Motion Picture News (Oct-Dec 1930)

86 Million Picture N e iv s October 4 , 19 3 0 Better Acoustics Boost BoxOffice; Speech Intelligibility a Big Factor Public Demanding Better Quality of Sound, Acoustics Engineer Declares; Explains Methods of Controlling Volume By S. K. WOLFE Head of Acoustical Dept. Electrical Research Ni IW that the box-office is being affected by the intelligibility of speech in the theatre, the exhibitor has become more concerned about the acoustic quality of his theatre. The public is no longer willing to pay for a sound picture that is not intelligible and presently they will be demanding an even better quality than what may be termed as "commercial sound," today. There is still, however, a surprisingly large number of exhibitors who do not appreciate what box-office value better acoustics have. Sound is a very comprehensive term — it applies to anything that is audible. Since in the theatre we strive for something more than mere audibility, the exhibitor must learn to differentiate between good and bad sound. Speech and music differ in aim as well as in character. Speech is a means of communication while music satisfies a less obvious need. The former is practical and the latter is artistic. Accordingly, speech permits an examination on an efficiency basis. Music is judged by its pleasing quality. The primary consideration of speech is understandability and while tonal quality is very important, it is of a secondary order. Rating by Percentage It is the writer's intention to limit the scope of this article to the intelligible recognition of reproduced speech. We can discuss this subject in terms readily understood by everyone, namely, percentages. A theatre can be rated in the percentage of intelligibility of speech which is an index of how difficult it is for the patrons to follow the story from the spoken words. Telephone engineers have found that a good measure of the efficiency of a transmission system is in the percentage of disconnected, meaningless syllables that can be understood through it. This is called an articulation test. An articulation test of normal speech direct from speaker to listener under perfect conditions gives 96 per cent. If there is any doubt in your mind that speech cannot be transmitted 100 per cent under ideal conditions, try this simple test. Ask your listener to close his eyes so that he may not read your lips. Then you say the following words once each — map, Nat, Mack, nap, mat and nack, and ask him to write them down as you say them. Providing you do not unduly emphasize the final consonant of these words, you will find that one or more of them have not been understood. This gives you an idea of the difficulties encountered in speech transmission. The loudness with which sound equip ment is operated is an appreciable factor in the intelligibility of the resulting sound. There is a fairly broad range of volume about equivalent to the volume used In average conversation, for which there is no depreciation in intelligibility. However, as tests have shown, if the loudness is somewhat greater or some S. K. WOLFE what less than the conversational loudness, we can expect a reduction of articulation of one to five per cent. Extraneous Noises Another factor influencing the intelligibility of speech is the amount of extraneous noise present. Audience noise is of two kinds. The first includes whispering, coughing, laughing, rattling of programs, etc., and is not controlled by the exhibitor. The other, scuffling of feet on concrete floors, is controllable and eliminated with the use of carpet". Further noise is often introduced into a theatre by and through the heating and ventilating systems, and street noises sometimes enter through this channel. This, too, is controllable. Tests have shown that if the aggregate noise is 20 per cent, as loud as the sound, the articulation will be reduced 10 per cent. Excessive reverberation is still another factor tending toward decreasing the articulation in the theatre. If, in any given theatre, the reverberation exceeds by two seconds a certain optimum value, a reduction of 10 per cent in the articulation results. It can be readily seen that this condition is often encountered in houses not properly treated acoustically when the audience present is small. There are two more factors to be considered before we can round out our estimate of the probable articulation of the theatre, and these are the percentage reduction necessary on account of the recording and on account of the reproducing system. Since the articulation rating for speech under the best conditions from the original sound source is only 96 per cent, let us assume that the best possible recording and reproducing would be 95 per cent each. Sound Ratings To sum up these reduction factors and to get an idea of how a theatre would rate under the conditions that I have outlined above, we get the following: Percentage articulation of original speech under perfect conditions... 96 ♦Percentage reduction due to incorrect loudness 5 ♦Percentage reduction due to extraneous noise in theatre 10 ♦Percentage reduction due to reverberation 10 Percentage reduction due to recording 5 Percentage reduction due to reproducing 5 ♦Controllable by exhibitor. Applying the above listed reductions to to the original 96 per cent in the regular commercial method of applying discounts, we find the resultant percentage articulation to be 67 per cent. Extensive tests by Dr. Fletcher of the Bell Laboratories have enabled him to draw a curve showing the relation between the percentage articulation of meaningless syllables and the resultant conversational efficiency in which the listener has the aid of context of the sentences in which the syllables are found. From this curve we find that in a theatre having an articulation rating of 67 per cent, the conversational efficiency would be 90 per cent. This means that the patrons would miss about 10 per cent of what was going on, which would keep them under a continuous strain to try to make it out. This strain is perhaps not conscious but does interfere with the ease and comfort of the audience. Loudness of operation, extraneous noise, and reverberation in the theatre are controllable by the exhibitor in ways described above. In addition to these measurable fac(Contimicd on Page 100)