Vizio M21d-H8 vs VIZIO SB3651-F6 comparison definitely makes sense. Based on our rating, M21d-H8 has a total rating of 5 out of 10 versus 6.8 for SB3651-F6. The competitors' control buttons are different: power, volume down, volume up, source, Bluetooth and power, input, Bluetooth, volume down, volume up, respectively.
Both soundbars have active amplification type. A significant difference between the units in the number of channels, the Vizio M21d-H8 has 2.1 versus 5.1 for the VIZIO SB3651-F6. Only the Vizio M21d-H8 has a built-in subwoofer. The Vizio M21d-H8 got our rating of 5 out of 10, and the VIZIO SB3651-F6 8 for its audio features and specs.
Soundbars do not have AirPlay support. Spotify support is available on the SB3651-F6.
Only the VIZIO SB3651-F6 can connect to the Internet via WI-FI. Rivals from our review have Bluetooth support. The Vizio M21d-H8 has 1/1 HDMI inputs/outputs versus 1/0 of the VIZIO SB3651-F6. The HDMI Audio Return Channel (ARC) feature supports both devices. Both soundbars have a USB connector. For connectivity, the M21d-H8 received a rating of 6/10 versus 8/10, respectively. App control is available for the SB3651-F6. A built-in microphone is present only on the M21d-H8. Soundbars do not have Multi-room support.
None of soundbars equipped with Dolby Atmos multichannel audio decoder. The soundbars do not support the surround sound technology DTS:X. For multichannel surround Vizio M21d-H8 got a rating of 5, and VIZIO SB3651-F6 6 out of 10.