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June, 1930] LOUD SPEAKERS AND SOUND REPRODUCTION
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associated with the condenser microphone. The recording mechanism shown permits of a rapid and accurate frequency response characteristic being taken in a few moments. A complete description of a similar sound pressure recording mechanism has been previously published. l
DISCUSSION OF EXPERIMENTAL RESULTS
The frequency response characteristics obtained are shown in Fig. 5. In order to enable a fair comparison to be made between the frequency characteristics of the two types of speakers the two frequency response curves have been so placed as approximately to overlap in the center of the range, i. e., between 300 and 800 cycles. This has necessitated raising the curve of the directional baffle type loudspeaker. (See later discussion under "Efficiency.") A careful
FIG. 4. High quality beat frequency oscillator and amplifier.
study of these curves enables us to make a competent comparison between the two types of speakers as regards frequency range, uniformity of response, and efficiency.
Frequency Range and Uniformity of Response. — It is immediately evident that the frequency range of the directional baffle type speaker is greater at both the low and high ends of the scale. The cut-off frequencies of the directional baffle type speaker are about 85 cycles and 6000 cycles at the low and high ends, respectively, whereas those of the horn type speaker are about 125 cycles and 5000 cycles, respectively. Thus at the lower end of the frequency scale the directional baffle type speaker has a half octave greater frequency range than the horn type and about Vs octave more at the higher end.
1 WOLFF AND RINGEL: Eng. (May, 1927).
"Loudspeaker Testing Methods," Proc. Inst. Radio