A small diaphragm microphone is a mic whose diaphragm (membrane) measures considerably less than 1 inch (2.54 cm) in diameter. The actual diaphragm size may vary considerably. The smallest ones measure just a few millimetres (about 1/8 inch), the largest small diaphragm mics are about ¾ inch (18-20 mm) in diameter. Typical small diaphragm mics are about 15 mm – slightly more than ½ inch. |
Usually, the terms small and large diaphragm apply to condenser mics only. While such a distinction may be useful for dynamic microphones, too, few manufacturers give diaphragm sizes for any mics other than condensers.
By the way, quite a few mics use capsules that are about 20 mm and thus in-between large and small diaphragm size. Some call those medium diaphragms, but mostly the manufacturers just call them either large or small diaphragms, depending on the type of mic they’re trying to market. In fact, there are a couple of manufacturers who offer small and large diaphragm mics using the exact same 20 mm capsule. In other words, there’s not always a clear cut distinction between small and large diaphragm mics.