Proffie 2.2 and 3.9 use the same amplifier, so it’s the same.
Two 4 ohm speakers in parallel basically equals one 2 ohm speaker, which is too low, and is likely to damage the amplifier. (See this thread for details.) If you want to use two speakers, you can, but they need to be 8 ohm amplifiers.
Note that the wattage specifies how much power the speaker can handle, not how much it will use. You can hook up a proffieboard to a 100-watt speaker, as long as it’s 4 ohms or more, it will be fine. (But it will of course still only provide ~3 watts of output.)
There are other options for getting more volume, you could:
- use bigger speakers. Larger speakers are better at moving air, so they provide more sound even though they don’t use more power. (See example here: https://www.youtube.com/watch?v=tljbajKx-z4)
- Hook up an external amplifier of some sort. One of the simpler choices is to use ENABLE_I2S_OUT and then buy some I2S amplifiers from adafruit or something. They have a breakout board that uses the same amplifier that the Proffieboard uses, so you could power the other speaker with that. Alternatively you could buy a much bigger/stronger amplifier to get some real punch.
- Make sure the “porting” of your build is good. Good porting creates twice as much sound from the same wattage. A good speaker case is built with good ports, but obviously we don’t usually have room for that in a prop. Also, acoustic porting design is very nearly a lost art, so it’s hard to do right…