IP Law Daily, PATENT—Fed. Cir.: Patent owner challenges Board’s claim construction regarding systems for sound-isolating earphones, (Feb 19, 2026)

By Steven D. Cole, J.D.

The patent holder was unsuccessful in arguing that the Board misconstrued certain claim terms referring to the detection of cessation of voice activity and the adjustment of audio content signals.

The Federal Circuit Court of Appeals upheld decisions made by the Patent Trial and Appeal Board (Board) finding that certain claims in two patents involving sound-isolating earphones were unpatentable as obvious. The owner of the patents, ST Case1Tech, LLC (ST1), alleged in one appeal that the Board erred in its construction of the claim term “detecting a cessation of the voice activity” by finding that the term broadly encompassed “word gaps” during speech. But the Board’s analysis was sound and supported by the specification. The other appeal was similarly unsuccessful, as the claim language did not warrant the particular interpretation tendered by the appellant (ST Case1tech, LLC v. Squires, No. 23-2387 (Fed. Cir. Feb. 18, 2026) and (ST Case1tech, LLC v. Squires, No. 23-2388 (Fed. Cir. Feb. 18, 2026)).

The ’542 patent. ST1 is the owner of U.S. Patent No. 9,491,542 (’542 patent), which pertains to a system in sound-isolating earphones designed to enable users to better isolate and detect speech in their immediate environment. When the system detects that the user is speaking, it amplifies the volume of the ambient sound and turns down the volume of any audio content and then combines these two signals. When the system subsequently detects that the user has stopped speaking, it retains the same settings for a set time.

Disputed claim construction. In an inter partes review (IPR), the Board found claims 1–9 and 11–18 unpatentable as obvious, citing (as relevant to this appeal) three prior art references: U.S. Patent App. Pub. No. 2007/0189544 (“Rosenberg”), U.S. Patent App. Pub. No. 2011/0096939 (“Ichimura”), and U.S. Patent App. Pub. No. 2011/0264447 (“Visser”). ST1 contended that the Board misconstrued the claim term “detecting a cessation of the voice activity” (cessation limitation). ST1 proposed that the cessation limitation should be construed to mean “detecting an end of speech,” which does not encompass momentary pauses within speech—i.e., “word gaps.”

The Court of Appeals sided with the Board’s interpretation that the cessation limitation was “broad enough to also encompass detecting the end of a word within a sentence or conversation.” The claim language recited “detecting voice activity of the user of the earphone device,” and then “detecting a cessation of the voice activity.” The court reasoned that because an ambient sound microphone (ASM) signal level may fall below a threshold in between words when a speaker is speaking, it follows that such “word gaps” are included within the phrase “cessation of voice activity.”

The specification provided further support, illustrating that when the ASM signal drops below a threshold such that voice activity is no longer detected, the voice activity detection (VAD) timer is started. This provides a delayed modification of the sound levels for a predetermined amount of time so that the levels do not change during short intervals of silence within the normal pattern of speech. Thus, “the VAD timer itself would alleviate ST1’s concern that allowing word gaps to constitute ‘cessations’ would lead to ‘too frequent and too abrupt’ adjustments.”

Claims 11 and 12. The Board additionally determined that claims 11 and 12 were “proven by a preponderance of the evidence to be unpatentable,” identifying no reason for this conclusion. These claims were not challenged in the petition for IPR originally brought by Samsung (which later withdrew its participation, after which the Director of the U.S. Patent and Trademark Office intervened, adopting Samsung’s brief). Thus, the court vacated the Board’s findings as to these claims, since “the Board may not invalidate patent claims on grounds it identifies sua sponte that are not actually raised by the petitioner.” Corephotonics, Ltd. v. Apple Inc., 84 F.4th 990, 1011 (Fed. Cir. 2023).

The ’244 patent. ST1 also owns U.S. Patent No. 9,270,244 (’244 patent), which generally relates to methods of automatically adjusting audio levels in user-worn devices in order to improve the user’s situational awareness. The Board, in an IPR, found that Rosenberg rendered 13 of the ’244 patent’s 30 claims obvious, and that Rosenberg disclosed every step of the 30 challenged claims.

The following limitation was relevant to this appeal: “adjusting a mixing gain of an audio content signal delivered to the earphone with the ambient sound pass-through during a voice timer pending voice activity; and wherein the audio content is one of a voice signal, music content, or audible sound delivered to the internal speaker for audible reproduction.”

ST1 argued that this “adjusting” of the volume must occur after the activation of the system’s voice timer, thereby distinguishing it from Rosenberg. The Board disagreed, and the court affirmed, noting that “[n]othing in the specification compels the rigid order of steps ST1 advocates.” Instead, the claim language indicated that the “adjusting” included maintaining and delivering relative levels of adjusted volumes “during a voice timer pending voice activity,” even if the actual moment that the first adjustment was made were to occur before the voice timer’s activation.

Furthermore, contrary to ST1’s suggestion, the Board’s construction did not render the phrase “activating a voice timer” impermissibly superfluous. Without this requirement, the claims could encompass an embodiment in which the adjusting of volume begins and ends without any voice timer at all.

The Case is No. 23-2387 and No. 23-2388.

Judge: Stark, L.

Attorneys: Timothy Devlin (Devlin Law Firm LLC) for ST Case1tech, LLC. Omar Farooq Amin, U.S. Patent and Trademark Office, for John A. Squires.

Companies: ST Case1tech, LLC

Cases: Patent FedCirNews USPTO