This high power 4" diameter speaker has 4 ohm impedance, rated for 20W continuous power. It also has four handy mounting tabs 3 inches apart, and a grill that fits on top. The grill is to protect the cones, and is not necessary for use.
This speaker has a nice wide range of 60Hz - 24kHz.
his is a 20W stereo amplifier This slim little board has a class D amplifier onboard that can drive 2 channels of 4-8 ohm impedance speakers at 20W each.
This powerful shield features the VS1053, an encoding/decoding (codec) chip that can decode a wide variety of audio formats such as MP3, AAC, Ogg Vorbis, WMA, MIDI, FLAC, WAV (PCM and ADPCM).
This 3 inch speaker is perfect for any audio project that requires 8 ohm impedance and 1W or less power. The speaker has four mounting holes (distance between holes is 60mm)