In the last article I was discussing spring guns and the mechanical noise they produce. Also, how utilizing a gas ram or nitro piston can reduce the buzzing and other secondary noises that go along with traditional metal spring powered airguns. In part 2, Im going to walk through the basics of gathering some sound pressure levels, i.e. what most DB meters register, so that we can all better understand how loud, or quiet, airguns can be.
Getting some baselines
If I say something is 90 DB its hard for most folks to know what that really means. However, if I asked you if youd ever heard a blender up close, youd probably have some frame of reference. 90 DB happens to be about what a blender would be at 3 feet. A lawnmower at 3 feet is about 110 DB. Normal conversation in a typical office environment is about 60 DB.
With a basic point of reference established, lets now look at how DB levels relate to loudness. The basic rule is that something thats 10 DBs louder is going to be twice as loud. For example, if a conversation is 60 DB, something thats 70 DB will be twice as loud. A good example of 70 DB, based on some research, would be a typical vacuum cleaner at 10 feet. Something that is 80 DB will be twice as loud as the 70 DB vacuum cleaner and 4 times louder than a typical conversation at 60 DB. So, when you see 100+ DB in a review of an airgun, you are looking at something thats got some volume to it.
Supersonic is loud. Period.
Any airgun, regardless of caliber and power system, will be very loud if a projectile is shot at supersonic velocities. Since most airguns have a fixed amount of power output, the way to ensure that you dont break the sound barrier is to use pellets that are heavy enough to reduce the velocity to subsonic levels. Most lead pellets are fine, but some of the newer ultra-magnum airguns like the Hatsan 125 and Hatsan 135, or the Umarex Octane, can push lighter lead pellets to supersonic velocities. Make sure that you get sufficiently heavy pellets; 8.5 to 10.5 grain pellets are usually fine. I like to use the H&N Baracuda line of pellets; i.e. Baracuda match, Baracuda Hunter, & Baracuda Hunter Extremes with these ultra-magnum airguns. For reference, my .177 Umarex Octane registers up to 119.7 DB when shooting ultra-lightweight alloy (1316.3 FPS!) pellets indoors, regardless of its integrated suppressor. Just a note, 120 DB is the average threshold for pain. Sound and velocity levels drop to 100 DB (indoors) and 916 FPS when I use the H&N Baracuda Match pellets which weigh 10.65 grains.
Inside or outside
What Ive found in the years of reviewing airguns is that theres a vast difference between DB levels registered indoors and those measured outdoors. Its also important to make sure to have your equipment set correctly. Lets start with that first. There are many ways sound levels, i.e. sound pressure levels, are calculated. One of the most critical is simply fast or slow. When you are trying to get a measurement of a noise from something like an airgun, you need to have your equipment set to fast. When measuring something thats running, like a lawn mower, gas generator, or the party next door, youd set your DB meter to slow. Having a meter set to the wrong setting will cause all kinds of false, inaccurate readings.
With that settled, Ill move on to indoor vs outdoor. Im going to take a typical, spring powered, non-suppressed breakbarrel airgun and measure the sound pressure level from about 5 feet at 2 oclock from my position. I place the meter there to capture both shot and mechanical noise. The rifle Im using is the Ruger Air Hawk and indoors it registers right at 101.5 DB. Im shooting into a silent trap to try and not capture the pellet impact noise. I want to just get the rifles sound on the meter.
When I set up the same test outside, the measurement drops to 94.6 DB. It will go up and down a little based on many factors: nearby buildings, elevation, humidity, etc. Pellet choice will also play a role.
How loud is your airgun?
Now here comes the fun part. In Part 3 (coming in a few weeks) well take a look at how you can get an idea of how loud your airgun is so that you can know, with at least a moderate sense of accuracy, how loud your airgun really is. So, keep your eye on the blog for Part 3 of Quiet Airguns!