Abstract: A speakerphone of a system with a digital signal processor, such as a computer, uses a filter set or network to provide acoustic coupling loss at a microphone to offset acoustic coupling gain produced by sound reflections resulting from various conditions in the system. The filter network processes an acoustic signal before the signal is provided to a digital signal processor to eliminate acoustic coupling gain that the digital signal processor is unable to cancel or offset. The filter network detects when the acoustic coupling gain in the acoustic signal at the microphone exceeds the maximum amount of acoustic coupling loss supplied by the digital signal processor. Alternatively, if acoustic coupling gain is desirable at the frequency location of the anomaly caused by the sound reflections, the filter network is used to boost the acoustic coupling gain produced by the anomaly.

Abstract: An expansion base with a rearward-emitting expansion speaker for emitting low frequency audio and providing surround sound capability. The frequency response of the expansion speaker includes subwoofer frequencies, and is also extended to 600 Hz or higher, to enhance surround sound and spatial impression effects.

Abstract: A method and apparatus for controlling acoustic gain during a non-speakerphone audio mode of computer system independent of acoustic gain during a speakerphone mode of the computer system is provided. The BIOS code of the computer system detects whether the computer system is in a speakerphone mode or a non-speakerphone audio mode. If the computer system is in a speakerphone mode, an upper gain limit is not applied to the microphone path of the computer system. If the computer system is in a non-speakerphone audio mode, a predetermined upper gain limit is applied to the microphone path of the computer system. The predetermined upper gain limit is preferably applied to the microphone path at either a microphone pre-amplifier or an audio mixer chip in the microphone path of the computer system.