How Does Distance Affect Sound Pressure Levels?

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SUMMARY

The discussion centers on calculating the free field sound pressure level produced by an omnidirectional sound source at different distances. The initial sound pressure level is 77 dB at a radius of 1.6 m, and the calculated level at a radius of 6 m is 65.5 dB. The formula used is p1/p2 = r1/r2, which relates sound pressure levels to their respective distances. The correct approach involves converting dB levels to pressure in Pascals, applying the distance formula, and converting back to dB.

PREREQUISITES
  • Understanding of sound pressure levels (SPL) in decibels (dB)
  • Knowledge of the relationship between sound pressure and distance
  • Familiarity with logarithmic calculations
  • Basic principles of acoustics and omnidirectional sound sources
NEXT STEPS
  • Learn how to convert sound pressure levels from dB to Pascals
  • Study the inverse square law in acoustics
  • Research the reference sound pressure level used in dB calculations
  • Explore the effects of distance on sound propagation in different environments
USEFUL FOR

Acoustics students, audio engineers, and anyone involved in sound design or noise control will benefit from this discussion.

starrlets
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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
 
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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.
 

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