July
2019

Country of Origin

Holland

Model One

Reviewer: Srajan Ebaen
Financial interests: click here
Sources: Retina 5K 27" iMac (4GHz quad-core with Turbo boost, 32GB RAM, 3TB FusionDrive, OSX Yosemite. iTunes 14.4), PureMusic 3.02, Audirvana 3, Qobuz Hifi, Tidal Hifi, COS Engineering D1, Denafrips Terminator, Soundaware D300Ref as USB bridge/SD transport, Jay's Audio CDT2 MkII & DAC2-SE
Preamplifier: Vinnie Rossi L2 Signature Preamplifier, Nagra Classic, Wyred4Sound STP-SE Stage II, COS Engineering D1, Vinnie Rossi LIO (AVT module)
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1 monos, SIT3. F5, F6, F7; Goldmund/Job 225; Wyred4Sound mINT; Nord Acoustics NC500 monos; LinnenberG Audio Liszt monos, Bakoon AMP-13R
Loudspeakers: Audio Physic Codex; Cube Audio Nenuphar; Kroma Audio Mimí; EnigmAcoustics M1; Albedo Audio Aptica; EnigmAcoustics Mythology 1; Boenicke Audio W5se; Zu Audio Druid V, VI & Submission; German Physiks HRS-120; Eversound Essence; Fram Midi 150
Cables: Complete loom of Allnic Audio ZL 3000; Zu Event; KingRex uArt double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo; Ocellia OCC Silver
Power delivery: Vibex Granada/Alhambra on all source components, Vibex One 11R on amps/sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands
Sundry accessories: Acoustic System resonators
Room: 4 x 6m with high gabled beam ceiling opening into 4 x 8m kitchen and 5 x 8m living room, hence no wall behind the listening chairs
Review component retail: €5'400/pr ex VAT

July 31st. Synchronicity. When it happens, it's like a bolt of lightning only you can see. Wondering what had happened to Metrum Acoustics since their ownership change of a year ago, I had logged onto their site to feel none the wiser. Less than two hours later, Cees Ruijtenberg's email arrived. "It's time to inform you of new things. A year ago I was full of ideas and started a small loudspeaker line just to use my creativity and have some fun. The first speaker, the passive Model One, will launch in a few months and the active Model Two is currently moving from studio to studio for evaluation. The Model Three will be a fully digital system which is in progress now. My plans are to send you my first set of passive speakers as soon as they are ready for shipment."

Cees believes the Model One to be "the probably most transparent conventional loudspeaker available today. Over the past two years, I dedicated intense research to explore new methods and materials which are now incorporated in the Model One for a premium speaker that offers absolute performance within the clean lines of its compact case work. The shape was designed to deliver detailed powerful playback usually associated with larger speakers. The technical criteria were quite simple: extreme stiffness from 15mm bituminized aluminum panels bonded with rubberized glue to avoid cabinet ringing of any kind and thus time smearing of fast powerful transients. Usefulness in a normal living environment was another requirement so performance would be to a lesser extent determined by placement close to a wall or corner. Furthermore, the design had to have decent efficiency and act as a simple load for a wide range of amplifiers from delicate tube designs to powerful solid state. The bottom line is simple. If your stereo lives in a smallish to medium-sized room and you hanker for the best, most accurate, most lifelike enjoyable sound, the Acelec Model One should be at the top of your list."

For specs beyond the graphs, there's an 18mm Mundorf air-motion transformer tweeter, a 15cm ScanSpeak mid/woofer, a rear port, 84dB sensitivity and 45Hz – 35kHz bandwidth with a claimed max deviation of ±2.5dB. Nominal impedance is 8Ω, minimum impedance 5Ω at 375Hz. Max SPL are an ear-shattering 110dBA and the crossover hinge sits at 1.8kHz. HxWxD dimensions are 28.5 x 19.5 x 30cm and weight is 17kg/ea. Standard finish is black or silver, custom-color anodize is available upon request.

"Again, the Model One compact monitor is made for small to medium-sized rooms. Besides the above criteria, simulation software identified a great match between our woofer and tweeter. To avoid coloration from woofer breakup modes, we force the system to operate at a lower crossover frequency than can normally be used on this tweeter. Looking at the specs for such units, they should be used above 2'800Hz, thus impossible for us. Our solution was quite simple as the efficiency of this tweeter is far higher than our woofer's especially with a passive crossover. For a good match, the tweeter should be attenuated by ~8dB. Assume that you feed the system 1 watt, correct attenuation will reduce this to 0.14 watts on the tweeter to equalize its efficiency.

"For good phase behavior, 1st-order filters are nice. At the same time it was very unlikely in our case when we want to avoid both overloading the tweeter and getting woofer coloration. The solution was a dual slope which acts as a first-order slope around the filter frequency. Further away from the crossover frequency a second slope creates the filter's second order. The result of the 1st-order part is that the vectors of both slopes are at 45°. By summing these slopes, you get 0° in the electrical part of the filter. The second slope of the tweeter protects the unit against too much energy. For the woofer, the second slope avoids unwanted energy in its higher reach. Some extra stuff around its breakup modes at 800-1000Hz renders the entire response ruler flat. Another advantage of our filter is a very constant group delay having a maximum very slow deviation of 220μs from tweeter to woofer despite the absence of any mechanical tweeter offset. The sum of a stiff cabinet, flat response and correct phase behavior produces a spatial sound without the blur normally caused by cabinet resonances and with more low-level details which would normally be masked by these mechanical resonances. The waterfall plot shows the positive effect of the rigid cabinet as well.

"Why a vented design? We know that a passive radiator can have certain advantages. However, with a rigid cabinet like ours, the sound inside the box leaks through the passive membrane which hasn't the same strength as an aluminium box. Now the radiator becomes more dominant than it would be in a wooden cabinet. Leaking data wouldn't be time related with the direct sound coming off the cone in the front. To give you an indication, the energy from our side panels is about 18dB lower than the same box using 25mm MDF panels. As a result, unwanted side effects such as sound leakage through a passive diaphragm are more audible with stiffer quieter aluminum panels and must be avoided. Another advantage of a vent is that it can be closed when too much energy is generated by room modes. Or when one loudspeaker is placed in a corner, its vent can be closed while the other speaker's remains open. That flexibility is impossible with a passive radiator. Finally, our vent doesn’t use a normal alignment and has a lesser effect than conventional implementations."

… to be continued…