The architecture of sound

Two new European concert halls have become the talk of musical circles: the Elbphilharmonie in Hamburg, inaugurated at the beginning of this year, and the Philharmonie de Paris, opened in January 2015. Both have been highly anticipated for their acoustics.

Their spectacular design did not make the acousticians’ work any easier: more than 2,000 people can be seated in each of the halls, which was the first challenge. In addition, they are intended to attract all types of music – not only classical symphony orchestras, but also jazz combos and pop, world music and rock concerts.

Neither of the two resembles a traditional concert hall. Instead, they are a hybrid of two forms that acousticians know well: the shoebox style and the vineyard style, which are designed specifically for symphonic music (others might be designed for opera, for example). The shoebox style is the oldest and most common. Boston’s Symphony Hall, Vienna’s Musikverein and Amsterdam’s Concertgebouw are all excellent examples. The Berlin Philharmonic, inaugurated in 1963, is built in the vineyard style, which was revolutionary for its time. The audience surrounds the stage on different levels, like terraced vineyards, breaking with the cold formality of the shoebox.

The new halls in Paris and Hamburg artfully combine the two traditional styles in a single structure. “They form an interesting hybrid that incorporates the advantages of both styles”, says acoustician Eckhard Kahle, professor at the University of Music Karlsruhe in Germany, who helped design the Philharmonie de Paris. “The shoebox style is appreciated for its high ceilings and reasonable width, which are optimal for lateral reflections and an even distribution of sound. The vineyard style brings the audience closer to the musicians, providing a more intimate, enveloping concert experience.”

Antoine Pecqueur, a French musician and journalist, prefers the acoustical experience in Paris. “It’s more generous and transparent. The sound is very precise for both listeners and musicians.” But he also appreciates the dynamic shades of the concert hall in Hamburg. “It gives the musicians a lot of liberty. Visually the Elbphilharmonie is appealing, too – inside and outside, offering a splendid view over the city.”

Ensuring sound balance

Collaboration between architects and musicians is now essential. Before the 20th century “acousticians weren’t called upon for their expertise”, explains Gerhard Müller, professor at the Technical University of Munich. “Architects took an empirical approach, copying the shape of a hall where they already knew the acoustic capabilities.” Previously, music was composed for and adapted to the acoustics of a building.

It wasn’t until 1900 that the first concert hall – Symphony Hall in Boston – was designed with acoustics in mind. Ever since, acoustic architectural demands have become increasingly complex: halls must be able to draw larger audiences and bigger orchestras. Musical instruments also have more powerful sounds now.

Any concert venue has a few basic requirements. The first is reverberation time, which is the time it takes for sound to decay until it stops. This is a function of sound richness and of a hall’s effects. “Reverberation was actually the only acoustic requirement until the mid-20th century”, explains Kahle. Ideal reverberation time is between 1.9 and 2.3 seconds for symphonic music, depending on the volume of the hall, the size of the audience and the type of music.

Favouring the overall experience

The challenge for acousticians is to strike the right balance. First, they must control the reverberations in the hall so that the music comes across to the audience as clear and powerful. When a sound is produced, it goes directly to the listener (direct sound) but also bounces to various places such as walls, the ceiling, balconies, decorations, reliefs and even the chairs. A concert hall needs these sound reflections: early ones followed by late ones, and the much-valued lateral reflections.

Acousticians also consider the level of sound that the audience will hear, the distance between the audience and the orchestra, and the volume ratios in the concert hall. “For optimal sound, we calculate 10 audience members per musician and 10 cubic metres per audience member, so 100 cubic metres per musician”, says Kahle. “The more musicians and audience members there are, the bigger the hall must be. And when more than 2,000 people are in the audience, there are even more challenges. The bigger and taller the hall, the further the walls are from the orchestra and the audience. You need to get creative and find ways to bring the walls closer, by using reflectors or playing with the front of the balconies.”

Beyond the scientific criteria, “how the musicians and audience feel has become increasingly important over the last 10 years”, says Constant Hak, assistant professor of building acoustics at the Eindhoven University of Technology. “This is a phenomenon called psychoacoustics: when musicians are playing, they must feel good and be able to hear their own play and that of their co-musicians correctly. As a result, they will play better.

The same goes for the audience: when people enter the hall, their experience will be more special if they feel enveloped by the music and the space, almost as if they were in a cocoon. Appreciating acoustics is very subjective. We don’t hear good acoustics – we feel them. The history of a certain concert hall will also have an effect on some audience members, causing them to evaluate their concert experience in different ways.”

The next generation of concert halls will have to integrate new technologies, says Hak. There is increasing interest in musical centres, either with several halls that can host various types of music or one large hall with variable acoustics. Indeed, not all types of music have the same acoustic requirements. “With electroacoustic solutions, like artificial reverberation and reflections using integrated microphones and loudspeakers, or with mechanical solutions, like curtains or rotatable panels, a single hall can be suitable for a variety of events.”