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In fulfilling Part I of this review using the Opal-air4 as a pair of conventional active analog speakers, I first connected them to my Macbook Pro with an Audience mini-to-RCA cable and then to a Marantz SA8260 using the same cable into its headphone output. (Most people will find it hard to believe but the headphone amp of this machine is not only superb but also an incredible preamp hooked up directly to power amps.) I listened to my favorite iTunes classical radios from ABC Opera to ZET Chopin and many of my best sounding and most dramatic silver discs. As mentioned earlier, upon initial listening through the RCA connection, I immediately noticed the richness in bass and the grandeur in scale unheard of with any active speakers I’d come across thus far. But more striking still was the same Mark & Daniel signature sound only more refined in density, dynamic immediacy, resolution and imaging than any of their previous monitor models. And this was just the beginning of a few days of run-in. I think one may attribute the success* first to the implementation of the Tripath bi-amping with the shortest signal paths between preamp PCB, low-pass/high-pass filters and power output through an active system configuration. (Of course one could always argue that cramming everything into such a small enclosure creates interference and vibrations. All I can say is that hearing is believing.)
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* It would seem that the core recipe here is a combination of electronic rather than passive crossover (which is far more accurate and doesn't suffer phase shift) plus active equalization which beside overall linearization will also produce more bass extension and power than the cabinet size alone would support. - Ed

Secondly I would applaud Daniel’s choice of R-core transformer-based linear supply which is demonstrably superior to commonly used switching power or the often overrated batteries that pose maintenance problems for non-frequent users like myself. The R-core transformer is a definite upgrade also from a toroidal transformer which is actually recommended on the Tripath datasheet. According to Daniel, the R-core transformer coupled with 2 x 10.000μF Nover LA series audio-grade low ESR electrolytics constantly supplies ±28 volts/60 watts* of stable and clean power to the Tripath chip to sustain lower output impedance crucial for efficient damping and dynamic response of the Super Xmax woofer. With the volume of the Macbook Pro audio output set to 75% and the Marantz SACD player headphone volume set to 50%, I never had to dial up the Opal-air4 volume knobs beyond 12 o’clock (actually only to 10:30 for most of the time) yet the ardor and vitality of the music seemed inexhaustible.
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* The TA2022 datasheet specifies operating voltage/current parameters as 12-36 volts for 20-80 watts compared to the P2050 used in Virtue TWO which wants to see 10-36 volts for 28-128 watts. Virtue offers two grades of PSU: 30v/90W and 30v/130W. How does that affecting performance? Please read page 4 of the Virtue TWO review.


When I shared my beyond-expectation contentment with Daniel, he told me that the review samples had been thoroughly field-tested during the Guangzhou AV Show at the end of last year and that he took a personal interest in aligning the system before dispatching it to me. Two words sum it up: total approach. "The rich bass and superb performance you experienced actually came from our total system alignment. It involves one of our most sophisticated circuitries ever. It is really easier for me to shape the system parameters and fine-tune the performance when we have the liberty to modify the active amplifier circuits to match the specs of our drivers. With a passive speaker it is far more difficult for us to control the outcome as it depends so much on being properly matching to various amplifiers and compromises from unknown factors."

One finding I didn’t mention to Daniel about the built-in Tripath amp is its resistance to switching transients. As we know, Tripath chips have all kinds of built-in protection circuits for overheating, over-current and over/under-voltage but they are also vulnerable to a popping noise during power up/down. We accepted that as normal since nobody seemed able to solve that amongst the Tripath amps I’ve come across. Almost every reviewer endorsed that ‘ceremonial’ pop and agreed that it was inherent in Tripath. Not only that, if I accidentally turn off the CD player before I power down my T amps, a disastrously loud pop punishes my speakers for my crime.

The Tripath amp in the Opal-air4 once and for all silences such beliefs in the necessity of farts. Switching on and off is dead quiet. Leave the amp on and unplug the power cord, it’s still dead quiet. Leave the speakers on under full power and turn off your computer or CD player during RCA connection (or unplug the uTX transmitter during the Air DAC connection as I found out later) and it’s still dead quiet. Not one peep of protest. I was dumbfounded. I didn’t bother asking Daniel for an explanation. Silence is golden. It’s more important for the designer to keep his recipe secret than for a reviewer to make himself an expert. At this point I couldn’t wait to recommend the Opal-air4 to anyone seriously searching for a pair of active speakers in the traditional analog sense. Granted, most active speakers offer more gadgetry from XLR inputs to HF/LF trim pots. They serve adequately as near-field monitors or desktop systems but fall short in the audiophile listening room. With everything preset, the Mark & Daniel Opal—minus air4 until now—was naturally balanced and effortlessly projective. It was the Pavarotti of compact active bookshelf speakers. But how about a wireless Pavarotti? Where was my security blanket now?

Part II: the wireless digital speaker. Curiosity prompted me to take a sneak peek at the unknown. A quick run to this NuForce web page gave me some basic understanding which I'll summarize as follows. Theirs is a 2-channel DAC that operates at 16-bit resolution with a 48-kHz sampling rate. Its frequency response is 20Hz – 20kHz, THD+N is 0.03% @ 1 kHz and S/N ratio is 91dB A-weighted. All these specifications are mere CD quality and hardly outstanding in today’s high-resolution world. The main attraction of this DAC is its wireless transmission protocol which utilizes the SKAA technology and HPX audio compression.

The SKAA wireless transceiver system was pioneered by Canadian company Eleven Engineering Inc. First launched in 2010 and soon known as the award-winning wireless audio innovation for mobile devices, it is based on spread-spectrum technology working in the 2.4GHz radio band. Within this spectrum of allocated frequencies, the receiver will detect and lock onto the available band to avoid interference from other wireless devices. The NuForce Air DAC receiver can receive compressed digital audio signals from up to four transmitters. Each push on its tactile button scans through the four usable channels in sequence. NuForce has made available two types of transmitters - uTX for computers with USB ports (Mac/Windows) and iTX for Apple music-playing mobile devices. Each transmitter can send signal to up to four receivers. So what does that mean in practice?

Talking about just NuForce, you can buy up to four Air DAC receivers to connect to four audio systems around your home; and up to four transmitters—uTX and iTX combined—to plug into your computers and/or Apple iDevice digital sources. Talking about Mark & Daniel's Opal-air4, you can get up to four speakers (good for two hifi systems or one in D’Appolito array) and four transmitters for four digital sources.

My Mark & Daniel review package arrived with only one uTX transmitter. I tried to see how user-friendly it would be so I purposely didn’t read the NuForce downloadable PDF instruction manual.


After plugging in the uTX to my Macbook Pro, I opened Audio MIDI Setup which automatically detected the SKAA transmitter without any driver. I tested the speaker connections on the 'configure speaker' window and pink noise came through both. But that didn’t mean I could play music until I assigned the SKAA transmitter as my audio output device by confirming 'choose this device as sound output' on the drop-down menu. Done. I turned on my favorite iTunes radio.

Strangely music only came through the right speaker. I checked the input selectors which both were set to Air DAC. On the working speaker the input indicator was green. On the mute speaker it was red. Pushing the button didn't change anything. It decided to stay mute and red. I now remembered that this was the speaker where the button and cover had fallen off from the Air DAC in transit. (The speaker had been undamaged though.) I unplugged the uTX and plugged it back in. Voilà! Both NuForce receivers automatically detected and locked to the streaming signal now and the red LED had turned green. So here’s the troubleshooting lesson. If there’s no music after you’ve confirmed all connections and settings, unplug and reseat uTX. As mentioned earlier, the Tripath amps won’t pop. The transmission range for uTX is said to be 15-30 meters. My Opal-air4 speakers were only 2 meters away. Playing iTunes radio really did give me CD quality performance. I couldn’t believe this was wireless!