Apple patent details a method of automatically adjusting the iPhone's receiver or speaker volume.

Based on your proximity to the device, the present invention relies on automatic detection of device proximity to the user to adjust one or more acoustic transducers. This means, if the device is a mobile telephone, and the user is using the receiver and holding the telephone against his/her ear, if the telephone detects that the user has moved the telephone further from his/her ear, the telephone will raise the receiver volume. Similarly, if the user is using the speaker, the telephone will adjust the speaker volume as user distance from the telephone changes.

‘’In another embodiment the telephone may fade between the receiver and the speaker. In such an embodiment, if the user, e.g., starts with the device near his face, the device could use the receiver output. As the user begins to move the telephone further away, the telephone will detect the decreased proximity and increase the receiver volume. Eventually, as the proximity decreases further, the telephone will switch from the receiver to the speaker, starting out at a lower speaker volume and increasing the speaker volume as the distance increases. The reverse would happen if while in speaker mode the distance to the user decreases.

Notably, Apple also accounts for the switch from receiver to speaker or speaker to receiver. For example, when going from the receiver to the speaker, the speaker would turn at low volume as the receiver reaches its maximum volume, the receiver would then fade its volume as the speaker volume increases. The procedure would be reversed when moving in the opposite direction.

Apple also says frequency response could be adjusted according to user proximity. Devices are designed to have a certain acoustic frequency response based on their position relative to the ear. If the position of the device is being changed appropriate frequencies could be boosted or deemphasized.

For example, lower audible frequencies are affected more than higher frequencies as a device is moved away from a user, increasing the volume of air in front of the transducer (e.g., speaker or receiver). Thus, if it is detected that the device is being moved away from the user, the lower frequencies could be boosted.’’ Has reported iPhone.