No matter how cool your super indie music no one's heard of before might be, it sounds terrible when you have to blast it through the tinny speakers of your smart phone. That's why you need speakers, subwoofers, soundbars, and the like! To impress people! With your taste in music!
Sound is made of waves, which everyone knows are made of ocean water, except sound waves are super tiny and invisible. So every time you hear something it's because a tiny invisible ocean wave slapped you in the side of the head. Isn't science amazing?