How to Disable Monitor Speakers
Some computer monitors come bundled with built-in speakers. The sound emanating from the monitor built-in speakers are often weak due to the limited abilities of bundling several features into one device. Users can purchase external speakers that feature better and higher sound quality. Disable the monitor speakers from the Sound properties of your computer system if your monitor speakers are still producing sound after attaching your external speakers.
Click "Start," then "Control Panel."
Click "Sound and Audio Devices" (Windows XP), "Sound" (Windows Vista) or "Hardware and Sound" and then "Sound" (Windows 7) from the Control Panel.
Click the monitor speakers from the list of sound devices in the Sound Window.
Click the "Properties" button. Click "Don't use this device (disable)" under "Device Usage" and click "OK."