For the longest time, there has been little or no point of contact between those of us who listen to loudspeakers in the home and the sound reinforcement world. We have largely stayed with passive loudspeakers in conventional cone-and-dome arrangements, and our professional brethren have gone for active line arrays and horn-loaded compression drivers. Some of this is entirely understandable, because of the nature of the two environments; the long-throw and high sound pressure demanded to fill a theatre are materially different to those that make a good sound in a small, domestic room. However, sound is sound, and what if someone made a pair of passive loudspeaker boxes for a professional environment…
Running both a pro-audio business and a domestic loudspeaker firm, Paul Graham of Graham Audio was perhaps best poised to do just that. And when the chance came to specify a loudspeaker system for London’s prestigious Royal Opera House, Paul turned to designer Derek Hughes to manufacture a loudspeaker for the opera house’s requirements, and those requirements were best powered passively.
In fairness, the Royal Opera House is not an auditorium, and is not likely to have stadium acts wanting to blast out rock at ear-splitting levels. Instead, the sound reinforcement requirements are more about good vocal articulation, clarity, and transparency (with the occasional thunderclap thrown in). This is still a ‘big ask’ for a conventional loudspeaker, requiring sustained SPL levels of about 120dB at one metre, in order to have any justifiable ‘point’ (sound reinforcement that isn’t as loud as the singer it’s supposed to reinforce isn’t really worth installing), and the system is to replace a five-way active system developed decades ago for the ROH.
The main unit is surprisingly similar in specification to any sealed box domestic design, with a 1.5” fabric dome tweeter made by SEAS, coupled with a custom three-inch dome midrange and a 10” bass cone. According to Hughes, the tweeter “hovers on the edge of what a dome can do”, which is why most systems at this level use a horn tweeter. But there is heritage here, because the loudspeaker system this replaces used a soft-dome tweeter, too. Nevertheless, the 1.5” driver offers significantly greater power handling and higher maximum volume levels than any one-inch dome (5dB more sensitivity and double the power handling of its predecessor). The Volt-made midrange and upper bass drive units are similarly designed for high power handling use.
The loudspeaker crosses over to the subwoofer at 160Hz, which is high for an audiophile perspective, but helps overall power handling considerably. With a port tuning at around 35Hz. This sub has two 10” drivers also from Volt, but with a heavier cone and more rugged surround than the one in the top box. Effectively this is a passive four-way design, spread across two boxes.
Active systems were tried, but according to Paul Graham, they “didn’t sound great, and some things in the mid weren’t sounding right. It was toppy and bass heavy, but it had plenty of oomph!” Midrange has been ignored by a lot of domestic and PA systems of late, although this is changing. “As far back as I can remember, this has been cyclic,” said Derek Hughes.
We heard the new speaker system in near-final form, undergoing on-site testing at the Linbury Studio Theatre within the Covent Garden complex. This is a smaller theatre than the ROH main stage, and is often used for a more mixed programme of material. In fact, this places even greater demands on the loudspeakers, as they might be used as the full audio ‘feed’ for a ballet, instead of providing reinforcement for singers, and although the Linbury is ‘smaller’, it’s still a 390+ seat venue.
Driven by a kilowatt-pumping Class D Lab Gruppen amplifier (something of an industry standard among theatres and tour buses), the loudspeaker was proving a success in delivering an incredibly clean and articulate voice (as demonstrated by a BBC test disc of a classic Received Pronunciation accent), music programme, and effects, although some fine-tuning was needed to make a thunderclap without causing the top-box to resonate on the subwoofer cabinet.
This is the advantage of rethinking the passive speaker box in 2015. The drive units can handle power, and that power is both on tap and easy to handle today. We’ve come a long way in passive loudspeakers since the last time they appeared in professional environments, and this Royal Opera House installation shows they still command respect.
But let’s be truly honest about this. Graham Audio’s professional division probably isn’t the start of a move back to passive loudspeakers, even though the installation at the Royal Opera House has sparked interest in opera houses around the world. The pro-audio world is still firmly bonded to active loudspeaker drive for a number of very good reasons. But the Graham Audio project shows there’s life in the old dog yet, and that passive loudspeaker systems need not be counted out quite so quickly.
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