Signal Transmission Using Sound Waves

[eidolon171]

Consider the following thought experiment...

You are an engineer with a very peculiar assignment. With a mind to reduce the investment of excessive human labor and material waste, you have been asked to build an apparatus similar to an old-fashioned voicepipe. You are asked to ensure that the voicepipe is capable of transmitting a sound produced at location A, and which can be heard distinctly at location B, exactly 5km away. You are allowed to have no more than a 5-second delay between locations A and B. Understand that you will be asked to demonstrate your apparatus by transmitting two distinct frequencies through the voicepipe: a 400Hz wave and a 4kHz wave (lets assume you are using two tuning forks to produce these signals). What do you think is the best method to accomplish this feat?

You may not use electronic devices to amplify your sound wave. However, please note the spirit of this requirement. We do not discount the phenomenon of electro-magnetism potentially aiding in your solution, only that electronic devices themselves are illegal in this scenario.

 

[berkeman]

Summary:: To better understand the phenomena of Acoustic Resonance over Distance, and how to propagate or maintain significant energy in a Harmonic system.

Consider the following thought experiment...

You are an engineer with a very peculiar assignment. With a mind to reduce the investment of excessive human labor and material waste, you have been asked to build an apparatus similar to an old-fashioned voicepipe. You are asked to ensure that the voicepipe is capable of transmitting a sound produced at location A, and which can be heard distinctly at location B, exactly 5km away. You are allowed to have no more than a 5-second delay between locations A and B. Understand that you will be asked to demonstrate your apparatus by transmitting two distinct frequencies through the voicepipe: a 400Hz wave and a 4kHz wave (lets assume you are using two tuning forks to produce these signals). What do you think is the best method to accomplish this feat?

You may not use electronic devices to amplify your sound wave. However, please note the spirit of this requirement. We do not discount the phenomenon of electro-magnetism potentially aiding in your solution, only that electronic devices themselves are illegal in this scenario.

(bold emphasis added by me) So you want to use sound to communicate supersonically over 5km. That doesn't sound very do-able without EM for most of the 5km. Unless you run a 5km long metal rod to couple your sound into...

 

[Dale]

Unless you run a 5km long metal rod to couple your sound into...

But without electronics I don't know how you could effectively couple the sound. Can you touch the base of the tuning fork to a long metal rod?

 

[Merlin3189]

If it is a pipe, can you fill it with water and add an impedance matching system to each end to efficiently couple to the air?

Though if the ban is only on electronic (as opposed to electric and electromagnetic), running apair of copper wires between two telephone earpieces would be easiest. Any sort of pipe would be much more "labour" and "material" wasteful. But how it (or any other solution) relates to acoustic resonance, I don't know.

 

[Vanadium 50]

long metal rod

fill it with water

Why not a microphone and loudspeaker? Then you only need to run wires.

 

[Dale]

Though if the ban is only on electronic (as opposed to electric and electromagnetic), running apair of copper wires between two telephone earpieces would be easiest.

Hmm, you think telephone earpieces are not electronics?

 

[Vanadium 50]

I think we need to understand what the OP's ground rules are - does he really require supersonic transmission?

We can add a steampunky solution - an ear trumpet at one end, a hydrogen-filled tube with membranes on each end in between, and a gramophone horn on the other.

 

[Baluncore]

Pipes can be used for communications when the velocity of the filling is less than the wall of the pipe. That is because the deviant wavefront energy is refracted and turned back into the tube, like light in a graded refractive index optic fibre.

In this case, the velocity in the wall of the pipe, and the internal velocity, must both be above 1 km/sec. Air is too slow, so it is out of the question.

A steel or polymer pipe filled with water would also solve the problem.
(Water = 1480 m/s); (Fe = 5950 m/s); (Polyethylene = 1950 m/s).
The problem with water would be the high attenuation of 5 kHz pressure waves.

If two metals were used, such as galvanised iron wire, the iron would need to be polished first, then heavily galvanised. (Zn = 4210 m/s; Fe = 5950 m/s ). The problem there is launching the energy into the iron core, and the wall being slower than the core.

 

[berkeman]

Looks like the OP is out voting, so we may need to wait until later tonight or tomorrow to get their feedback.

 

[eidolon171]

This is not meant as a criticism to any of the other commenters, but personally I like how methodically @Baluncore has decided to approach the issue. That said, I urge all commenters to consider the basics before jumping right into building your systems.

What kind of energy are you putting into your wave?
How could the tuning fork be made more energetic?
What impedances will your wave encounter?
How can the pipe be made more conductive?

Several people have raised questions about bending the rules (particularly with regard to EM). To be clear; circumvention of the ban on electronic devices is highly encouraged by your employer. But be careful, if your system looks too much like an electronic device you could be arrested!

Can you touch the base of the tuning fork to a long metal rod?

Yes. A metal rod is considered a conductor, you are allowed to use it.

For clarification: An electronic device is considered any type of functional Capacitor, Inductor, Transistor, etc. Of course, you as the system designer cannot be held liable for the naturally occurring EM behavior of some object or system, but you cannot intentionally rely on an electronic device to perform work.

If it is a pipe, can you fill it with water and add an impedance matching system to each end to efficiently couple to the air?

Though if the ban is only on electronic (as opposed to electric and electromagnetic), running apair of copper wires between two telephone earpieces would be easiest. Any sort of pipe would be much more "labour" and "material" wasteful. But how it (or any other solution) relates to acoustic resonance, I don't know.

You are allowed to fill the pipe with anything you want (including any rare form of matter). You may change the pipe form and material with anything you want. It can be closed or open. You can even use two separate pipes if you wanted to make an internal waveguide for each of the two frequencies.

Avoiding Harmonics altogether is not a valid solution to the problem as stated, but you are absolutely right that it is worth mentioning. I am sure that your employer is particularly interested in hearing if there is a “cheaper” alternative.

As stated in the reply above; copper wire is only considered a conductor, it is not considered an electronic device, therefore it is allowed. Although, when you use the term "telephone earpieces" that sounds like it might be an electronic device, and remember those are illegal!

I think we need to understand what the OP's ground rules are - does he really require supersonic transmission?

We can add a steampunky solution - an ear trumpet at one end, a hydrogen-filled tube with membranes on each end in between, and a gramophone horn on the other.

I very much appreciate the image you created in your response. I feel it adds a fitting visual element to the story.

I think I understand your request, and I will attempt to clarify, but please correct me if this is not the statement you are looking for:

Given that sound waves travel through the air travel at roughly 340 m/s, and given that you must devise a system that carries sound waves at 1000 m/s this would be a Supersonic sound system. Your proposal does include filling the tube with hydrogen, which should allow your wave to travel at about 1270 m/s, and that's marvelous, but without something to propagate the wave across such a long distance, wouldn't it lose energy before it ever reaches location B? If not how can you prove that to your employer?

 

[sysprog]

Technically a maser isn't an electronic device ##-## it doesn't rely on electron flow for signal propagation ##-## but it can still amplify a microwave signal.

 

[eidolon171]

Technically a maser isn't an electronic device - it doesn't rely on electron flow for signal propagation ##-## but it can still amplify a microwave signal.

I have not considered using a maser as a potential solution. Though I do think you might be able to make a case for converting the analogue acoustical frequency somehow, and transmitting it to a receiver that will convert it back into the original tone.

I will say that the anti-electronic device police agree with you that a maser is not, in theory, an electronic device. Having said that I do wonder about how you could apply such an apparatus toward fulfilling the intended function. I imagine that you would use your microwave transmission as a carrier wave, and add either your 400Hz signal or your 4kHz signal to the carrier. But that means you would have to modulate your microwave somehow at location A, emit that microwave transmission, and receive the signal at location B, analyze that transmission, and convert it into an analogue frequency. Could it be done without the aid of electronics anywhere in the process?

 

[DaveC426913]

A stick of dynamite will get a signal there in plenty of time.

I think you could make a seismometer without electronics.

But getting the frequencies right might be tricky.

(You might set off 400 sticks over a one second duration, but setting off 4000 over one second might be a little destructive.)