Airgun sound level measurement
by B.B. Pelletier
I promised this report last September and Kevin reminded me last week, so here it goes. We're all concerned about the sounds our guns make. Sometimes, we make analogies about how loud or quite a gun may be, but these are rough approximations at best.
This information is extracted from an article that ran in Airgun Revue #4.
Sometimes, we buy "sound meters" that claim they will give us the intensity of a sound, but the meters available across the counter these days just aren't the right tools for the job. In his recent video, Airgun Reporter Paul Capello gives you a sound level for the Hammerli Pneuma. Paul says the gun sounds loud to him, yet the number his meter gives is 104 decibels. Actually, that is really very quiet and would be more the level of a low-powered Walther 55 target breakbarrel. The Pneuma is really more like 123 decibels, but Paul's meter doesn't show that high a rating because it isn't an impulse sound meter.
I was at Crosman a few weeks back and they were testing a very loud pneumatic gun in a room with concrete walls about 10 feet apart. The sound meter registered 118 decibels for what I felt certain was over 130 decibels of sound. That meter was also not set up for impulse sound measuring. Everyone in the vicinity of the shooting was wearing hearing protection.
I'm saying this because I had a professional sound tester in attendance at the 1998 Big Bore Shoot at Damascus, Maryland. Steve Lewis, a state-certified audiologist, had performed sound testing for the federal government and published papers on the subject. When he offered to test some of the big bores we had at the shoot, I welcomed him. On the day of testing, we expanded his test to include regular airguns, as well.
Steve used a calibrated "type 0" three-scale sound level meter (SLM) to measure these sounds. His equipment could measure the peaks of the impulse sound, which is what all those inexpensive "type 3" SLMs you buy at Radio Shack are cutting off when they give their numbers. The numbers Steve recorded were much higher and reflected the potentially damaging impulse sounds that OSHA measures to gauge the need for hearing protection in the workplace.
Steve's SLM also froze the readings on all three scales, so you didn't have to watch the meter all the time. On a low-cost SLM, someone has to watch the meter as the noise is generated. The number that appears on the gauge is just temporary.
This testing was conducted outdoors in an open wooded area. Steve set up the pickup 90 degrees to the right of the muzzle and exactly 10 feet away. If the pickup was placed in a different spot, all the readings would change.
Sound level information gathered at the 1998 Big Bore shoot at Damascus, MD. Courtesy Steve Lewis.
I find the above chart fascinating because of all the relationships it shows. Look at the Career 707 Carbine, for example. You would call that rifle very loud, but how many of you would be able to relate it to a Sharp Ace Hunter? And for those who aren't familiar with the Sharp Ace, it's a multi-pump pneumatic that has about double the muzzle energy of the Sheridan Blue Streak. We didn't get a number for the Blue Streak, but my gut tells me it might come in around 118-120 dB.
Look at the big, brutish Webley Patriot. Many would insist it would be louder than a Beeman R9 in .177, but on this day the numbers didn't work that way. My guess is that the R9 had a very loud powerplant.
Look at the Beeman Crow Magnum. I've had several shooters tell me that rifles with gas springs make an extra crack when they fire, but I've never been able to hear it. Apparently, the SLM could!
Notice the large difference between two Beeman P1s. Caliber, alone, does not account for this much difference.
BB, please relate all this to something I KNOW!
I'll try, and then you'll see why I can't. Do you know how loud a .22 long rifle cartridge sounds? Several of you have raised your hands, but you moved too soon. The sound will vary GREATLY depending on the length of the barrel of the gun from which it is fired and the type of cartridge you fire. What I CAN tell you with some degree of certainty is that, when fired from a 20-inch barrel, a .22 long rifle high speed cartridge will exceed 140 dB, if measured exactly like Steve set up his measurements. So, nothing on that chart is as loud as a .22 long rifle.
Some of you are saying that I'm wrong about that. You own a Career 707 and shoot it next to your Ruger 10/22, and it sounds about the same.
Sorry to tell you, but your ears, like the cheap type 3 SLM mentioned earlier, are degraded and cannot sense the peaks anymore. Shoulda laid off the Metallica! Curb yourself before the other elevator riders hear you doing rude things because you are assured they are completely silent!
Is this an eye-opener, or what?
I've known about this since Airgun Revue was published back in 1998. Whenever I brush off a sound meter test, this is what has been behind it.
Some of you will argue that if I give you a number, AT LEAST it will be relative from one airgun to another. Yes, it will be, but standing in ice with your left foot and boiling water with your right does not put you in the comfort zone. By that I mean that being imprecise in sound measurement does nobody any good. If the 118 dB that Crosman was measuring was really 136 dB, what does it matter?
OSHA says the threshold for pain from impulse sounds is between 130 and 140 dB, depending on the person. Pain equates to hearing damage. With impulse sounds it is the combination of the numbers of loud sounds and their intensity that affects a person's hearing. Therefore, knowing whether something is 118 dB or 136 dB really does matter.
At any rate, that's my report on sound level testing.