Tyco 579-769 Manual do Utilizador descarregar pdf (Página 19)

2-9

Speakers are essentially “point sources” of sound. Sound radiates outward in all directions,

creating a spherical sound pattern. The sound pressure is spread over an increasingly larger

surface area as the sound moves away from the source. This causes a drop in loudness per unit

area. The drop in SPL is referred to as the “Inverse Square Law,” and originates from the fact that

as the diameter of the sound-sphere doubles, the surface area increases by a factor of four. This

behavior of outwardly radiating sound causes a drop in SPL of –6 dB per doubling of distance.

You can calculate the change in SPL at any distance from a speaker as follows:

D1 D2

Δ dB

spl

= 20 log

⎟

⎠

⎞

⎜

⎝

⎛

Equation 2-8. The Inverse Square Law

The figure below illustrates how SPL decreases with distance as you move away from a speaker:

Figure 2-3. dB and Distance Chart

Continued on next page

Speaker Basics

Inverse Square Law

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