The perfect sound

When we go to hear classical music, we know what we like: warm, immediate sound that makes us feel as if we are sitting in the middle of the orchestra. But not every concert hall or opera house delivers this. Some are too dry, some are too reverberant, some have terrible sightlines, and others are just desperately uncomfortable. 

Acoustic gems like the Concertgebouw in Amsterdam - currently celebrating its 125th anniversary year - and the Musikverein in Vienna are even more remarkable when you consider they were built before the physics of sound were really understood. Nineteenth-century architects designed empirically, culling the shape, size and decorations from successful existing halls. 

"The reason the Concertgebouw has rounded walls behind the podium is because the Gewandhaus in Leipzig did," said Rob Metgemeier. Now retired, the acoustician worked extensively on the Concertgebouw for about 15 years.

"The [original] architect didn't understand if the wall shape was important and now we know it isn't really, but it shows that he went to good halls and took the features," added Metgemeier. "They were not trying to invent something new, but rather make something that fit their purpose."

The science of sound

These days, all sorts of sophisticated computer modeling are available, but building an optimal concert hall is still as much an art as it is a science. In the same way luthiers have figured out the constituent parts of the varnish Stradivarius used on his violins and copied his patterns but can't replicate the instrument, knowing all the figures doesn't guarantee a good result. 

"I make my younger colleagues a little bit crazy because they like to make all their calculations on the computer," said Jürgen Reinhold, the German acoustician who worked on the Mariinsky II opera theater in St Petersburg starting in 2007. "I like to make very few and do the rest by feeling."

That feeling, however, should ideally be based on biological and physical facts, which have been learned over the years by means of trial and error.

The Salle Pleyel in Paris, for example, was built in the 1920s using a parabolic shape. The orchestra is in the focal point, which sends the sound straight to the back of the hall instead of bouncing off the sidewalls. What the architect failed to appreciate was that humans' ears are on the sides of our head, not the front, like horses. Humans need the side reverberations to help reconstruct the sound.  

In decades that followed - in the middle of the 20th century - architects were keen to leave Baroque excess behind. It was only after the halls were built with flat walls and very little decoration that they realized all the ornaments - golden ladies, upholstered boxes, heavy drapery - helped the ears as well as the eyes. 

Acoustics vs. architecture

For a project to be successful, acousticians have to be skilled at personality management as well as engineering. The acoustician/architect relationship can be fraught. Architects often want to try something new and most acousticians want to stick with what has been proven to work.

When Jürgen Reinhold was working with architecture firm Diamond and Schmitt on Mariinsky II, he asked to have the original five galleries reduced to three.

"If you build a lot of gallery levels, the openings between them are small and the sound will not reach the back of seats," Reinhold said. "An extreme example is the Met in New York. The galleries overhang quite a lot. In the third or fourth row it is fine, but in the seventh, eighth or 10th row you have no more acoustic contact to the hall. It is like standing outside and listening through a window."

Reinhold says it the success of the acoustics is a factor of how many risks you are willing to take and how strong you can be in negotiating with the architects. "If you are not too strong, then you might get 80 percent of your requirements, but the end result is not as good," he commented.

The practice of employing an acoustician is relatively new. Symphony Hall in Boston, built in 1900, was the first project where an acoustician was brought in from the very beginning and it wasn't until the 1960s and 70s when working with an acoustician from the start became standard practice.

The human ear

Optimal acoustics in absolute terms is an admirable goal, but concert halls are made for people, not measuring devices. The human ear is an amazing machine, capable of reconstructing the original sound from countless reflections they take in from the environment. The human brain, however, finds it much more difficult to forget past experiences, which make evaluating a concert hall a far more complicated matter. 

"People's taste for certain sounds is very much culturally defined by how we like to hear classical music," said Concertgebouw acoustician Rob Metgemeier. I worked on a hall in India for Indian classical music and found that they are not really concerned with the sound but with the intention behind it and the way all the improvisation comes together in the end. Reverberation or sound quality doesn't come into it." 

For performers, too, there is often a disconnect between what is actually happening and how the space makes them feel. "At the Albert Hall in London, you feel like you are in a small room and there are walls all around you," said world-renowned pianist and conductor Barry Douglas of the 6,000-seat concert space. "You look at the audience and it is like someone has painted a backdrop." 

People matter not just because they buy tickets or give the performers someone to play for. A hall full of bodies reduces the reverberation time by about 0.3 seconds or 13 percent. This physical interaction with the sound and space created by a correctly calibrated room is why performance sounds different in a concert hall than it does at home on your stereo. 

"The most important thing is to have a feeling of intimacy, aurally and visually," said Douglas. "When I first started performing I really struggled with nerves, but someone told me not to worry about it because I was only ever playing to one person. The audience isn't linked up with wires, so you are only ever playing to one to one. It's beautiful."

Indeed, the very best acoustics are those neither the performer nor the concert-goer never notices.