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FOCUS OF SOUND
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FOCUS OF SOUND

A room should have a uniform and sufficient intensity  [dB - decibel] distribution of sound.

Below some examples: 

  • The human voice in normal conversation, reaches about 50dB at 1m from the speaker 
  • The human voice, high-volume, reaches about 60dB at 1m from the speaker 
  • A whisper, reachs about 30dB, at 1m from the speaker.

 

 

For each doubling of distance from the speaker there is a reduction of 6dB (scheme below).

To be able to have a uniform distribution and a sufficient intensity of sound in all the room, the direct sound component must be reinforced by reflecting panels variously placed on the ceiling or hung above the performers. Approximately in a room the maximum acceptable distance between the speaker and the listener is about 30m using sound-reflecting panels. For higher distance is necessary to insert an electroacoustic amplification.

ONLY when the room reaches a huge size must be used an amplification electroacoustic system, which (however) always alters the sound quality. 

The table below shows the maximum volume in which it is possible to ensure a good sound quality (in an enclosed space), using sound-reflecting panels, without having to use other sound reinforcement systems, that may alter the sound.

Reflection coefficient 

The reflection coefficient of a material indicates the ratio of the acoustic energy reflected and received.
The following table shows some typical reflection coefficients relating to different types of material.

 

The specular reflection occurs if: 

1. the surface hase a huge size, if compared to the length of the wave


2. the surface is flat

As can be seen from the table "frequency-wavelength" for frequencies above 500 Hz (the middle and upper-middle) generally reflection on a flat surface follows the laws of optical reflection. The problem of the size of flat surfaces in order to obtain reflections that follow the laws of optical reflection, occurs with low frequencies. For low frequencies, if the surface is small, you'll have "diffuse reflections".

In order to be able to better understand the specular reflections think of billiards. The billiard's players know from the experience that in a shots without effect, the angle of incidence equals the angle of reflection. The law of billiards helps to predict in a simple way the functioning of a flat panel that is acoustic reflecting. When the sound hits a convex acoustic-reflecting panel, reflections are dependent on the curvature of the surface. It's important to remember that the "mirroring" acoustic reflections have a frequency response that is typically flat: the reflected wave has exactly the same frequency content of the incident wave.

 

 

 

 

 

 

 

 

 

 

 

 

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