Halcyon Days

Article by Keith Yates
Stereophile Guide to Home Theater, September 1999

Author's Note:
The article reprinted below is the full-length, uncut version of a sidebar I prepared to accompany a feature article on the Halcyon Home Theater that appeared in the September 1999 issue of SGHT.
Due to space considerations, some of the original content was necessarily left out.

The word can be traced to the Greek goddess of the sea, Alcyone. In time "halcyon" became synonymous with the kingfisher, fabled to have the power to calm the winds and waves during the winter solstice, when it hatched its young from a nest on the water. The seven days before and after winter solstice are still called "halcyon days," as are any times of peace and tranquillity.

True to its storied roots, the Halcyon Theater is a quiet refuge at the water's edge-in this case, on the third floor of a 200-hundred year old Georgian colonial-style home on the Tred Avon river a few miles upstream of the Chesapeake Bay. Its owners dreamed of carving out a weekend escape from their busy, Washington D.C. lives, a tranquil space to let their fantasies take wing.

A ten month undertaking, the project started with a phone call from Tim Rooney of All-Around Technology, Inc., a prominent A/V design and installation firm in Bethesda, Maryland. "This is my fourth project with this client," he said. "He's a wonderful, no-nonsense guy who's beginning to suspect that the gear he's buying is only as good as the room we put it in. He'll take the same show-me-the-numbers, bang-for-the-buck approach with the acoustics as he has with the Proceed electronics and Triad speakers. He'll read your articles, do his own research, ask a ton of questions. He's terribly refreshing. Do you have time for this kind of hands-on client?"

So began a project that brought together an owner's passion, an architect's inspiration, a builder's pride and joy, an A/V firm's management and installation finesse and, from the other coast, my drawings and specifications for the acoustical infrastructure to give shape to the magic we wanted to create together.

Shell Games
An extensive remodel project, Halcyon presented an immediate opportunity for the team to collaborate in reshaping the room's shell or "footprint" to improve its bass response. It's tough to get a room with roller-coaster reinforcement of the bass spectrum ever to sound like the real thing, no matter how much you spend on subwoofers or how aggressive your after-the-fact bass-trapping or knob-twiddling. Change the height, width and/or length and the effects show up in the room's modal profile, that is, its distribution of drone-prone standing wave frequencies. Rooms whose axial ratios (height to width to length) are on the "best dressed" lists (like Louden's 1 : 1.4 : 1.9 or Sepmeyer's 1 : 1.14 : 1.39) or fall within the "Bolt amoeba" tend to stand out from the crowd, with modes spread out such that each one-third octave band has the same or a greater number of modes than the band just below it.

It's easy to be seduced by famous ratios or impressive-looking printouts, but, like the glittering seductions in countless operas, they can be a prelude to a darker reality. Peek behind the spreadsheets and graphs and you'll discover that, for computational reasons, the calculations rest, uneasily, on a handful of fundamental assumptions, including one that forces the room to be a simple, shoebox-shaped affair with no "ells," clipped corners, pitched ceilings, soffits, raised seating platforms or other asymmetries or "flaws."

The real world isn't always so tidy, and Halcyon was no exception: Framing considerations forced clipping the two front corners at a 45-degree angle, and a similar, but more extensive excision down the length of the room at ceiling level, which turned it into something of a cathedral-type ceiling with a flat-top haircut.

The conflict deposits the room designer at a crossroads: How to deal with the fact that the room can't possibly conform to the sanitized shape the software requires before it can start crunching the numbers.

A 'Real Man's Projector Cowl'
Like any thoroughbred CRT projector, the Runco DTV-1000 makes a beautiful image … and a lot of racket. To keep fan noise from trampling soundtrack details—the rustling leaves, creaking floorboards and suspiring humans that give movies texture and a sense of place—Halcyon needed a "real man's" projection cowl, not a wimpy box with a little wad of fiberglass inside. At over 500 lbs., the resulting structure is based on careful management of the optical path, noise emissions and thermal environment, which never exceeds 78 degrees Fahrenheit. The angling of the bottom of the cowl was part of a larger strategy to improve dialog intelligibility at the seats against the rear wall.

I chose to model the theater several different ways, beginning by ignoring the clipped corners and ceiling line, that is, by assuming that the room was a geometrically primitive affair comprised of six unbroken planes accounting for the four walls, floor and ceiling. Room dimensions fostering the smoothest pattern of axial, tangential and oblique modes were printed and saved, and then a new round of simulations launched, based on what might be called "dimensions of volumetric equivalence," an approach that treated the ceiling height, for example, as the distance above the floor that a flat, planar but nevertheless imaginary ceiling would have to be to yield a room with the same cubic footage as the real room. The room's "primitive" and "equivalent" dimensions were adjusted and calculated an inch at a time and repeated until the regimen turned up a handful that passed muster on both test methods. Halcyon's sweepstakes winner turned out to be a room with a ceiling height of 10' 7", measured from the floor in front of the screen to the flat portion of the ceiling, a width of 16' 1-1/2" and a length of 23' 4".

Wall Construction
It has become commonplace for A/V designers to prescribe double- or triple-layer wallboard constructions in home theaters. The reasoning goes that beefing up the walls increases transmission loss (sound isolation) from adjoining rooms (it does, but usually only slightly) and that the added stiffness improves bass response (it occasionally does, but just as often makes it worse by exaggerating the room's modal idiosyncrasies).

Whatever the rationale, stiffening the walls forces the conscientious designer to turn to after-market pressure traps, diaphragmatic panels or resonant absorbers—devices that can chew through bass, the budget and bags of real estate—to balance the room's low-frequency reverberation time with its midrange- and high-frequency RTs.

As it turns out, the natural "give" in a sheet of standard half-inch gypsum material can be quite useful in controlling excess bass energy in residential-size rooms. Halcyon's wall specs thus called for a single layer of half-inch USG-brand Type X Sheetrock on wood studs at 16-inch spacing.

For additional low-frequency absorption the painted wood wainscot ringing the room's perimeter was recruited to function as a diaphragmatic absorber. Varying the volume of the trapped air cavity behind the bead-board facing enabled the wainscot to be tuned to control specific regions of the bass spectrum. The rear wall wainscot, for example, was detailed to soak up some of the 48Hz axial (2,0,0) mode associated with the length of the room, while the side wall wainscot addressed the 71Hz lateral (0,2,0) mode at the rear half of the right wall, with supplemental absorption "bracketing" this mode (65Hz treatment at the left wall and a smaller section of 79Hz treatment on the right wall) to account for the slight but inevitable disparity between a textbook formula and real-world, as-built performance.

These low-cost and essentially invisible measures contribute to good spectral balance in the room's natural reverberation, readily perceptible as enhanced articulation and punch throughout the bass range.

A Sense of Place
As any two-channel audiophile can attest, getting the most out of a playback system often comes down to tuning the locations of the speakers and listening chair in the room. With its clutch of sound sources (speakers and subwoofers) and multiple fixed elements (cabinetry, video screen, bolted-down seats etc.), the home theater is usually less accommodating of placement tweaks than an anything-goes music-listening space. Getting the most from speaker and listening layouts in the home theater thus requires careful planning before the speakers are even ordered.

Specifying Halcyon's exact speaker locations began by defining the allowable space a speaker could reasonably inhabitfor example, the center of the left channel's woofer must be more than 28 and less than 59 inches above the floor, between 22 and 37 inches from the left wall and between 14 and 19 inches from the front wall. All speakers, subwoofers and the primary listening location were similarly "bounded." The computer was then instructed to pick a layout combination and simulate the resulting net acoustic behavior in the 20-300Hz range both modally and in terms of speaker-boundary interference response (SBIR).

In Halycon's case, the process chewed through about 12,000 layout combinations of the 11 speakers and "money seat" locations before exhausting all possibilities. Ultimately, the layout that best met my criteria presented new challenges of its own, as neither the left nor right Triad InRoom Platinum subwoofers could physically inhabit their prescribed locations due to a conflict between their enclosures and those pesky clipped corners at the front wall. The solution: Have Triad fabricate a pair of custom enclosures with the same internal volume but with clipped corners of their own to enable us to get the acoustic centers of both subwoofer drivers in the optimized places.

Acoustic Treatment
With the room's envelope finalized and the speaker and listener locations nailed down, the creative part of the acoustical program could begin: the shaping of the room's sonic personality by controlling how the room surfaces reacted to sound energy impinging on them.

In addition to enjoying a broad spectrum of movie genres, Halcyon's owner wanted to be able to listen to classical music CDs and chat and entertain in the space comfortably without the dead, vaguely unpleasant effect often encountered in "acoustically treated" home theaters. (These sensations, which range from a blasι "I'm not swept away by this movie" to outright "turn it off, it feels claustrophobic in here!" are traceable in part to poor correlation between the visual and auditory reports that get routed to the deep layers of the superior colliculus, a structure in the brain where multi-modal sensory integration takes place.) The owner also had high expectations for sound quality in the far rear of the room.

"Oh, and one last thing," he slipped in. "My wife absolutely insists that we keep that big round window on the back wall!" It was an understandable request, as the window formed an important part of the home's curb-make that waterfront-appeal. Construction supervisor Tim Saulsbury and Graybanks Design Group responded with a clever detail to conceal a motorized black-out shade in the window's casing and to accommodate my request for a new 4-foot diameter sheet of glass, spaced a few inches in front of the existing window. This new pane was canted to steer sound upward, toward the acoustic treatment on the ceiling, which was designed to redistribute the energy spatially and temporally to enhance the sense of envelopment.

General layout of diffusors, reflectors, frictional absorbers, pressure traps and other acoustic elements was guided by a desire to suppress the kind of reflection patterns that corrupt timbral and spatial fidelity in untreated rooms, while maintaining the high-frequency life and sparkle that treated rooms often lack. Exact positioning was then fine-tuned by computer ray-tracing, which maps the pathways—e.g., speaker to wall to listener-sound takes in a room. Acoustic devices were mounted to the face of the gypsum board walls and ceiling, concealed behind acoustically transparent fabric stretched and tensioned on a Novawall track system that enables the material to be removed for cleaning, access, etc., and reinstalled.

The "space budget" between fabric and wall surface was fairly typical for projects of this scope--five inches on each of the side walls and ceiling, eight inches on the front and back walls, and about 22 inches in the room's four corners.

Team
Ask anyone involved in a successful home theater or screening room project and you'll likely hear the phrase "team effort." In Halcyon's case, the working team was unique in that it included the owner, whose drive for excellence was such that he tackled learning CAD software so he could stay "in the loop" with, and even direct, the rest of his team. It's a rare commitment … but entirely consistent with a project whose very name has exuded a magical resonance since antiquity.