I bought powered, wired, lavalier mics with 1/8thin jack. How can I use these with my 2011 MacBook Air?
The MacBook Air has a single headphone port, which should be more accurately called the “headset” port. Like the headphone port on iOS devices, this jack supports audio input as well as output – with this caveat: The microphone or headset in question must be of the three-ring variety, just like Apple’s headsets (and their compatible brethren).
Regrettably, your lavalier mics are undoubtedly of the standard two-ring variety. So you could plug them into your Air’s headphone port from now until the end of time and your laptop would look the other way as if it had no notion that it had another wire dangling from its side.
But hope is not lost. You simply have to find another way to make your Air aware of the mic’s existence. That way would be a USB audio interface. If you need just a single mic, an inexpensive and easy solution is Griffin Technology’s US$40 iMic. Plug one end into a free USB port and jack your mic into the audio input jack, choose the iMic as the input source within the Sound system preference and you should be in business.
If you were hoping to use both mics you’ll need an interface that supports multiple inputs. There are many such interfaces around. One that isn’t terribly expensive is Focusrite’s Scarlett 2i2. (I’m sure some of our audio-savvy readers will pipe in with recommendations of their own.) This interface bears 1/4in inputs, so you’ll need a couple of adapters that convert 1/8in plugs to this larger size.