The physics of the sounds we make, and how our bodies interact with them are so interesting.

There seems to be lots of conflicting ideas on what should be settled science.

One common conflict is the idea that the psycho/physiological phenomenon of "auditory exclusion" prevents hearing damage during a self defense event. It comes up when discussing keeping hearing protection on your nightstand by your pistol.

Since getting interested in suppressors, I am wondering about the sounds generated and modified, especially as applicable to self defense in closed and close spaces.

Some folks say suppressors are a waste of effort if you are using supersonic loads and that the sonic boom is still present and significant.

I am thinking that outdoors, it may NOT be significant to the shooter because of the shape of the pressure wave generated and its movement AWAY from the shooter. The suppressor diminishing the sound of the expanding gas at the muzzle may be all that's needed to protect the shooter's hearing.

But what about indoors, on a hard floor with an 8 foot ceiling and vertical walls very nearby?


Is the 'sonic boom' pressure wave directed back to the shooter and maybe even amplified? Is it therefore necessary to use subsonic ammo indoors but not outdoors to prevent hearing damage?

Depictions of sonic boom sound pressure waves seem to suggest that they are at maximum some distance ahead and laterally/vertically beyond the muzzle.

Here is an interesting discussion on a physics forum, if you have the time and interest to read it. There is some disagreement and heated tempers .

Here's a picture and an excerpt:



"I don't think that you hear the sonic boom of a bullet that you have fired yourself.


When the round shockwave reaches your ears, you hear the "bang" from the shot. The conical shockwave behind the bullet that causes the sonic boom never passes your ears. They are inside the geometrically extended cone from the start (or behind the cone if you will). So the expanding cone surface (sonic boom shockwave) never passes them. "

Reference https://www.physicsforums.com/...boom-why-not.531823/



Oooooh, another:



"

Figure 14-9 shows a bullet travelling along the barrel of a gun after it has been fired. The bullet acts as a piston and is accelerated by the expanding gases behind it. It must cause the air in the open end of the barrel to accelerate and, if the bullet moves at a speed in excess of where is the absolute temperature of the still air, a shock wave will form in the barrel and pressure will rise behind the wave. That shock wave travels faster than and cannot come to rest in the barrel. Instead the shock wave bursts out of the end of the barrel with a pressure of 1 bar in front of it and high pressure behind it. When it leaves the barrel the air will spread under the influence of this high pressure to form a shock wave and the high pressure will immediately collapse. In this process, air from the barrel will be diverted in all directions and air behind the shock wave will mix with it. The mass of air involved is small compared with that produced by the explosive charge so it will never be the dominant feature of the flow. I have shown the wave in two positions A and B and it is evident from the rapid increase in space for the flow that the wave will quickly die away. The shock wave will continue forwards at decreasing speed and spread like the shock wave from an explosion to create a hemispherical acoustic wave in front of it and possibly a hemispherical expansion wave behind it to complete a sphere. The wave will die away quickly as it expands but, at the same time, the bullet will emerge from the barrel to create its own cone shaped shock wave. It is this wave that we can see in figure 14-6. However there is still the gas that resulted from the burning of the explosive charge following the bullet along the barrel. It will be released suddenly when the tail of the bullet clears the end of the barrel. This is a much more powerful burst than that produced by the air ahead of the bullet and it will create another much stronger hemispherical shock moving forwards and possibly a hemispherical expansion wave moving backwards."

"The bow wave is evident and the surface is fairly flat aft of amidships. Over the rear part of the hull the water on the two sides of the hull is moving inwards and will inevitably collide. When this happens the two lots of lateral momentum are destroyed in the creation of a force that can only divert the flow upwards as in figure 14-19 to form a wave in which the energy in the two converging flows reappear as potential energy. That wave spreads out as can be seen in figure 14-18. It is too much like figure 14-17 to be coincidence.
The bullet is a solid of revolution with a square base. The flow over it may be everywhere subsonic but it is still at high speed. There can be no question of the flow curling round the circular rear corner to converge to the centre. It breaks away and the pressure on the base of the bullet drops to a very small value and so creates a pressure gradient that acts radially inwards. It produces a wave of expansion that widens as it progresses towards the centre. When the wave reaches the centre it is quite wide axially and it produces a rise in pressure over a significant length. This creates a compression wave that becomes flat fronted and behaves like an acoustic wave. In the cone of that wave there is an eddying wake.

The acoustic wave from the nose produces a sonic boom that actually sounds like a whip-crack and the compression wave produces a second whip-crack.
There are two other faint expansion waves but these are generated by a change in the radius of curvature of the bullet and die away quite quickly. The two oblique acoustic waves may persist over long distances.
I think that I have extracted as much as I can from Prandtl’s schlieren picture."

http://www.ivorbittle.co.uk/Bo...und%20a%20bullet.htm

I'm not an expert in acoustics, but I think there are some interesting questions regarding firearms.

Regarding "auditory exclusion," everything I've read on the subject says that it's a perceptual phenomenon, i.e. your brain doesn't perceive the sound because it's focused on the visual cues of the threat that triggered the stress response and the resulting auditory exclusion. The brain is not very good at multitasking, despite what many people believe. Add the stress of a life-threatening situation and the flight-or-fight response, and the brain focuses it's attention on what the eyes see, specifically the threat. This results in the tunnel vision, and sometimes heightened visual acuity, that is often reported by gunfight survivors. Jim Cirillo, member of the famed NYPD Stake-out Squad, reported being able to make out the serrations on the front sight of his service revolver during one such gunfight. Auditory exclusion is a perceptual phenomenon, therefore it doesn't influence the physical effects of high pressure soundwaves on the mechanical/neurological comnponents of hearing.

As far as suppressors and supersonic bullets, I'm more concerned about the "bang" of firing the gun. That produces a significant amount of sound pressure that can damage hearing. I think that is the primary benefit of suppressors, as well as hearing protection in general. I've never been in the presence of a suppressed firearm firing a supersonic round (I suspect video/audio recordings might not give an accurate representation of the sound), so I can't say what effect, if any, it's "crack" would have compared to the "bang."

Just my thoughts on the matter, FWIW.

quote:

Originally posted by RichardC:
"The bow wave is evident and the surface is fairly flat aft of amidships. Over the rear part of the hull the water on the two sides of the hull is moving inwards and will inevitably collide.

?

You won't hear the sound from the supersonic shock wave until the wave impacts something else, like a tree, wall or floor. Which means you hear it almost right away. If you are down range, you won't hear it until the bullet passes you, since it is traveling faster than the sound generated. Silencers (aka sound suppressor or "cans") contain, divert, slow and cool the high pressure gases coming out of the barrel. Even subsonic 22lr through a silencer are above 110 decibels, everything else is louder still.

I can tell through experience, as I am sure others here can as well, auditory exclusion is real. My ears didn't ring till the next day.

I agree that auditory exclusion doesn't have any bearing whatsoever on the physical damage that sound might be doing to your ear.

One is a brain thing and the other is a physical issue.

Now I remember all those headaches I got in Physics class.

If you are unconscious and experience a sound loud enough to cause physical damage, it's still going to happen.

I had a 9mm ND in my house. My ears didn't ring at all. But outside they do if protection is not used.
I was surprised that the"pop" was so minimal.

As the bullet accelerates to the point at which the shock wave forms, the acoustic energy radiates outward just like any other acoustic energy (at the speed of sound). So you definitely "hear it"

It only appears that you are "inside the cone" because you are looking at the steady state condition set up after the bullet has travelled for a ways and the shock wave has formed a characteristic wake angle. It has already past your ears by that time.

Suppressors work by diffusing the pressure wave at the muzzle, so they are reducing both the shock wave in front of the bullet, and also the blast pressure behind the bullet. They would be separated by only the time it takes for sound to travel the length of the bullet, so indistinguishable from a practical viewpoint.

Yes, the sonic boom can be reflected and even amplified by those reflections, depending upon exactly how the reflected surfaces are arranged.

As already pointed out, "auditory exclusion" is a perceptual phenomenon. The damage is done, you just don't know it until later.

FWIW Dept.....When I shoot my suppressed rifles here at home the sonic boom has all sorts of hills, trees, buildings, etc , to reflect it back to the shooter.

A can SURELY makes things quieter, but the "SNAP" of the bullet is still very much present.

Yet when I shoot at the long range area at my club, a large, totally open field. The same rifles have much less of a report that comes back to the shooter. Really almost the way silencers sound in the fantasy world of movies.

The IDPA timer could not *hear* my suppressed 8.9" carbine with 115GR supersonic 9MM ammo.
Sonic boom didn t count for much.

quote:

The IDPA timer could not *hear* my suppressed 8.9" carbine with 115GR supersonic 9MM ammo

Most timers have a sensitivity setting that can be changed.

I was able to shoot a .308 rifle with a suppressor on it. 200 yard range, outside, no hearing protection. Almost no muzzle noise. The supersonic crack, somewhere down range, could still be heard but was not loud or annoying.

Just waiting for the class 3 repeal on suppressors.