What car audio component is responsible for producing low frequency sound?

• Tweeter
  Subwoofers are a type of speaker that produce the lowest frequency sounds.
• Subwoofer
  Subwoofers are a type of speaker that produce the lowest frequency sounds.
• Receiver
  Subwoofers are a type of speaker that produce the lowest frequency sounds.
• Crossover
  Subwoofers are a type of speaker that produce the lowest frequency sounds.