Room Acoustics
A high-end audio system should have an excellent sound in any room
I have often read and heard the above statement browsing audio forums and talking with audiophiles.
I was in the lucky position to listen to a great Steinway D piano in a room and next day in another room. (You may say that a piano is not a usual sound system but, thinking after, a real piano might be considered as an ultimate high-fidelity audio system. High-fidelity sound is defined as a very similar sound to the source.) The first room, where the piano recital took place, was a drawing room of an old house. The second room was a gym. Both rooms had similar sizes, the placement of the piano was nearly the same and the pianist was the same, as well. Well, the fabulous sound, experienced in the drawing room of the castle became a mediocre sound in gym.
What scientific explanation may we find for the above phenomenon? Sound is the object of acoustics. The science of acoustics studies the propagation of sound in an elastic medium. Sound is a mechanical disturbance, which propagates with a characteristic velocity in an elastic medium. The propagation is supposed to be a wave-propagation. The velocity of the sound depends on the thermodynamic features of the medium (air in the above example). The propagation of the sound in the air can be described by second order partial differential equations.
According to this description, the sound in a space depends only on the source and on the distance from the source, if the humidity and temperature of the air are constant and the space is empty.
That means, if somebody places an audio system in the middle of an infinitely large room (far from all surfaces, including bottom) with fixed and temperature and humidity – the sound will only be determined by the source, by the sound system. The audio system should be far from all surfaces, so it will be tricky to fix it far above the floor. There is another condition that should be fulfilled, as well. The listener should be placed infinitely far from the source. Unfortunately, the listener will not hear anything because the sound pressure level (volume) is zero in this point of space.
If the listener would be closer, he acts as reflecting and absorbing medium and as a heat source, which causes inhomogeneity in the temperature distribution. As a result, the sound will not only depend on the source but the also on the listener. The bottom line is, the sound of 
each audio system depends on the listening room and on the listener.
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