The Meridian Microphone is an external, unidirectional condenser microphone with extremely smooth sound transmission and amazing feedback rejection. It is recommended for acoustic guitar and mandolin.
The Meridian Microphone has one serious advantage over an internal microphone: it is outside your instrument, where the true sound happens. Internal microphones tend to pick up excessive bass frequencies and, of course, various sound reflections and reverberations that do not represent the true tone of your instrument. An external mic captures the sound as you hear it.