GB1437129A - Method and apparatus for imparting to headphones the sound- reproducing characteristics of loudspeakers - Google Patents

Abstract

1437129 Simulating loud-speaker reproduction using earphones; stereophonic systems EUGEN BEYER GmbH [trading as EUGEN BEYER ELEKTROTECHNISCHE FABRIK] 29 Aug 1973 [8 Sept 1972] 40675/73 Headings H4J and H4R Signals for reproduction by a loud-speaker arrangement are applied to a network having amplitude and phase characteristics which give a listener using headphones the impression that he is listening to loud-speaker reproduction. Monaural, stereophonic or quadraphonic signals may be processed. However, the network cannot take account of movement of the listener's head. An electroacoustical transfer function A m (f), in a monaural arrangement, determines the relationship existing between an electrical voltage signal normally applied to a loudspeaker and a resulting signal pressure imping- ing upon an eardrum of a listener to the loud-speaker. A further electroacoustical transfer function A k (f) is equal to the ratio of the Fourier transforms of the driving voltage applied to the earphone pieces and the output signal pressures impinging upon an eardrum of the listener. The earphone is assumed to be a linear system. A circuit X (Fig. 5) having the characteristics of a transfer function A m (f)/ A k (f) has its output connected at points B and B<SP>1</SP> to two earphones (transfer functions A k (f)) and the pressure on the left and right eardrums is P TRl (f) and P TRr (f) when an audio electrical signal U 1 (f) is applied to the input of the circuit X, thereby simulating loud-speaker reproduction. In a stereophonic system where the sound reproducing characteristics to be simulated are those of a pair of loud-speakers (L 1 ) and (L 2 ), Fig. 6 (not shown), disposed symmetrically with respect to the listener's head, two pairs of identical transfer functions A s (f) and A e (f) take into account the fact that sound waves from the left loud-speaker (L 1 ) reach not only the left eardrum but also the right eardrum, and vice versa with respect to the right loudspeaker (L 2 ). Fig. 8 depicts a circuit arrangement for imparting to an earphone set up the overall electroacoustical transducer transfer functions of the arrangement. A k (f) again identifies the electroacoustic transfer function of the earphone set, the earphones being connected at points B and B<SP>1</SP>. A third embodiment (Fig. 9) for imparting to a pair of earphones the sound reproducing characteristics of four loud-speakers disposed symmetrically with respect to the head of a listener, is an elaboration of the two previous embodiments, but two additional summing circuits S 3 and S 4 take into account the fact that each ear receives signals from all four loudspeakers.