New system for measuring the noise level of and air rifle/pistol

[subscriber]

I believe the system will need to be two part as described above, one for the report and one for the mechanical noise then a cumalitive number for both. For example 5 report 2 mechanical 7 total. Now to get base measurements that make since for anyone in the world.

Travis,

I don't think sound adds in a meaningful way, because it follows an inverse distance squared function.  The sound generated nearer to your ear (or conducted by your cheek bones) will sound louder to the shooter.  For example; mechanical vibration from a springer sounds louder to the shooter than to someone 10 yards away.

Might it not make more sense to offer two measurements, described as "shooter's ear", and "bystander" (at some specified distance greater than one meter)?   

Let the mechanical and air noise values combine as they are perceived, or measured; rather then simply adding them mathematically.  This means that a springer may score "loud" to the shooter, while medium to the bystander.  Compared to a PCP, that may be quiet to the shooter and medium to the bystander; because the latter are more exposed to the muzzle.

In absolute terms, one would expect the shooter scale to be louder than the bystander scale; because sound level drops off with the inverse square of the distance.  And because sound from the muzzle is directional.  This does not matter, unless you try to add different sound measurement values.

When I want a better idea of how loud a springer would be to an observer, I fire it horizontally from waist level.  This happens anyway when I want to measure muzzle velocities with my chrono placed on a 30" high table.

[oldpro]

I believe the system will need to be two part as described above, one for the report and one for the mechanical noise then a cumalitive number for both. For example 5 report 2 mechanical 7 total. Now to get base measurements that make since for anyone in the world.

Travis,

I don't think sound adds in a meaningful way, because it follows an inverse distance squared function.  The sound generated nearer to your ear (or conducted by your cheek bones) will sound louder to the shooter.  For example; mechanical vibration from a springer sounds louder to the shooter than to someone 10 yards away.

Might it not make more sense to offer two measurements, described as "shooter's ear", and "bystander" (at some specified distance greater than one meter)?   

Let the mechanical and air noise values combine as they are perceived, or measured; rather then simply adding them mathematically.  This means that a springer may score "loud" to the shooter, while medium to the bystander.  Compared to a PCP, that may be quiet to the shooter and medium to the bystander; because the latter are more exposed to the muzzle.

In absolute terms, one would expect the shooter scale to be louder than the bystander scale; because sound level drops off with the inverse square of the distance.  And because sound from the muzzle is directional.  This does not matter, unless you try to add different sound measurement values.

When I want a better idea of how loud a springer would be to an observer, I fire it horizontally from waist level.  This happens anyway when I want to measure muzzle velocities with my chrono placed on a 30" high table.

Very good points! Thinking of a different approach now. THX

[mrbulk]

I know I'll never get clinically accurate sound measurements with my (lack of real) equipment.

But for my own personal anecdotally relative values I go into my closet, close the door and shoot the gun (un-leaded) at the ceiling with my phone's decibel app turned on, the phone is left in the same place and same orientation (face up) each time. Guns are shot with their muzzles at the same height from the floor and then I compare the readings from the app.

I know this is HUGELY unscientific, but that's all I got and I find it is fairly repeatable from gun to gun. Of course firing WITH a pellet might make all the difference in the world and maybe one gun that's louder unloaded will be quieter discharging a pellet but like I said ... no other equipment.

[Hoosier Daddy]

Assuming you meant "un-loaded" instead of "un-leaded"... don't do that with a Springer.

[mrbulk]

Assuming you meant "un-loaded" instead of "un-leaded"... don't do that with a Springer.

  Yes, I meant unloaded, oh wait, maybe I DID mean unleaded, but of course I never test springers anyway, leaded or not - because springers are Evil (but seemingly only to me) 

[subscriber]

In the case of very loud airguns (high power, without contained muzzle expansion volumes), we do care about sound pressure levels at our eardrums when we shoot. 

For lower power airguns (with contained muzzle expansion volumes), hearing damage is not much of a consideration (unless you shoot it in a small room, or with the muzzle pointing at and near a hard wall, without hearing protection). 

So, it is my considered opinion that the overriding consideration for an airgun sound evaluation system is:

At what distance can the sound of your airgun being fired;
(a) be detected at all; and
(b) at what distance does it suggest "gun shot"? 

This, where the human ear (or repeatable analog) is the instrument used to make these evaluations.


Perhaps you might argue that I have "a" and "b" backwards, but at least we would be talking "meat and potatoes".

[Mole2017]

Subscriber, your second sentence above reminded me of what happened when I shot my R10 at a 4"x4" piece of tough plastic about a foot from the muzzle... The plastic took the shot just great, but I was not prepared for the noise--between the blast essentially reflected right back at me and the "acoustic" reaction of the plastic getting hammered by a pellet it was the loudest event I've let my ears hear unprotected in a long time. They were ringing for a moment and I was kicking myself for not realizing this was a hazard. And this was a shrouded rifle!

As for the perceived sound at other distances, I was thinking of that today too. I managed to get a "video" of the sound recording of a shroud test I did for the R10. It was my first test in an "open field" to minimize the effects of anything in close proximity. While reviewing the test and messing with video settings, it crossed my mind I should try this with two computers and two microphones. The one "near" the shooter and target is what I did last year, but I should add one that is like 50 yards away for comparison.

Next time.

Meanwhile, here's that video. It's just a screen grab of Audacity playing the recording, first at normal speed and then slowed like I was describing. I was also playing with new-found toys to create a video like this--a first for me. Though all my settings were maxed out, it isn't very loud because I was trying to faithfully capture the loud blast of the naked barrel of my R10 and because it is just a "pop" in a field full of crickets. Get your headphones on and turn it up until you hear the crickets and maybe even a low rumble in the background for the best effect.

Anyway, there are a couple of takeaways from a sound measurement:

• Audicity can do the sound level measurements, though not in a "calibrated dB meter" sense. I didn't realize I could use it this way until I was almost done messing with things today, but there is a "VU meter" type display at the top of the Audicity screen that will "hold" peak levels, letting you get an idea of dB level changes from one configuration to the next.
  
• Measurments can get tricky. I had to place the mic and mess with recording levels so I wouldn't exceed my measurement range. The "naked" R10 almost went over the top.
• Adding a reference measurement to every test will help with comparisons later, especially if done days or even weeks apart. Of course, careful attention to repeatable test procedures is important too, but some sort of "standard" sound would be useful. In this case, I used an empty Crosman 1377 pumped up some number of times (I forget how many). It was convenient and repeatable. Almost anyone can find one somewhere. There are other ways, but it seems an air burst of some sort makes a nice standard reference. Other ideas?
• The sound at normal speed is what we and the neighbors are going to hear, but playing it back at slower speeds or zooming in on the details shows us things that are going on. For example, someone with good ears may hear the "blat" of the hammer bounce in this R10, but a closer look certainly shows it, though I had to take the shroud off to get a clean measurement (the shroud takes the distinctness out of the sound). A really close look showed the 1377 hammer actually bounced twice--not that it matters much, but I can barely see that the second bounce is in the data. Slower speed playback really drew out the tone difference to me. And that echo is just cool to hear. It's the sound of the blast echoing off trees and structures off in the distance and into the woods, rolling along the hills. Like a miniature version of setting off an Big Blast on a 2 liter bottle out in the hills--hilariously awesome roll from that!
• I haven't tried it with this data yet, but you can do your own dB calculations from a recording if you really want a number. Calibration is the tricky part (use that reference measurement!), but that doesn't affect comparisons you can make with your equipment in back to back tests.
  
• Think about where that pellet has to go as part of your test. If the trap or target is too close (or too noisy), it will overlap your report of the shot.

Awww...anybody see that typo? Oh well.

[subscriber]

Good stuff, David

I think having crickets in background provides a clue as to how the sounds compare.

The recorded shot sounds have a lot of "sharpness" to them.  I think it is that sharpness that draws attention; especially if it is repeated at fairly short intervals.

Of course the sharpness could be buried in a more distracting sound, such as an inner tube exhaust whistle (video below).    Easily done, if you have a bottle of HPA handy

The proper way to make a Mini Cooper sound like an open exhaust Corvette, is to stretch the inner tube with a small rectangle of plywood or Masonite inside.  Then to have about 1.5" length of inner tube free to flap at the end.  That is how I made them 42 years ago...



 

[JoeShmoe]

Well there's this reference scale.

[Plekto]

The standard is @1M with a calibrated device.  It's actually very easy to get accurate and consistent readings above 60db or so.

[WhatUPSbox?]

It's actually very easy to get accurate and consistent readings above 60db or so.

Quite bit of discussion, technical references, and some testing with high quality microphones on pages 7-9 of this thread. https://www.gatewaytoairguns.org/GTA/index.php?topic=118339.120.  An overview of the topic here http://www.smallarmsreview.com/display.article.cfm?idarticles=2907 while it is for PB's, the discussion applies to AG's.

The basic challenge is the fast rise time of the airgun impulse sound. If the microphone is not fast enough, then it is not clear what is being measured. The other question is why the measurement is being made. If you are interested in kid's hearing damage while they are shooting, that sensitivity depends on how fast the impulse is . If you are interested in not being heard by the neighbor further away, the perceived  loudness also depends (but differently) on how fast the impulse is.

Lots of interesting reading available. There are standards and sound meters out there. How well they apply to what you are interested in depends on the details.

[Fate]

From what I can determine this subject has already been figured out.

Since air guns are the subject, and that subject has been subjected to sound level tests ad infinitum, the relavant data already exists. We don't need to compare it to military jet aircraft using afterburners on takeoff... just other airguns. Right?

Will the sound level of any airgun influence one's chance of buying it? If so, read the reviews.

That's what the internet is for. It is the accumulated human knowledge base. Those looking to expand on it better have very deep pockets, an uncanny reputation for good luck, membership in Mensa, or lots of buds and friends to share it with while they reinvent the wheel.

[Plekto]

It's actually very easy to get accurate and consistent readings above 60db or so.

Quite bit of discussion, technical references, and some testing with high quality microphones on pages 7-9 of this thread. https://www.gatewaytoairguns.org/GTA/index.php?topic=118339.120.  An overview of the topic here http://www.smallarmsreview.com/display.article.cfm?idarticles=2907 while it is for PB's, the discussion applies to AG's.

The basic challenge is the fast rise time of the airgun impulse sound. If the microphone is not fast enough, then it is not clear what is being measured. The other question is why the measurement is being made. If you are interested in kid's hearing damage while they are shooting, that sensitivity depends on how fast the impulse is . If you are interested in not being heard by the neighbor further away, the perceived  loudness also depends (but differently) on how fast the impulse is.

Lots of interesting reading available. There are standards and sound meters out there. How well they apply to what you are interested in depends on the details.

Interesting.  So it appears as if manufacturers are cutting corners and (shocker) that $20 sound meter may not be adequate.  That said, provided you have decent equipment, it's easy to set up.  You will note, though, that your ear is much closer than 1m from the end of your barrel, and almost none of the airgun review sites seem to be using a 1m distance. 

As for sound in airguns, a few basics still apply:
Subsonic will always be much quieter than supersonic.  That crack isn't going to be lessened in any way by a moderator.  Shoot heavy and slow as a rule to keep fps below 1100 or so in bigger PCPs and springers.
Air will be quieter than CO2 or some expanding gas under pressure, if the pressures are the same. (insert bit on physics and dissimilar substances/fluids)
Not all moderators are the same.   
Indoors still requires hearing protection in most cases due to SPL levels and enclosed spaces.  Always toss those muffs on and keep your hearing working into old age.

[subscriber]

You will note, though, that your ear is much closer than 1m from the end of your barrel,

and almost none of the airgun review sites seem to be using a 1m distance. 

Sound is directional; and the airgun is between you and the muzzle.  So, with a pneumatic it is going to sound quieter to the shooter than someone 6 feet to the side, but in line with the muzzle, front to back.  Now, if you had a muzzle brake with rearward facing ports and a lot of blast, that might affect a few perceptions...

A medium power springer usually sounds louder to the shooter than a person nearby, because the spring and piston transmit vibration to the shooter's skull by conduction (stock cheek-weld), and springer muzzle pressure is not high, compared to a more potent, unshrouded PCP.


I also notice that airgun reviewers that provide instrumented sound readings seem casual about where the measurement device is placed.  So much for standardized readings.  I can handle them using their own standard (if they explain it), but to causally place the mic in a different position relative to the muzzle for every airgun they "test", is a bit much.  It is like showing groups, shot at non declared, non standard ranges...

[airrob]

This is an old report but it shows MUCH higher decibel ratings than other ones.  Assuming all this is true, we should be wearing hearing protection. Does anyone here do that?

https://www.pyramydair.com/blog/2009/03/airgun-sound-level-measurement/

[WhatUPSbox?]

Yeah, most of the measurements out there may be worse than useless, they can be misleading.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4896309/

One of many reasons to put an LDC on, especially if you are shooting indoors during the winter. A stock 2240 inside a garage or basement can get loud.

[Hoosier Daddy]

.. Assuming all this is true, we should be wearing hearing protection. Does anyone here do that?

Many here report wearing hearing protection.
My past years of Powder Burners and working on Jet aircraft along with massive Db of rock music took it's toll long ago. 

[FelixS]

Sound level testing is or can be quite complex. But for the purpose of what we want, how "loud" is my gun, it doesn't have to be.

If one were to desire comparisons across many users, first a baseline would have to be established. Then, a portable calibrated means of measuring the gun which one would want to compare it to would have to be used for all comparison sampling.

See the link: 

By using random sample collection devices, you really don't know what the results mean because they would not be based on a reliable measuring system standard.

[subscriber]

Felix,

Instruments have their place.  Especially if they can distinguish which frequencies sound louder to humans.  That is what really matters; and human hearing is known to have a highly non-linear perception with regard to apparent sound level through the audible spectrum. 

Most cheap hand-held sound measurement devices don't distinguish frequency.  The better ones have a mode that mimics human hearing.  All that are suitable for airgun discharge sound measurement have a "fast" mode, measuring and holding the peak sound level value of a short duration event. 

The instrument in that video appears to monitor sound over a working day, because total hearing damage is exposure related, not just a function of peak sound level.  This makes me think it is not appropriate for short duration peak sound measurement.  Despite the elaborate calibration device and procedure that you are advised to use, when renting the instrument.

What amuses me is the sound measurement instrument should be recalibrated before every use.  Not that in itself, but that the device used to generate the sound used for recalibration can be totally trusted to hold its calibration.  To be fair; one has a cord and more exposure to factors that could damage it than the other.

[FelixS]

if we want to compare one instance of a noise level to another, a baseline would have to be established as to what is "loud". controlled sample collection and controlled units of measurement are a requirement to establish this baseline. then the same would be required to compare collected samples against the "loud" value. this can only be done with calibrated instruments and controlled collection within acceptable parameters. so, the sample collection methodology ultimately determines whether the samples are viable to make a determination on what is "loud" and what is less than "loud". loud is subjective, so a dBa of X would first need to be declared as what is "loud", then sampled levels would need to be collected and compared to what is "loud" to make a determination on whether the sample is above or below the declared level.