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Lines Of Sight And Acoustics

( Originally Published 1916 )



FROM the theatergoer's standpoint the best seat is that from which he may see and hear well. One may not see well if line of sight is obstructed by bobbing heads or posts —although in modern theaters that have their balconies built on the cantilever principle, there are no posts—and one may not hear well if noise in the street drowns out voices on the stage. So the definition is quite inclusive. However, it carries these corollaries : a patron must not be blind or hard of hearing, and he must understand the language in which the play is rendered—these if he would enjoy advantages of the good seat to the full.

Necessity of a direct line of sight from a theater seat to the stage, presents a problem comparatively easy of solution—although it is rather a range of sight than a single line. If one might have an " ideal " theater—which, of course, one never may for sheerly practical reasons—one might wish for seats where occupants not only could see both sides of the stage, but also could not see too far into the wings. In interior scenes the view is effectually cut off by the side walls of the settings; but in exteriors, stage mechanism is too frequently revealed, or else too obviously screened with makeshift scenery. For this reason, in an ideal theater, there are certain " dead-lines " beyond which seats may not be placed. These are indicated in the diagrams printed at top of the next page.

It would not help matters much to extend the scenery further into the wings and have seats all the way front, because the stage space to be comprehended is just the zone of action. To be sure, no manager is going to let all that space between the first row and the stage go to waste; he prefers to mask the wings arbitrarily. There is, however, a tendency to throw the stage picture further back from the eye with a forestage, although not for the purpose of hiding the wings.

Interference of heads in front is reduced by placing seats directly behind divisions between chairs in the row ahead, and frequently eliminated by ranging the seats on a sharp incline. In New York, the law forbids a fall of the orchestra floor of more than three inches to the foot, but a sharper " rake " is permitted in balcony and gallery. In the large cities there is scarcely a structural point with reference to theaters that is not fully covered by building or fire laws.

THEORY OF ACOUSTICS

Passage of sound from the stage to the seat is beset with many difficulties. It is such a tricky subject, in fact, that most theater architects let it severely alone and build their houses on seemingly tried and proven plans without inquiring into scientific whys and wherefores.

We have in America one of the greatest constructive authorities on theater acoustics in the world—Dean Wallace C. Sabine, of Harvard. He has made his findings public on many occasions for the good of the theater in general. His views were expressed at considerable length in the American Architect of December 31, 1913.

He takes his text from Vitruvius, the ancient architect, who said that for a theater, a place must be taken where the voice falls softly and not so reflected as to produce a con-fused effect on the ear, natural obstructions being interference, reverberation, and echo.

" Just as a tidal wave, a storm wave, or a ripple may be made to separate and recross by some obstacle around which it defracts, or from which it is reflected, and, recombining, produce regions of violent and regions of minimum disturbances," says the Dean, " so sound waves may be diffracted or reflected, and recombining after traveling different paths, produce regions of great loudness and regions of almost complete silence. In general, the phenomenon of interference is produced not by the crossing of two waves only, but by the crossing of many, reflected from the various walls, from the ceiling, from the floor, from any obstacle whatever in the room, while other trains of sound are produced by the diffraction of sound around columns and pilasters."

As to reverberation, he says, " When a source of sound is maintained for a sufficiently long time (a few seconds ordinarily) the sound becomes steady at every point in the room. If suddenly stopped, it requires some time for the sound in the room to be absorbed. This prolongation is called reverberation." Of echo, he says, " If the source of sound, instead of being maintained, is short and sharp, it travels as a discreet wave, or group of waves, about the room, from wall to wall, producing echoes. The rapidity with which sound dies away depends on the size of the theater, on its shape, on the materials used for its walls, ceilings, and furnishings, and on the size and distribution of the audience."

Dean Sabine was called upon by Winthrop Ames to correct the echoes and interferences of the quondam New Theater. He succeeded so splendidly that when Mr. Ames prepared to build his own Little Theater, his plans were submitted to the Dean for criticism from the acoustical standpoint. And the Little Theater is therefore one of the most acoustically correct theaters in America.

Acoustics of a theater are now determined in advance from the plans, almost as readily as lines of sight; and the method of doing so is intensely interesting.

PHOTOGRAPHING SOUND WAVES

The process in favor is that known as the Toeppler-Boys-Foley method, devised by three authorities on the subject. First, a scale model of the projected theater is constructed. Sides of this are removed, and a sound is produced at that point corresponding to the acting zone of the stage. As the sound is passing through, the model is illuminated from one side by a fine and somewhat distant electric spark. After passing through the model, the light falls on a photographic plate placed at a little distance on the other side. This light is refracted by the sound waves, which act as their own lens in producing a photograph. The resultant picture shows a silhouette frame from shadows cast by the model; and all within this frame constitutes an actual photograph of the sound waves and their echoes. By taking a series of pictures at different times after the sound has been started, a complete record of the waves, their interferences and echoes, is obtained.

Through such analysis the new Scollay Square Theater in Boston was prevented from being acoustically faulty by a change in plan before any building operations were commenced. Minor adjustments are made in the actual theater after construction, for the scale model does not take account of seats, draperies, and so forth. These minor changes are commonly accomplished by placing reflecting walls and panels of acoustic felt—invented by Sabine himself—in various parts of the auditorium, removing heavy valances, rehanging chandeliers, and adjusting other details. There are architectural firms that make a specialty of acoustical correction.

Of the corrected New Theater, which, with its echoes, had been a target for much ridicule by persons who did not understand its problems, Sabine says, " It is safe to say there are few—possibly no modern theaters or opera houses —so free from this particular disturbance as the New Theater at the present time."

ACOUSTICAL CORRECTION

Sabine found the plans of the Little Theater, New York, well defined and presenting all points necessary for his profound consideration. It was designed, he was told, for production of plays which could be adequately rendered only by the most delicate shades of expression; it was to seat just less than three hundred, and all seats were to be as nearly as possible of equal excellence. The important assurance was given that every seat should be occupied at every performance. (Which indicates, parenthetically, another danger of empty theater seats.)

The Dean himself explains what happened : " The first sketch showed a slight reverberation; so the floor was lowered at the front, the ceiling was lowered, and the walls near the stage were brought in and reduced in curvature, with corresponding changes in architectural treatment. The rear wall was made straight; the side walls, near the stage, were curved. In order to still further reduce reverberation, and to break acoustically, the curvature of the side and rear walls, ` acoustic felt' was applied in panels—three panels on the side walls and seven panels on the rear wall." These panels, I may add, are hidden beneath painted tapes-tries.

When I issued a story from the press department of the Little Theater in 1915, declaring that in that playhouse the stage whisper had been perfected, I meant it. One can sit in the last row of the Little and actually hear a genuine whisper on the stage.



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