Umarex Notos CRK Review

[Firewalker]

15hrs32mins!

GOOD GOLLY!

Good job, Mike, that is going to be a beast!!

[Firewalker]

Dave,

The problem with getting an objective measure for sound is that unless you do it industry standard with a calibrated meter intended for muzzle report, you and your mates are using what amounts to an "elastic tape measure".  Rather than argue about absolute values, the thing to do with cheapo meters and apps is to compare before and after.  The change is less likely to be way off that the absolute measure.  Assuming your meter and setup do not "peg" or clip.

If before and after measure the same, chances are that you have reached the max level the meter can capture.  Or the measurement period is way off.  So, if you hear a clear drop that seems about half as loud, that is a 6 to 10 dB reduction.  If you can just tell a difference by ear, it is only 3 dB.  More to the point, if you hear a clear difference and the meter reads the same, the meter is wrong, or used incorrectly.

When you get that far, shoot with the "can" empty, then the original insert, then the alternatives; and so on.  I predict that the original insert is taking off 10 dB from the empty can.

The closer your meter is palced, and the more directly in front of the muzzle, the more only a few inches in relative placement and a small change in angle will skew the readings. 

Sound pressure drops off with the inverse square of the distance.  So the same reading at 3 feet will be four times louder than at 6 foot. 

Sound is very directional, so being level with the muzzle to the side is much quieter than being in front of the muzzle.  Being at normal cheeckweld position is a lot quieter than level with the muzzle. 

What ever you do, be sure to repeat it.  Also, you have to be able to call a reading BS if it is.  For instance, if you fired a .223 centerfire rifle and your meter gave the same reading as you airgun, the readings are decidedly suspect.  Just because a reading is reported by an expensive instrument does not make it real.  There are several other requirements that have to be met.  Even more so for a cheap meter.

Judging airgun report is a bit like judging music.  A meter may tell you how loud it is at a certain distance, but only human ears and minds can decide if the sound is pleasing or not.  In other words, once you are no longer concerned with "hearing safe",  muzzle report improvements are very subjective.  Nothing wrong with that.  It is like preferring the feel and balance of one rifle over another.  Subjective, but valid.

Yup, and its going to be FUN!!!!   

[subscriber]

For your amusement; just to show you how involved some design jobs can get, here is part of a custom design I did for a friend.  It features dual crossing Tesla Valves.  The video was captured while sweeping up through layers in Cura:

[Firewalker]

How would they work in suppressors?

[subscriber]

Dave,

Obviously there needs to be a straight open path, wide enough for the pellet to travel down.  To make the concept work for an LDC, you need to rotate your image, and align the black arrows to the flow path that the pellet would travel down.  Then see the red flow path as that part of the airflow that is redirected back on itself, via a curved path.

To help make sense of this, I have taken your image, rotated it, then doubled it up to make it symmetrical about the central pellet path.   Other than the radii of the curved paths being different, I think you can see the similarities compared to the section of my insert design.  Then, if you take my manipulated version of your Tesla Valve image, and place a copy at 90 degrees around the pellet path, you end up with my dual crossing air paths that redirect flow back upstream.

The rest of the open space contained in the casing between the Tesla Valve "tubes" functions as simple expansion volume. 

These designs also have to be configured for 3D printing, without "supports" being turned on in the "slicer" software.  You cannot remove printing support structures from closed 3D printed parts, so the design has to be self supporting during printing.  My designs can often only be printed in one orientation as a result.  Unfortunately that orientation makes printing them very slow...

The second image show the last cone of the design I did for you.  It has what might be called and open Tesla Valve geometry:  air flowing along the conical outer wall is redirected backwards by the central air stripper.  Air flowing down the middle, scooped off by the central airstripper runs into the air that flowed along the wall.  The difference is that the flow in an open cone design is less organized than if it has walls to constrain the flow.

Why not always place such flow directing walls in LDC designs?  The crossing Tesla Valve duct design shown in the images below has an outer diameter of 48 mm, to fit inside a 2" OD tube.   Scaling that down to a 1" or less ID makes the curves very tight, and uses up a lot of expansion volume with plastic material to create the curves and the extra walls.

How effective is the Tesla Valve insert compared to conventional cones?   People that sell such designs will tell you that they are superior.  As for my designs; the parts are being 3D printed right now.  We may have results in a month.  When I say "we"; I am not making the parts, nor testing the systems.  I simply designed the parts for someone like you, who are keen to experiment.  In this case, they suggested I look at STO products that use their "gas diode" interpretation of the Tesla Valve. 

Yes, I learn from what works along the way, by doing many designs for many people.  Your design is based on what I learned from the insert development exercise, covered in the thread about "taming the bark of an Avenger".  It answers the question; what is simple, light, compact and effective?

[subscriber]

Below are images of a single plane Tesla Valve Module.  It is less "leaky" than the cross-plane design above ("leaks" into the peripheral expansion space - not a problem).  However, it requires that the center air stripper have extra supports for printing, as that resides in the tube that is connected to the side panels, but "floats" in the middle.  Hence there are 6 permanent peg-like support "vanes" in the design under each of those air strippers, to enable printing with supports turned off.

Those who are familiar with STO designs might notice some similarities

[moose]

all this supressor stuff, I think I've ventured into another Dimension 

[Firewalker]

all this supressor stuff, I think I've ventured into another Dimension 

Thats the secret of the Tesla valve, time actually goes backwards before the sound is made, therefore you dont hear anything because it hasn't happed yet! 

[kbstingwing]

OK, I'm going to put a Micro Hadron collider on mine, it will make a black hole to absorb the sound and time jump point to put the pellet faster than light.....

[Rat Sniper (AKA: PaulT58)]

Okay, I know what happens when you break the speed of sound, what happens when you break the speed of light?

[kbstingwing]

Okay, I know what happens when you break the speed of sound, what happens when you break the speed of light?

Uuuuuh, "you miss".....  and then cause an interstellar war because the pellet traveled 200 light years and hit the windshield of an aliens spaceship,
Note to self; buy interstellar liability and Hazard insurance....

[avator]

HyperWarp Drive.

[chutesnreloads]

Can you beam me up now, Scotty?

[Back_Roads]

 I think  EDgun Leshiy might have figured it out 

[Firewalker]

Okay, I know what happens when you break the speed of sound, what happens when you break the speed of light?

Uuuuuh, "you miss".....  and then cause an interstellar war because the pellet traveled 200 light years and hit the windshield of an aliens spaceship,
Note to self; buy interstellar liability and Hazard insurance....

Progressive insisted that I use the "snapshot" device on my Tesla Valve, they said that the space-time continuum policy is backdated 14 parsecs. 

[smythsg]

My latest mods are being done by this tuner!

[Firewalker]

My latest mods are being done by this tuner!

Wait! BAKER air guns? 

[smythsg]

Maybe, in one of his many personas. 

[Firewalker]

I got the two new moderator inserts today and since I had 1-1/2 hours clear before I had to be off so I pulled out the dB meter, moved it 30 feet away inside the shop, opened the door and proceeded to take some noise samples.

First up was the original red split insert. 5 shots, 87, 86, 87, 88, 86 decibels, 87dB average.

Second was the lilac insert, 5 baffles, it knocked off 2 dB with the 5 shot sample of 80, 81, 80, 82, 80dB with an average of 81dB.

Third was the long Lilac insert but first, I had some work to do.

I promptly too took the Notos apart, chucked up the barrel/moderator housing and bored the housing out to 1". A few items to note, the housing interior was not centered on the barrel, the housing was molded out of round and the cap no longer seals tightly as it is now too small.

It took four passes to open up the housing to 1", there was a lot of chatter due to the soft material but it worked fine, I just had to take smaller cuts. I cut the housing down all the way to the interior base then pushed the insert into the housing to get a dry fit.
I got it about 2/3 in and the insert would no longer budge.

I went and got one of my 18" gauntlet leather gloves, put it over the end of the housing after mounting the barrel in the gun again and pulled the trigger!

POP! Out it came into the glove with no harm. I had to sand down the insert to make it fit but it was too long and I had to cut off the taper to fit it all the way into the housing.

The 5 shot sample was 78, 77, 78, 78, 79dB. This was noticeably quieter with much less 'snap' when fired. I even took a few more samples and shot an open housing shot to make sure the meter was working and yes, that seems to be the number.

Finally, I got the 8" black insert fitted by cutting off the last taper and sanding it down smooth. I then marked and drilled the pin holes, mounted it up and shot this jaw-dropping string of 5 samples, 66, 67, 64, 68, 69dB.

This a quieter than a finger snap. I also measured the dB at my ears using the long insert and I got 70dB on both sides which was interesting since the sound at 30 feet was 67dB on average.

Thanks to Mike and Subscriber for their work providing the designs and the printing. I am leaving the 8" insert in the gun since my POI didn't change from an empty housing and am still able to make 1/4" groups at 10m and this thing is just mouse-fart quiet! 

If anybody wants the 4" insert to play with, let me know, Ill be glad to send it to you to try.

[subscriber]

Dave,

It is difficult to predict how well custom insert designs will work, but what you measured is better than I expected.   Providing your ears agree with the meter's relative readings, I am very satisfied with the results.

You seem to have confirmed that my "plume style" baffles are good at taking the snap out of the report.   I came up with the idea to "fan" the baffle cone angles while increasing their spacing, and it first worked out well for the Avenger.  If there is casing or shroud length to work with, that style seems like a benchmark to compare my other designs against, for any given application.

Here is the latest happy customer benefiting from the same "technology" on his Avenger: https://www.gatewaytoairguns.org/GTA/index.php?topic=196584.msg156434566#msg156434566