at what decibels do you generally consider a pcp moderated quiet? 75..80..90?
Same as Steve. Or when backyarding, the report doesn't sound like a nailgun as it echoes off surrounding houses and wood fences.
I was taking down some crows with a suppressed stock 1377 some years ago as they all flocked to my far tree wondering why their buddies were laying in the grass, shooting from my basement window. I went outside to remove the 4 trophies that actually landed on my property and realized my neighbors had been outside the whole time and all 5 of them were staring up at the trees wondering what the crow commotion was all about. Their back yard butts up against mine. Now THAT'S what you call a quiet airgun!
Some folks will see it otherwise, but what I've found so far:
1. Less air used per shot, quieter. That usually works out to lower power for the most quiet.
2. Given two guns of the same power, then the same rule as #1 in that the less air used for is quieter (see rule #3).
3. Longer barrels are quieter than short ones at the same power level (becasue it works along with #2).
4. A small well designed and constructed LDC/shroud works better than a large less well designed/constructed LDC/shroud.
5. Hard flat surfaces close to the shooter refect noise. Clutterd close leafy areas tend to deaden it.
When testing for noise, I usually shoot into a pile of loose dirt to deaden impact noise and have someone listen about 5 yards off to the side (WARNING: sooner rather than later, your significant other will have enough of a pile of dirt in the back yard, and you'll end up doing yard work/gardening, which cuts back on your shooting time.)
if you have a air gun that shoots at 75 DB you will wonder if it really shot at all
80 to 90 is quite quiet
a Webley Alecto for example shoots at about 105 DB and at 20 DB less there is a big change and that is all indoors and as quiet as possible, the target was hanging cloth
Loudness vs. Volume... I might have this backwards but here goes...
Volume (the ability of the sound to carry), like a foghorn, is dependent on the energy release. Lots of air moving thru a pipe or high powered airgun.
Loudness is from the rate of expansion of the gas (propellant). Like a low-powered gun that is loud because the barrel is too short. But that sound won't carry very far because there isn't enough energy release (air/gas volume).
Longer barrels help with loudness. To limit the ability of the sound to carry, the rate and/or volume of gas release has to be reduced...
The problem is no one uses a Class 1 decibel meter. All the little DB meter apps on your phone or the little handheld meter you buy on Amazon are designed for constant noise like can be found in a factory. The Class 1 meter has a much faster circuitry, and they are the standard for measuring peak blast and firearm noise levels
I agree with Marflow but would reduce the high end of the range down a bit. I'd say below 85 decibels is backyard quiet. Here is a comparison I did recently on sound moderators. The rifles shot around 90 decibels without a moderator and were too loud in my opinion as the sound would echo through the neighborhood. The decibel reading in the low 80's is ideal.
Yeah, but it's too bad there's not much you can do to reduce...
...the whack/whop of pellet impacting target!
Try pointed pellets. I used to use a Sharp in .22 with a mod and shoot sparrows off the back fence and the only thing I had to worry about is someone seeing the puff of feathers.
Actually, there have been efforts in converting the gas (air or powder) to a ness noticeable noise. An 85 decibel car-horn honk/ weed eater buzz/ whistle/ or whatever is less alarming to a listener than the sharp/snap of a projective weapon.
Fortunately or unfortunately (it's a point of view thing), it's not something the powers-that-be approve of.
I worked on a smaller design that used motion (sliding internal baffle/piston) that used up the energy of the air with notion...basically it's all energy is uncontroled"work", if not used quickly it dissipates energy over time). Turns out that "LDC" actually is lead dust converter (basically, shrouds or LDC's are gas condensers..slowing the speed/energy of the exiting gas, but allowing any particulate matter to drop out of the gas flow as it slowed down)...and the motion would freeze up after a certain number of shots.