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The characteristics of orchestra halls include good carriage of sound, articulation response, management of echo or reverberation, and frequency balance. When an orchestra hall has all of these characteristics, the players' performance carries through the hall with minimal distortion. These characteristics thus are crucial to optimizing an audience member's listening experience and preserving performances of high quality that occur in the hall.
One of the first characteristics that architects address with orchestra halls is projection. Orchestra halls routinely seat several hundred or even a thousand or more people. Those who are at the back of the hall are further away from the performers, but those audience members still must be able to hear the sound easily. In excellent orchestra halls — those with high ceilings in particular — the sound therefore carries well.
The next characteristic common to orchestra halls is articulation that is clean and crisp. Composers often take painstaking care to direct the duration of and approach to pitch. When a hall is not designed properly, the physical aspects of the building distort what the composer has written, even when the players work very hard to accommodate the space in which they are performing. In a good hall, the articulation of the performers is true and is not "muddy."
Connected to the ideas of projection and articulation is reverberation. Reverberation is the continuation of sound after the sound source has stopped producing the noise. In a well-designed hall, projection and articulation balance. The result is that, even though sound can be heard throughout the hall, the hall doesn't produce distracting echoes.
All sound has a specific frequency, or sound wave length. Poor orchestra halls tend to favor the upper frequencies. Subsequently, the performers sound top-heavy and as though they are not grounded properly. A good hall balances the lower frequencies with the upper frequencies so that the entire spectrum of sound appears even and no single instrument overpowers the others.
Architects control the four primary characteristics of orchestra halls primarily by adjusting the amount of large reflective surfaces. This is why the walls and ceilings of orchestra halls often have unusual projections instead of being flat, and why architects try to get the walls to angle slightly overall. This is only part of the control, however. Architects also must choose the right materials, as different materials' densities impact how sound reflects or is absorbed.
An important consideration in regard to orchestra acoustics is that not all ensembles are the same. For instance, a massive 100-piece orchestra can be overwhelming if given the same acoustical considerations as a small quartet. For this reason, architects incorporate ways to adjust the hall, usually by shifting panels on the ceilings and walls. Climate and humidity control also impacts the sound response.