Noise Levels for Rifle Shots

[CA Raider]

Is there some research on the noise levels (dB levels) for rifle shots for various calibers? I'm interested in how loud the shots sound to observers in the general vicinity of the shooter (not just immediately beside the weapon). Has anyone seen any info like that?

thanks,
CA R

 

[Telekinesis]

Look at some suppressor tests. Usually they'll give an unsuppressed decibel rating as well as a suppressed rating.

For general reference, .223 looks like it is hovering around 165 dB, and .308 is usually between 165-170 dB (both measured around 1m from the muzzle).

Not to plug another site, but NFA Talk has a very good set of data about this (even if you're not interested in the suppressors that they were testing).

 

[MrCleanOK]

I'm not familiar with any real scientific data on the subject, but I can tell you that "it depends". It depends on the caliber, the barrel length, muzzle devices, weather conditions, distance, terrain between the shooter and observer, orientation of the shooter with respect to the observer, etc. There are a ton of variables. This sounds kind of like a leading question to "will I bother the neighbors". If it is, I will say that there are ways to build ranges or devices to mitigate sound pollution.

 

[geo57]

CA Raider, yes there has been.

While not as knowledgeable about mechanical decibel equipment or their readings, the high tech noise data report I got from my wife when she was in the area the first time she heard my Mosin Nagant M44 go off was " Son of a B**** , what WAS that ? " Mind you this is a woman that has been around firearms discharged for almost 50 years.


I hope you find that helpful.

 

[Reloadron]

There are web sites like this one that provide some information. There have also been several threads on the subject so a forum search may help.

Much of what is out there can be pretty subjective data. Taken from the Wiki:

Sound pressure level (SPL) or sound level is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level.

What becomes important in the first link or anytime we collect sound pressure level data is defining exactly where with respect to the source and how the measurements were taken. No shortage of variables to contend with.

So while the Internet is loaded with no shortage of sound level numbers just keep in mind much of it is relative and subjective data.

Ron

 

[Speedo66]

I don't doubt different brand or bullet weight cartridges in the same caliber in the same gun will have different readings.

 

[denton]

The SPL resolves down to simply the gas pressure in the barrel at the time the bullet exits the muzzle.

 

[Clark]

The gas ball at the muzzle expands super sonic without making a sound until it slows down to the speed of sound. At that time a wave is propagated with a peak of 2 atmospheres and a trough of cavitation [zero]. The frequency content is uniform down to a single pole roll off below the frequency where the gas ball diameter is equal to 1/2 the wave length. The peak pressure does not matter directly, as there is no sound until the ball gets down to 2 atmospheres.

Of course SPL falls off as the square of distance in open air, but due to gravity, we are all walking around on the surface that reflects the sound so it always falls off slower.

Quickload may predict the muzzle pressure, but this is not the only variable. The capacity of the bore and chamber is the next most important variable.

What does it all mean for kids?
Guns all make the same peak sound, but some have a deeper boom due to large gas ball [like woofer speaker].
Your .22 goes "bang" and your cannon goes "boom".
Just like your little dog goes "bark" while your big dog goes "woof".

What does it mean to the street wise?

If you try to measure the sound level of different cartridges, you will get information as useless as some internet guy measuring strain gauges on rifle chambers.

Lots of out of control variables in the surrounding reflective surfaces will allow some charlatan to make any reading he wants.

 

[benEzra]

The gas ball at the muzzle expands super sonic without making a sound until it slows down to the speed of sound. At that time a wave is propagated with a peak of 2 atmospheres and a trough of cavitation [zero]. The frequency content is uniform down to a single pole roll off below the frequency where the gas ball diameter is equal to 1/2 the wave length. The peak pressure does not matter directly, as there is no sound until the ball gets down to 2 atmospheres.

Does that take into account the fact that the initial high-pressure/low-pressure interface is a very thin annular discharge around the base of the bullet, gradually transitioning to an obstructed stream and then an unobstructed stream as the bullet clears the muzzle? Modeling the primary overpressure as a sphere works but may oversimplify how the earliest, highest pressure gas sheds its energy. Things like barrel-cylinder gaps in revolvers, and brakes on rifles, also result in large increases in radiated sound energy over the same loads fired from fixed unbraked barrels of the same length, and I'd love to know precisely how that happens.

I'd love to see a detailed treatment of the entire process...to be sure someone somewhere has done a paper on firearm acoustics at some point?

 

[Clark]

With Quickload predicting ~~10,000 psi at the muzzle for high power rifles, that gas ball is going to have to get big to get down to 64 psi.







To get the muzzle pressure to below 2 atmospheres I have had to have low powder charges and long barrels.
To get the velocity up, I have had to compress the powder for a higher peak pressure and higher expansion ratio.

 

[tuj]

I was doing RSO duty last weekend and I pulled out my phone and its sound measurement app. Where I was standing, about 50' off the range, the shots from .45 and .40 pistols and a .30-30 carbine where around 80dB. The .22's on the range were around 60dB. Again, this was standing away from the line.

 

[CA Raider]

that last post agrees roughly with some figures I found elsewhere through the links on this thread. seems like 22LR is about 20-25 dB quieter than a lot of other rifle and handgun catridges.

thanks for the info.

CA R

 

[Mohave-Tec]

Buy a cheap SPL (sound pressure level) meter or borrow one from a auto audio of home theater installed and find out. If I remember correctly, each increase of 6 dbl doubles the sound pressure/volume. A decrease of 3 halves the volume....I think.

 

[Mohave-Tec]

Clark, if all else is equal, if you point two identical charges at each other, will the resultant opposing wave forms cancel each other out?
LOL....don't answer that.

 

[Reloadron]

Buy a cheap SPL (sound pressure level) meter or borrow one from a auto audio of home theater installed and find out. If I remember correctly, each increase of 6 dbl doubles the sound pressure/volume. A decrease of 3 halves the volume....I think.

This will end up off topic but what the heck.

Actually and trying to keep it somewhat simple if we are looking at SPL (Sound Pressure Level) a +6 dB change doubles the SPL and a -6 dB change halves the SPL.

The dB is merely a ratio.

The decibel ( dB) is used to measure sound level, but it is also widely used in electronics, signals and communication. The dB is a logarithmic unit used to describe a ratio. The ratio may be power, sound pressure, voltage or intensity or several other things.

The Bel is a seldom used large unit so the deci Bel (1/10 Bel) is used.

Anyway, as applied to SPL the 6 dB points are half points. Increasing by +6 dB doubles the SPL and -6dB halves the SPL. The 3 dB points apply to power (expressed in watts) and a few other units.

Overall I really liked Clark's summary:

What does it mean to the street wise?

If you try to measure the sound level of different cartridges, you will get information as useless as some internet guy measuring strain gauges on rifle chambers.

Lots of out of control variables in the surrounding reflective surfaces will allow some charlatan to make any reading he wants.

Ron

 

[Owen]

Reloadron,

a 3dB change represents a doubling or a halving. 6dB represents 4x or 1/4x depending. 6dB is the change is SPL if you double or halve the distance from the source, which I've verified by mesurements.

The OP asked about changes in sound depending on position relative to the weapon: That will change drastically dependinging on the position. Out in front of the muzzle is far and away the loudest, with directly behind being the quietest.

From recent measurements I've taken 5m in front of a .308 can be as much as 20dB louder than 5m behind.

Regarding using car audio/cell phone/industrial sound meters for measuring gun shot SPL, the rise rate and response of the microphones is not sufficient to deal with the shockwave. On top of that, the max reading on the meters is probably too low to catch the peak reading.

 

[Reloadron]

Hi Owen, so then if the sound pressure level is doubled the sound pressure level does not increase by 6 dB? I guess what I am asking is I have a sound, when that sound is twice as loud the change in dB is not 6 dB but 3 dB?

Thanks
Ron

 

[tuj]

while I agree phone apps are no substitute for a proper spl meter, they are surprisingly accurate for what they are. I had about 30dB of headroom left while I was recording the shots and watching the graph. I agree that the microphone and electronics may not be fast enough to catch the most powerful of the transients, so that's a valid limitation.

I would still say that the relative difference between the 22lr and the other guns made a lot of sense. While I don't condone the practice, it is very easy to shoot 22lr (especially rifles) without hearing protection and not feel any immediate pain or discomfort. Unlike say, the .44mag I shot without hearing protection ONCE. STUPID. Anyway, given that hearing protection is worth around 22-28dB of reduction, that roughly equates to what I was seeing.