Adafruit Audio FX Manual page 11

All the way to the right is the Class D stereo amplifier. This is for connecting to a pair of speaker! The outputs are
bridge-tied-load (BTL) so do not connect R+ to L+ and R- to L- to get more power, it could damage the chip. If you only
need one speaker, simply connect the channel you want.
The amplifier can drive 8 ohm or 4 ohm speaker, up to 2.8W (10% distortion, 4 ohm) and 2.2W (1% distortion, 4 ohm)
4 ohm speakers will be louder than 8 ohm
Powering from 5V will be louder than 3V, so if you need more oomph, you can power from 4 x AA rechargeable
batteries, or 3 x AA Alkaline, or a USB battery pack. It's pretty damn loud tho!
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