How Far Can a Parabolic Reflector Detect a Whisper?

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The discussion centers on calculating how far a parabolic reflector can detect a whisper, given specific parameters like the reflector's size and acoustic efficiency. To approach the problem, one must first determine the minimum sound level detectable by the human ear and then calculate the sound power needed to be captured by the reflector. The intensity level of sound diminishes with distance, so understanding this relationship is crucial for determining the maximum distance from which the whisper can be heard. Participants emphasize the importance of researching sound intensity and efficiency to solve the assignment. The conversation concludes with a note of appreciation for the guidance provided.
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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