I too have wondered about the “Default communications device”.
My Windows 7 laptop has no modem, and, according to Control Panel, by default (at least, I didn’t do it) “Default communications device” is assigned to “Headphones (RTC)”,* and “Default device” is assigned to the “Speakers/HP.”* Most of the time, however, I keep some external speakers plugged in to the headphone socket, and my sound plays through there. If I unplug these, it plays through the built in laptop speakers. If, as I sometimes do, I reassign “Default device” to my TV (which is connected to the computer via HDMI), the sound plays through the TV’s speakers, even though the external speakers remain plugged in to the headphone socket. So what is the difference between the laptop’s speakers and its headphone output? They appear to be using the same channel.
Well, except for one circumstance. If I have audio playing over my external speakers (via the headphone socket) and one of my Skype contacts comes online, or sends me a text message via Skype, the sound output switches momentarily from the external speakers to the laptop’s built in speakers, as Skype alerts me to the message. (When I actually make a call via Skype, however, it plays the sound through the external speakers plugged into the headphone socket as normal, or, if they are not plugged in, through the built in speakers as normal).
Is this because I have “Headphones” set to act as “Default communications device”, so Skype is somehow using them to alert me of events? This does not make much sense, however, because it is the headphone socket that is providing the output to the external speakers, so it seems like it is the internal speakers and not the headphone output that is acting differently when Skype is trying to communicate with me.
Does this make any sense to anyone? Should I have the same device (either speakers or headphones) assigned to be both “Default device” and “Default communications device”? Does it matter at all?
Sorry if this is all totally confusing, but I am confused and I would like to understand what is going on. It is not really a problem; I’m just curious and I like to understand my machine as far as possible.
*I have no idea what RTC means. Presumably the HP is a reference to the fact that this is an HT laptop.