The suit, filed Thursday in federal court in San Jose, Calif., involves a patent called "Narrow Profile Speaker Configurations and Systems," which essentially covers various setups for directing sound from a small speaker or speakers toward a narrow, slotted opening in such a way as to produce the best possible sound quality.
The abstract of the patent says the speaker units "may be integral with or attached to electronic appliances such as desktop computers or flatscreen devices, or may be used in automobiles or other contexts."
The suit says the infringing Apple products include but aren't limited to the iPhone 4 and later models, as well as the company's iPad and iMac products, all of which "incorporate narrow-profile speaker units that output sound through a duct or aperture having a narrow dimension."
"Apple's infringement...has caused and will continue to cause THX both monetary damage and irreparable harm," the suit says, and it asks for damages covering lost profits or "at least a reasonable royalty."
Bloomberg, which reported the news earlier, said neither THX nor Apple would comment on the suit.