How NOT to Soundproof Your Workshop 

If you do any metal grinding in your workshop, I'd try taking a lighter to one of those outside to see what happens. Random Chinese foam + sparks/fire is probably not a good mix.

PARDON MY NOVEL... BUT.... DYNA-MAT offers several options, sticky mat and foil back sticky mat, and a few spray in solutions. Kinda costly, but, exceptionally effective... Pro's & Con's. If my lady didn't come down in the garage (master bed room above the garage) to dig into get some junk food ice cream, my yelling for her help after using the DYNA MAT system, she would have never heard me... The foam pads, barely worked.. and could even still hear the so called silent garage door opener with the foam pads.. But the DYNA-MAT... actually took some use to getting to... once it is done installed, it is kinda a creepy dead silence. no echo, and in fact, all the sound you make, you now hear with a high level of accuracy or to say, not muddied up with the sound bouncing off all the surfaces and walls. It really is a strange sound to hear only the sound of what you are doing, and not any of the echos that can last for a second or 3, pending how loud or metally the noise is.. Here is another strange issue, which is a good thing.... When you drop something on the floor, if you are lucky, you might just catch a slight glimpse of the direction it took off too... But, in a sound deadened space, you no longer need to catch a last split second glimpse of where it went to, you can hear where it went.. as strange as that may sound, you really can hear exactly where or what direction the scattering part runs off to on the floor.. It really is weird hearing only the sound of the impacts and not the echoing off the walls and other faces of stuff.. I did some test with a set of Wally World walkie talkie's, and to see what sounds she could hear and not hear, so I can gauge what I can bang around on, as I am a night owl, and my lady not only MUST get her 198 hours of sleep a night, she loved to sleep, and she is also one of those nutcases that wakes up in the morning and in a yippie skippy voice, tell you "GOOD MORNING" as if she had already been up for hours... She is one of those weirdo morning people.. But, I actually have an anvil in my garage, and can bang on that kinda okay, and she can hear that, but is it not like piercing.. So, that being one of the more sharper sounds that would wake her up, I showed her how hard I as hitting the anvil with hammer, so she could replicate it, so I too could hear what it sounds like from up in the master bed room... It sounded like a roofer with a an airnail gun, about 10 to 20 houses away on the same street.. Yes, you could hear it, and could tell that it was a metal on metal sound, but was faint enough, that not alarming enough that she might here it but not enough to prevent her from finishing up her 200th hour of sleep for the night... To do a full two car garage, ceiling of course, the three primary walls, the garage doors, cost about $1800 bucks.. Yes, it is kinda costly, well, it is costly, and actually called for a dual layer, and second coat where I used the spray stuff. NOW, it is important to note, they offer stuff that I should have used on the garage doors, which is not as effective but it is super lite weight. I had to add about 6 additional cranks to the lifting springs.. as the door openers were not having any of that... Yes, this stuff will add allot of weight, which for building structure, I don't know that this could be too much of a concern, but, for automotive application, it is not uncommon if installed thoroughly, can add at least 50 lbs, on up to 400 lbs, for the more serious audiophiles. Doing my garage, was the first real time doing a building structure, but I had used this stuff, literally 100's, if not a few over a 1000 times in the automobile world, for car audio performance and for my own cars and audio systems, that was the first thing I would do, INSTALL DYNA-MAT !!!!! Yank out ALL of the interior, including the dash, and press in / form the foil backed mat material sheets on/into every single surface including the pillars, roof, of course the floor, the interior layers of the doors, "both". the trunk floor and sides and lid/hatch. One might have to invest in heavier Strong-Arm lifting compressed gas springs for the trunk lid, from the new additional weight. It was common that I would spend about 2 to 4 days, installing this noise deadening material. This process was a pain, but highly rewarding, to do, and the end game of the sound being easily measurably more accurate for sound quality, or as I used to say, in order to sound like I was smart, even though I was just a stupid kid running a small business, I would call it, "electrical noise transduced replication production"..LOL.. Yes, I was an idiot, lol. All jokes aside, out side noise, kept out side, and likewise, all the sound inside, kept inside. logically, but, here is what was the real end game going through all that hassle of the installation, the sound was actually allowed to be lower, at the volume control knob, by allot, and the accuracy, was greatly improved by allot. The equipment didn't have to work so hard to get to the levels you desired, in fact, the system as a whole, would gain you dB. I used to do the loudness competitions with the BASS gameshow, but got old and just became show pieces in my demo room, but were I really rock & rolled, was the sound quality competitions. I couldn't have done as well as I did, with out the use/installation of these types of noise management. I am way off the mission here, as you are trying to dampen or contain or limit sound navigation, and my dummy self, is ranting about how to channel it for performance..lol.. I told you I was an idiot. I see also, another comment mentioned, fire hazard warning. A high end brand of this stuff, already has flame retardant built in to self extinguish when or if exposed to direct flame, for automotive application and D.O.T. certification and is required in order to be sold in the USA or manufactured in the USA for auto's use. Then for the UL (Underwriters Laboratory) CE/CSE-US (can be sold in USA/Europe) stamps/stickers approval, all reputable brands, also for residential factually is a required mandate. Now, there is a few commercial brands, that ON PURPOSE, do not have the fire retardant additive in their dampening material, but is clearly stated and you have to go out of your way to get that for you special purpose, otherwise, you are just always going to be sold with the fire retardant additive in the product lines you buy. Lastly, the spray on method, which there is a few types of spray in/on systems, as I am sure you know, once it is sprayed in/on, there is no turning back, it is there to stay. The sticky mating, in either sized tiles, or rolls, with a bit of effort, can be somewhat removed, at least for the higher end brands. The cheap fake stuff, that kinda works, but better then nothing at all, mechanical fasteners system, staples, etc, is recommended for of course the ceiling, but I was even say the walls. unless you buy liquid adhesive, as the fake brands, the sticky backer is just not effective. Can be okay in a floor pan of a vehicle, as it is holding itself down. Anyways, I am sorry for the novel, but, this brought back a few old school memories and thought, since you took the time to make a video and showcased your findings, that well, I will take the 5 or 6 minutes to write a novel telling my life's story. And it goes like this... When I was 7 years old, me and a friend of mine, we ending up at....... LOL Good luck.

Fiberglass insulation held up by 4x8 plywood sprayed with truck bed liner.

Rockwool insulation, then double sheet rock or dry wall and caulk between sheet boards. look into quite rock!

insulation between the joists will accomplish eliminating a lot of sound being transmitted through the air and also help insulate your house. Those foam tiles don't really accomplish much in ideal situations. but the dust collector being mounted to the joists means that mechanical vibrations are going to bypass all of that through the wood and go upstairs.

I like your transparency and the comments. Looking forward to your solution.