Acoustics :: acoustic acoustics sound

The concert hall is one of man's greatest joys; enjoying a fine symphony composed by the worlds greatest, performed by a world class orchestra. For months afterwards, the borgoise attendees will speak of the energy of the conductor, the orchestra responding to him, the power of it all. The crescendoes, the diminuendos, the stark silences between movements, the clarity of the soloist above the rest of the orchestra. Little do they know that were it not for the meticulous consideration of the architect at construction time, the patrons would not feel that they were getting their money's 'worth.' The architect is tapping into the world of acoustics; in this case, achieving the best possible sonic experience through differing techniques : different materials, certain shapes of rooms, sound traps, etcetera. Acoustics and sound, like so many physics branches, starts out relatively simple and quickly becomes a gigantic headache. Massive amounts of planning must go into a large structure such as a concert hall, a dance hall. Even small structures, such as the phonebooth, have hours of careful planning put into their design, in order to achieve the desired effect with the varied sound sources. This page is designed to inform the reader in the basics of acoustics, using the theory behind acoustics and the examples of the concert hall and the dancehall. Technically, the definition of 'sound' is a pressure wave in an elastic medium. This means that our pressure wave can be present in air, water, wood, steel... many different solids as well as air (and liquid). One of the most common units of measurement of sound is intensity, or the rate at which sound energy is being transmitted into the medium. (low sound intensity would be something like somebody clapping between movements, high sound intensity would be the applause after Beethoven's 9th) The unit of intensity is the decibel, or db. We use a logarithmic scale to measure these, as it is difficult to understand the range of the decibel in linear terms. Other units of measurement are the period and the amplitude of the wave. As we see in the graphic, we have the graph of time versus sound pressure, with our little wave traversing it. The amplitude is the highest value the graph reaches before descending again, while the period is the amount of time it takes for the wave to complete a full cycle. Other terms of note for the diagram are compression, which is represented by the parts of the graph in the positive region of sound pressure, and rarefraction, which is represented by negative pressure.