The system bell or beep is a feature of the X server, which attempts to make good use of the available hardware. However, it isn't always possible for the X server to actually make a beep sound with exactly the parameters selected due to hardware limitations. For example, on most PCs, volume control is not very good so the X server seems to fake low volume with a reduced duration of the sound. Thus, if the settings don't seem to do anything, this is because the X server and/or the hardware don't support anything better.
User's are able to set the following parameters for the bell:
volume (percentage of "maximum" volume)
pitch (in Hz)
duration (in milliseconds)
You can use the test button to hear how the current settings will sound.