Although I do enjoy my fair share of live bands in dingy pubs where the amplification leaves my ears ringing for the rest of the night there is nothing quite the same as a massive orchestra going nuts over a Beethoven symphony. Not to take anything away from the performers but it’s not just their talent and skill that is on display. The design and shape of concert halls around the world is not just luck…
You may not be able to hear yourself scream in outer space but you certainly can in a concert hall. Not only is there air to transmit the sound but chances are your scream will be optimised, amplified and reverberated in the space. Instruments themselves have inbuilt resonance chambers (think of the body of a violin or a guitar) which lengthen and project the sound. But what makes a concert hall so good at this?
It mainly has to do with the shape of the hall and the materials used. But before we get onto that, let’s have a quick look at some sound science. The reverberation time, or the time it takes for sound to decay from normal speech to inaudiable (measured scientifically, of course) is around 2 seconds in a good concert hall (check out the link to Boston Symphony Hall below). Too short a reverberation time and the sound will be thin, too long and the clarity is lost, especially in fast passages.
Typical reverberation times:
Coincidentally, a lot of music from the Middle Ages (where music was thought to be sacred and therefore should be only performed in church) contain beautiful harmonies and polyphonic texture (many voices singing different melodies).
Firstly the shape of the concert hall is important. Scientists have found the best shape is a shoebox, with the stage at one end. The sound travels uniformly through the space, bouncing off the side walls and entering the audiences’ ears evenly. The Boston Symphony Hall has a classic shoebox shape (and a good site).
The amphitheatre shape, designed originally by the Ancient Greeks, has been popular choice in concert hall design (possibly because it allows more people to fit in the audience). The Adelaide Festival Theatre and Sydney Opera House contain modern amphitheatre spaces. The main drawback with the amphitheatre shape is that some echoing can occur as the sound is reflected off the side walls.
A circular hall produces dead spots in the space and the reflection of sound may also cause some notes or harmonics to reverberate meaning the sound is not even.
The material used in the hall also contributes to the sound. Soft furnishings absorb sound while harder surfaces reflect it. Designers also have to account for the sound the audience will absorb! The Hamer Hall at Melbourne’s Arts Centre uses material in each seat that absorbs the same amount of sound as a person, so there should be no change in the sound whether the theatre is full or empty!
So next time you find yourself in a concert hall look around at the type of materials used and the shape of the space.
If you want to see some more info, have a look at the studies from Salford Uni in the UK.