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" Intimacy "or " presence " will benefit from this recommendation. Good "intimacy " should give the impression to all members of the audience that the sound is emanating from the characters on the screen. This is primarily achieved by the reception of direct rather than reflected sound.
Closely associated with the reverberation-volume relationship is the ratio between volume and seating capacity. For good acoustic conditions the volume of the auditorium per seat of audience should lie between the maximum and minimum curves given in Fig. 6. If a greater volume per seat than that recommended by tion is likely to occur ; and if unnatural quality.
Fig. 5. Absorption at various Frequencies.
the curve be adopted, excessive reverberaa lesser volume, the sound will have an
Reflection Effects
When a sound wave strikes a wall or other object its energy is dissipated in three ways: it is partially reflected, transmitted and absorbed. In the case of surfaces large in comparison with the wave-length of the sound, the reflection is analogous to the reflection of light ; and the angle of incidence of the sound is equal to the angle of reflection. The relative amounts of acoustic energy reflected and absorbed by a material vary not only with the angle of incidence and with the frequency of the sound, but also with the nature and quantity of the material itself. Whilst it is possible only to double the sound energy at any one point due to a single reflection, the decreased level or cancellation effect can be infinite, and thus any absorption at a point of reflection will tend to decrease both the additive and subtractive components of sound, and thus minimize anv modifications of the characteristics of the direct sound.
The choice of the building materials ot the walls and ceilings and the natureof the furnishings have a large influence upon the acoustic conditions in the auditorium. The absorption coefficients of building materials vary greatly, and as will be seen in Fig. 7, each material has widely different absorption coefficients at different frequencies. Judicious choice of materials used is therefore necessary if the components of complex sound are to maintain their proper relationship. The materials selected should possess a smooth absorpFig. 6. Ratios of cubic feet volume per tion characteristic and Particularly with seat (maxima and minima.) adequate absorptivity throughout the
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