Apple AppleVision monitors (OS 7.1) - Manual (Page 22)

Adjusting the alert sound volume
To change the volume of the sound the computer makes when it needs your
attention, follow these steps:
1 Open the Monitors & Sound control panel, then click the Alerts button.
2 Move the System Alert Volume slider to adjust the volume of the alert sound.
For information on selecting and recording an alert sound, refer to Chapter 7,
“Alert Settings.”
Note: The maximum volume of the alert sound is limited by the current
volume setting for the sound output device. You can set the Alert sound
quieter than other sounds, but not louder.
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