Patent ID: 8867772

Claim:
A non-directional condenser microphone unit, comprising: a diaphragm holder; a diaphragm having a circumferential edge attached to the diaphragm holder; an electrically insulating spacer disposed on the diaphragm at a side opposite to the diaphragm holder, and a fixed electrode made of a metal material and arranged to face said diaphragm at a predetermined interval through the electrically insulating spacer, the spacer being contacted with the fixed electrode, wherein a rear space of said diaphragm is closed, the rear space is communicated with an outside on a front surface side of the diaphragm through a communication part serving as acoustic resistance for pressure equalization, the communication part is formed between the spacer and a blind groove formed on the fixed electrode along a surface with which the spacer contacts and reaching an outer periphery of the fixed electrode, the blind groove includes an annular groove formed in an inner side of the fixed electrode, and extends from the annular groove to the outer periphery of the fixed electrode, one side of the communication part is communicated with the rear space and another side of the communication part is communicated with the outside of the fixed electrode at the outer periphery of the fixed electrode, and the communication part passing through the outside of the fixed electrode is communicated with the front surface side of the diaphragm through a gap formed between the holder and a unit case covering the outer side of the fixed electrode and an outer side of the holder.