Exhaust Sound Level


Introduction

As time marches on, we find that more and more of our autocross sites are within earshot of residential areas, often even ones that don’t seem like they are. At the same time, more and more people are coming to us to compete with cars that are varying degrees of “loud”. Autocross sites are really, really hard to come by! So, we have decided to implement an exhaust sound level limit in an effort to be “good neighbors” and reduce the likelihood of noise complaints that could contribute to the loss of an autocross site.

We did a lot of sound measurement over several events at different locations and found that the great majority of our competitors have cars that register below 90 dbA. (nearly half are below 87 dbA) We also determined that without question, any car that registered 94 dbA or greater on the sound meter was “loud”. Because our sound limit is self-imposed, we have opted to make our sound limit higher than that. We’re setting it at 96 dbA. Bear in mind that the db (decibel) scale is not linear. An increase of 3 db indicates DOUBLE the sound pressure level. So, the difference between 94 and 96 dbA is significant, and the difference between 96 and 99 dbA is again TWICE as loud.

The Official FAST Exhaust Sound Level Policy

If we think your car is loud enough to warrant measurement, we will measure it. If our meter is unavailable, we may rely on our ear! (we’ve taken enough measurements now to have a good idea of what’s what) We will measure your car as it leaves the starting line at a distance of approximately 50 feet from the rear of the car and at approximately 45 degrees to one side.

If we determine that your exhaust sound level is below 96 dbA, you’re fine. We might caution you to not do anything that would make your car any louder, but that’s it.

If we determine that your exhaust sound level is 96dbA or greater, we will take one of the following actions.

Soft Limit – 96 dbA – If your car’s exhaust registers greater than 95.9 dbA, but less than 99 dbA, you can still compete in the current event. But, we’ll recheck at the next event and if it is the same, you will not be permitted to run at that event. If it is measurably quieter the second time, but still over the limit, you will again be allowed to compete and we’ll recheck again at the next event. As long as you’re making an honest effort to meet the sound limit, we’ll work with you.

Hard limit – 99 dbA – If your car’s exhaust registers greater than 98.9 dbA, we reserve the right to NOT allow you to compete at this sound level. This is REALLY loud! In addition to not wanting to disturb our neighbors, we don’t want to expose our starter and other course workers to sound levels that could cause permanent hearing damage.