How Does Distance Affect Sound Pressure Levels?

[starrlets]

Homework Statement

An omidirectional source produces a free field sound pressure level of 77 dB at a radius of 1.6 m from the centre of the source. What free field sound pressure level in dB does it produce at a radius of 6 m from the centre of the sound source?
Answer: 65.5 dB

Homework Equations

p1/p2 = r1/r2

The Attempt at a Solution

p1/p2 = r2/r1
77/p2 = 6/1.6
3.75p2 = 77
p2 = 20.5 dB

 

[Dick]

Your formula is for pressure (in Pa). Sound pressure level is a log of the ratio of sound pressure to a reference level. You'll have to look up what the reference level is, find the actual pressure corresponding to 77dB, use your formula to get the pressure at 6m and then figure out how many dB that corresponds to.