title_body: What factors affect the noise level of propellers? I've noticed that the noise level of different quadcopters can vary quite a bit, especially in the sub 3" range. For example, some of the Tinyhawk models are extremely quiet, while other similarly sized builds end up much louder while flying.
  
  I'm currently working on a park flyer build; while I won't be next to anyone, I do expect there to be people within earshot so I don't want to be flying a weed whacker. Rather than just buying props and testing them, I'd like to at least have a working hypothesis on which ones will be loudest before purchasing them.
upvoted_answer: Since only you can be the judge of what you feel is too loud, and noise level from a drone is the result of many parts working together, this is a tough question to answer and I'm not sure you will succeed in finding "the" prop to suit your needs.  That said, if reduced noise is what you are looking for, and we remove the other parts of the drone from the equation, I'd suggest stiffer props from the manufacturer of your choice.  After flying for a while, if you feel that the noise level is getting worse, change props (all of them).
  
  In my experience, as long as the props are balanced (most manufacturers have gotten better and producing consistently balanced props), on the stiffer side, clean, and free of any kinks or abrasions, they will be as quiet as they can be.  This is why drones sound quieter when they are first flown compared to after a few landings when they get grass and other debris sticking to them, along with abrasions and kinks on them - making them less efficient and more noisy as a result.
  
  I use DALPROP T5045C and HQ R38 props.  Both are on the stiffer side and both are quieter than the thinner, more flexible props I had used a few years ago.
  
  I hope this helps.  Good luck!