In this series, we’ll take a look at how certain elements enhance the greatness of a live performance experience, all thanks to science.
PART TWO: ACOUSTIC II - THE VOICE OF THE HALL
Play a single note. The sound created will travel and bounce off (or be absorbed by) obstacles on its way. If you only hear a single clear sound, it could either mean no sound is reflected, all sound is absorbed or all reflections are early. If you suddenly hear it distinctively repeating several times, those “repeated” sounds are called echos. If you hear the note blurred out, but can’t quite distinguish what’s coming with the note you played, that is the product of reverberation.
What is reverberation?
Reverberation time is a term to describe how long it takes for sound energy to decay in a certain venue. The longer the reverberation time, the longer the sound lingers. Without this, a sound is very “dry”, like dropping a rock onto serene water and it sinking immediately, barely leaving a trace behind.
Reverberation is as if a sound is making a statement, that it is there and should not easily be forgotten. The lingering of sound, especially one after one another, creates an impression of depth and richness. It extends the life of a single sound just long enough to tingle the senses of the listener before moving onto the next.
As you can imagine, for each and every venue, there’s a different reverberation time. The same piece being played in different venues would result in different feelings. Richard Wagner, the famous German classical composer and musician, explicitly initiated the construction of the Bayreuth Festival Theater (Bayreuther Festspielhaus), an opera house designed solely for the performance of his one specific stage work. He shared the idea with his friend Ernst Benedikt Kietz, a respected German painter:
I am thinking of really portraying Siegfried in music, but I do not intend to rely on my luck and let it be performed on even the best stage: quite the opposite, I am going to carry out the boldest wildest plan. [...] Then I would put together right here [...] such a theatre performance, have all the most competent singers come to me and everything necessary for this very occasion realized, that I could be certain of it being one otherworldly opera. [1]
What Wagner precisely imagined and wanted of his work is beyond our knowledge, as the theatre currently standing in Bayreuth right now has been through modern restoration. However, it is safe to believe from his determination, that each musical piece carries its own story and feelings. And if it were to be played in a suitable venue that could assist its goal, a place whose voice could harmonize with it, that would be the dream.
And this is exactly why the right reverberation is significant.
So what exactly affects reverberation in different venues?
The formula to calculate reverberation time was proposed by Wallace Sabine, an American physicist known as the founder in the field of architectural acoustic:
RT60 = (0.16 x V) / (S x 𝛼)
This implies the dependence of reverberation time on the venue’s volume (V), total surface area (S) and its absorption coefficient (𝛼).
The first key to manipulating reverberation lies heavily on the letter alpha. Each material has its specific absorption coefficient going from 0 to 1. The greater it is, the more sound will get absorbed. An open window reflecting no sound would have a perfect 1 as absorption coefficient, while a smooth hard surface such as a mirror would have the absorption coefficient approaching 0.
Acoustic architects decide whether to use a material in the venue, where exactly and how much, depending on the purpose of the venue. Lecture halls, for example, have a rather short reverberation time being under 1 second. Most concert halls go between 1.8 and 2.2 seconds, among which lie opera houses or theatre halls, where it is equally important for the audience to understand speeches and enjoy musical performances, at a shorter reverberation time.
In Wagner’s case with his ambitious plan for the Bayreuth Festival Theater, it was, however, the unique interior design with consideration upon auditorium structure, seating plan and orchestra placement that delivered his imagination. The design was not only to manipulate reverberation but also to influence natural human conceptions and therefore, enhance the live experience of Wagner’s operas to the fullest possible.
The original interior of the theatre comprised of mainly wood, uncomplicated yet effective, for wood has a rather neutral absorption level. It reflects sound well enough so that music wouldn’t be dry, yet absorbs well enough so that songs and speeches are still comprehensible. The seating plan in combination with the stage is, in my humble opinion, the star of the show. Wagner expressed his idea of creating a “classless” theatre, meaning that every member of the audience could enjoy the performance equally from any seat in the house. As a result, the seats were arranged in a single steeply-shaped wedge, much like what we would see nowadays in a plenary hall. What focuses the audience’s attention to the drama on stage, even more, is the double proscenium (which means “stage” in simple English) with a hidden orchestra pit - one stage hidden away from the audience’s sight for the orchestra and one visible stage for the drama. This design not only ensures that the audience is not distracted by the motion of the conductor and musicians but also corrects the balance of volume between singers and orchestra.
Although the dedication put into this project did not compensate for the construction cost, it is today one of the most iconic theatres in terms of acoustic design. It is a complicated process to get everything just right. Moreover, every live performance is different with alternating purposes and focuses. At the end of the day, there is really no single method to arrive at the right decision. You could go as far as crowdfunding your own theatre hall, after having played around with structural designs and materials on a computer programme. The combinations are endless, and so is a live experience. But maybe, the concert that was not your cup of tea might have been conducted in the wrong hall.
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