Parameters for sound testing

[Ryan]

Hi,

  My car was running a bit loud on the weekend.  I’m going to be making a few changes to quiet it up. I’d like to do some testing, and was wondering how I should go about that. Is there a certain distance I should take the readings at?

Thanks,

[Curtis]

This is from the 2024 ASN AutoSlalom Regulations,

5.8 Noise Limit Adequate muffling devices must be installed on all vehicles with a sound level to a maximum of 96 decibels unless there is a lower noise limit required for that facility/track listed in Appendix I, or in the Supplementary Regulations. Organizers may apply to NSC for lower noise limits if the facility/track requires. Such limits must be sent out to all competitors in the Supplementary Regulations 60 days in advance of the event and must be posted at the site on the day of the event. Please note that some facilities require a lower decibel reading and, in order to compete there, vehicles will have to abide by those lower decibel limits.

5.9 Noise Measurement Measuring shall be done from a distance of 15 meters perpendicular (50 feet) to the vehicle wherever safe to do so. The final decision as to adequacy shall rest with the Steward. Any vehicle deemed to be excessively loud must not be permitted to compete without acceptable modification being made, regardless of the existing exhaust system. Please note that some facilities have their own measurement procedures and, in order to compete there, vehicles will have to abide by those measurement procedures. Event organizers should include a notice in the event’s supplementary regulations when such measurement procedures occur.

[David Klassen]

We have done some informal noise monitoring @ GMP, in accordance with ASN 5.8 and 5.9. What ASN doesn't stipulate, but should (IMHO), is that:

1. the vehicle should be under full acceleration before, during and after passing the measurement location, with the engine near 75% of redline
2. the sound level meter should be set for 'fast' response. (fast response means the meter can measure sounds 0.125 seconds in duration, an essential factor when measuring the fleeting sound of a passing vehicle)
3. the highest reading of this test is the determining factor

 

[Curtis]

This is from the 2024 SCCA Solo Rules, which have been recently updated (the old info is crossed out)

 

APPENDIX H - SOUND MEASUREMENT PROCEDURES AT SCCA® NATIONAL SOLO® EVENTS

The maximum allowed vehicle sound level will be 100.0 dBA. 108.0 dBC. The measurement will be taken at a point where vehicles can reasonably be expected to be under load at full throttle. The measuring point will be 50 feet from the edge of the course using an ANSI Type 2 sound meter set to “A” “C” weighting, “Slow” response. The microphone will be 3 to 4 feet above ground level, positioned perpendicular to vehicle direction of travel. The microphone will be away from structures (e.g., buildings) as is practical.

If a driver in a vehicle exceeds 96 dBA 100.0 dBC, the Chief Steward or his/her designated representative will be notified by the Sound Control Steward or representative. The driver of any run producing a sound measurement over 96 dBA 100.0 dBC will be notified, as soon as reasonably possible following the run, by the Chief Steward, Sound Control Steward, or representative.

If a driver in a vehicle exceeds 100.0 dBA 108.0 dBC, the driver will be allowed to attempt a viable remedy to functionally alter the exhaust system to reduce the sound level of the vehicle before his/her next run that day. (A “mechanical delay” per Solo® Rules Section 6.8.D may be used.) If the excessive reading occurs on the driver’s last run of the day, the Chief Steward, Sound Control Steward, or designated representative is authorized to impose a DNF penalty on that run.

The use of an adjustable directional exhaust exit to laterally aim the exhaust output away from the sound meter position does not constitute a viable remedy. Adjustable directional exhaust exits may only be aimed straight up, straight down, or straight back.

If a viable remedy has been attempted in the judgment of the Chief Steward, Sound Control Steward, or representative, the driver will be allowed to take his/her next run. If the driver declines any viable remedy or if the change is deemed inadequate by the Chief Steward, Sound Control Steward, or representative, the driver will forfeit all subsequent runs in the vehicle (unless an approved viable remedy is completed before the next run). If the driver in the vehicle exceeds 100 dBA 108.0 dBC again on any subsequent run, that run will be scored a DNF and all additional runs the for that driver will be forfeited.

If a sound violation which would incur a DNF occurs on a run for which a rerun would otherwise be granted (per Section 7.4), the sound-based DNF will stand and there will be no rerun.

For the purposes of sound measurement and enforcement, a “run” is defined as any attempt at driving through the course, whether or not it is scored or a rerun is allowed.

Any functional remedies implemented to reduce the sound level of a vehicle may not be removed (including the next day of the event) and may be subject to re-inspection by the Chief Steward, Sound Control Steward, or representative. If the remedy has deteriorated after passing the sound level requirements at the measuring point, the sound level of the vehicle must be functionally addressed again. The Chief Steward, Sound Control Steward, or representative has the right to disallow a repeat of the same remedy that deteriorated. The remedy may be changed or modified to improve its quality and/or further reduce the vehicle sound level. Drivers that receive a DNF for non-compliant sound levels implement additional functional remedies to reduce the sound level to compliant readings before starting runs the next day.

These general sound level regulations will NOT override specific local area and/or SCCA® Regional sound level requirements, regulations, and/or penalties.

 

 

[Ryan]

Thanks for all the info. I’ve put my stock mufflers back on. It’s much quieter. I should be good to go.