Bestbuy offers Sonos Sub 4 Wireless Subwoofer for $850 (reg $899) with free shipping.

Product Description:
Sub 4 unlocks the full power of Sonos sound. Pair this subwoofer with your Sonos soundbar or speaker for pulse-pounding bass that immerses you even deeper in movies, TV, and music. Updated with a matte finish, the iconic design features dual force-canceling woofers that virtually eliminate distortion.

• Pulse-pounding bass
  Dual Sonos-engineered drivers generate deep, dynamic low frequencies. The ported enclosure enhances the bass response so you feel every beat, roar, and rumble in your chest.
• Transform your home theater experience
  Pair Sub 4 with Sonos Arc Ultra, Arc, or Beam for dramatically deeper bass and clearer highs that draw you deeper into movies, shows, and games.
• Bring your music to life
  Hear the nuance in every note and enjoy a greater sense of spaciousness when you pair Sub 4 with Sonos Five, Era 300, or Era 100.
• No buzz or rattle
  The acoustic architecture creates a force-canceling effect that virtually eliminates distortion.
• Perfectly tuned for the room
  Trueplay optimizes the sound for the unique acoustics of the room and placement of your speakers.
• Iconic design
  With its elegant sculptural shape and updated matte finish, Sub 4 is designed to look great in your home and to match your Sonos speakers.
• Plug and play
  Simply plug in the power cable and open the Sonos app to add Sub 4 to your system.
• Place it where and how you want
  Sub 4 reliably connects to your Sonos soundbar or speaker over WiFi so you can place it anywhere in the room even on its side and under your sofa.
• Double the drama
  Pair two with Arc Ultra or Arc for bass so deep and sound so immersive, you'll forget you're at home and not in an actual theater.
• Toned down impact
  Sub 4 uses fewer materials and is more energy efficient than previous generations.
• Upgraded technology
  With increased processing power, memory, and new WiFi radios, Sub 4 is the most advanced Sonos subwoofer to date.