There's nothing quite like having dual speakers on a smartphone. The effect is immediate and the robust sound makes portable movie watching a stellar experience... or as stellar as it can be anyway. But even in 2018, a lot of smartphones don't come equipped with the feature, but that doesn't mean you can't force the matter.
Developer acervenky from the XDA Developers forums has released a mod that will allow those that own a OnePlus 6 to activate the earpiece speaker and use it as a secondary speaker when playing music, movies, and more. As you can imagine, when the mod is engaged, music that normally would only play through the bottom speaker will also start flowing from the earpiece. Naturally, the speaker wasn't built for this kind of use, so if you choose to have a bit of fun with this, do so at your own risk.
Source: XDA Developers