How Far Can a Parabolic Reflector Detect a Whisper?

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SUMMARY

The discussion centers on calculating the maximum distance from which a whispered conversation can be detected using a parabolic reflector with a 1.20-meter aperture diameter and a 10mm collector tube, operating at 20% acoustic efficiency. The intensity level of a whisper is given as 20dB at 1.0 meter from the source, which is treated as a point source. Key calculations involve determining the minimum sound level detectable by the human ear, the sound power required to be captured by the reflector, and how intensity levels decrease with distance.

PREREQUISITES
  • Understanding of acoustic efficiency and sound power calculations
  • Knowledge of sound intensity levels and their relationship with distance
  • Familiarity with parabolic reflector principles in acoustics
  • Basic concepts of sound wave propagation
NEXT STEPS
  • Research the minimum audible sound level for human hearing
  • Learn about the inverse square law in sound propagation
  • Study acoustic efficiency calculations for parabolic reflectors
  • Explore methods for calculating sound intensity at varying distances
USEFUL FOR

Students in acoustics, audio engineers, and anyone interested in sound detection technologies, particularly in applications involving parabolic reflectors and sound amplification.

skinnyl
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Hi there all !

i have been given a question for my Advanced Acoustics assignment as follows:

An MI6 agent uses a large parabolic reflector of aperture diameter 1.20meters to focus a sound into a tube of diameter 10mm at 20% acoustic efficiency which then goes to the ear.

how far away can a whispered conversation be heard from the system?

assuming the intersity level of a whisper is 20dB at 1.0m from the source, which maybe assumed to be a point source.

i have no idea where to start with this. I am not asking for it to be done for me but a shove in the right direction would be appreciated. what methods should i be looking to use or research?

Cheers a lot

Jack
 
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skinnyl said:
Hi there all !

i have been given a question for my Advanced Acoustics assignment as follows:

An MI6 agent uses a large parabolic reflector of aperture diameter 1.20meters to focus a sound into a tube of diameter 10mm at 20% acoustic efficiency which then goes to the ear.

how far away can a whispered conversation be heard from the system?

assuming the intersity level of a whisper is 20dB at 1.0m from the source, which maybe assumed to be a point source.

i have no idea where to start with this. I am not asking for it to be done for me but a shove in the right direction would be appreciated. what methods should i be looking to use or research?

Cheers a lot

Jack

To start, you need to know the minimum sound level that can be heard by the ear. Then you need to use the efficiency information to figure out how much sound power has to be captured by the reflector to deliver the minimum needed to the collector tube. Then you need to figure out how far away the reflector can be from the source and still capture that much power. How does the intensity level vary with distance?
 
Hi, that great. helped a lot!

Cheers
 

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