The tricky -- and costly -- art of making a theater sound right

Problem: What to do with a large theater that was designed (poorly) for the celebrated New York City Ballet, but also became the home of this city's second opera company, the New York City Opera.

It is a matter of record that the New York State Theater was ill-conceived from the beginning. Architect Philip Johnson used an acoustician who apparently felt Broadway-house sound quality was all a ballet company needed. When the New York City Opera decided to move from the New York City Center to the State Theater, the edifice was already complete. Not much could be done, even when it was discovered that, acoustically, the place was at best undesirable.

Across the plaza at Lincoln Center, the then Philharmonic Hall had had to undergo numerous changes to try to solve its own very poor acoustics. Eventually , in 1976 a major gift from Avery Fisher was used to gut and rebuild the hall under the guidance of Dr. Cyril Harris.

Mr. Harris has rightfully observed that the best halls in the world are shaped like shoe boxes and that the safest way to ensure good sound, therefore, is to copy that shape whenever possible. This, however, means that some 250 to 300 people have to endure limited visibility as a result. Harris was also consultant to the Metropolitan Opera House, which has basically fine acoustics, and the Kennedy Center Opera House, a particularly ugly theater with some of the finest opera acoustics in the world.

Well, wheels had been constantly turning at the City Opera offices, but no solutions ever seemed in sight because the money was not to be had. Beverly Sills, the current artistic director, once hinted that discreet amplification by microphone might be the solution, and a howl of protest erupted in the press.

Meanwhile, the company's young singers had nightly been pushing their tender young voices way out of shape in desperate attempts to be heard in a hall where sound evaporated through a gold-mesh ceiling and bounced against the side walls of the hall (muffled by an air-conditioning system three times louder than acceptable), and was swallowed up by the overstuffed theater seats.

Amyas Ames, director of the New York State Theater Project Committee, noted at a recent press briefing that ''New York must have the finest performing halls to achieve the excellence that is required of us (as the cultural capital of the land).'' In her quest to achieve that aim, Miss Sills was finally able to raise Theater viable acoustics for the first time in its 19-year history.

The finished product was shown off at the end of last month, making it the first in a series of six new or revamped halls nationwide to be ''unveiled'' this month. This project is, Mr. Johnson noted, essentially cosmetic, particularly since there was never any question of tampering with the basic (and to some unsightly) design of the theater itself. And Dr. Harris added, ''This is not a renovation - making a hall like new - or a restoration, but rather, a reconstruction.''

The final bill comes to nearly $5.3 million, but just what has been done? The meshwork ceiling has received 30 tons of plaster to provide a solid surface for sound to bounce from, rather than to pass through and become dissipated in the no-man's land between ceiling and the roof of the theater (Dr. Harris noted that the best sound in the theater had gone to that useless space).

Special polycylindrical diffusers were fixed to the walls of the theater so sound could not travel along the walls but would be broken up and dispersed evenly into the theater. (In older theaters the decoration and statuary performed this function. Here, the walls had been smooth.) These changes were executed during last spring's opera season, so, as Dr. Harris stated, ''it was apparent to anybody who knew the hall that voices were clearer and words were more distinct.''

The entire theater has been reseated with comfortable red-plush seats that are backed with wood in the acoustically correct style of today. The proscenium arch - a huge stage-floor-to-theater-ceiling concave affair - has been replaced by a convex, shiny gold-mesh one lowered in height to make room for a group of plaster panels extending up and out from above the arch to deflect sound from the orchestra out into the hall.

This was all done to control the manner in which sound decays in the theater. At this writing, the results of the complete job have not been heard in the hall. Audience members will have had the chance to judge for themselves as of last night, when the fall season opened with a new production of Lehar's ''The Merry Widow.''

Of course, the ballet will benefit as well. The newly expanded orchestra pit will make life easier for the players for both opera and ballet, and the new overhang will project the sound more satisfactorily into the theater.

Miss Sills recounted how New York City Ballet artistic director George Balanchine told her, ''If there is a need in this theater for one company, then there is a need for both companies.'' She continued, ''The opera company is forever in Mr. Balanchine's debt for his efforts.'' Miss Sills announced that a special event for both companies will honor Balanchine and the New York City Ballet Nov. 16.

A full row of seats was removed to enlarge the orchestra pit, which can now comfortably accommodate up to 80 musicians and, when needed, can squeeze in as many as 96. Those seats were not lost, however, for the new ones are a bit narrower - there are more to a row, with no net change in the number, 2,729.

Perhaps the best news of all was that the construction work was actually finished a week early - what we saw was a finished product - no scaffolding, only a few workmen working on auditorium lighting and cosmetic details.

Another change not visible from the audience is the new lighting board in the control room for stage and auditorium lights. Miss Sills added excitedly, ''It's a dream come true for an opera company to perform in a theater that sounds as good as it looks.''