Last week, NASCAR tested the muffler that will be used for Sunday’s Clash at the Coliseum.
“Heresy,” some fans cried. They argued that it is against the laws of man and nature to muffle racecars. That noise is an integral part of the fan experience. That you’re not supposed to be able to have conversations during races.
The cars will be plenty loud.
Loud is fast
Engines produce power by combusting fuel and air in their cylinders. Each combustion produces high-pressure gases that push the piston up. The same gases make a loud popping sound when they escape the cylinder and finally the exhaust.
At 8,000 rpm, an eight-cylinder engine performs about 520 combustions every second. The faster an engine runs, the more combustions per second and the higher the frequency of the tailpipe noise.
That’s why NASCAR engines sound like grizzly bears and F1 engines, which run at higher speeds, sound more like angry mosquitoes.
Maximum horsepower requires getting the spent gases out of the cylinder as quickly as possible so the next combustion reaction can start. And that’s the problem with mufflers, from a racing perspective.
Mufflers on street cars bounce sound waves from the engine around a metal can. The waves interfere with each other, which decreases the overall volume coming from the exhaust.
Mufflers can also mitigate noise by directing the exhaust through a sound-absorbing material. Borla, the sole-source supplier for this weekend’s muffler, makes commercial racing mufflers that feature a robust sound-absorbing material superior to the commonly used fiberglass.
Both methods slow the exhaust gases — the first more than the second. The ideal racing muffler diminishes sound with minimal horsepower reduction.
Sound-level measurements come in decibels (dB), a unit named after Alexander Graham, not Christopher — and apparently by someone who wasn’t the best speller.
But decibels don’t tell the whole story. Sound intensity decreases with distance, so you need to specify how far away the sound source was.
The easiest way to explain the decibel scale is to relate it to real-world noises, as I’ve done below.
- Zero dB is the threshold of human hearing.
- A whisper you can just barely make out is about 20 dB.
- Most everyday noises are in the 60 dB to 100 dB range but are sometimes louder.
- Exposure to 130 dBs can be painful.
- A 150-dB sound can cause permanent hearing damage in a very short time.
Ringing in your ears the day after a rock concert was a badge of honor in high school. Older me wishes I had been a little smarter.
Hair cells — not to be confused with ear hair — facilitate hearing. Sound bends these hair-shaped cells, and the cells convert sound into electrical signals that the brain interprets. Loud sounds can bend these cells so much that they break.
Unlike animals such as sharks, zebrafish — and even the lowly chicken — humans cannot grow new hair cells. Once your hearing is damaged, you can’t get it back.
How loud are racecars?
A noise mitigation study for the proposed Nashville Fairgrounds track measured a single Next Gen car at COTA generating 112 dB on a straightaway at 100 feet.
A 2008 study measured the sound level inside a Gen-6 car to be an average of 114 dB. The study also compared sound in the stands, the infield and the pits.
Let’s add those numbers to our graph.
- The Next Gen car at 100 feet is about the same loudness as a person screaming at top volume 1 inch from your ear.
- The Next Gen car at 100 feet is just a bit quieter than sitting inside the Gen-6 car.
- Bristol reached peak sound levels loud enough to cause permanent hearing damage.
The graph data suggests that inside the Next Gen car should be around 10 times louder than inside the Gen-6. Some drivers made new earmolds to cope with the additional noise in the cockpit.
Because of the way sound works, the numbers don’t add like you’d expect them to. A Next Gen car might be 112 dB, but two Next Gen cars are more like 115 dB. A full field would be only 5-7 dB louder.
The mufflers won’t muffle much
NASCAR expects a six to 10-dB reduction in sound with mufflers. A 10-dB reduction would make the Next Gen car about as loud as the Gen-6 car was.
Another way of looking at it: Good earplugs reduce sound levels by 25 to 30 dB. Wearing earplugs just barely gets you into the range of being able to hold a conversation if you stand very close to each other and you both shout.
You won’t notice the change in sound inside the track.
You also won’t notice a change in speed this weekend, despite a drop of 30-40 horsepower. The Next Gen car takes around 14 seconds to traverse the L.A. Coliseum’s quarter-mile track. That means cars won’t be going much faster than typical expressway speeds.
If you’re headed out to the track this weekend — despite the mufflers — bring earplugs or over-the-ear headsets. This is especially important for children, as their hearing is more easily damaged.