.22 LDC bore clearance study print files

[subscriber]

V3 "aims" the lower vent openings at the middle of the upstream baffle bore, to more effectively dissipate the shockwave inside the previous expansion chamber.

[WobblyHand]

Finished printing the Chimera-2.  Sprayed the platen with hairspray and used a brim.  So this one stayed attached.

The C-2 is close in tone to mine, although truthfully, I'd give a slight edge to the C-2.  I'd like both to be lower toned, but that's because I'm spoiled by either one of these LDCs on a 2240.  That sounds like a low snort, not a shot.  Perfect for indoor shooting. 
Lot more high frequency content on a PP700.  Lower pitch usually means bigger diameter.  I could comfortably go to 32mm OD.  Beyond that gets unwieldy.

Need to get a better microphone, the built in one on my laptop isn't very good.  I'll check out Stan's suggestion.

[WhatUPSbox?]

https://www.daytonaudio.com/product/1117/imm-6-idevice-calibrated-measurement-microphone

Note it has a trrs 4 ring plug

I was using it with an older laptop so I used this USB soundcard

-https://www.amazon.com/gp/product/B00KGK0YZ0

[WobblyHand]

Anyone got a recommendation for a not too expensive microphone I can plug into my PC? 

I think you said you had a 96Khz sound card. This is the mic I got for these type of measurements.
www.amazon.com/gp/product/B00ADR2B84

How do you use it?  Kind of puzzling from the listing.

[WobblyHand]

https://www.daytonaudio.com/product/1117/imm-6-idevice-calibrated-measurement-microphone

Note it has a trrs 4 ring plug

I was using it with an older laptop so I used this USB soundcard

You posted while I was writing mine.  The link you provided helps.

[WhatUPSbox?]

It shows up as a mic input in windows and Audacity. You just need to make sure the 96 khz is selected in both if that's what you are using.

[WobblyHand]

It shows up as a mic input in windows and Audacity. You just need to make sure the 96 khz is selected in both if that's what you are using.

Is the calibration file downloadable from a browser?

[WhatUPSbox?]

I didn't use it but yes, if I remember, it is on the Dayton website.

[subscriber]

Lower pitch usually means bigger diameter.  I could comfortably go to 32mm OD.  Beyond that gets unwieldy.

Does the length of the tube affect the pitch?  I would have thought it had more effect on tone than the diameter, as in "tuned length" intake and exhaust runners; or organ pipe.

Are you tempted to evaluate V-3 of the long tube bypass monster?  STL here: https://www.gatewaytoairguns.org/GTA/index.php?topic=211053.msg156489512#msg156489512

[WobblyHand]

Lower pitch usually means bigger diameter.  I could comfortably go to 32mm OD.  Beyond that gets unwieldy.

Does the length of the tube affect the pitch?  I would have thought it had more effect on tone than the diameter, as in "tuned length" intake and exhaust runners; or organ pipe.

Are you tempted to evaluate V-3 of the long tube bypass monster?  STL here: https://www.gatewaytoairguns.org/GTA/index.php?topic=211053.msg156489512#msg156489512

It actually is a function of both the area of the tube and its length.  But since it's area, that goes up as a square of the radius, whereas for length it is just linear.  So double the radius, the frequency goes down by a factor of 4, where as doubling the length, the frequency goes down as a factor of 2.  So a minor change in radius is a significantly faster way to lower the frequency.  Or at least that's how it is for the low pass filter that I studied.  Recirculating designs might look a lot longer, so there is that.

Had enough printing for the day.  I'll take a look at your file, though.  Printing bothers my eyes, so I can't do it a lot in my office.

[Back_Roads]

 The multi tube design reminds me of how Bose gets tons of base response from a tiny speaker.

[subscriber]

The multi tube design reminds me of how Bose gets tons of base response from a tiny speaker.

If that bypass tube design does something useful, I'll find a nicer way to package it.

[WobblyHand]

I was dying of curiosity about that last design, so I did print it last night.  It looks like a Buck Rogers/Mad Max sort of thing.  It has a big bore at 8.5mm which printed around 8.3mm, which is cavernous compared to my earlier prints.  PrusaSlicer warned me that it might have issues with tipping over and suggested a brim and supports.  I only added a brim.  It was printed in draft mode 0.3mm layer, with variable layers for the threads.  Required no tapping, which was nice.  Saved me a trip to the shop for the tap.  4hr 44min, so like most 3D printing, kind of slow.

I'll say it works better than I expected, although it's a bit louder than the C-2.  Doesn't seem to be much sonic difference with adjusting the hammer spring on the PP700SA.  This is with dry firing.  In previous LDCs, there didn't seem to be a noticeable aural difference between dry and live fire, so I didn't bother using a pellet.

I ordered the electret microphone.  Hopefully I can set up a better rig for taking audio measurements so I would have a chance at repeatable measurements.

[miksatx]

Doing it now on my new printer, my 3 s1pro failed to print it.

[subscriber]

Interesting, Bruce.  Try them with pellets, when you get a chance.

Yes, I grabbed the 8.5 m bore when I meant to grab the 7.5 mm.  Could easily modify the bore after the fact, if anyone cares.

[Mr.P]

3-D printing potentially allows for some really unconventional procedural surfaces and shapes - things with complexity that really defy modeling and are typically generated mathematically instead. For example, different infill patterns with 3-D prints. Some of those are very complex, and some new ones very fractal like.

What about filling the space with something like infill structure?  For example, what if you had a bore surrounded by hundreds of small tubes radiating outwards and all angled at whatever is optimal for diverting flow?  I recognize a lot of volume is lost, but this could be just for one section like one baffle could have some kind of diffusing characteristic.  I think I saw one moderator that actually has a 3-D printed sponge like material that breaks up shockwaves I guess

How about taking a look at biological systems that might be well adapted - for example branching bronchial passages with little chambers like alveoli at the ends?

There’s gotta be something special waiting to be discovered there if anybody can do it it seems like it would be you guys.

[WobblyHand]

Interesting, Bruce.  Try them with pellets, when you get a chance.

Yes, I grabbed the 8.5 m bore when I meant to grab the 7.5 mm.  Could easily modify the bore after the fact, if anyone cares.

As you might imagine, the sound is subjective.  Think it is snappier and perhaps longer duration with max max, than C2.  Maybe there's reverberation with mad max.  C2 has a shorter duration and seems a little quieter.  Both could use some additional lowering of the pitch, but maybe that's just a personal preference. 

For the above test, I used a 22 cal barrel and pellets for the PP700SA. 

[subscriber]

How about taking a look at biological systems that might be well adapted - for example branching bronchial passages with little chambers like alveoli at the ends?

As I was reading your description I thought, "that sounds like lungs".  Then I saw the bit above.

Interesting idea.  Someone skilled in infill placement would have to figure out how to do it.  The infill pattern used by the guy making the foam filled mufflers is called "gyroid".  My skill would end at producing CAD for the tubes, or vents feeding the infill.

Of course, lungs are flexible, so the inside should be printed with TPU or other rubbery material. 

[subscriber]

Thanks, Bruce

Perhaps the tubular bypass idea should be bypassed, for now.  As a concept, it seems much easier to control bypass air leakage via baffle bore diameter.

[WobblyHand]

Cobbled up something.  Not that pretty, but worth a try.  I put in a lot of vents towards down range.  The vent sizes are small and only should pass ultrasonic frequencies.  However, the area of all the vents combined is comparable with the bore area.  Going to give it a try.  It's wide, a 40mm fat boy.  May or may not work.  It's a print over night kind of deal...  Kind of like the C-2, but with forward micro-vents.  I'm trying long 1.5mm diameter vents.  Think they only pass stuff around 130 KHz, nearly 7 times higher than most of us can hear.

I'll know in the morning, that's if I get a good print.  If it fails, umm, I'm not sure I want to try another, its over an 8 hour print on my machine.  I don't have that much patience.

In the meantime, I need to make an aluminum insert adapter for one of my LDCs.  It has a 1/2-20 internal thread, and a 3/4-20 external thread with a flange.  It's also has threads to attach to a CF tube.  Maybe I will start out with a simple version that doesn't thread into a CF tube.  Then I only have to do 2 20 TPI threads, an internal and an external.