Journal of the Society of Motion Picture Engineers (1930-1949)

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616 Louis MALTER [j. s. M. P. E. As regards uniformity of response the directional baffle type of speaker obviously has the advantage. Between 300 and 5000 cycles the response of the directional baffle type is slightly more irregular, but between these limits the variations in the response of the horn type are greater. Below 300 cycles, however, the horn type speaker is appreciably less responsive than the directional baffle type. As will be seen below, this deficiency in low frequency response in the horn type speaker is a serious defect. Efficiency. — In order to enable a fair comparison to be made between the frequency response characteristics of the two types of speakers, the response curve of the directional baffle type speaker was •//e«/V Tlf£ Lout>**e.#KeK snrAi. BIFFLC Trf>e »•« ^s••» FiteaueNer Cyetcj Pit Sfccva FIG. 5. Relative frequency response characteristics of two speakers. raised 7 decibels. In order to determine the relative average efficiencies of the two types of speakers the curve for the directional baffle type speaker was placed at its proper level, and the average response between its cut-off limits (90 and 6000 cycles) determined by means of a planimeter. The result obtained is 15.6 decibels. The average response of the horn type loudspeaker for the same input power and between the same limits is 18.3 decibels. The average straight-ahead response of the horn type loudspeaker is thus 2.7 decibels greater than that of the directional baffle type loudspeaker, for the same power input. This corresponds to a power efficiency ratio of 1.9 to 1.0. This difference corresponds to between 1 and 2