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June, 1930] LOUD SPEAKERS AND SOUND REPRODUCTION 619
In addition the claim for power efficiency ratio of the horn type speaker to flat baffle type of 10 to 1 refers to a single cone in a flat baffle. In practice cones are never used this way in theaters, being either used in multiple on a flat baffle or, as is commonly the case, being set in a directional baffle. Either of these setups results in a marked increase of efficiency. A comparison of a horn type speaker with a single cone is thus not representative of the relative characteristics of standard apparatus.
The radiation resistance characteristic shown for a horn type loudspeaker with a 50 cycle cut-off is not typical of the horns employed in practice. The construction of a horn with so low a cut-off is very expensive and the size of the horn would probably be such as to make it too large for the average theater. Aside from these considerations, the smooth cut-off shown is attainable only with an infinitely long horn, that is, attainable only with the unattainable. The frequency characteristic of a finite horn always exhibits horn resonances such as those which appear on the actual horn characteristic given in Fig. 4. In addition, as has been shown above, considerations of efficiency favor the horn type of loudspeaker only to a slight extent.
CONCLUSIONS
The above results can now be summarized as follows. In power handling capacity the two speakers are about the same. In efficiency the horn type speaker is somewhat superior. The directional characteristics of both types are satisfactory. As regards frequency response characteristics, the directional baffle type speaker is markedly superior to the horn type in the reproduction of both speech and music. On the basis of these factors it appears quite conclusively that for theater reproduction, of the commercial devices in use at the present time, the directional baffle type loudspeaker yields more satisfactory
results.
DISCUSSION
MR. RYDER: Does this paper deal with two types of speakers driven by the same motor or with each of the speakers as a complete unit?
MR. MAI/TER: In considering the reproduction of speakers one cannot consider merely the characteristics of the component parts but must consider the characteristics of the reproducing system as a whole, since the various units exercise an influence on each other. The purpose of this paper has been to compare the characteristics of the two most widely used types of complete units. As I pointed out, on the basis of the measurements the directional baffle type speaker is the louder. The directional baffle and the horn type do not allow the same driving unit to be used owing to differences in construction.