How do "decibels" work (in an easily, layman's understandable way)?

[Reply]

@Crafter_Man

Here is the horsepower to dB mapping for the power outputs of six engines:

So, dumb question here (I never understood much math or physics):

What does it mean to say that horsepower = decibel? (Or, for that matter, 1 W = 30 dB)?

I’m confused about the three uses of dB here:

1. As a “volume” to the layperson
2. As a ratio between two measurements of power (?)
3. As a measurement of power itself (?)

What does it mean to say that a certain power output is also a certain volume…? Like wouldn’t a 100W bulb “sound pretty different” than a 100W vacuum cleaner, the same distance away? Is there some secret connection between heat and what we hear as sound waves…?