TAU: Speakers Made From Recycled Cardboard | Click through for the full post!
Patent US6343134 - Loudspeaker and horn with an additional transducer - Google Patents
Always wondered what's inside a Bose Acoustimass Speaker System, 2 woofers in 'tandem' in an internal closed box, helping each other. A sealed enclosure delivers a more refined bass. Here combined with 2 ports.
Patent US8391528 - Loudspeaker slotted duct port - Google Patents