Hear my voice twice in Headphone while recording

Hi dear people,

new here.

In order to keep control and focus while I’m recording my voice, I need to hear myself.
I found out in the preferences the option ‘play through’. Before this I didn’t hear my voice at all while recording.

But now I hear myself twice! That is of course very annoying…

Anybody out there knowing how to fix this issue?

I’m using an external microphone with USB SpeedLink. The headphone is also connected through SpeedLink.
OS X 10.13.6 High Sierra
Audacity 2.3.3

Thanks a lot!