Adjustable acoustics fit variety of music

Complex, sometimes unseen acoustical elements will guide the sound quality of Miami's new John S. and James L. Knight Concert Hall.

by Fred Tasker / The Miami Herald
August 17, 2006

When an orchestra plays in the Carnival Center's concert hall, it sends out powerful sound waves not just forward, the way the instruments are pointing, but in all directions.

And for years, acousticians Russell Johnson and Tateo Nakajima and their Artec firm have been working on an acoustical system to blend those waves, seeking the balance of clarity and complexity so a true, undistorted sound reaches a listener's ears.

''What the audience hears is both the direct sound and the sound that is reflected from every surface in the room,'' says Nakajima.

That includes natural surfaces -- walls, floors, ceiling, seats, even audience members. It also includes ''adjustable acoustics'' elements that Artec has built into the hall so it can be used by a hundred-piece orchestra one day, a chamber quartet the next.

The elements include the acoustic canopy, reverberation chambers, acoustic drapes and an acoustic gap that separates the audience chamber from the noise of the outer building.

On Friday, the Cleveland Orchestra begins three days of private rehearsals, playing while Artec's experts fine-tune the hall.

The process will continue after the orchestra finishes on Sunday, right up to the hall's October opening and beyond, using jazz groups, Latin ensembles, the Master Chorale of South Florida, the South Beach Chamber Ensemble and others.

Even on opening day the tuning process will be less than half-done, Nakajima says. ``It takes 12 to 24 months to adjust a hall.''

Not all concert halls are adjustable. Disney Concert Hall in Los Angeles has ''fixed'' acoustics, built in by acoustician Yasuhisa Toyota and adjusted once -- for the Los Angeles Philharmonic. (The fixed acoustics limit the ability of other groups to play there.)

In Miami's adjustable system, the reverberation doors open onto a vast, empty chamber stretching two-thirds around the room. With a full orchestra playing, the doors are open to let the sound waves enter the chamber, reverberate inside and come back out. They arrive at listeners' ears a millisecond later than the sound waves coming from the orchestra -- long enough to create complexity, but not to be perceived as an echo.

''Even when the music stops, everybody's holding their breath, and you still hear its reverberation in the air,'' says Nakajima. 'That's called the `tail.' You only get it in a really good hall.''

When other groups perform -- a solo pianist or a rock band -- the hall's acoustics are adjusted.
For the pianist, the acoustic canopy would be lowered, in order to distribute sound more directly and to create more visual intimacy in the 66-foot-high room.

When an amplified band plays, the canopy goes into the ceiling, three big banks of speakers descend above the stage and heavy, motorized velour drapes descend in front of the reverb doors to muffle the sound waves. In Miami's concert hall, two levels of balconies continue around the back of the orchestra.

They can seat a choir of 200, lifting the choir above the orchestra so they can be better heard. When there's no choir, the audience can sit there.

''A lot of audiences love it,'' Nakajima says. ``The sound can be excellent. And they can see the conductor's face.''

With an infinite number of settings of the various acoustical elements, Nakajima says performers usually don't have to tune the hall to each group.

``They usually settle on just four or five standard ones -- for solo performance, string quartet, jazz band, 110-piece orchestra, heavy-metal rock band at full amplification. It's like giving a painter different-sized canvases.''