An electromagnetic vibrator for a bone conduction hearing aid, said electromagnetic vibrator comprising: a magnet arrangement comprising a central portion , a coil wound around the central portion and being configured to generate a dynamic magnetic field (φ D ) in response to an electric current and at least one permanent magnet (6, I, II, III, IV) configured to generate a static magnetic field (φ S ); a vibrator plate arranged in a position with respect to said central portion such that a gap (Gi), extending across a longitudinal axis (X) of the electromagnetic vibrator is formed between the vibrator plate and at least one of said central portion or at least one permanent magnet (6, I, II, III, IV); an encasing surrounding at least a portion of the magnet arrangement , wherein the magnet arrangement comprises a bobbin assembly comprising the central portion , the coil and the at least one permanent magnet (6, 1, II, III, IV) and the encasing comprises a gap adjustment mechanism that is configured to move the bobbin assembly relative to the encasing for adjusting the gap (Gi) between the vibrator plate and at least one of said central portion or at least one permanent magnet (6, I, II, III, IV), and at an end portion of the encasing a coupling is arranged, and where the coupling is configured to detachably attach to an abutment, and where the longitudinal axis (X) extends along a distance from one end of bobbin assembly towards the coupling , and wherein the gap adjustment mechanism comprises: a first adjustment part formed as a threaded portion provided at an outer periphery of the bobbin assembly ; and a second adjustment part formed as a corresponding threaded portion , configured to operationally co-operate with the threaded portion , provided at an inner side of the encasing . a magnet arrangement comprising a central portion , a coil wound around the central portion and being configured to generate a dynamic magnetic field (φ D ) in response to an electric current and at least one permanent magnet (6, I, II, III, IV) configured to generate a static magnetic field (φ S ); a vibrator plate arranged in a position with respect to said central portion such that a gap (Gi), extending across a longitudinal axis (X) of the electromagnetic vibrator is formed between the vibrator plate and at least one of said central portion or at least one permanent magnet (6, I, II, III, IV); an encasing surrounding at least a portion of the magnet arrangement , wherein the magnet arrangement comprises a bobbin assembly comprising the central portion , the coil and the at least one permanent magnet (6, 1, II, III, IV) and the encasing comprises a gap adjustment mechanism that is configured to move the bobbin assembly relative to the encasing for adjusting the gap (Gi) between the vibrator plate and at least one of said central portion or at least one permanent magnet (6, I, II, III, IV), and at an end portion of the encasing a coupling is arranged, and where the coupling is configured to detachably attach to an abutment, and where the longitudinal axis (X) extends along a distance from one end of bobbin assembly towards the coupling , and a first adjustment part formed as a threaded portion provided at an outer periphery of the bobbin assembly ; and a second adjustment part formed as a corresponding threaded portion , configured to operationally co-operate with the threaded portion , provided at an inner side of the encasing . <EOS>