These instructions apply to Yeti, Yeti Nano, and Snowball microphones.

1. In your Utilities Folder there lives an application called Audio MIDI Setup and open the app.
2. In the bottom left corner click on the plus sign > Create Aggregate Device > Plug in both mics 
3. Under Audio Devices there should be either two or four USB Microphones listed
   1. Yeti: 4 devices - select all four to aggregate device
   2. Yeti Nano: 2 devices - select both to aggregate device
   3. Snowball: 2 devices - select both to aggregate device
4. The Aggregate will now act as your Input Device within any software or applications you plan to use. Please set it as the default device in the recording tab of your sound menu, and in your application.