A Delaware federal judge on Feb. 16 invalidated a patent held by D&M Holdings Inc. as the company continues to face off against rival wireless speaker-maker Sonos Inc. in a protracted infringement fight.

U.S. District Judge Richard G. Andrews of the District of Delaware said in a 13-page memorandum opinion that plaintiff D&M’s patent was directed to an abstract idea and thus was not patent eligible. Nothing in the patent claimed an inventive concept that would make it valid under U.S. patent law, he said, reviewing the case under the U.S. Supreme Court’s Alice framework.