I’m looking for the sound of a ball dropping into a (vertical) tight-fitting tube. Sort of a thwump sound. I can hear the sound I want in my head, but I don’t know how to describe it any better. And I’ve had no success searching for such a sound since I don’t really know what to look for. I’ve tried everything I can think of to search for.
Any suggestions on where to find such a sound, or even what to look for, would be appreciated.
A great site is freesound.org 
The closest I can think of such a sound is a bank drive-through when it sends wads of cash in a tube through a bigger tube via vacuum pressure into your bank account. Good luck.
freesound.org indeed is the place for many sounds, like @thestubborndev already mentioned.
Check this pack for example:
Freesound - Swoosh WHOOSH air effects by Robinhood76
And keep in mind, you can slow or pitch down sounds if they are too high freg… and you can also try to make that kind of sound with your very own mouth or just swing your hand near mic.
Thanks. I’ve searched freesound/org and many other free sound sites. It’s not where to look that I’m having trouble with, it’s what to look for.
Yes, that vacuum pressure tube sound is sort of what I was looking for. However “vacuum” is not a good search terms it yields MANY sounds of vacuum cleaners.
I use freedounds.org often, too. You can almost find everything there.
But remember to check the licensing of each sound to not risk getting biten in the ass.
When doing a search the safest thing to do is, when you got the results listed, to klick on “Creative Commons 0” under licenses on the right side. Those are sounds you can use without having to give credit, paying and can be used for commecrial and non-commercial products.
Love how everyone seems dead set on talking about everything except the actual question. Stay on topic, folks. Perhaps the word “pneumatic” would help?
–Eric
Cant really see how everyone talking everything except the actual question here? @Fuzzy did give some offtopic info here, but still “Stay on topic, folks”? 
lol
And for OP: its not really easy to describe sound with words, so any sounds similar what you are looking for?
What about something like these?
As for general tips for searching sounds, I find that trying to describe the sound you want in terms of materials involved and how they are interacting gives better results that searching for very specific. In this case, I started searching for stuff like ‘plastic hit’, ‘plastic impact’, ‘hollow plastic’ etc. and listening to what I get.
Yeah, I know where to find sounds and am familiar with copyright issues. Just looking for the right search term. The search term “pneumatic” hits are a lot of equipment sounds, like drills. Unfortunately, my best descriptive term for the sound, “thwump” doesn’t give me anything.
It’s like when I was looking for the sound of a spring being sprung. In the search results for “spring” I had to sort through MANY sounds of chirping birds and babbling brooks.
Yeah yeah, I’m the evil off-topic guy, who just wanted to this guys ass.
But well, it’s not easy to get something just by a vague description. going bei the “thwomp”, maybe a “thump”?
like this?
Try this: Freesound - thwump.wav by Reitanna
I finally found it! It’s the sound of a mortar loading.