.(.v i.i.i-.ctRic.ii. rRr.oif-xcv .is.ii.y/.i.u m7 



pii-ki'il up by a coiult-nsor transiuittc-r.' Tlio rcverl K-ration in the 

 room probably had a larfje (.■(Tcct on the rliarartor of this record. 

 With such a stiurcc of fn.'t|ui'ncy the analy/.cr may be used to study ■ 

 the acoustics of nnims. Fij;. 10 is a record of the same noise as in 

 I'ig. 9 but as picket! up l)y a common l>'pe of telephone receiver 

 placed in the same position as the condenser transmitter. A com- 

 parison of Figs. 9 and 10 will sliow tlie inadaptability of such a receiver 

 for use as a transmitter. The receiver, owing to the resonance of 

 its diaphragm, is seen to be relatively sensitive in the region of 600 

 to }S00 CNcles and insensitive at most other frequencies. When this 

 instrument is placed against the ear, as when used as a receiver, 

 the diaphragm resonance is damped so as to give more nearly uni- 

 form response. 



B>' nu'ans of the calibration of the condenser transmitter and its 

 amplifier, it is possible to make an anaKsis of the absolute intensity 

 of a sustained sound in the air. This method has been used to study 

 the frequency characteristics of musical instruments. I'ig. 11 shows 

 the analyses of three low-frequency organ pipes. These are plots 

 of r. m. s. pressure change in the sound wave as obtained from the 

 analyzer records. Kach vertical line corresponds to a peak on the 

 original record. The upper chart shows the almost pure tone given 

 by a 64-cycle Bourdon pipe. In the case of the cello pipe, also hav- 

 ing a fundamental of 64 cycles, the third harmonic is seen to be more 

 prominent than the fundamental or second harmonic. The third 

 chart is for a 128-cycIe trombone pipe which was found to be rich 

 in harmonics. The pressure in the single components of the cello 

 and trombone pipes is less than in the case of the Bourdon pipe, 

 and a larger scale of ordinates is therefore used. 



To illustrate the use of the attachment which permits the making 

 of two simultaneous analyses, a few double records will be presented. 

 \n electric wave filter which has been used in the study of telephone 

 quality was connected to the buzzer source whose output is shown 

 in F"ig. 2. Simultaneous analyses of the current delivered to and 

 transmitted through the filter are shown in Fig. 12. This filter is 

 designed to pass all frequencies below 1000 cycles and to suppress 

 all others. The input is represented by a more or less continuous 

 series of peaks along the entire length of the record. The peaks 

 corresponding to the output coincide rather closely with the input 



* "A Condenser Transmitter as a Uniformly Sensitive Instrument for the Ab- 

 solute Measurement of Sound Intensity." E. C. U'ente, Physical Reeiru;, July 1917. 



"The Sensitivity and Precision of the Electrostatic Transmitter for Measuring 

 Sound Intensities." E. C. Wente, Physical Review, May 1922. 



