Remember, the audio amplifier chip in the phone - the thing that produces the audio signal that's fed to the speaker - has a maximum output (It just can't produce more) and it's being run close to maximum as the phone comes stock (close to, because the maximum allowable varies with temperature, and if they designed it to run at max in Fairbanks, AK in the winter, it would blow the amplifier in Houston, TX in the summer - which would require a motherboard replacement.
There are apps that shape the audio (equalizers) to make it sound louder to your ears (everyone hears "loudness" differently) and some apps that drive the amplifier harder, but that also drives up the distortion. (Considering what I've heard some teens listening to, as long as the song is barely recognizable, it doesn't matter how distorted it is.)
But you're not going to get 10 Watts of audio out of a Note 3 without an external amp and speaker. (And considering these 250 Watt per channel car setups, you should realize that 10 Watts isn't that loud.) Even if you could, that little speaker in the phone would probably blow out at the first click.