Why is speaker size important outside for outside speakers?
|2 inch speaker|
Larger speakers simply move more air
Since they can move more air than smaller speakers, they generate more movement in the surrounding air molecules. The impact over the larger area will do two things, disperse the sound at a wider radius and two, possibly have a greater impact on the surrounding molecules, pushing the sound further out into the surrounding environment.
|6 inch speaker|
Why does my small bluetooth speaker sound loud in my living room then?
Several factors come into play with smaller speakers when played indoors. 1. the size of the room and 2. placement of the speaker. One advantage any speaker indoors is that it's working with reflective surfaces. Sound will bounce off and resonate on surrounding surfaces, which help amplify and distribute the moving air that reaches your ear. Think about it, indoors the air may only be able to move so far before either hitting a wall, ceiling or object while outside it can quickly dissipate.
Does wattage and speaker design have an effect?
Both wattage and speaker design will have an effect on how loud a speaker can play. But fundamentally for sound to be loud where you are standing the air pushed by the speaker needs to be strong enough to impact your eardrum.
So if you want outdoor speakers to rock your next outdoor party, invest in a quality set of outdoor speakers with 5 inch drivers or larger.
Important side note: Multiple small speaker drivers in a speaker cabinet can sound louder and produce deeper bass than one. More on this next time.
Here is a more technical discussion on speaker size and wattage.