed closer to its centre to minimize vertical nulls. The claimed benefits are:

• better directivity control
• linear horizontal coverage for great off-axis response
• reduced vertical coverage for less ceiling and floor bounce
• wider listening area for a huge sweet spot
• improved imaging and clarity
• reduced high-order modes to eliminate 'horn honk' where internal reflections cancel certain frequencies or cause distortion

As nothing in real life is perfect, a few shortcomings can be listed too. The limited depth of the SEOS horns (3.5 inches for SEOS-12 and SEOS-15) provides little acoustic loading, leading to potential reactivity in the pass band and to a possible lack of soundstage stability. It might also suffer excessive ripples and possibly higher distortion. The SEOS shape is prone to standing waves in the pass band and can present resonant peaks at fairly high frequencies. 

All wave guides have resonant modes but ideally those are below the pass band or at least right at the bottom edge. As the flare profile is not purely oblate spheroidal, it is more likely a secondary flare of arbitrary radius. Like every horn-loaded realization, the overall result will rely on the choice of amplification and setup. It’s a more complicated task to identify proper amplification because of the high efficiency as well as resonant peaks which might be exacerbated by minimally damped tube amps. If room interaction is often our greatest enemy, wave guides are more about finding the best overall balance between components rather than fight room influences.

Description. The SEOS FP was originally designed to meet the demands of the US DIY market but is now available as kit or complete loudspeaker. The SEOS waveguide uses Dr. Earl Geddes’ oblate spheroidal contour but with a linearly changing super-elliptical cross section. The SEOS FP-15 logically expands upon the hORNS' FP family to sport the bigger SEOS-15 horn with a 1" BMS 4550 compression tweeter and a B&C 15CL76 15-inch woofer. The BMS-exclusive voice-coil technology employs a lightweight copper-clad aluminium wire wound inside and outside of the Kapton former to improve heat dissipation, dramatically increasing acoustic output and reliability whilst minimizing its power compression. It was chosen also in consideration of affordability, elevated sensitivity (113dB@1W/1m) and its lower possible crossover point at 800Hz.

The B&C 15CL76 is another affordable lightweight unit with ventilated 3-inch copper voice-coil to reduce compression. It specs out at 98.5dB sensitivity and extended bandwidth of 40 to 3’000Hz. Both drivers cross at 1’000Hz through a 12dB/oct. 2nd-order electrical filter. Overall efficiency is an elevated 96dB, heaven for any SET amp. A top-of-the- range option is a Beryllium compression driver accompanied by a €3’000 price increase to hit a €12’000 final sticker.  At this price, they will suffer aesthetic comparisons against many a conventional speaker. But it is quite difficult to compare them in their own hornspeaker class. I might christen them civilized hornloaded two-way full-range monitors. The polyglass baffle can be customized in a wide choice of colours that will match most demands. There's also a choice of veneers for the enclosure. The FP-15 comes with a pair of dedicated stands perfectly tuned to the size of these maxi monitors. Optional heavier stands are available by demand supplied by another Polish company called Rogoz Audio.