MOVING PICTURES
Not only a reference-quality cinema, but moving seats too
While our main reviews in Sound+Image necessarily focus on equipment, we know full well that the room in which the equipment operates is perhaps the most important element of all — its shape, its acoustics, the ambient level of sound before you start cranking the gear. So it’s always a pleasure to cover a home theatre project involving Wavetrain Cinemas, because their designs deliver often-award-winning combinations of room plus equipment, all of which, in the final event, just disappears behind a full-blown home cinema experience.
And in this case, the experience is even more moving than usual, because five of the seven seats are equipped with D-BOX motion systems, described by their Canadian manufacturer as “the best non-distracting cinematic motion available in the world”, thereby carefully distinguishing them from the stomach-churning rollercoaster ride delivered by some rival systems. D-BOX chairs are actuated by codes which play in precise synchronisation with the movies, aiming to create an extra dimension of immersion. It’s hard to describe in words, but once experienced, ordinary static theatre can seem just a little dull by comparison.
The lucky owner of this home theatre had already experienced D-BOX, and had five of
the seven seats here so equipped largely on Wavetrain’s recommendation; the last two are D-BOX-ready so can be upgraded later. The main requests for the cinema were for a “reference-quality dedicated system” to be designed for a space which was currently a double garage under the house. The client already owned a couple of arcade gaming machines, so he wanted these incorporated into the space — along with a bar area using the available natural light.
Controlling the channels
Getting everything to fit while keeping the room proportionally effective was difficult, says Wavetrain’s David Moseley, but the final cinema room is a comfortable seven-seater with a 141-inch-wide (158” diagonal) screen and a hushboxed Sony 4K projector.
As for the audio system, given the size of the room it is perhaps a surprise to find a 16-channel system courtesy of the Trinnov processor delivering 9.1.6-channel sound to the Pro Audio amplifiers and speakers in the cinema. Overkill for the space? Not at all, says David Moseley.
“The channel count in a space this size allows a seamless sound field — the balance is beautiful,” he says. “But of course there are acoustical considerations in achieving that. My goal was a reverb time around 200ms, and we measured just under that in the final room.”
He detailed some of the treatment used to keep the room at that point between too ‘dead’ and too ‘live’.
“At first reflection points for the left and right front speakers we always diffuse the reflection for the main seats, so as to create a wide soundstage with plenty of life,” he says. “We’ve used curved diffusers to eliminate slap echo which can still occur on a Schroeder diffuser. Slap echo at ear level can become critical. The combination here of randomising diffusers for front left and right, with hybrid absorber/diffusers for the rear-wall first reflection points, eliminates this slap echo all the way down into the lower midrange, without taking out too much life from the room. Additional diffuser panels were added to control slap echo generally.
“Meanwhile for centre speakers we absorb rather than diffuse at the first reflection, so as to provide the best voice intelligibility and a really tight centre image. The ceiling also provides some absorption, but is primarily a bass trap.”
While aesthetic considerations set the style of the cinema room and its external bar area, the carpet was chosen specifically to allow further absorption down into the midrange.
“It’s got a 30% wool/rag underlay under a high quality wool carpet,” says Moseley. “This provides 22mm of absorption, along with the ceiling, so floor/ceiling slap echo is treated down to a very low frequency. The ceiling is also a general bass trap, using various slat sizes to allow a broadband bass absorption down to approximately 100Hz before rolling off. The side walls have bass traps also effective down to around 100Hz before again rolling off. But the main bass absorption for frequencies below 100Hz comes from the custom bass traps we designed into the floor seating platform by perforating the front edge and filling the space with absorption.”
The size of the room did, however, affect Wavetrain’s normal preference for treatment around the screen.
“We normally eliminate any comb filtering or diffraction problems off the edge of the front speakers by creating custom diffusers,” Moseley explained. “But here the cinema was too small, so instead we used absorption board as a baffle behind the screen. The difference to reverb time is around 50ms in a room this size, but it was a necessary compromise.”
Reference levels inside, silence outside
But there was another priority for the sound. Not only did it have to be up to Wavetrain’s usual reference standards inside, it had to be very well isolated from outside. This was flagged by the owner as a significant requirement, given he wanted to use the cinema late at night, and didn’t want noise complaints from the neighbours, who are relatively close.
“The main house construction was brick and concrete, so we had mass in the system,” explains David Moseley. “So our issue was therefore more to prevent vibration transfer. The budget didn’t allow a fully isolated structure, a floating floor or Resilient Mounts [furring channel fixing clips with a fastener that is isolated by acrylic pads] for the walls, though these were used for all speakers except the height channels.
“Instead we battened off the walls with timber battens — which also allowed us to level the walls and ceiling — and used cyclonic metal furring channels which are direct screw-fixed to eliminate rattles. Metal furring channels are a cheap way to help mitigate vibration transfer while also increasing the cavity depth. Two layers of board were used, with insulation — a first layer of plywood to provide a screw fixing all around the cinema, and a second layer of plasterboard, with Green Glue between as a dampening compound. Green Glue with masonry provides a great combination, delivering 70dB of attenuation.”
Paths were created for the ventilation ducts to ensure these did not void the sound isolation systems, while the key potential leakage point of the door between cinema and bar was custom-designed with commercial seals. Indeed Wavetrain treated the bar itself “as an air-lock to the rest of the house and the outside area, with a minimum of 30dB attenuation through the glass”.
Vibration isolation achieved! The cinema can be heard neither inside the main house nor outside, where the noise floor is high.
Staying cool
Wavetrain is renowned for the use of dedicated air-conditioning designed to be nearsilent, and non-obtrusive in terms of the room design. But here there was neither the budget nor space for a full ducted system; indeed there was an existing ducted system for the home above, which needed to be built around.
“It was difficult to get all ventilation done correctly without impacting the room,” admits David Moseley. “We core drilled the slab above and extended the pipework so we could move the existing ducted system up one level, which gave us much needed space back and eliminated it as a source of noise.
“Then for the cinema room itself we used a wall-mounted A/C fan coil, as they are available in very quiet units. A separate duct has been run into the bar area to allow the room to release pressure [since this is a 100% sealed room] and bring fresh air into the cinema. There is a small gap under the door to the main house which is deep underground, so always cool. While the system is running it pulls cool fresh air from the house into the bar, to the cinema and then outside.”
There’s also a ventilation system to exhaust air from the projector hushbox, pulling cool air from the cinema into the front of the box and out at the rear/top, ducted through the ceiling down a vertical riser and into the seating platform, where an inline fan with variable speed ducts this air outside the house. The entire run is sound isolated from the cinema to prevent sound going out from the exhaust hole towards those nearby neighbours.
With all the major electronics and fairly cool-running digital amps outside the cinema area in a swingable rack room, this AC system performs amazingly well, confirms the client.
Conclusions
We’re not in the least surprised to hear that the client is thrilled with the quality of this home cinema, and the ability to entertain himself, family and friends without fear of disturbing anyone in the house or the neighbourhood.
“The end result is a functional space that is a pleasure to inhabit,” says David Moseley. “And he is now the biggest D-BOX advocate — he says can’t imagine watching movies without it.”