Motion Picture News (Oct-Dec 1930)

K/vtober 4 , 19 3 0 M o t i o n Picture N c zv s 111 Cones or Horns, Which is Better? {Continued from Page 85) horn type speaker is a serious defect. 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 baft'e type speaker was 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 straightahead 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 steps on the average gain control and is consequently of minor importance. The radiation distribution characteristics of both types of speakers as now used are sufficiently good to yield satisfactory results. These distribution characteristics are fairly uniform through angles of about 20 degrees to each side of the normal to the mouth opening. In the average size of theatre this is sufficient. In wider and larger houses, two or more speakers may be used, thus securing good directional characteristics as well as permitting an increase in the total amount of radiation as required by the larger size of the house. Xo accurate measurements were made with respect to this quantity. However, it has been our observation that similar houses require the same number of speakers of either type for satisfactory sound reproduction. This indicates that. in view of the somewhat greater efficiency of the horn type speaker, the directional baffle type speaker has the edge in respect to input power capacity. This is what might be expected from the fact that the radiating surface of the directional baffle type speaker, i. e„ a cone, is much sturdier than the fragile metal diaphragm of the horn type speaker. Results in Theatres It is exceedingly interesting to compare the results obtained with both types of speakers on listening tests in theatres and see to what extent these results are explainable on the basis of the measurements described above. Comparisons of this sort must be made separately for both speech and music. If. in the reproduction of speech, we fix our attention upon the understandability only, we find that each of the loudspeakers is equally good. However, although speech on each of these speakers is equally understandable, the reproduction on the directional baffle type speaker is far more natural than on the Use Fader Cues IN the proper presentation of sound pictures the importance of the fader cue sheet can not be overstressed. Too often there is a tendency to ignore this important item and then blame the equipment for any reproduction defects which may occur. The cue sheet is a dependable guide to the projectionist in advising of changes in volume. It is far more efficient than the signal system by an observer in the audience. If you are not arranging fader cues on your programs you are overlooking a real bet in the proper presentation of your shows. horn type speaker. Reproduction on the horn type speaker has an unnatural quality. All voices sound very much alike whether of the same or opposite sex. Looking away from the screen makes it sometimes difficult to distinguish the sex, except from the context. Male voices, particularly, sound too high pitched and unnatural. These results are easily explainable on the basis of the obtained frequency characteristics. It is well known that the elimination of all frequencies below 300 cycles and above 4000 cycles exerts a negligible effect upon the understandability of speech. Since, on the whole, the response of the two speakers between these limits is the same, we would expect ;he understandability to be the same. This is what is actually observed. However, the characteristic frequencies of the speaking voice lie below 300 cycles. They center around 125 cycles for the male voice and around 250 cycles for the female voice. It is these "fundamental" frequencies which give to each speaking voice its individuality and distinctiveness. A lick or deficiency of the frequencies below 300 cycles will rob a voice of these characteristics. This accounts for the superiority in naturalness of speech reproduction on the directional baffle type loudspeaker. The response of the directional baffle type speaker, between 100 and 300 cycles, is considerably greater than that of the horn type speaker between the same limits. This is particularly true below 140 cycles. Around 100 cycles the difference in response is around 12 decibels. The reproduction of music is also adversely affected by the deficiency in the response below 300 cycles. Music reproduced on a horn type speaker lacks the fullness and depth apparent in the reproduction by the directional baffle type speaker. The complete reproduction of the lower register instruments is impossible on the horn type speaker. The result is that music loses its real quality and retains merely its melody. This is particularly true for music of a symphonic nature. In a recent paper certain statements are made in a discussion of horn and cone (or baffle) type speakers. The cone (or baffle) type speakers referred to in that paper are of a type wherein cones Matter Discusses Speaker Types are set in a flat baffle, a type which is much less widely used than the directional baffle type speakers. Some of the claims made for the horn type loudspeaker are not borne out by our experiments. Thus it is claimed that the horn type loudspeaker and flat baffle type of loudspeaker are equally satisfactory as regards frequency characteristics. This may be true in theory but tests of actual devices as used in commercial practice show that the upper and lower cut-off frequencies of the flat baffle type of loudspeaker, which coincide approximately with those of the directional baffle type using the same cone, are much more widely separated than those of the horn type loudspeakers. 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 theatres, 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 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 theatre. 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. 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 theatre reproduction, of the commercial devices in use at the present time, the directional baffle type loudspeaker yields more satisfactory results. Developing' Foreign Field Xavier de Nice, veteran export executive, has been appointed export manager for Electrad. Inc.. New York, manufacturer of radio and talking picture products.