Acoustics

Acoustics. The Greek open-air theatre, built into the hillside, provided a perfect place for sound, as did the Roman, with its towering façade. The medieval cathedral must have presented difficulties not so apparent in smaller churches, though even there some sounds probably got lost in the roof. In the market-place, audibility must have been as chancy as it is today in a flat open space. But the use of rhymed couplets, and a good deal of miming and horseplay, must have helped comprehension. In both the classical and the Elizabethan open-air theatres the use of verse helped to carry the voice over the auditorium, and the actors seem to have had good voices. Acoustics became a problem in the theatre when all plays were given indoors, often in rooms acoustically unsuitable for the purpose. Luckily the development of the Italian opera-house produced in the 18th century buildings which, repeated all over Europe, provided a good place for the sound of music. Because the tiers of boxes were heavily draped, the reverberation was short. The flat ceilings, without domes, and the plentiful use of baroque ornamentation, diffused the sound and so prevented echoes, and the large amount of wood used in the buildings meant that the orchestral tone was adequate, in spite of the size of the auditorium. But for the spoken word these theatres were not so well equipped. The theatre built by Vanbrugh in the Haymarket (see HER MAJESTY's), with its high vaulted roof, concave in shape, was found, on its opening in 1705, to have sacrificed audibility to architecture. It was said that scarcely one word in ten could be heard distinctly, and that the articulated sounds of the speaking voice were drowned by the hollow reverberation of one world upon another. Luckily the smaller, more intimate English playhouses were better suited to spoken drama, and Vanbrugh's theatre became the first English opera-house, being used for a number of operas by Handel from 1711 onwards. The large theatres built at the beginning of the 19th century, while preserving the horseshoe auditorium which was good for sound, though not always for sight, adopted the domed ceiling, which led to some notable echoes focused from a particular stage position. Even when echoes were not noticeable, curved ceilings gave an unequal distribution of sound, so that some seats were better for hearing than others. But the baroque tradition of ornamentation, stage boxes and heavy drapery was retained, and helped to keep the reverberation short. Later in the century the rise of domestic comedy and drama led to the building of smaller theatres, offering intimate acoustic qualities.

In the 20th century, the design of theatres everywhere was radically changed. Baroque ornamentation was replaced by large continuous surfaces in hard plaster, the stage boxes were removed, the auditorium became fan-shaped, and large areas of sound-absorbing velvet drapery were removed. At first the new fan-shaped plan and splayed proscenium were approved of on the grounds that they provided useful reflecting surfaces, and audibility in the rear seats was improved. But it was then discovered that any return of sound from surfaces at the rear, including balcony fronts, ceiling coves, and balustrades, found its way to the front seats. Complaints of inaudibility now came from the occupants of the expensive stalls. It had been too readily assumed that a powerful sound-absorbing material on the rear wall behind the audience would prevent any return of sound; but in practice, commercial sound-absorbents, often covered with paint, were found to be less effective than modern hard plasters on the reflecting walls and ceiling. Another factor which adversely affected the acoustics was the relatively large area occupied by the rear wall, which was too often given the most dangerous curve possible, struck from a centre near the stage front. The result was not a complete echo but a prolonging of word-endings, likely to obscure rapid speech. It was clear that the fan-shape needed modification, and that the rear wall should not be curved on plan, but straight or polygonal: also that in large theatres it was wise to avoid curved parapets, seat risers, and gallery fronts, and to restore the side-boxes and draped proscenium. A large bare forestage also increases the risk of reverberation in the front of the house. The value of the convex curve, instead of the concave, has now been recognized in the profiling of reflecting canopies and in corrugated ceilings, the latter being also stepped instead of splayed.

The modern demand for the open stage and particularly for theatre-in-the-round has brought with it further acoustic problems. The human voice has a direction, and is not equally well heard behind and at the side, particularly since the old-fashioned projected speech has been discarded in favour of an intimate conversational tone. New techniques are being evolved to overcome these problems, and also those of flexible staging. Where drapes and carpets and upholstered seats are discarded for the sake of easy convertibility, there is all the more need for good distributed sound-absorbents on walls and ceilings in order to reduce reverberation. Electronic amplification has now become commonplace in musicals, though still resisted in the straight theatre. Modern public address systems can compensate for excessive reverberation times and have been used with particular success in large spaces such as cathedrals; these too however are seldom acceptable on orthodox stages.