How can I set an audio input device for Speech SDK v.11 recognition?

Take a look at articles under "https://msdn.microsoft.com/en-us/library/dd371428(v=vs.85).aspx" section, especially at

"https://msdn.microsoft.com/en-us/library/dd370819(v=vs.85).aspx". Quote:

InStarting from Windows Vista, the waveOutOpen and waveInOpen functions always 
assign the audio streams that they create to the default session — the process-specific session 
that is identified by the session GUID value GUID_NULL.

In your case you have to

step 1: enumerate capture audio devices, choose one via waveInOpen function.

step 2: use SetInputToDefaultAudioDevice() method for speech recognition.

that's probably because while modern windows usually detects a few endpoint audio devices on modern hardware, its user who chooses which one he uses at the moment somewhere under "sound etc" control panel item (shown on attached image). guess so, i ain't sure. but you cannot rely on user in your case, aren't you?

try to find an easier (than CRT API) way to set default audio input device. i hope CIM/WMI classes have a method for it.
OK, i'm sure you found a solution monthes ago. But whatever...)