Noise Levels enforced at the next AX!!!???

[MR LIPP]

I think we have a volunteer

[ttweed]

My stock car measured 92.5 and 93 db at a PCASDR Qualcomm event last fall when this all started...Having to worry about this is not fun and have chosen to not participate until there is a policy in place to clear this up.

This example illustrates my concern perfectly. I don't think anyone with a completely stock Porsche exhaust (even a GT3 sport setup) could or should exceed the Qualcomm sound limits. The modern P-cars are built to comply with fairly stringent Euro Union sound requirements, no? Inconsistent or unreliable measurement policies and techniques are not fair to competitors and discourage participation.

I have the same worries with my "classic" old 911, as at different times my car has been measured both as complying and then being grossly non-compliant. I remember people years ago leaving an event grumbling about being thrown out when they had been judged as OK running the same car with the exact same exhaust system at previous events. This kind of uncertainty is a buzz-killer! It is not always just an exhaust problem, as intake noise can be a significant contributor in the older cars with carbs or MFI induction.

My current car happens to have a later engine with a stock, enclosed airbox, so I am mostly concerned at the moment with my exhaust, which is a custom SG-modified dual-out sport muffler. No one has ever warned me verbally at an event that it was too loud, but I read all the recorded sound levels published here after the events last season and was fairly amazed at some of my reported measurements. Subjectively, my car doesn't sound any louder to me from inside or out than the 3.4 liter, carb'd, hi-compression race motor with dual-outlet sport muffler that I had in my AM car, which i ran for several years without ever being dinged for sound at either Qualcomm or Laguna Seca. Nevertheless, I have already gone to the expense of purchasing a stock early 911 muffler with full baffling and single outlet just in case. Before I go to the further time and expense of installing it (which, BTW, is not just a bolt-it-on-in-the-pits-between-sessions operation, but requires modifying my rear valance and also re-tuning the fuel mixture for the decreased flow), I was hoping for some clarity, or at least some consistent guidance/evidence as to the necessity of doing so. At this point, I was planning to just continue running the car like it is until someone tells me I can't, but the risk of being perceived as a "bad citizen" and/or being chastised and thrown out of an event for non-compliance is distasteful to me, to say the least. I am just advocating for some sort of consistency and clarity to reassure people like Peter, Gordon and myself.

I've nominated Tom Tweed

Although I realize that being the PCA King of Sound Regulation might allow my subjective perceptions about my car to reign supreme, absolving it from loudness forever, I think tech inspection still needs me more.

TT

[gocart]

So how does SCCA monitor and enforce the sound levels at their events at the Q?

[Sawfish]

Hi I work for the Navy in the biosciences division. We do a lot of sound studies. This thread is very interesting and after reading most but not all of the posts I spoke to one of our resident PhD’s on the subject. I asked him if the cumulative sound of more than one sound producing item will affect the overall sound levels recorded and the answer was yes. That is to say the most accurate assessment of a vehicle engine/exhaust noise would be done one vehicle at a time. Adding additional vehicles running within the proximity will add Db but not in a linear fashion.
Not sure if this is important but thought I would throw in my two cents.

Chris Harris 780 AP

[Kim Crosser]

The club used to enforce the sound rules much more tightly in the (distant?) past, but got kind of lax over the past few years. We are now resuming the monitoring that should have been done continuously. The Stadium has published rules - does anyone really want to chance getting kicked out for failing to follow them?

I and others have talked with members in other clubs (BMW and SCCA, for a couple) and per them we appear to be the only car club using the Stadium that has not been rigorously enforcing the noise. Even the dragsters are required to keep the sound at or below 93 db.

Sound levels are additive. A single 93 db car on a track produces a certain sound power level, but that increases when there are more cars on the track at the same time. When we are running 6 (or more) 93 db cars at once, that overall level is a LOT more than 93 db. Measured at the same distance, each additional noise source adds another 3 db to the total sound power. 2 x 93 db cars = 96 db, 6 x 93 db cars = 108 db. A chain saw produces 110 db.

Open Google maps (maps.google.com) and draw measurement lines from the upper left of the West lot to the condos across the street. Similarly, check the distance from the SE lot East side to the condos on the other side of I-15. Most of our tracks are within 300 feet of some of those condos, while the dragsters and the race legal guys (who arguably break the 93 db level) are no closer than 600 feet at their closest points.

Sound pressure does decrease over distance, but linearly, not as the square of the distance as you might expect. This is why I can easily hear that poorly muffled motorcycle or truck on Del Dios Highway 1.5 miles from me, and why our car noise isn't damping very fast before it hits those condos.

Unlike the dragsters and race legal guys, who run two cars at a time for 8-10 seconds and then pause for quite a while, we are essentially running 3-6 cars concurrently from 9am to closing, with no breaks.
How would you like it if your neighbor decided to run their leaf blower (90-100 db) and lawnmower (90 db) together nonstop from 9am until 4pm on the weekend?

Assuming we are measuring 93 db at 50 feet, at 300 feet from the track the sound from one car is still over 77 dbA. If we have 6 x 93 db noise sources (108 db total), then at an average distance of say 600 feet the perceived dbA level is 86.4 dbA. So basically, residents in those nearby condos are listening to a constant level of sound that is between 80 and 90 dbA.
If we were measuring 93 db at 100 feet, then the corresponding numbers are 83.46 dbA at 300 feet for one car, and 98.5 dbA at 600 feet for six cars. 100 dbA is a jackhammer at one meter distance... ouch!

If we aren't measuring the sound appropriately or consistently, then we should try to fix that. However, the objective should NOT be to take our measurements so that everyone passes, but to try our best to comply with the Stadium's noise limits.

[gocart]

To add more confusion, the exhaust noise limit in California is 95 dB. http://www.apexi-usa.com/content/pdf6366.pdf
This is measured next to the car, however.

[JERRY B]

I will have a plan to show at the board meeting, Here is scca's sound logs
http://www.sdr-scca.com/solo2/results/2 ... -sound.PDF

[ttweed]

So how does SCCA monitor and enforce the sound levels at their events at the Q?

I posted this the last time we had this discussion back in Oct. last year:
"Anyone who would like to review the SCCA SDR Supplemental Regs, I have uploaded a PDF file of them to one of my websites. You can download it here: http://plowshare.mobi/SDSCCA2008_Supp_Reg.pdf Look at section 6, beginning on p. 19 to see what they do."

The supplemental regs contain their local procedures, in excess of (or in addition to) the national SCCA Solo regs. The national regs have only begun to address sound issues this year. The SCCA-SDR supplemental regs are much more stringent. What Jerry posted above is a sample of the logs they keep at the sound station during each heat of each event.

I can deal with anything the board/chairs decide to do, but I would just like to know what to expect and when. People need to be informed about DQ procedures and assured that they will be applied even-handedly, only as necessary, based on factual, repeatably accurate data and measurements.

HTH,
TT

[Curt Yaws]

We will discuss this at the April 7 board meeting tomorrow, and I hope we get it resolved.

[Don Middleton]

We will discuss this at the April 7 board meeting tomorrow, and I hope we get it resolved.

OK. End of discussion. Curt's going to fix it. Excellent! Next issue...

[ronaldtrotter]

Thank you Don. Let's see what happens tonight.

[Kim Crosser]

To add more confusion, the exhaust noise limit in California is 95 dB. http://www.apexi-usa.com/content/pdf6366.pdf
This is measured next to the car, however.

Yes, and if you are measuring 95 db at 20 inches from the exhaust, then at 50 feet that is only 65 db, or 59 db at 100 feet.
I am not sure we want to try to comply with that standard...

[gocart]

Yes, it would be much quieter the greater the distance that it was measured.

But, at least in my paranoid mind, it would be theoretically possible to have a car that is street legal, possibly measure over 93 dB at the stadium. Depending of course on the way it was measured at the stadium.

[thunderbox]

I just found this on the internet. Who would have thought that somebody researched this.

Funny and quite possibly true.

[Kim Crosser]

Yes, it would be much quieter the greater the distance that it was measured.

But, at least in my paranoid mind, it would be theoretically possible to have a car that is street legal, possibly measure over 93 dB at the stadium. Depending of course on the way it was measured at the stadium.

The "20 inches" distance is the official measurement distance they use for the 95 db reading.

Actually, no modern "street legal" car should be hitting 93 db if the car complied with the California noise rules. California Vehicle Code 27200 sets db limits for autos as:
After 1974 - 80 dbA
After 1972 thru 1974 - 84 dbA
After 1967 thru 1972 - 86 dbA
Pre 1967 is not specified

Per VC 27200, no dealer is allowed to sell, or offer for sale, any vehicle that exceeds those numbers. And VC 27151 says exhausts on autos under 6000 GVW must test at 95 db or less at 20 inches (e.g., 65 db at 50 feet). Under the old SAE J1169 standard referenced in the VC, the measurement was supposed to be at 3/4 of maximum rated engine speed (e.g., if your car redlines at 7000, then 5250 RPM for the test. If your car really tests at under 95 db at 20 inches at over 5000 RPM (or under 65 db at 50 feet), you aren't going to have ANY problem keeping it under 93 db at the Stadium. (And you will probably be able to sneak up on corner workers. )

By the way, the ISO has taken the SAE J1492 standard (replaced J1169) and has a new standard in progress. For 4-wheel passenger cars with max engine RPM between 5000 and 7500, the standard requires running the engine steadily at 3750 RPM for at least 1 second of measurement, then popping off the throttle and measuring the entire deceleration period (better hope no backfires!). The measurement is made at 0.5 meters from the exhaust tip and the vehicle's noise level is the maximum sound pressure measured at any point in the entire test period.

Note that per VC 27150, we are exempted from the noise limits of VC 27200 while our "... passenger vehicles [are] being operated off the highways in an organized racing or competitive event ...". Unfortunately, we aren't exempted from the Stadium contract limits.