7
$\begingroup$

I have a story where one side of a war takes advantage of psychological warfare, where a plane on an altitude of 60k ft or 15.2km has massive speakers to play horrifying, disturbing sounds recorded from people being tortured and replayed over and over to keep enemy soldiers from resting and possibly scaring them to desertion. This sound can be heard to 50km away.

My question is: is it possible for a speaker to play this loud of a sound, and a plane to handle the vibrations? And even if yes, it is, what kind of ear protection would the pilot have to wear to avoid being deafened?

$\endgroup$
21
  • 3
    $\begingroup$ One thing that will be working against you here is the stated altitude. Air is much, much thinner at 60k ft than at sea level. About 1/14. As such, sound does not propagate nearly as well at that altitude as it does near sea level. $\endgroup$
    – reirab
    Jan 5, 2023 at 17:51
  • 3
    $\begingroup$ @JBH Not necessarily. The XF-84H Thunderscreech managed 200 dB and a 25 mile (~40 km) audible distance during ground runs, and it was a tiny little fighter/bomber. The hard part here is producing anything other than either rumbling or a very loud bang, though in theory maybe you could modulate the engine speed to replicate sounds (fidelity would be seriously horrendous, but I’ve actually seen even stranger things done before to create ‘music’). $\endgroup$ Jan 5, 2023 at 19:37
  • 8
    $\begingroup$ But why? If you can produce such loud sounds and project them over long distances you might as well just play those sounds a little closer up and make all the enemy combatants deaf. $\endgroup$
    – DKNguyen
    Jan 5, 2023 at 20:52
  • 5
    $\begingroup$ @AustinHemmelgarn: A sound wave cannot go to more than 194 dB SPL in air at 1 atmosphere pressure, because pressure cannot go below zero. (And those 194 dB SPL are purely theoretical, in an ideal model; in reality, the behavior of the air becomes very non-ideal as sound waves go beyond 150 dB SPL.) Explosions and sonic booms can of course be stronger, but they are shock waves, not sound waves. $\endgroup$
    – AlexP
    Jan 5, 2023 at 21:09
  • 7
    $\begingroup$ At risk of belaboring the obvious... if your pilot could wear hearing protection effective against such a phenomenally powerful sound, so could the troops on the ground. $\endgroup$
    – Cadence
    Jan 5, 2023 at 23:53

8 Answers 8

21
$\begingroup$

No?

The loudest sustained concert volume ever recorded was 139 dB, during a sound check for Manowar.

Using this calculator, at 50000m in a straight line, it'd be about "the same as a refrigerator running". 45 dB.

(Digression: I personally had one refrigerator that sounded like a nearby Meshuggah concert in one of my flats when I was at university, but that was a while ago now and my whiteware's sounds are now more like the beginning of Haydn's Surprise Concerto).

In addition, sound waves of different frequencies travel different distances (they attenuate more or less) and even at fractionally different speeds. So the sound's integrity would be lost.

If the loudest ever heavy metal band with all their amp stacks, power supplies, etc, can't do it, I doubt you can either. And the pilot probably can't be protected. But 5 or 10 km is a different story.

$\endgroup$
3
  • 1
    $\begingroup$ You're assuming omnidirectional speakers. You could get a lot more than 45dB if you allocated the energy efficiently. $\endgroup$ Jan 7, 2023 at 3:18
  • 1
    $\begingroup$ @LorenPechtel I am. This is well outside my expertise. The varying attenuation with frequency remains an issue with a directional speaker. $\endgroup$
    – user86462
    Jan 7, 2023 at 5:11
  • $\begingroup$ But you can adjust the energy you put into each frequency if you know how far it's going to go before it reaches the ground. Your 45db is a lightbulb, I'm picturing a searchlight. $\endgroup$ Jan 7, 2023 at 17:34
16
$\begingroup$

One method that "might" work, would be beam formed sound. You mention speakers, yet its not explicitly clear what type of methods are available.

One of the main ideas working against you is spherical propagation. A lightbulb and a laser of similar energy output have very different visibility at distance. However, to see the laser output, at least to any significant intensity, it needs to be aimed toward the target.

This technology is an example of the ideas that currently exist for audio beamforming.

Another option might also be beams of a different type that interacts with a region to produce a sound that is then heard locally. Kind of a Laser Microphone in reverse.

Further, basic or common speakers are not highly directional. Shown by the chart below from Wikipedia, low frequency sounds are almost omnidirectional, and higher frequency sounds have significant directivity. Speaker Radiation Patterns

By Binksternet (talk) - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=4525812

Alternatives available with modern technology that can help with this are:

  • Horn speakers, that would hopefully have a radiation pattern closer to this behavior:
  • Phased Array Speakers, that help to cancel out some of the off axis sounds, and back propagation to the source. Hopefully with a sound pattern similar to:

Neither of these are what most people would consider "common" speakers for concerts or other types of normal human sound generation, because the pattern is far too directional for enjoyable listening. Stand in a slightly different place in the crowd at a concert and you might get an extremely different experience.

At some point it also depends on how "real" you care about the idea being, how closely it "needs" to be tied to the modern 2023 human experience, or how much you really want to work through the details. A lot of stories hand-wave and say it happens, plus technobabble.

$\endgroup$
4
  • 1
    $\begingroup$ You might even get really good results if you fly two or three planes in formation, and they each have a few speakers. The whole formation could become a phased array if properly coordinated. This would give excellent directional control of the sound, especially since the array is effectively larger than a single plane. $\endgroup$
    – Brianorca
    Jan 6, 2023 at 21:27
  • 2
    $\begingroup$ @Brianorca I think that's a little too demanding — you would want them to remain in formation to within say 0.1 or 0.2 wavelength, which would be in the neighborhood of 1cm towards the upper end of the audible range. $\endgroup$
    – hobbs
    Jan 6, 2023 at 22:41
  • 3
    $\begingroup$ @hobbs That kind of depends on the technology available. If there are high speed DSPs, and some way to evaluate the planes spacing (ex: laser rangefinders), then the formation could effectively calculate the distance between planes in real-time and then adjust the output based on the plane to plane spacing. Aperture Synthesis and VLBI are kind of these ideas. Probably lose "some" fidelity, yet still be able to aim the noise. $\endgroup$
    – G. Putnam
    Jan 7, 2023 at 0:16
  • $\begingroup$ Yeah, that's a thought. :) $\endgroup$
    – hobbs
    Jan 7, 2023 at 1:34
9
$\begingroup$

Let's start with the most important aspect, the survival of the pilot:

  • For the pilot to survive, they would have to be flying the aircraft remotely.

A statement that without specific comment explains the other part of your question. About the only sound that's audible over that sort of distance is an explosion, and even then it depends on atmospheric conditions.

$\endgroup$
2
  • 7
    $\begingroup$ Not just any explosion, the kind of explosion that gets you on Wiki's list of largest non-nuclear explosions. #4 on that list, Oppau, was heard about 300 km away, so (depending on how sound falls off with distance) you'd probably "only" need a half kiloton or so. $\endgroup$
    – Cadence
    Jan 5, 2023 at 8:59
  • 2
    $\begingroup$ @Cadence Also, those explosions were mostly at sea level. From 60,000 feet, the sound wouldn't travel nearly as far, due to much thinner atmosphere. $\endgroup$
    – reirab
    Jan 5, 2023 at 17:50
5
$\begingroup$

Could you mount a speaker on an aircraft and use that to scream at people thousands of feet below and 10s of miles away? Nope. You can do some fun things with canon speakers and directional sound production, sure, but getting the sound balance right with different attenuation per frequency range will make this basically impossible.

All is not lost however, since we don't have to limit ourselves to classic speakers. Fortunately there are a variety of alternatives.

First, we might be able to use tuned phonon-laser arrays to direct beams of sound at a small target area. With amplitude control over the individual frequencies - one frequency per emitter - you can adjust somewhat for any expected attenuation profile. I suspect that the phonon beams would decohere fairly quickly though, so this might not get us the range we need.

So rather than transmitting the sound through the intervening atmosphere, how about creating the sound at the target itself? Specifically, we use modulated laser-induced optoacoustic transduction. Tracking lasers accurately enough to hit a pinpoint target at range from a moving platform is obviously a lot harder than doing it in a lab, but that's just engineering. (I trust you'll pay no attention to the frantic hand-waving there.)

Personally I'd prefer to just fire missiles (or UAVs) that disperse tiny speaker drones or simple screamers over a target area. You could probably make a few thousand little screamer packages for the cost of a single actual warhead. Make them small enough to be hard to shoot out of the air, with a power supply that can hold enough watt-hours to scream for a few minutes before triggering a small self destruct charge. Maybe set some of them to start screaming after the touch down, or add a random delay so any that you get hours of entertaining reactions. Sound or motion activated screamers could lay dormant for days before some poor soul encounters one.

The more I think about it, the more evil that sounds. Pretty sure it's not a war crime though.

Yet.

$\endgroup$
2
  • 4
    $\begingroup$ Your leaflet missile idea has potential. It's been done before, of course, but never with those annoying Hallmark cards that sing at you - that's a new twist. (I've often thought those should be a war crime, but c'est la guerre.) $\endgroup$
    – Cadence
    Jan 5, 2023 at 23:57
  • $\begingroup$ A weapon designed to sap morale and induce fear and despondency might have the opposite effect, as Hitler's blitz did on Londoners. It would create a huge incentive to find a way of shooting it down, and it is hardly going to be difficult to locate, is it? $\endgroup$ Jan 6, 2023 at 14:38
3
$\begingroup$

Yes. Sort of.

During the testing for the Manhattan project, the explosion could be heard for about 100 miles. Aircraft can carry comparably-sized bombs, so aircraft can play sounds that can be heard that far away.

(Someone might be tempted to object that an explosion doesn't count as "playing" a sound. To that person I would say, 1812 Overture.)

But to answer more specifically to your scenario: Sort of. Roughly, a 52,000m distance (50km over and 15km up) is two to the 16-and-a-bit, drop-off is about 6dB/doubling, so you get about 100dB of dropoff. Here is a quick description of a 165dB speaker someone made (Why?!). That leaves you something like 65dB of sound at 50km. Which is a lot, about like the volume in a crowded restaurant.

Weight-wise, that trivially fits on a plane. Where your plan will run into problems is intelligibility.

On PPE: cutting-edge modern man-mounted technology can only make it safe up to (very roughly) 130 dB. It's a problem. Anything above that you would need to deal with by soundproofing the cockpit. You likely need about 40dB of very, very serious isolation. Remember, this requirement would be in tension with the need to attach the cockpit securely to the aircraft frame. It's probably doable, but far from trivial.

Lastly though, just because something is technologically possible doesn't make it a good idea. Think about what that side is trying to actually accomplish (seize land, favorable trade deals, etc.) and consider how this tactic supports that strategic objective. If it doesn't support their war objective, the side using it is hurting their own cause.

$\endgroup$
3
$\begingroup$

Yes

They have extremely advanced technology that utilizes a sonic boom as their "speaker".

There are no current technologies that do this, but your military in your story figured it out.

This lets the aircraft "charge" a sonic boom over some distance, then "release" it over its target.

Sounds too fictional? Well, an F-16 attacked Iraq forces in 2003 using sonic booms!

$\endgroup$
1
  • 1
    $\begingroup$ This is the way to go! It might not even be so difficult to get this working. Take any powerful supersonic plane, attach a winch for a sturdy cable that can be extended at Mach 1.5 to trail the plane, attach some kind of beads to the cable that hard-code the sound to be “played”. Each bead creates its own little sonic-boom shock cone, and by spacing out beads of different size the superposition of those cones gives you quite a lot of freedom to approximate arbitrary waveforms. The duration is limited by how long a cable the plane can tow, but you can extend it by flying planes in formation. $\endgroup$ Jan 7, 2023 at 19:20
3
$\begingroup$

I'm late to this, so there are already many suggestions - some rational, some less-so… but…

All other theories/pitfalls aside [& no, I don't think this is even possible in ideal conditions*] what about the cross-winds?
How are you going to aim this thing? … & aim it you must, beam-form or 'massive not-thought-through-properly hifi', you have to be able to direct this energy or you may as well drop leaflets [which could also land several hundred miles away from that height].

At altitude the jet-stream can reach speeds of 275mph. I don't really need any math to know this is not going to help your transmission, especially through low-pressure air at those altitudes.

Think up another idea. This one has not a hope of working.

*Suggestions that it could reach the ground still at 85dB SPL allow the possibility that out in the quiet countryside, you might notice something distant has made a sound.

Consider what thunder sounds like from a couple of miles away [you can count between lightning flash & sound as 5 seconds per mile, roughly] - a low rumbling boom. Yet if you're unluckily close, it's almost a single pulse of energy, a massive deafening spike of all frequencies at once [170dB SPL or more].
The rest is the dissipation & echo/reverberation that happens in just a couple of miles.

Douglas Adams came up with a fabulous bit of 'handwavium' - no explanation anywhere as to how it was achieved, when the Vogons arrive to tell us of Earth's impending destruction…

Then there was a slight whisper, a sudden spacious whisper of open ambient sound. Every hi-fi set in the world, every radio, every television, every cassette recorder, every woofer, every tweeter, every mid-range driver in the world quietly turned itself on.

Every tin can, every dustbin, every window, every car, every wineglass, every sheet of rusty metal became activated as an acoustically perfect sounding board.

Before the Earth passed away it was going to be treated to the very ultimate in sound reproduction, the greatest public address system ever built. But there was no concert, no music, no fanfare, just a simple message.

“People of Earth, your attention, please,” a voice said, and it was wonderful. Wonderful perfect quadraphonic sound with distortion levels so low as to make a brave man weep.

“This is Prostetnic Vogon Jeltz of the Galactic Hyperspace Planning Council,” the voice continued. “As you will no doubt be aware, the plans for development of the outlying regions of the Galaxy require the building of a hyperspatial express route through your star system, and regrettably your planet is one of those scheduled for demolition. The process will take slightly less than two of your Earth minutes. Thank you.”

The PA died away.
Douglas Adams - The Hitchhiker's Guide to the Galaxy

$\endgroup$
2
$\begingroup$

Yes, if you aren't too picky

Let's start with the basic "can a vehicle make that much noise". A jet engine makes noise at 140dB at 25 meters. Based on the calculator passed on by @SeanOConnor, that produces a sound at about 82dB at 60,000 ft., or around 69 dB at 50 miles. So, it can produce "a noise" that loud.

Now we want it to actually produce the sound of people being tortured. Would it be possible to modulate a jet engine to cause it to sound like people being tortured?

This isn't actually very far fetched. They've already looked into installing noise-cancellation speakers into jet engines. To make the engines play a specific noise, you could introduce vibration in the outgoing air stream. It wouldn't be high fidelity, but you would get your point across.

$\endgroup$
4
  • 2
    $\begingroup$ I live at about 17 km (10 miles) distance from Bucharest's main international airport. I have never ever heard any airplane engine noise. In fact, I have never ever heard the engine noise of any passenger jet flying overhead at cruise altitude. $\endgroup$
    – AlexP
    Jan 5, 2023 at 23:54
  • $\begingroup$ @AlexP, 140dB is for a fighter jet taking off. A passenger jet only hits about 120dB on takeoff, and 80dB while cruising. This answer wasn't referring to those. $\endgroup$ Jan 6, 2023 at 3:27
  • $\begingroup$ You wouldn't hear 82 dB SPL if you were standing near a busy road. You'd barely hear 69dB SPL indoors, unless you switch the dishwasher off. The numbers you quote are 'theoretical', but fail to take anything into consideration other than direct propagation. The cross-winds at 15km would basically just dissipate your sound long, long before it reached the ground. If it did, closing your living room window would deal with the rest, same as it does traffic noise… & that's before you even consider actual intelligibility. $\endgroup$
    – Tetsujin
    Jan 6, 2023 at 18:52
  • $\begingroup$ @Tetsujin, You wouldn't hear 82dB if you were at the bottom of a bunker with headphones on, either, or under water, or deep in an arboreal forest, or inside a vacuum enforced silence chamber. None of these details change the reality that it would be audible by someone without those limitations. $\endgroup$ Jan 9, 2023 at 20:23

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .