ASC president and TubeTrap inventor, Art Noxon, PE Acoustical shares his acoustic discovery in Hollywood’s world-famous Grauman’s Chinese Theater.
Here’s what Grauman’s Chinese Theater looks like from the downstage center position. It’s where the giant movie screen is located and is looking across the seating towards the back of the hall. At the back is a balcony with the projection booth in the upper back of the theater. In the upper foreground is a huge mandala, also referred to as the “Doily”. Along the side walls are huge decorative cylinders, easily 12’ in diameter.
Back around 1990 Sylvester Stallone made some comments about garbled bass in the theater. It was as if the auditorium was suffering from some type of excessive bass boomyness. The manager decided to look into the matter and here’s the story of how it went.
I am an acoustic engineer, a specialist in acoustic bass control in rooms. One day I got a call from the management at Grauman’s Chinese Theater. They wanted me to drop by and inspect the theater next time I was in town. It didn’t take long before I was there and accompanied by an entourage of interested parties, the sound tour began.
There was no movie or other sound being played which might have led to some sonic observations. So, this sonic adventure would be based on what we see, rather than what we hear. Walking into the theater, the first thing I noticed were the huge cylinders along each side wall. I knocked on the surface of the pillar and determined that they were hollow, empty inside.
I began figuring how I could turn these huge cylinders into gigantic versions of TubeTraps, which is the bass trap/treble diffusion product I and my company Acoustic Sciences Corp, were well known for building and installing in high-end audio listening rooms and recording studios. I imagined this might be why they had asked me to drop in for a look-see. But then, something kept nagging me, it was a giant 60’ diameter sculpted mandala overhead in the middle of the ceiling of the theater.
As I looked at it and then into it, past the layers of gilded flourishes and shadows, I could see that it was a mandala, a real multi-layered mandala pattern through which a path, an air path, was visible. Initially, I figured it was an ornate air diffuser for the HVAC system. Acoustically such a big HVAC air duct could be a source of reverberation.
In acoustic work, probably like so many other fix-it projects, It is always better to find the source of the problem. If we can fix it at the source, we fix the problem before the audience hears it. Otherwise, we end up fixing the problem after the audience hears it, which means only reducing how bothersome the problem is but not eliminating it. So, I asked how to get above the ceiling and inspect that HVAC duct work.
It was dark and very dusty, with one vertical ladder leading to the next vertical ladder and so on. And the entourage was not expecting to be climbing way up here, wearing nice shoes and office clothes. The all-knowing janitor led the way. He was already familiar with everything up here and where we were going but he didn’t know what purpose it served.
Eventually the space opened up into the attic, the part of the theater between the back side of the ornate ceiling and the bottom side of the concrete roof. Catwalks went everywhere and this is what it looked like. Photo is from a 2012 expedition by others. What this shows is the beginning of the ”HVAC” duct that is located just above the mandala.
We can see that the duct which is curving up and extending to the right is suspended off of wires that are attached to clips anchored in the concrete roof, much like acoustic ceilings are done today. The metal framework is what is holding the ceiling up. This is all looking a little too elaborate for an HVAC duct. The duct starts in the middle of the seaitng section and continues off to the right getting smaller and smaller and ending at a room just in front of the proscenium wall.
There is a door along the left side of the duct. We opened it and went through. Here’s what it looked like inside the beginning end of the curved duct. This photo is also from the same later 2012 expedition into this area. The walk boards are laid across the steel framework that is holding the mandala in place. These people are part of the 2012 expedition, not our 22-year earlier 1990 exploration.
The lower end of the duct is to the right and the raising part of the duct is to the left. You can see a tapered transition up from the mandala towards the left into a wide low rectangular duct. Everything is now (2012) covered in fiberglass “duct board” but when I was there around 1990, it was bare stucco type of surface. There were no sound panels anywhere inside the duct.
To get a better perspective on what is going on up here, let’s look at a cross section of the original 1927 blueprint. We can count 7 huge pillars down the side wall, tall ones on the main floor and they get shorter as the seating sections rises towards the back. The ceiling mandala is above the 2nd, 3rd and 4th columns, pretty much the entire high ceiling part of the theater.
Below is an expanded view of the attic with the huge duct. We can see the sloping duct between the mandala in the ceiling on the right up and into a room on the left. The room has a man door at the lower left. There is an opening to the duct through the wall of the room. The height of the duct doesn’t change, stays about 6’ but it width tapers from 30’ above the center part of the mandala to about 10’ wide at the entrance into the room on the left.
The room was large with a high ceiling with plaster in front of concrete walls. At the time, it looked like a reverberation chamber to me with an expanding tunnel between the openings in the mandala and the reverb chamber. But that was wrong, later I discovered that the room was really an organ loft fit with ranks of organ pipes and the giant tapered viaduct was the “tone chute” by which the organ pipes spoke to the audience through the vents in the “doily” as it was called, the mandala. Sound was supposed to float down through the mandala “as if it came down from heaven”.
This is a photo of the organ pipe room. The man door shown on the lower left in the section view is here, from the inside of the organ loft, on the lower right hand side. The large rectangular opening to the tone chute is seen on the left wall, now boarded over. It seems to be at least 6’ tall and 10’ wide.
The organ pipes were removed in 1935, leaving the sound conducting mandala vents, tone chute and echo chamber remained behind. Although intended as a one-way tone chute, from pipe loft thru tone chute thru vents in the ceiling mandala into the audience space, it also works just as nicely in reverse. Sounds from the theater loudspeakers can travel through the mandala vents up the tone chute and into the echo room where it turns into reverberant sound which then expands back down the tone chute thru the mandala vents and back to the audience.
It was true for early concert hall designers to add an echo room to the hall design. The echo room needs an adjustable door to control the loudness of the reverb being returned to the hall. Today they do the same thing with electronics. Although this acoustic system was intended to transport the reverberant sound from the organ loft to the theater, it worked in reverse just as well, to collect amplified sound from the theater, conduct it to the echo room and return it back to the theater.
My recommendation to then management was to add sound panels above the mandala and use them to block the entrance into the tone chute and also to close up the opening between the echo chamber and the tapered duct. When the team in 2012 arrived, that is exactly what they found and the bass boomyness problem for the theater had been long gone.
Just think, someone forgot to close the reverb chamber door, what maybe 60 years before when they removed the organ pipes? And no one working there even knew that an echo chamber remained was connected to the mandala vents.
All it took to get the door found and closed was for Sylvester Stallone to tell the theater management that he would not let his next movie have a premier showing in that theater until the boomy bass problem got fixed. He didn’t appreciate the garbling effect that was happening to his voice. No one in the entourage even knew about this acoustic reverb reinforcement system, except the janitor. He knew it was there all along but he didn’t know what it was there for.
Oh, and because this was just a visit to tour the theater, I never did send an invoice for my work.