Review: Grover Notting Code 1.5 Nearfield Principal Monitors

When Frank Hinton of Grover Notting told me he was designing a series of principal studio monitors, I was outwardly encouraging but secretly cynical. It was September 2009 and Grover Notting had been enjoying some success with their CR series of cross-reference monitors [reviewed by Andy Stewart in Issue 65]. In fact, I’d recently bought myself a pair of CR1s after using them to cross-reference some recordings I’d done for a Josh Pyke DVD. I was impressed by their stereo imaging, their easy-going nature compared to the nagging NS10s that sat beside them, and by how well the results translated to the outside world. The CR series were successful because they filled the hole left in the market after Auratone’s 5C and Yamaha’s NS10 had faded into irrelevance. I could see no such hole in the principal monitor market, however, and felt that another series of principal monitors was precisely what the world didn’t need. I listened politely nonetheless, eyebrows raised to 50% in half interest, as Frank enthused over his forthcoming ‘Principal Monitor’ series.

“These new monitors build on the Audio Information Band concept we developed for the CR series,” Frank began. Grover Notting defines the ‘Audio Information Band’ as the extremes of the human vocal bandwidth, from 80Hz to 11kHz, and believes that a useful monitor must be able to reproduce that bandwidth with a linear amplitude and phase response. I raised my eyebrows to 60% out of respect for the CR series.

“All these new monitors use infinite baffle enclosures – no ports,” he declared. Interesting… I had always preferred the clearly defined low frequency performance of an infinite baffle enclosure to the more extended but woollier ‘thump factor’ provided by most of the ported enclosures that dominate the market. My eyebrows involuntarily notched up to 70%.

“There are no amplifiers bolted onto their backs,” Frank continued. Eyebrows to 80%. When active monitors first hit the market I loved the idea of integrating the amplifier into the speaker enclosure, but I had since grown to dislike the added weight and cabling. I yearned for the days when amplifiers lived in ventilated racks where they belonged, and monitors could be moved around without slipping a disc or popping a hernia.

“They’re all using passive crossovers designed by Dr Neville Thiele…” Eyebrows at 90%. Dr Neville Thiele is one of the world’s leading experts on the design of loudspeaker enclosures and filters. In 1961 he and Dr Richard H. Small published their famous paper, Loudspeakers in Vented Boxes, replacing all the guesswork of vented (i.e. ported) enclosure design with a methodical approach backed by solid mathematical formulae. The ‘Thiele/Small parameters’ are now a fundamental part of loudspeaker enclosure design.

Frank’s enthusiasm was contagious, but I still had doubts. How could an infinite baffle enclosure compete in a market dominated by ported enclosures that, on a size-for-size basis, produced more low frequency output? If only there was a way to combine the low frequency clarity of the infinite baffle enclosure with the extended bandwidth of a ported enclosure.

“They’re also the first loudspeakers in the world to use Graeme Huon’s patented Bandwidth Extension Module,” Frank concluded, clasping his hands. “Think of it as a passive electronic version of a port. It gives an infinite baffle enclosure the extended bandwidth of a ported enclosure, without any of the acoustical problems inherent in ports.” My eyebrows ran out of headroom at this point. By now Frank had my undivided attention, and I hope I’ve still got yours…

THE CODE 1.5, EVENTUALLY

Now in production, Grover Notting’s Principal Monitor series consists of six models intended for applications from desktop mixing to large scale mastering. Proudly designed and manufactured in Australia, the series represents a complete re-think of critical monitor design with no ports, no built-in amplifiers, no active crossovers [except for the models incorporating sub-bass drivers] and a strict adherence to the Audio Information Band concept. Every design decision was made to achieve the highest performance, rather than meeting a price point or following a market trend. They’re not cheap, but if you’re looking for a no-compromise studio monitor that was designed entirely in response to the needs of working audio professionals, you might find it in the Principal Monitor series.

The Code 1.5, reviewed here, is the smallest in the series. It’s a passive two-way system in an infinite baffle enclosure measuring 285mm x 175mm x 164mm and weighing a satisfying 6kg. Intended for use in desktop mixing and similar near-field applications, and as a portable monitor for location work, it offers a frequency response of 75Hz to 32kHz (–3dB), a sensitivity of 85dB SPL (1 watt @ 1m), and typically less than 0.2% THD in the mid-band.

The Code 1.5 uses a 149mm (a tick under six inches) mid/bass driver and a 26mm soft dome high frequency driver. The drivers are the heart of any studio monitor and these ones are worthy of their own reviews, but I don’t have the space for that here. You can read about them on Grover Notting’s website (www.classicaudiodesigns.com.au), and in the interview with Frank Hinton that accompanies this review on the AT website.

A passive fourth-order Linkwitz/Riley crossover, designed by Dr Neville Thiele, as mentioned earlier, provides the frequency division at a respectably high 2.5kHz. Finally, Graeme Huon’s Bandwidth Extension Module adds an extra half octave or so of low frequency performance while sharply filtering out any low frequencies that cannot be reproduced by the system, thereby easing the load on the mid/bass driver and the amplifier. Speaking of loads, the Code 1.5 has a nominal impedance of 8Ω.