All Serato DJ intro controllers have built in sound cards. When connected to your computer via USB using Serato DJ Intro, sound will only come out of the controllers master output, not your computer. If you don't own external speakers to connect to the master output of your Serato DJ Intro controller an alternative is to run your controllers master output back into your computer and use the onboard speakers.
This guide will help explain how to do that.
You will need to purchase/use an RCA to 3.5mm Jack cable like this one:
Connect a RCA to 3.5 mm jack from the RCA master output of your controller to the input/output on your Mac.
If you have a 13" Mac laptop you'll have to change the input/out port via System preference > Sound > Use audio port for: > 'Sound input'
Next you will need to download and install the free application 'Line In' : Click Here
- Set the 'Input from' > Built-In Input: Line In
- Set the 'Output to" > Built-in Output: Internal Speakers
- Enable 'Pass Thru'
When you now open and play songs in Serato DJ Intro from your Virtual decks you should hear the music coming through your computer speakers.
If this still doesn't work for you please start a help request here