Decibal Test Results, Need Input Please

[Hate The Rain]

Had the family over to do a sound test. Thought I would find the quietest of mods for my Notos. All I got was a little confused or got a little information clarified. I'll describe what we did and attach the results. Looking for input on doing a better test structure please.

A gentleman was very kind and sent me a box full of various mods for the Notos. Our goal was to see which one was the quietest. What we found was that most of the mods are very close to each other in decbal readings. We had a decibal meter directly under the exit of the mod. and then one 10 feet forward and 10 feet to the right. The third position was 10 feet back and 10 feet to the left. All were on the same plain as the Notos. I always thought the stock unit was fairly quiet, I have some hearing issues. But I put the first test subject on and took a shot. I definitely heard less "noise" from the Notos. This noise reduction turned out to be repeated with all my family members but for different mods. However, the decibal readings were all within points of each other. A bit confusing. We thought there would be a noticable, varifiable reduction on the meters, and there really wasn't. Are mods just modifying different tones, and we hear or don't hear a tone based on what that specific mods eliminates from its sound production?

Our goal was not to pick at any manufacturer of named product out there. We truly were just looking for quietest. So hopefully no one will take offense.

Our summary is that all the mods produced similar decibal readings. However, each mod reduced various portions of noise produced with each shot. So it came down to who was listening to it and what they heard versus what they considered loud. It seems to all be based on subjectivity.

The variables we had: 4-5 mph tail wind, turkey gobbling, driving cars about 50 yards away, noisey Jays, more stuff along those lines.

We did notice that if we waited for a reduction of wind, there was definitely and effect in the decibal reading, slightly higher.

What I have come up with for a new test approach is to get a 4 inch ABS or the like T. Place it in a box and surround it with insulation. Place the decibal meter in the bottom opening of the T and shoot through the T to hopefully get a more consistent and repeatable reading with much reduced outside interference.

Would really appreciate any and all suggestions in an effort to clear up the confusion. Is there really very little difference between decibel readings of mods? Or, was our first test flawed due to the variables?

Will have to work on the attachment. Doesn't seem to want to attach as an Excel or snipped from Excel. Will post the results as soon as I figure this out.

Thanks

 

[Hate The Rain]

 

[kwaping]

Are you sure the decibel meters can respond quickly enough to the shot sound?

 

[subscriber]

Hate The Rain,

Thanks for collecting that data and for sharing it. You have discovered how difficult it is to collect objective data and make sense of it. Rather than specify how it should be done, I have some general comments, that should be considered my opinion only:

Accurate repeatable dB data is most useful for designating a suppressor hearing safe. When you are dealing with an airgun that is very much hearing safe already, and want to rank sound reduction dB meters are less useful. I say that, because if you are trying to prevent your neighbors from hearing your airguns, or at least not being alarmed by the sound, then consider that they use their ears and not a dB meter to make that determination.

Also, your neighbors' ears are not located 1.5 meters above the ground and 1 meter to the side of your airgun muzzle (the standard for measuring dB with a suppressed firearm). Your neighbors are further away than that, with no single distance to define their location. That said, I think you 10 foot ahead, to the side, and behind are the closest in representing what your neighbors hear. They are not alarmed by 70 to 50 db noises coming from next door, because that is the level of normal speech. They are alarmed by sounds that might sound like a gunshot.

If I hear a centerfire rifle report from 1/4 mile away at night, what grabs my attention is not the dB level, because it is quite low at that distance, but the sharpness and the echo of the sound. So, the nature of the sound is more important than the dB, once we are talking about hearing safe dB levels. Depending on the people involved that could be 80, 90 or 100 db measure at one meter from the muzzle. The perception of sound is relative to the sound "floor". In the day the sound floor tends to me much higher than at night. One expects noise during the day, so the odd popping noise once in a while does not insist on explanation. While at night, a longer period of silence broken by what has a gunshot signature grabs attention. Especially if it is repeated.

I designed a shroud for a gent on the GTA forum. He calls it "three bird quiet". He used to shoot one starling raiding his chickens' food, and the other starlings would fly off. Now he can shoot three in succession before the other starling realize that they are at risk, and fly off.

My attitude is if the results from a dB meter and method of using it do not correlate with the ears of the average person, then the dB readings are not useful to me. No matter how accurate the meter is claimed to be.

One reason for the ranking of mods being different at different ranges is that the high frequency component is more rapidly absorbed by the air than the lower frequency component. Also, apparent sharpness is much worse in front of the muzzle than behind it, as is the perception of loudness. Part of that is because sound is directional. Mostly, we are shooting away from people, but if you have a wall in front of you, sound can echo off that and sound louder behind you, than if you had tall, dense vegetation in front of the muzzle.

It is possible to be too close to the muzzle and measure the same dB, bare muzzle, as all or most of your test mods. In that case, you may be saturating the meter, and it simple reads near the highest reading it can produce. If a louder sound to your ears measures the same on you dB meter as obviously quieter ones, move the meter further away until the readings have some differentiation between them that you can believe.

Cheap dB meters produce different readings to each other and to expensive ones. Insisting on getting the same readings is an exercise in frustration. Such meters are still useful to compare different mods, even if the absolute readings are off. As long as the meters dp not clip or saturate.

I see airgunners place their dB meters a foot from the muzzle, as if they think that will provide a more accurate reading. Meanwhile, sound level drops off with the inverse square of the distance. So, the measured sound is very distance dependent. An inch variation in meter placement is much worse at one foot than at 3 feet or 10 feet.

Another factor is the placement of the target trap. Too close and the impact can be louder than the report. You can tell the difference, if the trap is far enough, but the meter simply captures the loudest sound. Be sure that it not the trap by placing it very far away, and us trap material that damps the sound. Rubber mulch or duct-seal are good choices. Watch out; the carboard box containing you trap material can be pretty loud too.

 

[kwaping]

@subscriber I want to know your profession.

 

[subscriber]

kwaping,

I am a retired mechanical engineer, that designs airgun mods for fun.

 

[TN_Yankee]

…if you are trying to prevent your neighbors from hearing your airguns, or at least not being alarmed by the sound, then consider that they use their ears and not a dB meter to make that determination.
…
They are not alarmed by 70 to 50 db noises coming from next door, because that is the level of normal speech. They are alarmed by sounds that might sound like a gunshot.
…
So, the nature of the sound is more important than the dB, once we are talking about hearing safe dB levels.
…
The perception of sound is relative to the sound "floor". In the day the sound floor tends to me [sic] much higher than at night. One expects noise during the day, so the odd popping noise once in a while does not insist on explanation. While at night, a longer period of silence broken by what has a gunshot signature grabs attention. Especially if it is repeated.
…
One reason for the ranking of mods being different at different ranges is that the high frequency component is more rapidly absorbed by the air than the lower frequency component.
…
Also, apparent sharpness is much worse in front of the muzzle than behind it, as is the perception of loudness.
…
Another factor is the placement of the target trap. Too close and the impact can be louder than the report.
…

Hopefully I haven't butchered @subscriber's post too badly, & all emphasis (and hence possible errors) is mine, but upon reading it, these things jumped out at me. If we take out the visual aspect of someone seeing us shoot (like poor @.20calguy's recent experience), and are keeping the muzzle sound down to hearing-safe levels, I think these are key to successful shooting at home. One crazy idea that is likely overkill, is the potential use of technology/electronics to alter the muzzle sound so that it doesn't sound like a shot at all. Sound is energy, and energy can be transformed. Rambling thoughts early in the morning...

 

[subscriber]

I like to loop drum solos when I shoot, so anyone that walks by locks onto a repetitive slapping sound to figure it out has an easy answer to, "what was that".

 

[PumaCarl]

Awesome, that besides collecting numbers, that everyone argues their worth over, you collected people too. That's the 'opinion' that matters, more so than any data. The data doesn't call the police on you. With that being said, what Sunscriber said, about different sounds falling off quicker or carrying further, and people's reaction, is spot on. You should really place your helping sentient acoustic meters where you don't want the noise going, while you shoot where, and how, you normally would. If everyone still can't really agree on which one is quieter, take the opinion of the person closest in age to your neighbors because the pitches you hear definitely change with age. Still no consensus? Just go with the empirical numbers you got, which would seem to be the V-7.

Great test, superb commentary, nice read, well done!

 

[Hate The Rain]

Thank you all! Absolutey agree with everyone. The target material was 1 inch rubber mat, or stall mat at 30 yards. I can only answer the meter response capability as, I think so. They responded immediately to sounds and we had other eyes watching meters at all times. To my ears, the No Mod and the Deci Bell were the quietest. But I did think the stock one was pretty darn quiet as well. So my idea of creating a quieter "test chamber" wouldn't work, based on Subscribers saturation input. (Thank you Subscriber for the designs that participated in our experiment) I had a room mate(electronicial engineer), he dabled in ham radio. Dabled is the polite way of saying, 25 foot across antenna and 30 feet in the air. Neighbors were thrilled when he went on the air. He would micro adjust that thing for better results. It did seem to work, he had contacts all around the world and one day was waiting for the space station to pass by when they were responding to callers. He got bored and went to mow the lawn. As soon as he went outside I heard the Space Station conversations, he wasn't happy he missed out.

Anyway, the moral I am understanding, it sounds like we could micro adjust our testing and end up in the exact same spot. What's that old saying, The hearing is in the ear of the beholder?

Cameron

 

[graycrait]

I designed a shroud for a gent on the GTA forum. He calls it "three bird quiet". He used to shoot one starling raiding his chickens' food, and the other starlings would fly off. Now he can shoot three in succession before the other starling realize that they are at risk, and fly off.

I think this is the definitive test if one is focusing on starlings. Might be another thing with squirrels or rats, I dunno.

I had this same group of mods that Hate the Rain had. I used 2 Notos'. My wife stood about 30' to the left even with the muzzle but behind a tree. I shot into the yard, no noise. About 20' to the right was the garage. I held the Notos being fired out in front of me so I could hear without my ear laying next to the mechanics. I would fire 3 shots out of one Notos and then 3 out of the other. Whichever mod was quieter of the two I left on and switched out the Mod on the other Notos. My wife, who likes to disagree with me, and I came to the same conclusions at the end.

It was more an academic exercise in that my MIL lives 125 yrds to the north and the next neighbors live about the same distance to the south. No neighbors to the west. The house is between us and the neighbor to the east and he is almost as old as I am so I doubt he would hear anything and he has never mentioned it to me. Any of the Mods were good enough for me in my situation.

My wife agreed that the Tango Sierra and the B Version of the Subscriber were tied, along with the "giant" Kycirion. I think there was one other that was so close to those 3 but I forget which one. I chose to send a long all the mods to Hate the Rain so he could test them and had my friend on this forum, plinker4life, make a couple of his version of the original Subscriber as I like the small size and performance seemed good enough.

I think for me tone is as or more important than a couple of decibels. I have a .22 Streamline that I have 2 mods for, an FX and a Hugget. I only use the Hugget on that rifle because of its low tone. It may sound like a jet engine to starlings but to me it is quite comfortable to shoot without hearing protection.

I'm not sure there is much to be learned by all this other than everyone needs to choose what they think works the best for them in their situation. Now I wonder if the 3 Starling moderator sound is the quietest for nosey neighbors, or maybe there is a nosey neighbor mod that doesn't work as well for Starlings

 

[subscriber]

graycrait,

Unfortunately not everyone has the opportunity to try several mods, and choose what works best for them. They are left with buying mods based on forum reputation, or using published dB values. As you mentioned size of the mod, that could certainly be as large a factor in a purchase decision, as dB or tone. This leaves us with impressions and tests results, as published by you and Hate The Rain. Much more valuable than dB values by themselves.

 

[graycrait]

graycrait,

Unfortunately not everyone has the opportunity to try several mods, and choose what works best for them.

@subscriber ,That is sort of why I ended up with all those mods you designed in that blast of designing a couple of months ago, plus the 4 I had already purchased and a couple of variants by plinker4life. I had the opportunity to try that many so I did.

I even put a mod on my CMP Daisy M853 .177 that fires around 450FPS. Do I need a mod for that rifle with its small bore and small volume of air, probably not, but there is a bit of difference between mod or unmodded. Plus I had a small diameter light weight mod that worked with that rifle.

Partly due to this air gun moderator thing I am experimenting with sling shots and have somehow acquired 7 archery bows and a cornucopia of support equipment for that endeavor.