There are laptop which has 2.1 speakers which subwoofer is connected to master mono pin of the STAC codec , The ".1" subwoofer is most likely the result of a Low pass filter attached to the mono pin
Maybe - I'm not pretending I've seen all possible configurations. Since the idea I'm discussing is to just add some new models for several laptops with subwoffers, ultimately it doesn't matter which pin has the subwoofer connected, it just have to be correct pin for a given laptop family (0x17 for mine, whatever corresponds to Master Mono for someone else's etc).
Seem that your Lenovo are not using ALC670,
Nope it doesn't. It is Lenovo Y550P with ALC272, and in my system, the subwoofer is connected at pin 0x17. I'm not at it at the moment, but I can send alsa-info.sh later if it is of any interest.
Valentine.