Where is the microphone located?

For the regular 3DS, the mic is the small hole under the Start button.

For the 3DS XL, it is on the right of the Start button. It is a small hole marked with a 'mic' label above it.

Here is a pic I found showing you where the mic on the Nintendo 3DS is located! Hope it helps!

The 3 buttons under the touch screen(select, home, and start) is where you can locate the microphone on the 3DS. it is right under the start button but a little to the right.