Editor’s Note: This article originally appeared in the January 1990 issue of Recording Engineer/Producer (RE/P) magazine.

Any discussion of major sound systems on the road during the past year must take into account the stadium system Clair Bros. Audio fielded for the Who’s 1989 North American tour. Audience sizes ranged from 40,000 to 65,000, and many music critics found the Who’s show much to their liking. One review of the tour’s show at Kansas City’s Arrowhead Stadium stated that the system “may very well have set a new standard for sound at large outdoor concerts.”

So what’s happening here? What is Clair doing with those S -4s that we haven’t already seen and heard many times before? Aren’t those just larger piles of the usual amplifiers and loudspeakers in a very familiar box format?

The answer is no. It’s not the same old thing. The Clair touring system today is a far cry from its early predecessor. A tremendous research and development effort spanning the past few years has drawn on everything from innovative electronic design to modern structural engineering. It has made a noticeable difference.

Design Philosophy

Clair continues to rely on the S -4 enclosure package as a building block in assembling temporary sound systems of all sizes. However, the company has converted its inventory to the new Series II enclosures, which has been configured in standard-use (F series) and far-throw (P series) versions. Each enclosure weighs approximately 400 pounds and measures 43” x 45” x 22”. (See Photo 1)

The F series box contains wider-coverage horns, a wider-coverage tweeter array and a vertical line array of 10-inch midrange drivers. The P series box includes four 10-inch speakers in a rectangular group, along with long-throw horns and super -high components. The new S-4 Series Il was designed to be an incremental improvement to the standard box design.

“Our goal was to achieve better sound for all ticket holders while reducing hanging and trucking weight,” said Ron Borthwick, speaking for the Clair engineering team. “Even though the outward appearance remained relatively unchanged, no internal parts escaped our redesign process.”

After a survey of available transducers, the best available bass drivers for this application were loaded into the proper box volume with a port tuned to the proper frequency. To hold and protect the various speaker components, a new enclosure was designed for the Series II. Aerospace composite materials technology was used to increase cabinet wall rigidity while reducing box weight. This technology was adapted to increase the wall damping, among other considerations.

“This is of greater concern for speaker enclosures than for aircraft structural parts,” Borthwick said. “An aircraft part has some natural ‘give’ to it. But flexible cabinet walls will add to bass coloration, and will reduce radiation efficiency. Hitting a properly designed cabinet with your fist should feel and sound a lot like hitting a 6-inch slab of concrete. Thus, we applied the principles of structural engineering to achieve this effect.”

The low frequencies did not receive all of the attention. With all speakers hung in their final configuration, the midrange direct-radiating elements are formed in a shaped array, which modifies the distribution of the sound to more closely match that which is required to cover the typical concert venue.

Computer modeling was used to generate a double-driver, high-end horn assembly. The goal was to minimize interference patterns and throat distortion, while yielding the coverage pattern required for each part of the array. Also, the horn coverage angles are varied to suit the seating area to be covered by that part of the array.

Above 7 kHz, coverage angles of super-high frequency components need to be adjusted throughout the array. The required devices are not commonly available to accomplish this. Because the usual components didn’t suit its purposes, Clair designed custom devices that were built in conjunction with a major manufacturer.

Because the modular S-4 enclosures are all the same size, regardless of internal components, assembling large arrays is relatively simple. For stadium shows, the boxes are typically raised with chain-motors and stacked in rows two or three high.

To make it easier for technicians to handle the boxes, Clair designed a special dolly system that enables one person to move the stacked boxes by locking the 2-wheeled unit into a strong, extruded-aluminum channel at the edge of the S-4 cabinet. Using leverage, the built-in cam lever and swivel handle maneuver the stack. With this method, one person can lift an end of a 3-box stack (1,200 pounds) a 1/4-inch off the deck, and can then carefully position it.

For the show that I observed at the Los Angeles Coliseum, a total of 144 S-4 Series II enclosures were used for the main system. The 72 boxes per side were arranged in nine stacks, three high on two levels (45 standard, or F series S-4 Series Its and nine P series per side) with an additional double-high stack of long-throw (18 P Series) S-4s on each top deck. Some quick addition shows a total of 90 Fs and 54 Ps in the system, or roughly a 2-to-1 ratio of standard to long-throw boxes.

“I can remember when a major outdoor system would use 80 cabinets, and that was a big deal for 10 years ago,” recalled Clair crew chief Joe Ravitch. “There had never been a bigger system. Now, the size of the system has grown with the times.But instead of getting harder to put up, things have gotten easier. Our guys usually put this stadium rig up in four hours flat, depending on things like truck access and stage crew size.”

Supplemental loudspeaker systems included a subwoofer section comprising Clair’s custom 2” x 18” low-bass enclosures. Each heavily braced enclosure housed a pair of JBL 2245 woofers. Twelve boxes per side were arranged in a horizontal line array at ground level. (See Photo 2) A Crown Macrotech 10,000 amp was set up to power each dozen of the subwoofer cabinets (a total of 24 18-inch speakers per side in the subwoofer system).

A supplemental delay array, positioned high atop scaffolding behind the house mixing position, was set approximately 200 feet from the stage to give an added boost to high frequencies. Clair’s custom long-throw high-frequency units were arranged in a gentle arc that offered wide-angle coverage. Arranged in three separately adjusted zones, the delay system relied on a Yamaha YDD-2600 digital delay unit, Loft Model 402 crossovers, dbx 903/905 signal processing modules and Carver amplifiers.

“I’m not a big fan of too much in the way of extra delay systems,” said Ravitch, who is responsible for the primary system setup design. “In the bigger stadiums, though, you need some help on the high end as you move farther back. I find it’s best to have it all in one cluster in the center. That makes the setup easier; you don’t end up having AC and signal cable strung out all over the field, with lots of chances for things to go wrong.”