A Night At The Opera

How the Royal Opera House is redescovering passive loudspeakers!

A Night At The Opera

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.

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