Question about pcp tuning and lower muzzle report.

[mackeral5]

I know the subject is muzzle report, but there has been some mention of ping. 

In my very limited experience I tend to associate ping with an inefficient tune.  At least that's typically what I see with my regulated guns.  For example, it takes a lot of HST to make my Edgun ping.  In my qb78 bottle gun the plenum will sometimes ping with excessive HST. 

[nervoustrigger]

For what it’s worth, I thought the ping was simply a resonant ringing resulting from the sharp impulse response of the valve being knocked open.  The air tube is stretched taut like a guitar string because of the high pressure contained within it, so a sharp smack makes it vibrate at its resonant frequency…a frequency which is relatively much higher
than one would expect from an untensioned tube of the same dimensions.
 
Placing a piece of snug-fitting rubber tubing or a bottle brush into the tube damps the vibration and breaks it up into different frequencies.  Or by installing a regulator, you’re isolating a short section of tube that is subject to the impulse.  That is analogous to pinching the guitar string at two points close together and then plucking it…it’s super stiff so the amplitude is much lower and it decays quickly.
 
The precise contribution of the air to all this is a bit nebulous to me.  At high pressure, it’s acting more like a liquid than a gas but I don’t know if that means the impulse is transmitted from the valve to the tube by way of this semi-solid substance or if it’s directly related to the movement of the “fluid”, or something else.

[Taso1000]

Jason,

My first thought is that the air tube ping is like what happens with a bell.  I assume the vibration in the bell propagates back and forth through the bell material till the initial energy dissipates. 

I have read that a regulator in the tube will stop the ping.  So that makes me think the regulator orings are applying outward pressure on the tube and changing the resonance frequency.  I've never understood how the bottle brush would work.  It can't be applying that much pressure to the air tube wall to change the resonant frequency.  So I thought it would work if the sound wave was propagating via the compressed air.    I think the ping is more the bell effect though.  i could be wrong though.

So I guess we're not seeing the bell effect propagate down the barrel.

Ok, I just had another thought.  Could we induce a vibration in the barrel to cancel out the barrel harmonics of the shot impulse to increase accuracy?  We would have to figure out in which vector and amount to apply the new cancelling vibration.

I must be the worst off topic offender on the forum!  Can I get kicked of my own thread?   

Thanks,

Taso

[oldpro]

 The shorter the dwell the higher the ping wave will be in pitch. The most efficient tunes with short dwells will give off the highest pitch ping Ive tested this many many times. When the poppet slams shut fast the return wave amplitude is higher and moving faster creating a very high pitch ping. I built a cobra valve .22 that sounded like a ping generator it was so bad. I tried to record it but it just doesnt sound the same over a microphone recording as it does in person.

[mackeral5]

The shorter the dwell the higher the ping wave will be in pitch. The most efficient tunes with short dwells will give off the highest pitch ping Ive tested this many many times. When the poppet slams shut fast the return wave amplitude is higher and moving faster creating a very high pitch ping. I built a cobra valve .22 that sounded like a ping generator it was so bad. I tried to record it but it just doesnt sound the same over a microphone recording as it does in person.

Very interesting info.

[oldpro]

Jason,

My first thought is that the air tube ping is like what happens with a bell.  I assume the vibration in the bell propagates back and forth through the bell material till the initial energy dissipates. 

I have read that a regulator in the tube will stop the ping.  So that makes me think the regulator orings are applying outward pressure on the tube and changing the resonance frequency.  I've never understood how the bottle brush would work.  It can't be applying that much pressure to the air tube wall to change the resonant frequency.  So I thought it would work if the sound wave was propagating via the compressed air.    I think the ping is more the bell effect though.  i could be wrong though. Think of the poppet like its a bullet and the ping is the sonic boom moving away from the bullet.

So I guess we're not seeing the bell effect propagate down the barrel.

Ok, I just had another thought.  Could we induce a vibration in the barrel to cancel out the barrel harmonics of the shot impulse to increase accuracy?  We would have to figure out in which vector and amount to apply the new cancelling vibration.

I must be the worst off topic offender on the forum!  Can I get kicked of my own thread?   

Thanks,

Taso

The ping is a sound wave it travels at high velocity from the valve to the opposite end of the tube and back a regulator sits in its way thus disrupts the wave as it has no where to go. The same type of thing works with the bottle brush the wave traveling at high speeds runs into all those bristles and is broken up into slower moving particles thus the wave is diminished.

[Taso1000]

Hey Travis,

So you think the ping is a sound wave through the air in the tube and not the tube itself ringing? 

I guess one way to test is to apply Dynamat or other damping material to a tube exterior and see if the ping is reduced.  If yes, it's the tube.  If no its a sound wave through air.

Interesting.

Taso

[oldpro]

Hey Travis,

So you think the ping is a sound wave through the air in the tube and not the tube itself ringing? 

I guess one way to test is to apply Dynamat or other damping material to a tube exterior and see if the ping is reduced.  If yes, it's the tube.  If no its a sound wave through air.

Interesting.

Taso

2lbs of dynamat or 8g depinger. Id go depinger every time. But I understand what your saying.

[Taso1000]

Yup, disturbing the sound wave through air is definitely much easier.

Taso

[shorty]

There is another thing about dwell and report in regards to throat size and porting (in a conventional valve).

The larger the throat and matching exit port reduces the needed dwell to achieve a targeted power level.

Boy that doesn't sound like it makes much sense.

Let's take my 22 synrod as an example:
Stock with a throat of "something like" .2" and porting of .14" gave a very loud report to hit 38/40fpe with a ton of dwell. Now with a .25" throat  and .168" porting sounds like 20fpe when its's running at 38/40fpe.

The decrease in opening to achieve the power level reduces the dwell time since their is more space for the HPA to travel through.

The interesting thing about the cobra valve and or ART valve is that I am unsure if we really know if the dwell is reduced or if the valve does not have to open as far. It is just hear say as far as I am concerned until the lift and dwell data is provided.

Bob did a cool "study"  thing with lift (opening). I am curious if this was done with the Cobra and or ART SS valve to prove that it was actually reducing dwell or it was just the lift.

[Ribbonstone]

JUst a couple of notes.
 First note: ping
Have had one rifle, tuned to a nice energy level and efficency that "pinged" so lound, my wife (who is real use to airguns being shot) had to come out and ask "What the XXX was that?".

Retuned the rifle (different pressure range, different striker spring setting, and a little less energy (but about the same efficiency) and it didn't ping.

That shouldn't be a surprise.   Tweo idential factory rifles.  Often one has a noticed :ping" and one doesn't.  It's not that they are made seriously differently internallly, just that they run a bit differently.



Second note: transfer port.


Not too terrible long ago, was trying to find a "happy place" for a SPA M10 .22.

Got ti running well at a typical pressure range (seomthing like 2900-1900 PSI).  Turned out, the best range for ALL the transfer port settings (so far as the 4% sweet spot) ran from 2800-2000psi.


So I went to the trasnfer port (which is removavle without totally taking the rifle apart) and tried 5 sizes.
Only kept track of the "run" of velocitys in the 4% varation range.

5mm port: 16 shots/ 56 foot pounds (890  4% fpe total)
4.5mm port: 18 shots / 52.1 foot pounds (937  4% fpe total)
4mm port = 20 shots / 50.4 foot pounds (1000  4% fpe total).

OK high power fans...lost about 8 1/2 % energy going from 56 to 50.4 foot pounds, but gained about 25% in shot count, and (just by ear) quite noticeable gain in quietness. 


3mm port = 25 shots /41.8 foot pounds (1040  4% fpe total)
2.5mm port = 35 shots / 25.5 foot pounds (892  4% fpe total)

JUST POINT OUT:

Can sometimes can use the "simple part" todetune, not lose much energy per shot, and gain  both useful number of shots AND a very noticiable decrease in noise.

[rsterne]

IMO, ping is the air resonating inside the reservoir.... the shorter the reservoir the higher the pitch (frequency)…. Plenums may be so short for the pitch to be above human hearing, or nearly.... Disrupt the sound wave, stop the ping (or at least minimize it), be that with a depinger or a regulator....

For a given gun (valve and hammer), more lift equals more dwell, and you can't reduce dwell without reducing lift at the same time.... Having said that, a lighter hammer changes the relationship between lift and dwell, for the same lift you get less dwell.... which means less power unless you increase the hammer energy (more spring or travel) to get the AREA under the lift/dwell curve back to what is needed for a given FPE... Bigger ports can move more air in the same time, so you can get away with less lift and dwell.... That means the pellet hasn't moved down the bore as far, so the air released by the valve has more time/distance/volume to expand.... That reduces the muzzle pressure, and hence the report....

Bob

[Ribbonstone]

So with "ping" (considering my personal-weirdness).  would take it that:

1. A "depinger" slows or "moderates" the presure wave (which is one way of saying it spreads the internal air movement over  longer/more diffuse time frame).
2. The larger the sudden drop in pressure on one end of the air cylinder, the stronger the pressure wave.
3.  Depending on #1 nd #2 above, the amont lenght is either going to resonate or not.
4. The speed/length of travel of travel of the pressure wave  makes a difference.


5. So a fat/short tube would resonate/ping most with a a quick/short prerssure wave, and a long skinny tube would resonate/ping most with a slower pressure drop?

[mackeral5]

My Edgun STD will ping fairly loud when I am leaning on the HST too hard and getting well out onto the plateau of the shot curve.  It is regulated with approximately 40ish CC of plenum. 

Under mild tunes, for example pushing JSB 25gr 900fps or less, it is a very snappy gun.  A very crisp shot cycle.  Unscrew the offset LDC and it sounds a lot like a rimfire---pull the trigger and POW!!  I credit this largely to the MASSIVE valve return spring..  Add a hammer weight at the same HST setting (increasing dwell) to start pushing 34's  just below 900fps and it starts to have a louder, more prolonged report.  Push HST any further and it gives a loud ping. 

I would love to see what an SS valve would do in this gun....