the first embodiment represented on fig1 comprises a local unit 1 - 6 and an outer auxiliary processing unit pu that can be a few meters distant . the local unit 1 - 6 comprises : a chest piece 1 that is placed on the location where the user wants to hear sound . the chest piece 1 comprises a diaphragm 2 on the bottom side . a conventional flexible tube 3 , attached to a ribbed stem 4 of the chest piece 1 . a conventional headset made up of two metal eartubes 5 , 6 , a tension spring 7 , and two eartips 8 , 9 . the chestpiece 1 comprises a cup shaped cavity 16 limited by the diaphragm 2 and by a metal wall 17 ; and a second cavity 18 containing an acoustical chamber 15 , a loudspeaker 14 , two electronic units 11 - 13 , a switch 12 , a microphone 10 , and a battery not represented . the microphone 10 is placed in a hole 19 cut in the wall 17 , for converting the sound transmitted by the diaphragm 2 into an electric signal . a first electronic unit 11 amplifies the auscultation signal supplied by the microphone 10 , samples it , and digitizes it . the first electronic unit 11 further comprises a bluetooth transmitter that sends the digitized auscultation signal to an outer processing unit pu , which is a personal digital assistant for instance . a second electronic unit 13 comprises a bluetooth receiver that receives a digitized signal from the outer processing unit pu . this signal is the auscultation signal that has been processed by the processing unit in such a way as to provide more valuable diagnostic information . the received auscultation signal is amplified and then applied to the loudspeaker 14 . the ribbed stem 4 is connected to the acoustic chamber 15 placed in front of loudspeaker 14 . this loudspeaker 14 has preferably a broad diameter ( four centimeters for instance ) in order to correctly reproduce the low frequencies . the association of this broad diameter loudspeaker 14 and of the classical flexible tube 3 provides an audio transfer function that is not flat , but is similar to the transfer function of the association of the diaphragm and of the tube in a classical acoustic stethoscope . so the audio signal provided at the eartips 8 , 9 sounds familiar to a physician who has been trained to auscultation with a classical stethoscope . the outer auxiliary processing unit pu in real time processes the auscultation signal . a current personal digital assistant , or a personal computer , has a computation power appropriate for applying sophisticated filtering methods which need much computation power . examples of such sophisticated filtering methods can be found in the followings documents : acoustic echo and noise control a practical approach , authors : hänsler eberhard , schmidt gerhard , wiley editor . ieee signal processing letters , vol . 11 , no . 4 , april 2004 , a fast converging algorithm for network echo cancellation , mehran nekuii , student member , ieee , and mojtaba atarodi , member , ieee . in addition , the processing unit pu processes the auscultation signal for displaying a waveform on a screen 20 of the processing unit pu . a method for such processing is described in the document u . s . pat . no . 5 , 025 , 809 incorporated here by reference . the auxiliary processing unit pu provides a richer man - machine interface , than any electronic stethoscope . it may comprise an alphanumeric keyboard , a touch screen , a voice recognition software , etc , which are very useful means for controlling the functions of the stethoscope , and that could not be embedded in a stethoscope alone . a graphical interface displays menus in order to enable a user to switch between several transfer functions for the filtering , and several display parameters for displaying waveforms . several sets of filter coefficients are stored in a memory of the processing unit pu . the switch 12 enables to bypass the bluetooth link to the auxiliary processing unit pu . it can be used either when no processing unit pu is available , or when the physician wants to hear the auscultation signal directly , without any filtering , for comparing with the filtered signal provided by the processing unit pu . fig2 shows a more detailed block diagram of this first embodiment . the first electronic unit 11 comprises in series : an analogue preamplifier 30 , an analogue - to - digital converter 31 , and a bluetooth radio transmitter 32 . an input of the analogue preamplifier 30 is linked to the microphone 10 . an output of the analogue preamplifier 30 is linked to an input of the bluetooth radio transmitter 32 . the output of the analogue preamplifier 30 is linked to an input of the analogue - to - digital converter 31 and to a first terminal of the switch 12 . the output of the analogue - to - digital converter 31 is linked to the input of the bluetooth radio transmitter 32 . the second electronic unit 13 comprises in series : a bluetooth radio receiver 33 , a digital - to - analogue converter 34 , and an output amplifier 35 . the output of bluetooth radio receiver 33 is linked to the input of the digital - to - analogue converter 34 . the output of the digital - to - analogue converter 34 is linked to a first input of the output amplifier 35 . this latter has a second input linked to a second terminal of the switch 12 , a first output linked to the loudspeaker 14 , and a second output linked to a connector 30 where a headphone , or several headphones , can be connected . a micro controller controls the bluetooth radio transmitter 32 , the bluetooth radio receiver 33 , and the output amplifier 35 . a rechargeable battery 42 supplies power to a power unit 43 regulating a dc voltage distributed to all the electronic components of the stethoscope . a charging unit 41 linked to a connector 40 , at the surface of the housing , can charge the battery 42 . when the stethoscope is not in use , an ac power adapter ( not represented ) is connected to the connector 40 . in a preferred embodiment , the outer auxiliary processing unit pu is a personal digital assistant that comprises a classical bluetooth transmitter 21 and a classical bluetooth receiver 22 . they are associated to the classical bluetooth transmitter 33 and the classical bluetooth receiver 32 of the stethoscope in a classical way . a peculiar application software is run by the personal digital assistant , which : enables the bluetooth receiver 32 to receive an auscultation signal from the processing means 11 , 13 of the stethoscope , processes the auscultation signal received by the bluetooth receiver 32 , to improve the diagnostic value of the auscultation signal , for instance by a peculiar filtering , and enables the bluetooth transmitter 33 to send the auscultation signal back , to the processing means 11 , 13 of the stethoscope , after processing . fig3 shows a block diagram of a second embodiment of the stethoscope according to the invention . this embodiment is designed to convert a classical stethoscope into an electronic one . a local unit 1 ′- 6 ′ comprises a housing 1 ′ with an upper ribbed stem 4 ′ and a lower ribbed stem 4 ″. in this example , the classical stethoscope comprised : a chest piece qui comprises a diaphragm 54 on one side and a bell 53 on the other side . a conventional flexible tube 3 , attached to a ribbed stem 52 of the chest piece . a conventional headset made up of two metal eartubes 5 ′, 6 ′, a tension spring 7 ′, and two eartips 8 ′, 9 ′. cutting the tube 3 into two segments 3 ′ and 3 ″, then attaching the segment 3 ′ to the upper ribbed stem 4 ′ of the housing 1 ′, and the segment 3 ″ to the lower ribbed stem 4 ″ of the housing 1 ′. the lower ribbed stem 4 ″ continues into the housing 1 ′ by a first acoustical chamber 51 containing a microphone 10 ′. the upper ribbed stem 4 ″ continues into the housing 1 ′ by a second acoustical chamber 15 ′ containing a loudspeaker 15 ′. the housing 1 ′ also contains two electronic units 11 ′, 13 ′, a switch 12 ′, and a battery not represented . these elements have respectively the same functions as the corresponding elements in the first embodiment . the auscultation signal is transmitted to an outer auxiliary processing unit pu ′ ( a personal computer in this example ) for filtering , and for displaying wave forms on a screen . the auxiliary processing unit pu ′ restitutes an improved auscultation signal . it is then transmitted back to the housing 1 ′ for reproduction by the loudspeaker 14 , coupled to the tube segment 3 ′ by the acoustical chamber 15 ′. the upward and downward link with the outer processing unit preferably is wireless , however a wire could be used as well , for instance using the usb 2 technology ( universal serial bus version 2 ). the radio transmitter 32 and the radio receiver 33 preferably use the bluetooth technology , however they can use other wireless transmission technologies as well , for instance zigbee or uwb . they can use two different technologies respectively for the transmission from the stethoscope to the processing unit pu , and for the transmission from the processing unit pu to the stethoscope , these technologies being chosen in order to minimize the power consumption in the stethoscope , while providing bandwidths respectively adapted to the two signals to be transmitted . the preferred embodiments comprise a remote loudspeaker coupled to a headset by flexible tubing , however the invention can be also applied to a stethoscope wherein the headset and tubing are replaced by headphones and a wire between the housing and the headphones .