This situation has happened to all of us- you and your friends want to listen to some music on your smartphone/iPod/iPhone but you don’t have any speakers laying around. The downward-facing speakers built in just aren’t loud enough to play music for everyone to hear over background noise. Good news! There is an easy solution, just drop your iPhone, smartphone or mp3 player into an empty glass.
When placed onto a hard surface, the glass amplifies both bass and volume so that everyone can hear. We have personally tested this in noisy kitchens, backyards, and even running water. The volume is significantly and instantly increased to a decent level.
Do It And How 
I stumbled upon this trick about a year ago. I noticed that when my phone was on a small wooden shelf in my office, it not only sounded the ring tone, it resonated the wood. I’ve since put a clear glass coffee mug on the wood shelf, and drop the phone in it each evening. Between the ringer, and the vibration resonating in the glass and the wood, it’s hard to miss it anymore. And the phone doesn’t vibrate off the shelf and onto the floor!