Muzzle pressure and decibel level?

[andym79]

Hi guys, bit of a strange question, but is there an approximate way of calculating the decibel level from a rifle (I know you can buy meters).

Does anyone have any ideas I know for example that a 25-20 at 1500fps is a lot quieter than a .243 at 3600fps but by how much?

[Oldbloke]

Andy, why the question? Bit of an odd one.

[Lorgar]

I doubt anyone can do it by ear as actual increase in volume and perceived increase in volume are not parallel and things quickly get louder than you can handle.

From memory the discharge from a rifle ranges from about 130dB for a 22lr to 180dB for the larger centrefire cartridges. Add a muzzle brake and it would be louder again from the shooter position, though I can't say by how much exactly.

Rule of thumb is for every 10db increase in actual dB SPL the perceived volume doubles.

If 130db is your base...

140dB seems 2x as loud

150dB seems 4x as loud

160dB seems 8x as loud

170dB seems 16x as loud

180dB seems 32x as loud and so on.

You quickly (almost immediately) reach the point where each level is just ear-splittingly loud and I don't think anyone could quantify the differences.

[Usurper]

I see a case for suppressors being made legal...

[Homer]

G'Day Fella's,

Andy M, your usual modern Super-Sonic centrefire, has a muzzle pressure of approximately 10,000 PSI.
This varies quite a bit obviously, depending on the chamber pressure, expansion ratio and barrel length, etc!

Other than using an acoustic meter, there is no other reliable means that I'm aware of, to registering the muzzle blast Db level!
Jaycar sell an elcheapo $100.00 meter, and this will give you an indication but probably nothing that would stand peer review.

Hope that helps

Lest We Forget
Homer

[combo12]

For what it worth (cost nothing) I have a SPL meter on my mobile phone. Free download that would give you some comparative readings just for starters...

[Chronos]

I'm not sure it could be calculated easily but I'd love to see some data gathered using good equipment from points at the butt, at the muzzle and say 10m infront. I think it would be a very interesting way to analyse what happens when you play with things like brakes and even supressors.

I know that in Australia shooting orgs have been reluctant to approach the use of suppressors from a Health and safety angle as there are concerns I t could open the door on other analysis that could go against sporting shooters but the reality is the PPE available to us simply cannot give enough protection to bring firearm noise levels down to a level considered safe

Class 5 hearing protection may only reduce levels by 26db or so which is a small reduction from 180db, still leaving plenty of noise to do samage.



Chronos

[Oldbloke]

From one of my earlier posts on the sbject.

As it happens I know a little about this subject & it has come up in the past so I have taken the time to explain in some detail. I hope my comments are of assistance. I apologize for it being long winded but it is difficult to reduce it much further & still include al the info. Many people ignore hearing protection and regret it during their retirement. (particularly young men) Ignoring it will effect the quality of life during your later years.

NOISE FACTS
According to the current Australian OHS/WHS regulations exposing employees to noise levels over a peak of 140db or to noise at or above an average of 85dB(A)leq for the period of an 8hr shift. 
It is the “peak” of 140db that applies to shooters.

Some examples for shooters of noise levels are: (I did not take these measurements but the source is fairly reliable)
22Lr 140 dB peak
12g 165 dB peak
3006 170 dB peak

So every time you fire a rifle (without hearing protection) you are doing a little damage to your hearing and the damage compounds throughout your life. The loss of hearing will not become noticeable until later in life and by then it will be too late. 

And when measuring noise you must remember that an increase of 3dB is double the sound power. So an increase of just 2 dB is very significant. Immediate irreversible damage is likely to occur at 140dB.

HEARING PROTECTION
In Australia hearing protection is sold in 5 classes that are laid down in Australian Standard 1270. Class 1 being the lowest level of protection class 5 the best. Below is the minimum reduction (the technical term is attenuation) in dB required of each class of hearing protection, Muff or plug at the ear.
1. 10 - 13
2. 14 - 17
3. 18 – 21
4. 22 - 25
5. 26 or greater

Muffs & ear plugs perform differently at various frequencies further complicating which muffs to purchase. The above is essentially an average at various frequencies.

So if the noise level of a 3006 is 170dB you can expect a class 5 muff to reduce the exposure to the ear down to at least 144dB, but perhaps not all frequencies. So the wearing of anything less than a Class 5 would be fairly useless to shooters. Even the class 5 may not completely prevent hearing loss. However it will certainly go a long way in reducing hearing loss. Continued and regular exposure to gun fire of say 130db will still damage hearing over time.

Many retailers such as Bunnings sell ear muffs but you get what you pay for and often it is not clear what “class” they are on the packaging. As mentioned above, this is important. In addition cheaper muffs generally wear out very quickly, significantly reducing the level of protection provided and the wearer is usually unaware that they now have reduced hearing protection. So you start off with say a class 3 and a yr later it is a class 1 muff for example.

WHAT SHOULD I BUY?
Ear muffs, both standard and electronic provide the best protection and I would recommend class 5 for shooting. The down side of standard ear muffs is the effect they will have on communication and possibly not being able to hear other hazards nearby, e.g a truck heading in your direction. 
Ear plugs, I cannot recommend the use of off the shelf ear plugs I rarely see them worn correctly. However if worn correctly and they fine, very effective and convenient to wear in the field. Personally fitted plugs should be a better option for most users if you prefer plugs check what the expected attenuation will be before purchasing.

As mentioned earlier electronic muffs are great and fitted with a microphone and amplifiers that automatically switches off at 85dB. This allows you to hear normal sounds and your ears are protected from loud sounds. However quality ones are expensive & you get what you pay for. 

If you are shopping around for a pair of muffs I suggest you visit a safety specialist retailer such as protector alsafe or safety equip. In my experience the staff generally know about the products they sell and will steer you in the right direction. And they also sell muffs of the less expensive brands. Stick to well known brands is always good advice. Avoid overseas purchases on ebay etc as you may not get the level of protection you need.

EDUCATION
Here is a couple of links for two very good videos. If links do not work copy & past the line below into your browser address bar.

Here is a link to a general video about sound and hearing protection that all shooters should watch, about 18 minutes. The hearing video 
http://www2.worksafebc.com/Publications ... rtid=34284

Here is a link to a 70 second video showing how to fit ear plugs correctly
Fitting video

https://www.youtube.com/watch?v=ghNFKsxJuvY

I hope this helps people to better understand the importance of looking after their hearing and how to do just that.

[Chronos]

Always good info from you on this topic OB and worth posting twice

More and more often i'm using class 5 ear plugs under class 4 electronic muffs for the added protection at the range

Chronos

[Oldbloke]

"More and more often i'm using class 5 ear plugs under class 4 electronic muffs for the added protection at the range"

Chronos, I think that's the go for range work. For hunters like my self, I use correctly fitted plugs. Why, well At the end of the day I don't fire many shots.

[<<Genesis93>>]

Hi guys, bit of a strange question, but is there an approximate way of calculating the decibel level from a rifle (I know you can buy meters).

Does anyone have any ideas I know for example that a 25-20 at 1500fps is a lot quieter than a .243 at 3600fps but by how much?

Andy, you know we're a curious bunch of so and sos.....what are you up to this time...??

There's probably a way of calculating the degradation of the sound pressure level at a distance....maybe that what your thinking....

[Oldbloke]

db reduction over distance.jpg (242.45 KiB) Viewed 5553 times

Sound reduces by 6db for each doubling of distance.

[Gwion]

^^^
That's a good graphic, OB. Very handy to know. Some good electronic muffs are in order, methinks.

[WayneO]

i used to use ear plugs until we went shooting one day with an E.N.T Doctor. He spent a great deal of time explaining that the plugs do nothing to reduce the damage to the eardrum caused by vibrations picked up behind the ear.
That was 15 years ago and electronic ear muffs had just come out and were insanely expensive. Now my brother is deaf so I know the frustration of being hearing impaired, so I sold one of my rifles and bought myself a set of class 5 electronic ear muffs. Since then i never go onto a range without ear protection.

[Oldbloke]

"I used to use ear plugs until we went shooting one day with an E.N.T Doctor. He spent a great deal of time explaining that the plugs do nothing to reduce the damage to the eardrum caused by vibrations picked up behind the ear."

I disagree, the main problem is that about 90% of people do not fit them correctly.
Perhaps some noise is picked up through the scull behind the ear, but 99% comes in via the ear cannal and drum. So I think that is BS.

[Chronos]

"I used to use ear plugs until we went shooting one day with an E.N.T Doctor. He spent a great deal of time explaining that the plugs do nothing to reduce the damage to the eardrum caused by vibrations picked up behind the ear."

I disagree, the main problem is that about 90% of people do not fit them correctly.
Perhaps some noise is picked up through the scull behind the ear, but 99% comes in via the ear cannal and drum. So I think that is BS.

I agree OB, while some some pressure is transferred through tissue the reduction must be significant otherwise there would be little perceived difference when using plugs or putting your fingers in your ears for example


I've heard in the past that ear muffs do offer superior protection to plugs of similar rating because they tend to seal around the top of the jaw bone and behind the ear but to say plugs do nothing is absurd

Also hearing damage has nothing to do with the ear drum. It's the permanent damage to the tiny hair like fibres that sense vibration in the fluid of the inner ear. Normal sound moved the hairs, loud sounds move them more violently. Some may be damaged but heal like the day after a concert, when they break the loss is permanent. The more you break the more hearing loss occurs.

Chronos

"How can noise damage our hearing?
To understand how loud noises can damage our hearing, we have to understand how we hear. Hearing depends on a series of events that change sound waves in the air into electrical signals. Our auditory nerve then carries these signals to the brain through a complex series of steps.

Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.

The bones in the middle ear couple the sound vibrations from the air to fluid vibrations in the cochlea of the inner ear, which is shaped like a snail and filled with fluid. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.

Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave.

As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cell, creating an electrical signal.

The auditory nerve carries this electrical signal to the brain, which translates it into a sound that we recognize and understand."

[WayneO]

Thank you very much for this explanation Chronos, I always just took what the Doc said as being fact.

[Gregg]

Great info all round guys

[Oldbloke]

Chronos has explained that very well. Should have been a bloody doctor. Lol

[WayneO]

Doc Chrono

[Zilla]

I disagree, the main problem is that about 90% of people do not fit them correctly.

Only my personal observations here but I notice a number of guys fit plugs loosely so they take a tiny edge off the sound but leave hearing mostly intact for the benefit of conversation.

Which is stupid given the setting of course...