Built-in microphone stops working when headphones are plugged in

Question

I have a Lenovo T470 laptop with a combined microphone/headphone jack. It is running Windows 7 with Realtek HD Audio 6.0.1.8142.

Whenever I plug headphones into to my laptop's audio jack, my laptop's internal microphone will stop detecting any sound. If I unplug my headphones, or if I use headphones that don't come with a microphone, the internal mic will start working again.

If I open Sound → Recording, it only lists a single sound device. This makes me think the headphones are overriding my default mic, rather than treating it as a separate device.

I have tried reconfiguring my mic as "Desktop Microphone" in Control Panel → Sound → Recording → Configure → Set up microphone, but it had no effect. Additionally, I could not find any way to disable the microphone in Realtek HD Audio Manager.

Why can't I use my laptop's internal microphone when headphones are connected?

Solution

Headphones with microphones built in have a TRRS (Tip, Ring, Ring, Sleeve) connector while headphones without a microphone (and most speakers) have a TRS (Tip, Ring, Sleeve) connector:

These connectors are usually wired as:

Tip -> Left Channel | Ring -> Right Channel, | Ring -> Microphone | Sleeve -> Ground

Because the connectors are physically different, the audio hardware detects the microphone ring is not grounded (having some resistance about a certain ohms) and switches the mic accordingly, since most people that plug in a headset mic want to use that mic instead of the built in array.

To prevent this, you have three options:

1) Disable the port detection in the Realtek software. Failing that, there's an answer that talks about doing so in the registry: https://superuser.com/a/1194903/74377

2) Use headphones that don't have a microphone built in.

3) Use an adapter that has a male TRS plug and a female TRS or female TRRS port so the mic ring is physically separated from the audio port.