It’s the little things that count

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Bruce Black, Project Acoustic Designer

In January 2022, Paul Masse, an Oscar-winning re-recording mixer, has started building a personal Dolby Atmos mixing room near his Los Angeles home. Bruce Black, the project’s acoustic designer, documents the process in this ongoing special series of Mix Field Reports. Don’t miss the parts 1, 2, 3, 4, 5 6 and 7!

Phew! Paul’s new mixing room has become a hive of activity! With the enclosure wall completed, we are now focusing on all the little details that will put Paul’s room to work and make it world class.

First, there’s nothing quite like lighting up a dark room, so Craig’s team install three rows of linear LED lights. These have an additional element pointing upwards, so that they also diffuse diffused light into the room. They are each on dimmers and have an adjustable color temperature, so Paul can dial them in to create a very comfortable workspace. It was welcome by all to work in a well-lit space. “Let there be light,” and all that.

The room now has a coat of paint, lighting is in place, and Unistrut and in-ceiling speakers are installed.

During this time, the piece received a coat or two of paint. Paul asked for black, providing a low-distraction environment to help him stay focused. All ceiling elements are also painted black, so that they visually disappear and do not interfere.

Finally, we’ll add some color by covering the wallcoverings with a contrasting acoustically transparent blue fabric. That will be nice.

When designing new mixing rooms, I’ve found that many mixers like to move their console forward or backward until they find their sweet spot. I want Paul to be able to do it too. But with Atmos, Dolby’s specifications for distance and angle between ceiling speakers and mixing position are pretty strict, as they should be for a fully immersive experience.

Console movement

To allow Paul to move his console around while meeting these crucial requirements, I specified two sets of Unistrut ceiling channels to hang the ceiling speakers from. They can now be moved to their correct position

Ceiling diffusers and ceiling speakers. Note the Unistrut channel.

position if the console is moved. The structural engineer designed the ceiling support to support the weight of the loudspeakers, as well as the high isolation ceiling itself (STC 84 design and TL 60dB at 100Hz), so that all hanging things will stay where they are put.

While all of this is going on, the HVAC team is installing the mini split air conditioner. These units can provide heating as well as cooling, but usually mixed rooms like Paul’s only need cooling. Nice cool air to work with during those long mixes, especially with the long hot Southern California summers; simple but essential…

Meanwhile, Audio Intervisual Design’s team of installation and integration technicians, led by industry veteran Jim Pace, arrives on site. They have a lot to do, install the ceiling speakers, measure the surround speaker positions, install the speaker stands and possibly mount all the speakers themselves. They are also starting to run all technical and low voltage wiring.

Every good movie mixing room needs an image projection (duh…), so master builder Craig’s team builds a video projector rig outside the back wall of the outer room and cuts an opening for the projector port. To prevent the port from being a path for room sound to escape, the interior wall and exterior wall feature tightly sealed wood-framed glass projection ports, one for each wall. We must be good to our immediate neighbours.

Acoustic treatment

And now it’s time for the treatments. We use a combination of custom QRD diffusers designed by yours truly, along with the previously mentioned tuned Helmholtz resonators, and good old absorption.

The loudspeaker wall is covered with a Linacoustic RC duct covering just above the subs and resonators to the

Detail of the custom MediaRooms QRD diffuser.

ceiling. It is a fiberglass insulation with an acoustically transparent membrane, allowing it to be exposed directly to the room without losing fiberglass particles. It is designed for use in air conditioning ducts without introducing particles into the airflow. It also works well for our application, and its flat black color helps the image pop.

Next, Craig’s team installs 24 of the custom, black-painted QRD diffusers on the ceiling. This room surface is often overlooked, yet it is the largest acoustically reflective surface in any room. Ignore it at your peril.

The overview with right and rear processing frames with diffusers, ceiling diffuser and speakers, plastic-wrapped console, etc.

Craig is now building frames to house and dress the acoustic treatments on the side and rear walls. The sides mostly get diffusion with a touch of absorption (supplied by former stand-by, Owens Corning 703), while the rear wall gets a cluster of six diffusers. All of this is then covered by the acoustically transparent blue fabric.

Once the frames are in place, stuffed with acoustic treatments and covered in fabric, the folks at AID wire up all the speakers and technical equipment.

Helmholtz resonators can be sized to fit any available space and then tuned to the desired frequency by adjusting the port size. So how do you know what frequency to tune them to and where to put them? These essential data come from an acoustic analysis. I test and measure the part using software that gives me very detailed information.

Acoustic analysis

The projector port. Note the speaker wires for the rear speakers.

The most useful chart is the waterfall chart. This shows me what frequencies the resonances in the room are (“modes”). I tune the resonators to the most significant.

I then note which resonances are at the very top of the waterfall graph, oldest in time, and which are further down the slope of the waterfall, later in time. Yes, time is one of the most overlooked characteristics in acoustics, yet it is one of the most important.

The resonators for the first frequencies are installed under the screen, where they are closest to the sound sources, the loudspeakers. Resonators for later resonances go to the back of the room, behind the client’s couch.

For the rear wall, Craig built a single device with four separate cavities for the resonators. This allows for four different frequencies, but I’ve set them to three. A particularly unruly frequency gets two resonators. Further testing will reveal the need for other resonators.

Another useful graph is the decay graph. Going back to the panel absorber business, this graph shows me if any wall or ceiling panels vibrate sympathetically. A vibrating panel will create a dip in the response between 80 Hz and 130 Hz., but not before 100 milliseconds. or; that’s inertia for you… It doesn’t show up on an RTA or frequency response plot, but it does in a decay graph. Our tests show that everything is fine.

Closing at the end—front view.

And with that, the room’s low-frequency performance has been suitably tamed. So!

test signal

Meanwhile, Paul’s Harrison console is unpacked and set up. AID experts complete the wiring and test the console, speakers, Pro Tools rigs, and associated equipment in the engine room. Once everything passes inspection, Dolby stalwart Andy Potvin comes along and works his room-tuning magic. Which guy!

Closing at the end – rear view.

And now, that magical moment that everyone has been yearning for since day one has arrived. The hall is full and Paul begins to lead the hall through his trials.

Be sure to check out our epilogue, the next and final field report of this journey through the process of building Paul’s new mixing room. We’ll do a final acoustic analysis, perform listening tests, and make sure his room is ready for him to do what he does best: mix the sound of major films in a world-class mixing facility.

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