(See update #2—I solved my own mystery) Maybe pre-Mavericks, whenever I had headphones plugged in, I could Option-click the sound icon in the menu bar and, with headphones plugged-in, select "Internal Speaker" as an audio-out option. This was convenient because one didn't have to keep plugging and un-plugging headphones to create the same effect. What happened? Update #1: if I wan't clear enough: I can still Option+click in Mavericks. I'm asking why "Internal Speaker" is no longer an option. In other words, I can no longer toggle between Internal Speaker and Headphone without actually having to remove the headphone. Here's Output Devices when headphones are removed. Notice "Internal Speaker is now listed only when headphones are removed—where as pre-Mavericas you could select either. Update #2: Mystery Solved You know what? Now I remember: I used a headphone/mic combo that plugged into my iMac via two cables simultaneously—USB and headphone-in. I don't know what it couldn't just use USB, but there you go. It must have activated some driver, and I could keep it plugged in, yet use Option-click on the sound icon to switch between headphones and "Internal Speakers". Those headphones broke last year, and so this option not being available to me didn't come to mind until now. Shame too, because apparently Windows allows this, so had Apple followed in it's software it would be a major convenience for users who like to keep headphones plugged-in more permanently.