That's the word playfully coined by theater consultant Joshua Dachs to describe the still-nameless science of how a performing arts venue ''feels.''

Tongue firmly in cheek, he mentions other options.

Paying tribute to Thespis, believed to be the first actor of ancient Greek, Dachs comes up with ''thespis-ionics.'' Then he hits on ''raumgeist-ology,'' based on the German word ''raumgeist.'' That translates as ''spirit of the space'' and is related to the more familiar ''zeitgeist,'' which refers to ''spirit of the times.''

The essential point is that Dachs — unlike his counterparts in acoustics — has no absolute, high-sounding term for what he does. And that's a bit inconvenient, since theater planning and design are a thoroughly critical element of the Nashville Symphony's future concert hall project.

Symphony hall planners hired Dachs even before they hired acoustician Paul Scarbrough or even the chief architect, David Schwarz, and Dachs has worked closely alongside that pair to give shape to Schermerhorn Symphony Hall, a 1,886-seat neoclassical structure destined for the city-donated lot bordered by Third and Fourth avenues and Demonbreun Street.

In town the other day — only eight months ahead of the scheduled groundbreaking — Dachs sat down with The Tennessean and explained what he does and how he came to do it. His view is that the way a venue ''feels'' is, in the end, ''what it's really all about.''

''It sounds a little bit touchy-feely, but you really do walk into a room and it feels a certain way. The seating capacities might not even be that different between two rooms, but they feel that different. That's a lesson I learned when I was 17.''

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A native of New York City, the 46-year-old Dachs grew up playing the violin. He attended the New York performing arts high school that inspired the film Fame and was fortunate enough — while still a teenager — to perform eight times in storied Carnegie Hall and six times in Avery Fisher Hall at Lincoln Center.

''It's a pretty impressive thing, especially when you're of an impressionable age,'' Dachs said. ''When you walk out on the stage (at Carnegie) and see that beautiful room wrapping around you and realize that Tchaikovsky conducted the first concert there, you know you're standing on pretty hallowed ground. ''That left a big impression on me.''

Opting not to pursue the violin as a future profession, Dachs ended up an architecture student at Cornell University, where, by his second year, he had developed an abiding interest in building sets for the theater department. That soon connected with an interest in lighting design, which led to a summer internship with New York's Jules Fisher Lighting, where he has remained ever since.

''It could not have been a better background,'' Dachs said of his training. ''Somehow I managed to stumble on to the firm that did exactly the things that my life had accidentally prepared me to do.''

Today, Dachs has lent his own name to the firm, now Fisher Dachs Associates, and helped plan and design hundreds of performing arts buildings, including Fort Worth's Bass Performance Hall as well as the renovated Severance Hall, home of the Cleveland Orchestra.

Both of those undertakings, incidentally, also involved Schwarz as architect, so the Nashville project again brings the pair together.

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Performing art projects, Dachs has discovered, are ''probably the most interesting and complex projects in the world. If you think about it, the layers of complexity are truly astonishing,'' and in some cases Dachs' involvement begins with urban planning and the most basic question of where to put a venue.

Ultimately, though, it boils down to this: ''It has to sound good, it has to look good, and it has to feel right. And that is a fascinating problem.''

Working closely within exacting parameters set by both the acoustician and the architect, it has been the job of Dachs in Nashville to come up with a basic design strategy that serves, as well as possible, everyone's sometimes conflicting needs in this $120 million project.

Within the building but outside the main hall, Dachs must find the best possible placement, size and shape for such diverse spaces as conductor Kenneth Schermerhorn's suite (with sufficient room for a piano and other amenities), storage for the percussion equipment, even a catering pantry for the donors' lounge.

Within the hall, expected to be one of the most acoustically impressive spaces anywhere, Dachs must resolve yet another range of challenges, such as how best to align the balconies, how many rows of seats to install, where to put the wheelchair positions and where to place the doors to the upscale boxes on the lower tier level.

''It's a constant process of refining,'' he said.

More subtle but supremely important choices involve designing the lighting for the stage, which in this case must suit a classical concert but also be appropriate for the symphony's own pops events as well as other amplified, more rock-style concerts. In fact, Dachs predicts, Schermerhorn Symphony Hall will stand out worldwide as a venue where there is an unusually high sophistication of lighting, including robotic fixtures borrowed from the technology of the entertainment world.

A main goal, of course, is to create great sightlines that ''get people as close to the action as possible.''

''There won't be a bad seat in the house,'' Dachs said.

A main emphasis is on variety. There are those who think the best sound is from the back of the top balcony, and even those seats will boast grand views of the entire scene, he said. Other patrons ''who want to see the sweat on the brows'' will be able to get very close, including up on the stage itself. That's where five rows of choral seats will be installed to put viewers face to face with the conductor — a unique view for audiences at live concerts.

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Dachs estimates that the design process — which accounts for more than half of his overall contribution — will be wrapped up by Christmas. Beyond that, he will remain on board to deal with any issues that arise during the long construction process.

The current plan is for the hall to open in the fall of 2006. Though still more than three years away, for area music lovers that must ''feel'' pretty good.

Symphony hall seats on wheels

One thing other than the promised world-class acoustics that Nashvillians may come to admire in their new symphony hall is — perhaps unexpectedly — the main floor.

The unique feature isn't simply the fact that the 34th (and last) row of the upwardly sloping orchestra level will rise nearly seven feet above the first row.

No, the rather bizarre thing about Schermerhorn Symphony Hall is that the mere pushing of a few buttons will — within a mere two hours — remove all seats from the main floor and replace them with a wide-open space that's perfectly flat and suited for everything from banquet dining to ballroom dancing.

This remarkable ''flat floor feature,'' as it's simply known, is a feat made possible by what amounts to a technological marvel. It turns out, says theater planner Joshua Dachs, that the rows of chairs sit on a series of eight platforms set on wheels, with the section nearest the stage actually positioned on top of an elevator of sorts.

Once the electronic motors are put in motion, the first section drops down to the basement level and is moved back into a storage position. Meanwhile, the sections on the floor upstairs shift forward, one by one, to that elevator shaft, where they in turn are brought below. What remains above after the last section has moved to the front and dropped into the basement is a flat floor that the symphony envisions for many uses.

Elsewhere in U.S. and Europe, Dachs says, there are only a few venues with some version of this feature, but none as sophisticated and simple to use.