Invalidity dossier
US 6975734
Audio apparatus of negative driving with adaptive gain control
Current assignee: Yamaha Corp
Added 9/23/2026, 2:59:58 PM
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Patent summary
Title, assignee, inventors, filing/issue dates, abstract, and a plain-language overview of the claims.
Patent Overview — US 6,975,734 B1
Title: Audio apparatus of negative driving with adaptive gain control
Assignee: Yamaha Corporation (original assignee Yamaha Corp; inventor Eiichi Suzuki)
Priority date: 1998-12-25 | Filed: 1999-12-23 | Granted/Published: 2005-12-13 | Anticipated expiration: 2019-12-23 | Status: Expired – Fee Related
Purpose: To generate low tones efficiently from a small loudspeaker using a combination of Helmholtz resonance and "negative driving," while avoiding clipping that occurs when the input voltage level rises. In the prior-art circuit (FIG. 4), the amplitude-frequency characteristic has a strong low-band peak, so a limiter must be activated early—even at low input levels—making the limiter overly effective and producing unnatural sound as volume increases.
Plain-language scope: An amplifier drives a loudspeaker, and a feedback path positively feeds back a signal corresponding to the loudspeaker's driving voltage with a variable feedback gain. This creates a negative impedance that cancels the loudspeaker's internal impedance. An adjustment device lowers that variable feedback gain as the driving voltage (detected as the loudspeaker's load voltage) increases, thereby adjusting the amplitude-frequency characteristic and suppressing the low-band peak before clipping.
More specifically, a signal detector senses voltage across a sensing resistor in series with the loudspeaker; an AC/DC converter (e.g., rectifier plus smoothing/integrating circuit) converts it to a control voltage Vc fed to a voltage-controlled amplifier (VCA) whose gain k·A provides the positive feedback. Per the described embodiment, k stays at "1" until loudspeaker output reaches 5 W, then decreases linearly (or nonlinearly) as output rises. When k·A(R1+R2)/R1 exceeds 1, output impedance Zo becomes negative. A limiter may be retained but triggers at a higher input level than before—or may be eliminated entirely.
What the excerpt does not establish: It provides no complete claim set, no detailed description of alternative embodiments beyond the above, no drawing-derived dimensions, no prosecution history, and no independent verification of the listed legal status or assignee accuracy (Google Patents expressly disclaims these as assumptions). Prior-art discussion is limited to Japanese Publication Nos. Hei 1-302997/1-302998 and U.S. Pat. Nos. 4,987,564 and 4,989,187, incorporated by reference.
Generated 10/1/2026, 9:51:50 PM
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Prior art
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