title_body: Which IPA phones can be made and understood underwater? I have a human culture that gradually develops an underwater civilisation. They still require mouth and nose breathing and will be living in air bubbles, retaining traditional phones. They do spend a lot of time swimming around and I want them to be able to communicate through water as well. Modified and new underwater phones will develop over time etc.
  
  What I'm interested in and haven't been able to find an answer to is, of our current available phones, which ones can be made, heard and understood underwater?
  
  
  let's work off the idea that there is no breathing equipment in the way of these vocalisations. Free diving.
  
  
  Before I start constructing modified sounds and augmentations etc I would like to know what I can keep of our current soundbank. What do I have to throw out completely. I may ask a later question on constructing/modifying new sounds for underwater languages.
  
  
  I understand that humans hearing underwater is affected by bone conduction, skipping the first 2 ear bones. We will be able to hear much higher frequencies and from further away, although direction will be hard to discern. I'm still reading up on all of these features but just wanted to say I was aware of these various facts. For the purpose of this question, I'm just focused on using current known sounds underwater.
upvoted_answer: From reading the answers to the Worldbuilding SE you reference, I would draw the following conclusions:
  
  
  anything unvoiced goes out of the window. So no /f/, /p/, /k/, /t/, /s/ etc. They are pretty useless, as they are predominantly in the higher frequency ranges (especially the fricatives) or very short and without much energy (which would be provided by the glottis). And higher frequency sounds travel less well in water.
  consonants in general are either short (plosives) or prefer higher frequency bands (fricatives), so apart from /r/ and /l/ (and possibly /v/, /z/) would not carry well underwater.
  vowels seem best suited. And looking at the frequency characteristics, those with lower formants seem slightly preferable, so /u/ and /o/, and the back /a/: vowels produced at the back of the vocal tract. The fronted vowels (/i/, /e/, frontal /a/) would have a higher frequency component again.
  
  
  So in summary I would think a vowel-based phoneme inventory might be best. This inventory could be supplemented by some approximants (/l/, /r/, /j/, and /w/). Which is weird, as consonants usually carry most information in natural language! 
  
  Compare:
  
  
  Whch s wrd, s cnsnnts sll crr mst nfrmtn n ntrl lngg!
  i i ei, a ooa uuay ay o ioaio i aua auae!