Patent attributes
A head-mounted wearable device (HMWD) provides audio output from a first speaker that is driven with a first signal and a second speaker that is driven with a second signal. Based on a volume level setting, an equalization profile and inversion frequency are determined. The equalization profile selectively amplifies or attenuates particular frequencies or ranges of frequencies. Those frequencies in the second signal that are above the inversion frequency have their amplitude inverted, relative to the first signal. When driven by the first signal and the second signal, the first speaker and the second speaker operate as acoustic dipoles below the inversion frequency and acoustic quadrupoles above the inversion frequency. Sound from the first and second speakers with frequencies above the inversion frequency exhibits destructive interference. As a result, the user wearing the HMWD is able hear audio output while audio amplitude perceived by the bystanders is significantly reduced.
