Hi,
I own an Acer Aspire R7-572G which has a combined 4-pin 3.5mm headset jack.
I would like to use a normal microphone with an 3.5mm connector. The microphone did not work by directly plugging the connector into the socket, therefore I bought an adapter which splits the 4-pin output into speaker & microphone sockets.
Now the microphone does work properly, however, unless I am connecting external speakers I am not able to use the internal notebook speakers. (maybe because the notebook assumes that a headset is plugged in)
>>> Is there a way to use my external microphone and the internal notebook speakers?
One more thing to mention: If I plug in the cable, a popup on the notebook appears asking which device I just plugged in. Sadly my only three options are "headphones", "speaker output" or "headset". NO MICROPHONE OPTION !!! argh... 
Kind regards,
Mario