•I fir. SI iiiK^rnosF.," .i\ i-.i.ectkic.m. sthi iioscorn 5j.i 



t-xpri'ss rflati\f loiidiu'ss. A powiT r.ilio sc.ili' is iilso slinwii .it llii- 



li-lt ami ihf powiT .It 100 ryrli-s is assumed i(|iial lo uiiily as a ref- 

 finicf point. 



'Phis curvi- shows tlio ri'lati\-c cflicieiiry of transmission for frc- 

 (|iii'ncifs up to 2,000 cycles. The successive peaks are due primarily 



to resonance of the air columns anti are partly determined !)>• the 



length of the stethoscope tubing. Resonance thus increases the 



-2C rjv 



FREQUEncr-acLts per SECono 



100 100 300 400 MO TOO W 1000 



miCOlC I 

 MlrtlCAL noTATion 



Kiij. .1 — Frequency characteristic of open hell stethoscope 



efficiency of transmission at and above the fundamental peak fre- 

 (juencv-. .As the frequency scale is ascended' from this point, the 

 transmission falls off gradually. 



In a subsequent test, the open i>ell and Bowles types of stethoscopes 

 (Figs. 1 and 2) were compared directly with one another. For this 

 test, a vigorous sound was imparted to the sternum of a patient and 

 the sound was picked up over the apex of the heart. Below 1.50 

 cycles, the Bowles stethoscope averaged approximately 1.5 TU less 

 etVicient, whereas, disregarding the somewhat different arrangement 

 of the resonance peaks, between 300 and 1,000 cycles, it varied from 

 .5 to 10 I'L' more efficient than the open bell type. These features 

 of the Bowles stethoscope are due to the chest piece diaphragm. 

 .As will be shown in another paper, much of the energy of systolic 

 and diastolic murmurs is made up of frequencies between 120 and 

 OGO cycles per second. Thus, concurring with obser\ali(jns macle 



