The invention pertains generally to a system and method for providing wireless communication between individuals and in particular to audio communication.
While audio communication has become a common form of communication, new challenges are posed by the fact that the devices for audio communication are becoming increasingly small. For example, when a audio communication device is small, the microphone and the speaker cannot be placed far apart. Thus, when the microphone is physically close to a speaker in a full-duplex system, the voice of an individual received through the speaker may feed back into the microphone and cause the talker to hear himself like an acoustic echo even though the talker is talking at an appropriate volume level.
Sound waves travel from the speaker to the microphone in two ways: mechanically and acoustically. The transmission of sound to the microphone may occur at least partly mechanically due to vibration of various physical components around the speaker, such as the housing or a printed circuit board. The energy of the sound waves propagates through the physical components until when mechanical-acoustic coupling occurs and the mechanical energy converts into acoustic energy coming off the surface of the vibrating physical component. This energy off the surface of the physical component travels through air in a purely acoustical manner to be coupled with the microphone.
The mechanical vibration may be reduced by placing foam or a rubbery material around the microphone, thereby decoupling the microphone from the purely mechanical vibrations. However, the foam or the rubbery material does not reduce the acoustic transmission of sound waves from the speaker to the microphone. When loud enough sounds are output from the speaker, the sound energy mechanically output from the rear side of the speaker may stay inside the housing, experience mechanical-acoustic coupling, and travel via an effective acoustic passage to the microphone regardless of the presence of the foam material. When the speaker and the microphone are placed in a small device, this problem become more prominent than in a large device due to the proximity of the two components and the thinness of the device walls (for lighter weight).
Therefore, as communication devices become increasingly smaller and lighter, new methods of controlling the coupling of speaker sound energy to a microphone become necessary. Some solutions that would have once been considered obvious, such as placing the microphone and the speaker sufficiently far apart to prevent this type of unwanted sound coupling, is not a viable solution for small, handheld voice communication devices. The problem is compounded by the fact that small communication devices often use thin plastic housing in order to make the device as light as possible. Devices housed in thin plastic tend to be especially vulnerable to acoustic transmission because vibration of the thin housing walls create acoustic waves, in a similar way that drumheads generate sounds. Thickening the housing walls solves the acoustic transmission problem but has the “side effect” of increased device weight.
A method and apparatus for reducing sound transmission from a speaker to a nearby microphone with minimal extra volume and weight are desired.