How to test your exhaust's sound level

[concept]

Latest development: I just had a talk with a CA noise-testing employee. He sent me a more detailed guide with layout of the test setup. I changed my drawing to the attached.

Here's the youtube link:

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[sabrownfl]

I created a video that runs through various state restrictions regarding exhaust noise levels and how to test your car for compliance. My test was with the stock exhaust as a precursor to a test of an incoming Dinan cat-back.
Of course, my stock exhaust system passes. It'll be interested to see how the Dinan does. Note: Yes, youtube rotated my photo.

Measuring at 20 inches, you're likely to fail. Here is my Dinan measured at about 15 feet. I also have a high-flow catted downpipe.

 

[concept]

Measuring at 20 inches, you're likely to fail. Here is my Dinan measured at about 15 feet. I also have a high-flow catted downpipe.

At 20 inches, you'd catastrophically fail!
I do agree that the CA test description is not very clear. I kept my sound meter at level position but 45° from the tail pipe (which is level with the ground) position.

You angled your sound meter to about 45°.
I may contact the referee to clarify.

I do expect the Dinan to fail in Sport mode, but thankfully, I have factory-installed downpipe and cat. Many Supra owners do not.

 

[FLtrackdays]

I use the pain in my ears and Apple Watch that warns me to put earplugs in ?. So I have these nice foam inserts on my AirPods or similar earbuds when driving mine.

Wonder how accurate the decibel meter on the watch is? I realize what y’all are doing is more detailed but it’s a nice way to know (remind me) at the track to put my earplugs in. Anyone want to buy a heavily used but now welded, track tested, exhaust?

 

[concept]

I use the pain in my ears and Apple Watch that warns me to put earplugs in ?. So I have these nice foam inserts on my AirPods or similar earbuds when driving mine.

Wonder how accurate the decibel meter on the watch is? I realize what y’all are doing is more detailed but it’s a nice way to know (remind me) at the track to put my earplugs in. Anyone want to buy a heavily used but now welded, track tested, exhaust?

Before buying the sound meter, I used an app in my phone to measure sound levels for various things (like the house and shop vac noise levels) to help me determine whether to use ear plugs or noise-blocking headphones.
But when it comes to being more precise, a dedicated sound meter by a respected manufacturer is almost always a better choice.

The same is often true with multimeters. You can buy a very inexpensive one at Harbor Freight to teach kids how to check continuity or see if a battery is dead, but I wouldn't rely on it for more critical testing.

 

[concept]

6/26/2025: I updated the setup drawing and video in my first post.

 

[MK5_Ger]

We use the same distance and angle here in Europe, specifically in Germany.
But our measurement method is a bit different:
The driver has to slowly rev the engine up to 3750 rpm, then release the accelerator. Only the rev drop is measured.
Each side is measured 3 times. The difference between each measurement can't exceed 2dB.

The paperwork for my 2023 model allows 86 dB at idle.
There’s a tolerance of 5 dB, so anything up to 91 dB is fine.
With my valved exhaust, that’s no problem

 

[concept]

We use the same distance and angle here in Europe, specifically in Germany.
But our measurement method is a bit different:
The driver has to slowly rev the engine up to 3750 rpm, then release the accelerator. Only the rev drop is measured.
Each side is measured 3 times. The difference between each measurement can't exceed 2dB.

The paperwork for my 2023 model allows 86 dB at idle.
There’s a tolerance of 5 dB, so anything up to 91 dB is fine.
With my valved exhaust, that’s no problem

That appears to be more "forgiving" than our California test. Thanks for explaining your requirements, which make more sense than ours. The part that bothers me the most is that whether we get a ticket or not is very subjective. I was told that many cars from the factory will not pass the test. The good news is that everyday city driving rarely involves revving the engine to 75% of the engine speed at its rated HP. That's about 4350 RPM.
We also have a requirement for front license plates but many officers don't consider it as a priority to ticket drivers.

 

[concept]

Here's what I measured after my Dinan cat-back was installed. The tone is noticeably lower but not as loud as the Borla Atak videos I've seen.

 

[MisterSkiz]

Interesting - thanks!

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