"77//;" \/7;77/()/'//().V /•:.■■ ./.V ELECT KU.M. STI-.TIIOSCOIT. 541 



r;llfs ami ct-rtain t\|H's ot lirr.iihinn mxitkIs cm In- nliMiM-d in iln- 

 i^rratest a<l\antagc. 



Thf low-pass 1,UX) cycli- filter passes the iii^lKT frec|uency com- 

 ponents of very high-pitelied nuirmurs and liiKli-pitched rAles in a 

 majority of cases. 



The high-pass 130 cycle filler serves a iinitiiie .md important pur- 

 pose. It may he regarded as in value second only to the low-pass 

 ().")() cycle filter. In many cases, the loud normal .sounds tend to 

 mask or obscure the faint higher-pitched murmurs. The high-pass 

 I'M) c\cle filter serves to weaken greatly the normal heart sounds so 

 that the murmur sounds occurring in the intervals between the 

 beats appear with its use to be relatively much louder. In this 

 filter, the amount of attenuation in the low frequency region has 

 been maile such that the residual low frequency energy and the 

 higher frequency components of the normal heart sounds are just 

 surticiently audible so that the murmurs may be timed with relation 

 to their positions in the cardiac cycle. This filter is also very useful 

 for weakening the heart sounds when rSles or pericardial friction 

 sounds are to be observed in areas where the heart sounds are loud. 



The high-pass 130 cycle filter may be connected into the circuit 

 jointly with any one of the low-pass filters, thus making a\ailable 

 a group of band-pass filters with a lower cut-otT frequency of 130 

 cycles. 



7. Output Receivers 



When the stethophone is used for teaching or consultation pur- 

 poses, a number of high impedance receivers are connected in parallel 

 in the output circuit. Hach observer is provided with a single 

 receiver tcj which the f)rdinary stethoscope earpieces may be readil>' 



OUTPUT RtCCIVtR- 



U--^^ 



Fig. 7 — The output receiver 



attached as shown in Fig. 7. This method of transmitting sounds 

 from the receiver diaphragm to the ears minimizes leakage loss of 

 sound energy and ser\es effectively to shut out room noises and 

 other annoying sounds. This result could be even better obtained 



