Academic Reading — All-Types Test 14

Reading passage

The Acoustics of Concert Halls A. Long before the physics of sound was formally understood, builders of theatres and worship spaces relied on intuition and imitation to shape how a room would carry music. A hall that flattered a singer in one city was copied elsewhere, its proportions preserved as a kind of folklore. Only at the turn of the twentieth century did the field acquire a scientific footing, when a young American investigator was asked to remedy a lecture room in which speech dissolved into an unintelligible blur. By methodically adding and removing seat cushions and timing how long a sound lingered, he arrived at a single measurable quantity that has governed hall design ever since. B. That quantity is reverberation time: the interval a sound needs to fade to one millionth of its original strength once its source has stopped. A large stone cathedral may let a chord hang in the air for seven or eight seconds, which suits slow organ music but smears the rapid passages of an orchestra into mud. A recording studio, by contrast, is deliberately deadened so that almost nothing lingers. The comfortable range for symphonic music lies between roughly 1.8 and 2.2 seconds, long enough to blend successive notes into a warm whole yet short enough to keep fast rhythms crisp. Every surface in the room contributes, because each material soaks up sound at a different rate: heavy plaster reflects almost everything, while an audience in thick coats behaves like a sponge. C. Reverberation alone, however, does not make a hall great. What reaches a listener first is the direct sound travelling straight from the platform, followed a fraction of a second later by reflections bouncing off the walls and ceiling. The ear fuses these early arrivals with the original if they come close enough behind it, and the fusion lends the music a feeling of loudness and presence that the direct sound alone cannot supply. Crucially, reflections that arrive from the sides rather than from overhead give the impression that the sound wraps around the listener. This sensation, known to engineers as spatial impression, is now thought to be one of the strongest predictors of whether an audience judges a hall to be excellent, and it partly explains why the tall, narrow shoe-box halls of the nineteenth century are still admired. D. The shoe-box shape, with its parallel side walls set close together, delivers strong lateral reflections almost by accident. When designers in the twentieth century widened their halls to seat more people and improve sight-lines, they often destroyed this quality, and several celebrated modern auditoriums opened to disappointed reviews. The fan-shaped plan, splayed outward towards the rear, spread listeners across a broader arc but starved most of them of side reflections, leaving the sound thin. Some architects have since reintroduced the missing energy artificially, hanging reflecting panels above the stage or breaking the side walls into a series of niches and balconies that scatter sound back towards the seats. E. A further complication is that a hall must serve the performers as well as the audience. Musicians on stage need to hear one another clearly in order to stay together and balance their volume; if the platform swallows their sound, ensembles drift apart and play too loudly to compensate. Designers therefore treat the stage enclosure as a small acoustic instrument in its own right, tuning its walls and overhead canopy to return just enough sound to the players without trapping it. The finest halls achieve a delicate compromise in which the same reflections that guide the orchestra also enrich the experience of the crowd beyond. F. Modern practice combines computer modelling with scale physical tests. Before a single brick is laid, the proposed geometry is simulated so that the path of every early reflection can be traced and troublesome echoes eliminated. Where doubt remains, a model of the hall may be built at one-tenth scale and filled with ultrasound or even nitrogen to mimic how full-sized sound waves will behave. Yet designers concede that no calculation fully captures the verdict of a live audience, and the reputation of a hall is ultimately settled not on paper but on the opening night, when players and public alike deliver judgement that no instrument can predict in advance.