Amplification: Turn it up, or turn it down?

Amplification is a hot-button subject for opera lovers, about the biggest no-no there is. Opera is supposed to be about the trained voice moving, unamplified, across the space of a theater, conveying pure emotion.

The facts are somewhat different. For at least 50 years, amplification has regularly been used in opera houses for oracles and offstage voices. It has also been used to transmit the sound of the orchestra to the singers, and vice versa, and to circulate the sound of the ongoing performance throughout the backstage area.

Some recent operas, like John Adams's ''Nixon in China," were written for amplified singers; there is no way the singers could be heard over Adams's constantly churning orchestration. That was a controversial step in itself. What raises the ire of operatic purists, however, is the electronic manipulation of performances of works not written with amplification in mind -- even though it is often necessary in venues that weren't built for the special acoustical requirements of opera.

Rumors have swirled for years about amplification at the Metropolitan Opera, although the company swears it doesn't use it in Lincoln Center. It certainly did use it back in its touring days, in places like Cleveland's 10,000-seat Public Auditorium and in Boston's old Hynes Auditorium. The New York City Opera, performing in a theater built for ballet, now has a system involving more than 200 speakers. Sarah Caldwell regularly employed it in the Opera House, although her rule was that if anyone noticed it, there was too much.

Carole Charnow, executive director of Opera Boston, says that the company has used amplification only in ''Nixon." Jenny Kelly, manager of the touring Teatro Lirico d'Europa, says the company has never used amplification in this country, but they are considering it for at least one of their most problematic venues (not in Boston).

The Boston Lyric Opera used some sound enhancement for its production of ''The Little Prince" earlier this season to help the voices of the young performers and to balance the Pilot with the boy sopranos. And the company has now decided to experiment with more systematic enhancement in certain areas of the Shubert Theatre; the first experiments were made during Tchaikovsky's ''Eugene Onegin," which closed Tuesday night.

The Shubert presents acoustical challenges because it was built primarily for spoken theater, not for opera. The elliptical auditorium does not diffuse natural, unamplified musical sound evenly throughout, and there are special difficulties for seats under the mezzanine and balcony. The sound is also affected by the stage setting -- back walls and hard surfaces work best -- and by the positions of singers and chorus onstage.

According to the company's music director, Stephen Lord, the Lyric has been talking for years about how it could improve the public's experience. ''It made sense, after bringing in equipment for 'The Little Prince,' to begin an experiment," Lord says. ''What we want to accomplish is for everyone who buys a ticket to have the same musical experience."

The system now is very simple: three sets of mikes on the stage floor that project sound through speakers on the sides of the boxes and across the rim of the mezzanine. The soundboard takes the space of 12 rear-orchestra seats, so the company relocated those subscribers.

''We are not talking body mikes here, and we are not using a Broadway system which would make 'Onegin' sound canned, like 'Rent,' " Lord says. ''And we are certainly never going to cast people in roles they couldn't sing without a mike. The idea is not to amplify the sound, and the last thing we want is for a performance in the theater to sound like something on your home stereo. The enhancement we used for 'Onegin' didn't reach anyone sitting in the first 15 rows or up in the balcony. What we want to do is to aim the sound at places in the auditorium that it doesn't completely reach, where the audience doesn't receive a full sound picture."

Listening to ''Onegin" from three different positions Tuesday night was instructive. The best sound, by far, was high up in the last rows of the balcony -- just as the Family Circle, the topmost balcony, is the best place to hear performances at the Met. From the balcony you could hear the richness and detail of Tchaikovsky's orchestration, balanced with the solo voices, which had a remarkable fullness and presence.

The rear of the mezzanine was much less satisfactory; the enhancement didn't seem to reach that far back, and the sound was dull, even muffled.

The rear of the orchestra, which used to sound equally dull, has now come alive. The balance seemed a little artificial -- voices dominating the orchestra, as they do on most operatic recordings -- and directionality was an issue. From a right-side seat, the offstage voices of Tatyana and Olga in the opening duet appeared to be coming from stage right, but moments later, the singers emerged from the left, where they had actually been singing.

The chorus was usually at the rear of the stage and therefore wasn't picked up by the mikes as clearly. But the whole performance of the first act had a palpable presence.

''What we are after is that sense of presence throughout the auditorium," says company managing director Janice Mancini del Sesto. ''The sound enhancement should never sound as if it were there -- once it does, we have failed. So far it is an experiment, and it will be a different experiment for our next opera, 'Flight,' which doesn't have a chorus, but which does have a lot of percussion in the orchestra."

Lord says, ''We want to spend a couple of years trying out various approaches and then decide whether or not we really want to go ahead with it. Or not -- we might just stop it at any point."