Like gleaming black prey trapped in an enormous spider web, two grand pianos hovered in a network of rope and steel wire. For their "Long String Installation" and performance at the National Building Museum, which opened last night, Dutch multimedia artists Paul Panhuysen and Johan Goedhart rigged up a system of vibrating strings that stretched to and from the Great Hall's uppermost tiers. In doing so, they transformed the space into a Renaissance palazzo-style sound box.

As they made music by gently running their fingers along the strings, Panhuysen and Goedhart captured an astonishing array of overtones. One of the pair would provide a continuous low note; the other would gradually shift in pitch and volume for several seconds. Together they built up to a noise like distant chain saws on a windy day, until quickly fading into the next sequence. Although remarkable for the ears and eyes, this demonstration begged for the inspiration of musical minds -- perhaps more instruments; definitely more means of producing sound and varying the simple drones.

Last night's was an "interactive" performance. As instructed by the Washington Project for the Arts, the evening's co-presenters, the audience milled about in silence. The diligent did their homework, trekking the hall's arcaded loggias in search of the sounds' various mutations.

Just as 13th-century French composers of organum exploited Notre Dame Cathedral's formidable resonating powers, Panhuysen and Goedhart proved the rewards of creating music for a particular space. But their simple musical means hardly matched the surrounding grandeur.

The installation will remain until Aug. 19.