You can find PART 7 HERE.
So round one established primarily two things:
1) putting rubber in the shroud takes up precious volume and actually makes them considerably louder.
2) the general spacing and number of baffles, which is to say 3 or 4.
Given that the name of this game is testing baffle design, I opted for a 4 baffle design in the hopes I could improve baffle efficiency. Foam integration was done in between baffles, in the mostly “waste space” at the inside top of the shroud, rather than in a separate end-terminus section. This resulted in four simple designs. The idea here is that, once the basic baffle configuration has been affirmed, you want to play around with various little tweaks in an attempt to further optimize sound attenuation. And that is what is happening here. Some failures are expected, but this is a key part of the purpose of experimentation. Keep in mind the point here is to only introduce a single variable in each design, this way causality is obvious.
One other noteworthy thing here is that I messed up the captures for the long trace seen above the detailed trace. As a result you can see equidistant from before to after the trigger. The result shows something else very interesting: all the noise the gun makes BEFORE the pellet exits the front of the moderator. Cool huh?
Factory – 227.3 – This is the factory shroud insert, tested again as it is the perpetual benchmark. It makes both a high peak and sustained sound as loud as the uncorking sound. Sometimes this can be an indicator of optimization.
Control – 158.6 – Four baffles, flat faced, symmetric, the end. This is the vanilla designed to be a benchmark for what a more efficient eccentric conical design can/should be. And it performs okay, in that you can tell it is quieter than the factory insert.
Enhanced Blast Chamber – 172 – Four baffles but with the entire chamber separated into two sections. The bottom section houses the baffles. The top section is open and houses a little damping foam, but primarily is there to act as an expansion area/pressure reservoir for the muzzle blast. The idea was that maybe a large initial chamber would take some of the load off subsequent baffles and better attenuate sound. The baffle design is otherwise identical to the control. As you can see, it clearly didn't work. What is more interesting in its not-working is how it ramped up in sound. So the blast volume did work, capturing the air temporarily, it just made quite a lot of noise subsequently releasing it. (and all the traces look like this) It also looks like it made a pretty solid ~6kHz in doing so, which is well within human hearing range. As you might have guessed, that is annoying. Don't believe me? Have a listen to this:
Major asymmetry – 144 – Four baffles with an opening aggressively angled upward to induce the air to fill the top of the shroud. This design likely will introduce unacceptable turbulence, but is a worthwhile point of curiosity. It does perform better than the control, but not by a huge margin. I actually had higher expectations for this design. But this is why you test: you just don't know what is going to happen until you try it. It should be noted that this design was probably the quietest post-peak, however it just couldn't get that peak down.
Bilateral symmetry – 146.6 – Four baffles with a design loosely based off the old LIM moderator core from the earlier days of my airgun moderator experiments. The idea is that bilateral symmetry is maintained, however cross-flow may improve sound attenuation. Again it worked, beating the control, but audibly wasn't the best design here. Like the factory shroud it brings the uncorking sound down, but makes a fair bit of noise subsequent.
Tilted conical – 115 – Four conical baffles with the mouth ever so slightly angled upward. This should induce the air to fill the top of the shroud more efficiently, and indeed it appears to do exactly that. This design was noticeably quieter than all the others, it really worked a treat, it sounds great. So, much to my surprise, I think I have a winner here in this round. And looking at the trace, it really does look good.
So what is next? Well there are a couple little changes I want to make to optimize sound attenuation, improve printability, ensure compatibility with the 350mm extended barrel/shroud thingy, and of course I want to do a finished version in 20% carbon fiber reinforced nylon. It is much much more durable than PLA and much more solvent resistant than these ABS test cores. I also want to do some experiments with the endcap to make it a little more visually appealing. Once that is all done I'll do one final test check on accuracy and sound attenuation, and then I guess it is a wrap. I don't want to prematurely take a victory lap here, but my stretch-goal was to get the Leshiy down to 100 and it looks like I've essentially arrived. It is actually about the same peak as a DonnyFL Sumo on an FX Crown in .22 (which metered at 108 avg. in my test) so that is pretty good in my book. Now I just have to confirm compatibility and make it look pretty.