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2023-11: Warosu is now out of extended maintenance.

/sci/ - Science & Math

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2082223 No.2082223 [Reply] [Original]

Ok, I really need your help.

Can anyone give me a basic idea how to determine the maximum distance depending on the diameter between two parabolic dishes, so that the voice of person A talking into the focal of dish 1 can still be heard by person B in the focal point of dish 2?

>> No.2082229

I don't think the math for this exists yet.

>> No.2082244

>>2082229
>>2082229

Well what I need know is how to determine the loss in intesity when the sound waves are reflected in dish 1?

>> No.2082269

>>2082229
You can do it but you'd have to make alot of assumptions based on average speech levels and average hearing ranges.

>> No.2082283

>>2082269
>>2082269

Ok i just need a basic idea what to do. What kind of inteferences could damp the sound waves?

>> No.2082320
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2082320

This is a very fuckng lame attempt at trolling.

If you were really engaging in such a formula you would be speaking the correct language.

I refuse to give you the correct formula. Anyone with a basic knowledge of waveforms and psycho-acoustics would know how to solve this.

And for the record, it's amplitude, not intensity you fucking tard.

Inb4 read a fucking book on sound theory.

>> No.2082353
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2082353

>>2082320
>>2082320

Yes and I don't have basic knowledge nor do I happen to be a native speaker. But we can continue that discussion in german, would be a lot easier for me.

But since I have to turn in at least something next week it would still be nice if you could help me.

>> No.2082373

>>2082223
A few things to consider:

1. If the diameter is small, the silhouette of speaker and listener will obscure a significant portion of the dishes.

2. The dishes won't be perfectly reflective. Some sound energy will be absorbed by the dishes. You may be able to determine this using the acoustical impedance of air and that of the dish material.

3. Ideally, the dishes will reflect all the sound waves in a parallel. So you can probably nix the inverse square law in your estimate.

4. Still, the air between the dishes themselves will dampen the sound waves passing between the two. You should be able to find a coefficient for this somewhere. It may depend heavily on temperature and humidity.

5. Oh, and the absorptivity of the dishes and damping of the air will probably depend on frequency to some extent.

I would estimate your whisper volume and frequency. Then I'd look up how loud a whisper at the frequency must be to be comfortably heard. For the sake of the estimation, I'd say that all of the sound energy leaving the mouth arrives at the listener's head (excepting that absorbed by the dish and dampened by the air.)

Sounds interesting. What's this for?

>> No.2082379

>whisper dish
>Ideally, the dishes will reflect all the sound waves in a parallel.

The point of the whisper dish is that only the other person standing at their whisper dish can hear you, and not even people right beside you. This requires that the sound waves bounce at an angle and converge at the point of the speakers head on the other dish.

>> No.2082398

>>2082373
>>2082373

I am an engieering student and have to construct one of these things. Just don't know much about acoutics yet.

>> No.2082402

>>2082379
I was unclear.

What I meant was this: I assumed the dishes were parabolic. Waves leaving the speaker at the focus will spread as normal, but regardless of where they meet the parabolic surface they will bounce along a path parallel to the axis joining the two dishes.

My point was that since the waves don't spread during their journey between dishes, you won't need to apply the inverse square law.

>> No.2082414

>>2082402
Wait, are the sound waves leaving the speaker, bouncing off the dish, and converging at the listener?

or are they leaving the speaker, bouncing off the speakers dish, traveling parallel to the axis, bouncing off the listener's dish, and converging at the listener?

>> No.2082419

>>2082414
The latter, I assumed.

>> No.2082415

>>2082398
Keep in mind that it need not be a dish. A vertically straight wall which is curved when seen from above could also work pretty well. And it'd be easier to make.

>> No.2082421

>>2082402
>>2082402

Thats right.

But there has to be some loss due to diffraction? on the edges of dish 1.

>> No.2082460

>>2082421
Well, I'm no expert on the subject, but I don't think diffraction applies to the reflected wave. It's a change in direction as the wave passes from one medium to another. And I was assuming that anything which passed into the dish material was lost. That could be a lousy assumption, though.

>> No.2082467

Have to go. It's one in the morning here. Got a lot to read tomorrow. Thanks for your help so far. Bye.