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An acoustician's Night at the Opera

How is it that opera singers can reach the back rows of the upper balcony of a 2000-seat theater, without amplification? Is is something to do with acoustics?

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Before movies were invented, there is no doubt that opera was the world's most expensive art form. In fact even now, it is probably the second most expensive art form in terms of production cost. No wonder the ticket prices are so high.

But it is also an art form that relies more than any other on having good acoustics. Opera is performed in auditoria of up to 2000 seats, and sometimes more, without any form of amplification.

That accounts for the vocal style of opera. Opera singers have to sing with throats wide open simply to shift enough air to reach to the rearmost rows of the upper balcony. You can consider top opera singers to be vocal athletes on a par with Olympic medallists.

However, the acoustics of the opera house have to help. Theaters and concert halls generally come in two shapes - the 'shoe box' shape approximating to a cuboid, or fan shape where the body of the auditorium progressively widens towards the rear.

It is commonly felt that the shoe box or narrow fan concentrates sound so that it doesn't lose so much level as it travels. This will certainly help the singers.

The singers can also be helped by the stage directions and even the set. If a singer is close to the front of the stage ('downstage'), then the energy of his or her voice travels directly into the auditorium. But in the far upstage, a lot of energy is lost into the fly tower of the theater where it is absorbed by the backcloths hanging there.

So if the director wants to give singers a hard time, he will have them sing their important lines from an upstage location.

The directionality of the human voice is fairly wide, particularly in the lower frequencies. So any hard surfaces in the set will provide reflections that will reinforce the sound. Particularly if the singer and set are in a downstage location.

Now a problem - the orchestra. The orchestra in an opera performance is capable of many times the sound power of a singer (although it has to be said that sopranos can be very penetrating). So the orchestra is sunk into a pit - the orchestra pit - so not only does it not obstruct the stage visually, it is also screened acoustically.

People sitting in the stalls seats will neither be able to see the orchestra nor hear it directly. To compensate for a slight dulling of the orchestral sound this can produce, many theaters have a section of the ceiling over the orchestra pit inclined at 45 degrees so that sound rising vertically from the orchestra is reflected into the auditorium.

The problem of keeping the orchestra down in level so the singers can be heard clearly was certainly on opera composer Richard Wagner's mind. So much so that he had an opera house built - the Festspielhaus Bayreuth - with an extra-deep pit

With such acoustic problems it is a wonder that opera works at all. In fact sometimes it doesn't...

There are many occasions in opera where composers have misjudged the balance between singers and orchestra. And these days directors expect a high degree of freedom in where they can place singers on stage.

So on the odd occasion where a singer is not clearly audible, amplification may be provided. This is not done throughout the opera, but just the specific lines where the problem occurs. Ideally no-one in the audience should be aware that there is any sound engineering involved.

Not even acousticians.

One last point is that opera singers sing so loud that they sometimes cannot hear the orchestra clearly, even though it is right in front of them. So it is not unusual to provide foldback from the pit to the stage. So even if nothing is amplified for the audience, the singers on stage can benefit from modern sound engineering techniques.

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By David Mellor Thursday March 10, 2011
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