Symptom
Hot-plugged USB speakers do not respond to volume changes from the Volume menu bar item.
Note: "Hot plug" refers to the ability of USB and FireWire devices to be plugged in and unplugged when the computer is turned on.
Solution
This issue is resolved by updating to Mac OS X 10.1.1, which you may do with the Software Update feature of System Preferences. Even with Mac OS X 10.1.1, you should select your USB speakers in the Sound pane of System Preferences the first time you plug them in.
In Mac OS X 10.1, you can adjust volume after hot plugging by using System Preferences. Follow these steps:
1. Open System Preferences.
2. Click Sound .
3. Click the Output tab.
4. Be sure that your speakers are selected in the Name column.
5. Click the Alerts tab.
6. Be sure that your speakers are selected in the pop-up menu for "Play alerts through."
7. Adjust the volume using the "Main volume" slider.