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If I blow really hard from a whistle near someone's ear, it'll hurt a lot. But if I blow directly at a person's ear, it won't hurt nearly as much. But shouldn't the whistle (or any other obstruction) strictly reduce the amount of energy hitting the person's ear? So why is something with strictly less energy hurting the ear significantly more?

The only explanation I can think of is that blowing through a whistle produces higher+purer-frequency oscillations, which may resonate more with ones ear-drums, causing more damage.

By the way, I will preempt this question getting closed by saying that https://physics.stackexchange.com/a/414987/218638 absolutely does not answer it. That is focused more on pressure, and directly apply pressure to someone's ear (e.g. by covering it with ones mouth and then blowing). I'm particularly asking about blowing out in the open, without increasing pressure significantly.

Lastly, if resonance is the answer, my question is: which frequency is the actual resonant frequency of someone's ear drum? Or around what rough range are frequencies most dangerous to listen to?

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    $\begingroup$ Couldn't one use this same logic to argue that getting hit by water from a garden hose should hurt less when a finger is placed over the outflow to restrict it, because that's taking energy from the water flow (to push back on the finger)? $\endgroup$
    – T.E.D.
    Commented Mar 8, 2023 at 16:28
  • $\begingroup$ @T.E.D. No, one couldn't. The hose jet will have more energy when you restrict the nozzle compared to leaving the hose open end (I tried to start an explanation, but it gets too long for comments. If you're interested, formulate that into a question and I'll answer there). $\endgroup$
    – Apfelsaft
    Commented Mar 8, 2023 at 23:16
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    $\begingroup$ Objects don't respond uniformly to vibrations at different frequencies. They have different "frequency responses". Blowing air into the ear provides effectively near-0 Hz input, whereas a whistle provides something like 2 kHz input. The amount of energy that gets absorbed at each frequency is different. $\endgroup$
    – user541686
    Commented Mar 9, 2023 at 5:08

7 Answers 7

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The eardrum is damaged if it is stretched too far. The stretching is caused by an imbalance of pressure on either side of the eardrum. Blowing into the ear creates a stream of air that tries to enter the ear. When the blowing starts, some air enters the ear canal, which raises the pressure and pushes on the eardrum. However, the change in pressure is limited because the increased pressure in the ear pushes away any more air from entering. This is like trying to pour water into an already full cup. Human lungs are not capable of creating a powerful enough stream of air to greatly increase the pressure on the eardrum (only enough to be very annoying). Compressed air tanks with nozzles can do this, as can blanks fired from a gun, which is why caution needs to be exercised when using either of these or any other high-pressure system.

Now, why does sound damage the ear? When sound travels through air, the overall motion of air particles is back and forth, with no net movement of air. When a sound enters your ear canal, the amount of air in there does not change. The average pressure inside the ear canal is the same as the outside air. So, there is no impediment to sounds entering the ear. This means that louder sounds are not prevented from entering the ear and pushing on the ear drum. Even though the average pressure has not changed, the momentary peaks and troughs in the wave can be very much greater or very much lesser than ambient air pressure. Peak pressures push the ear inward, trough pressures pull the ear outwards. The louder the sound, the greater the peak pressure on the ear drum, and the greater chance for permanent damage--either by killing sensory cells or even tearing the ear drum.

As for different frequencies, a quick search yielded two papers. This somewhat gruesome one describes subjecting animals to very loud sounds and then examining the damage afterwards. Loud, low-frequency (125 Hz) sounds seemed to do damage to a large area of the cochlea, resulting in hearing loss in a wide range of frequencies. Loud high-frequency (4000 Hz) noise seemed to only damage a small area of the cochlea, resulting in hearing loss in a narrower range of frequencies. This paper with human subjects finds that loud (but not damaging) low-frequency sounds do affect a person's perception of sound for several minutes after the exposure.

It looks like all frequencies do damage to the ear when the noise is too loud. The only difference is whether the range of frequencies affected is wide or narrow. One last note: sounds you can't hear, whether ultrasonic or infrasonic, can do damage to your hearing if they are loud enough.

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    $\begingroup$ It's worth noting that the ear has protective mechanicsms that reduce its sensitivity when exposed to loud sounds; this lessens the change of damage. But there's only so much these mechanisms can do, and a loud enough sound will still cause damage. $\endgroup$ Commented Mar 8, 2023 at 20:05
  • $\begingroup$ well.. it can't be only the pressure levels: considering loud sound level pressures around 1kPa ( en.wikipedia.org/wiki/Sound_pressure#Examples_of_sound_pressure and) and the presssure a human can produce: 10kPa..20kPa (quora.com/How-much-air-pressure-can-a-human-typically-produce), there has to be more to it. $\endgroup$
    – Apfelsaft
    Commented Mar 8, 2023 at 23:25
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    $\begingroup$ @CarlBerger Importantly, that pressure is against an occluded airway. Blowing air is a different matter since air can escape to the side. $\endgroup$
    – Mark H
    Commented Mar 9, 2023 at 1:00
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    $\begingroup$ I know you weren't advocating it, but that animal experient just sounds awful. What kind of human would do that.. $\endgroup$ Commented Mar 9, 2023 at 4:47
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    $\begingroup$ @LamarLatrell Yeah. To me, that experiment yields too little useful information for the pain and suffering it caused. Then again, natural experiments in this area are can be just as grim. Here's a blog post describing a study on the damage to human ears due to explosions that started with an army cannon accidentally exploding in 1887: skullsinthestars.com/2019/09/22/… $\endgroup$
    – Mark H
    Commented Mar 9, 2023 at 6:06
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It hurts more for the same reason that giving someone a pat on the back doesn't hurt, but doing the same pat with a tack in your hand hurts a lot more.

Your question is about damage, but you mention about pain. Let's be clear that those are different things: pain is a sensation in your brain generated by certain stimuli. What causes pain can be a variety of different things, and "level of pain" does not strictly map to "amount of damage involved".

The phenomenon you're referring to doesn't sound like it's related to eardrums and rupturing those - those tend to happen at much higher decibels. Rather, the pain is probably from the stereocilia - little hairs in the inner ear that help to detect frequency.

However, I'm not a biology expert, so I couldn't tell you much more. What I can tell you is the difference between whistling and blowing on a physics level. There are two main effects going on here:

  1. A whistle has a much stronger bias towards certain frequencies than blowing. While a few frequencies dominate the whistle to make it more distinctive, the many frequencies in blowing will counteract one another so that a lot of the vibrational energy (sound) gets cancelled out.
  2. A whistle is a better device for converting air pressure into sound. Energetically, there is simply more energy present as sound than there is in blowing. Conversely, for blowing, most of the energy remains as the movement of air that will easily diffuse harmlessly.

I think what you're missing is the second part - that vibrations (sound) are a different form of energy than net movement of particles ("pressure" against the eardrum in this example). That combines with the better "targeting" of frequencies against certain parts of the ear to make a whistle right in your ear a very unpleasant experience.

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Being able to perceive distinct tones requires some sort of resonances (harmonic oscillators). If the resonances are mechanical (which they are in the inner ear, at least partly, because the inner ear is also said to be somewhat nonlinear), it can be over-excited like any other mechanical resonance (think of the Tacoma Narrows Bridge 1940). Since the resonance filters out a certain frequency band, the amount of energy in this frequency band determines the damage. Btw., it is not the resonance of the eardrum that matters, but the resonances of sections of the Cochlea inside the inner ear.

A blow of air basically contains a strong DC component superimposed by a broadband noise spectrum. In the DC (ultra low frequency) the inner ear is insensitive and only the eardrum can be damaged. The broadband noise may contain a lot of energy, but this is distributed over all frequencies, so that a single narrow oscillator only catches a small fraction of it.

On the other hand, a whistle is "designed" to concentrate as much energy as possible into a single tone. Hence the greater damage it can do to the inner ear.

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If I stand 100 metres from you and blow a whistle, you will hear it - even over background noise. If I stand 100 metres from you and blow hard without a whistle, you won't hear a thing.

A whistle makes a note of one frequency - that frequency is designed to be in the medium to high part of the human hearing range. A very narrow range of hair cells in your ear will be violently and repeatedly agitated.

Just blowing hard without whistling makes white noise - it's spread across the spectrum. The hair cells in your ear will be approximately equally displaced and very little.

The loudest referee whistle Valkeen – 127.6 dB

A motorcycle is 100 dB, a loud rock concert is 115 dB and pain starts at 125 dB. Decibel meter at whistle test was at 2 meters, so players better not come close to the referees with the loudest whistles. https://www.dutchreferee.com/the-decibels-of-popular-referee-whistles/

About the pain

Within the cochlea, one kind of nerve fiber has long puzzled scientists. These mystery fibers resemble pain fibers elsewhere in the body. ... a lab at Johns Hopkins University found that when certain sensory cells of the cochlea are damaged, as might occur during very loud noise, they release a chemical that activates the mysterious pain fibers.

https://www.statnews.com/2016/02/18/noise-induced-ear-pain/

enter image description here

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Other answers have touched on this, but not really focused on the main misunderstanding of your question.

The pain from a whistle is 0% caused by air being blown in your ear. It is caused by the intensity of the vibrations of the air, which can trigger pain receptors in the ear or even cause physical damage to the drum itself of the hair sensors within it.

Blowing air doesn't do much towards vibrating the air in such a fashion, though someone skilled at whistling could do something similar with their lips and/or fingers.

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This answer is highly speculative.

First suppose that there is more than enough energy contained in the act of someone blowing air to damage the ear drum.

But now consider the pressure fluctuations in frequency space. Someone blowing air the pressure basically goes from room pressure and then increases a little bit and then doesn't really fluctuate. So the frequency of the fluctuation from someone blowing is basically DC.

The ear/eardrum can basically withstand relatively large amplitude DC fluctuations in pressure.

In the audio range (2 kHz - 20 kHz), however, the ear is very sensitive since this is where our ear actually acts as an audio sensor. In this range there are components in the ear that can pick up tiny amplitude fluctuations if they are at the right frequency. These sensitive components are only sensitive in a narrow frequency range, but they will result in pain signals or damage at some moderate amplitude, especially compared to the amplitude of the DC pressure fluctuation from someone blowing air.

So while someone blowing air might have a lot of energy and result in a large pressure change, this is all happening at DC in frequency space, and none of the sensitive ear components have responsivity at DC.

When someone blows into a whistle, the whistle acts as a sort of cavity or resonator which up-converts a fraction of the energy of someone blowing into oscillations in the audible frequency range where the ear is very sensitive. It's true that this oscillation only contains a fraction of the energy of someone blowing directly, but the ear is much much more sensitive in the audio frequency range than at DC.

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The inner ear is not a pressure sensor. It is a pretty sensitive vibration sensor. There is a membrane inside it where different parts have different eigenfrequencies, and there are tiny, extremely sensitive hairs that pick up vibrations in each part of it.

When the ear drum is just pushed by someone blowing into your ear, nothing much will happen. The membrane inside your cochlea won't vibrate much, and the hairs won't be excited. The ear can handle as much pressure as the ear drum lets it.

When the ear drum is rapidly vibrating due to, for instance, the sound of someone blowing a whistle into your ear, then this will set off the sensing machinery in your cochlea. Membrane and hairs will vibrate violently in resonance with the sound. If the resulting vibrations are too much for your the insides of your cochlea, damage happens.

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