A HEARING AID COMPRISING A DIRECTIONAL MICROPHONE SYSTEM

The application relates to a hearing aid comprising a BTE-part adapted for being located behind an ear (ear) of a user. The BTE-part comprises a) a multitude M of microphones ( M BTEi , i = 1, .., M ) for converting an input sound to respective electric input signals (IN i , i=1, ..., M ), the multitude of microphones of the BTE-part, when located behind the ear of the user being characterized by transfer functions H BTEZ (¸, Õ, r, k), i= 1, ..., M , representative of propagation of sound from sound sources S located at ( ¸ , Õ, r ) around the hearing aid to the respective microphones ( M BTEi , i=1, ..., M ), when the BTE-part is located at its operational position, (¸ , Õ, r) representing spatial coordinates and k is a frequency index, b) a memory unit comprising complex, frequency dependent constants W i (k)', i=1, ..., M, c) a beamformer filtering unit (BFU) for providing a beam formed signal Y as a weighted combination of said multitude of electric input signals using said complex, frequency dependent constants W i (k)', i=1, ..., M, : Y(k)=W 1 (k)'·IN 1 + ... +W M (k)'·IN M , and wherein said frequency dependent constants W i (k)', i=1, ..., M, are determined to provide a resulting transfer function H pinna ¸ Õ r k = ˆ‘ i = 1 M W i k ‹ H BTEi ¸ Õ r k , so that a difference between the resulting transfer function H pinna (¸, Õ, r, k) and a transfer function H ITE (¸, Õ, r, k) of a microphone located close to or in the ear canal (ITE) fulfils a predefined criterion. The application further relates to a method of determining constants W i ', i=1, ..., M. The invention may e.g. be used in hearing instruments, headsets, ear phones, active ear protection systems, or combinations thereof.