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Inside the Caterpillar Sound Labs, some of the quietest spaces in Illinois

Caterpillar's heavy earthmoving equipment undergoes testing in the sound lab at the company's Proving Grounds in Washington.
Caterpillar's heavy earthmoving equipment undergoes testing in the sound lab at the company's Proving Grounds in Washington.

Did you know that Caterpillar has two of the nation’s most advanced sound labs, right here in central Illinois?

One is at the Tech Center in Mossville; the other is at the proving grounds in Washington. Inside these labs, engineers and technicians test machines and components to ensure they comply with global sound emission requirements. They also use sound to troubleshoot, to provide feedback to operators, and to ensure the safety of people around their machines.

Sound Chambers at the Caterpillar Tech Center

David Copley is a senior engineer with Caterpillar Global Sound and Cooling. He says that sound is a critical element of their machines, and that that every component has its own unique sound signature.

“Particularly any type of rotating machinery, whether it be gear trains, pumps, hydraulics… they all have some very unique signatures,” Copley says. “As a sound engineer being around Cat machines now for close to 30 years, it's a bit like an orchestra conductor can kind of hear when the flute section is out of tune—or can pick out that oboe even though the percussion section might be pretty loud. That’s what we can do with some of our technologies.”

Copley manages the Sound Lab at the Tech Center, which is comprised of two very different sound chambers. One is a reverberation chamber. The other is a “hemi-anechoic” chamber. Anechoic means “no echo.”

“These two extremes allow us to make some very precise measurements,” explains Copley. “We also can use our computer models in these kind of ideal environments to correlate with these tests, which then allows us to do more realistic and more validated computer modeling and design in the virtual space.”

The reverberation chamber at Caterpillar's Mossville plant.
The reverberation chamber at Caterpillar's Mossville plant.

Inside the reverberation chamber, sound bounces off the walls and echoes. The room has hard concrete walls and diffusing panels on the ceiling which help scatter the sound.

“If I want to know what’s called the sound power emissions of a device—and this is similar to like a light bulb, how much radiated power… I would place it into the reverb chamber. And I could measure the sound power very precisely because it integrates the sound all together, because it’s bouncing all around.”

The hemi-anechoic chamber is located right next door to the reverberation chamber. This room is so quiet, you can practically hear the blood pumping past your eardrums. Foam wedges line the ceiling and walls and absorb any sound created within.

“If I have a component where there’s a number of different noisemakers, and I want to know how much sound is coming from one particular area, I can place that component into the hemi-anechoic chamber where I have no echoes. And I can pinpoint exactly from where the sound is coming.”

Listen to the impact sound of a hammer hitting a toolbox, first in the hemi-anechoic chamber:

Hammer 1 - hemi-anechoic.mp3

And here is the same hammer sound in the reverberation chamber:

Hammer 2 - reverberation.mp3

“So you can hear that decay that occurs within the reverberation chamber,” Copley explains. “The microphone, or in this case the listener, is basically the same distance away in both cases. And I think that’s important to note because of how different they sound between the two chambers.”

Sometimes the two chambers are used simultaneously—like when they want to measure how much sound passes from one to the other. This is ideal for simulating the cab floor of a machine, where noisemaking components are located directly beneath the operator.

“We can generate a lot of sound within the reverberation chamber, that will then pass through that cab floor into the hemi-anechoic chamber, where we can measure how much sound gets through and from where it's coming,” says Copley. “And so we can get an idea of what parts of the floor need to be enhanced.”

And when a component has a problem, sound can be used to identify and troubleshoot it. “Sound is a great diagnostic tool,” he notes. “It may be an indicator that something needs to be fixed, something needs to be replaced. And so sound can often be used to say, Okay, this is what a healthy machine sounds like, and this is one that needs some repair.”

Sound Lab at The Proving Grounds

Across the river at the Caterpillar Proving Grounds, a very different sound lab is used to test the entire machine after it’s been put together. It’s a large, open building with bi-fold doors and some 43,000 sound-absorbing wedges lining the walls and ceiling.

“We can bring a machine into the sound chamber and park the machine in the middle, and we will close the bifold doors. And then we have another additional internal door that is another wall of foam wedges. And that will close, fully isolating the center of the building from the outside,” explains Peter Zuehls, a sound engineer at the Caterpillar Proving Grounds.

“We do what we would call investigative or development testing, where we would look at all the different noise sources of the machine, try to put them in harmony with each other so the operator can operate the machine efficiently and use the cues from the machine to understand what it's doing, as well as to give him a pleasant working environment.”

lf a machine is having a problem, customers can send Caterpillar an audio recording, and their engineers will listen and try to determine the issue. “We use the software in the labs to identify the sound and identify the root cause of the noise,” Zuehls notes. “And then we come up with a solution to eliminate that noise.”

This is the sound of a Caterpillar motor grader with a gear noise in it:

motor grader 1 - gear noise.mp3

And here is the same motor grader after it’s been fixed:

motor grader 2 - fixed no noise.mp3

“After we identify the noise, then we would go back, apply some solution to the machine,” Zuehls explains. “In this case, it was a different set of gears with a slightly different profile, and then test again and verify the solution worked.”

Machinery undergoing troubleshooting at the Caterpillar Proving Grounds in Washington.
Machinery undergoing troubleshooting at the Caterpillar Proving Grounds in Washington.

When a machine component has a problem, the problem also has a unique sound. “Hydraulics, you can get pump whines; you can get valve chatter. Undercarriage on a track type tractor—you can hear track slap from a long way away,” he adds. “Or if a wheel loader was operating at a quarry near your house, you could hear a backup alarm. There’s all kinds of noise sources on our machines. And the beauty part is, we get to work on all of those. As a sound engineer, you get to touch every aspect of that machine.”

Recently, a customer was having a problem with a D8 Dozer that was making a loud noise in the cab. Caterpillar engineers were able to identify the problem from the sound alone.

“He took it into the dealer, and the dealer couldn't find anything wrong with it,” Zuehls recalls. “So the dealer took a video with his cell phone. The engineers looked at the video and could pinpoint what was causing it by the frequency of the sound. And they knew where that frequency… what line the sound was traveling through the hydraulics, and then found where that would be touching the cab and creating that noise.”

A large boulder had broken through the undercarriage and bent the fenders up into the cab. “And they tried to bend it all back but they missed one line,” Zuehls says. “And that was the line that was touching the cab. And we were able to determine what the issue was without ever seeing the machine.”

Today at Caterpillar, sound engineers have the tools and technology to troubleshoot from a distance—and the ability to sculpt the very soundscape of their machines—from state-of-the-art sound labs located here in the Peoria area.

D8 Dozer startup.mp3

And that is the sound of a Caterpillar bulldozer starting up.

Jonathan Wright is a correspondent for WCBU. He joined the station in 2022.