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Sound Decibel Limit - 2022


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Although this will be covered in the upcoming supp regs for 2022, I wanted to give everyone as much notice as possible.

 

We are enforcing a 96db @ 50’ limit for ALL of our upcoming events for this year. 
 

Please use this thread for positive and helpful discussions only.


There will be future exceptions to this rule during “Special” events such as Vintage Weekend etc.

 

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The following info is based on known principles of noise propagation:

  1. sound will reduce by 6db for every doubling of distance (+/- dependent on temperature gradients and wind), see the attached chart
  2. the closest residential areas are from 1 to 2km away from the GMP circuit
  3. so, 96db @ 50’ on track, would result in between 54db and 60db in the residential areas
  4. some portions of Winnipeg noise ordinances prohibit residential neighborhood noise louder than 55db during the daytime hours, typical residential noise levels are between 30-40db.
  5. so a car emitting 96db @ 50’ on track would most definitely be heard in nearby residential areas.

The only way we’ll know how good a neighbor we’ll be is by measuring in the neighborhood.

db over distance.pdf

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It’s an interesting development. There should be a ‘standard’ test and more importantly, the desired results established/defined. I’m sure it will take a bit of work and time to do that. Many factors are relevant such as the location of the exhaust exit on the car or cars tested and which side of the track (infield, outfield and/or height above the track) the sensor should be mounted - not to mention environmental conditions (trees, buildings, wind, etc) and at what location on the track is going to work (end of straight, fastest corner exit, etc) as has been mentioned.
Either way, as a club we should welcome this, we have been immune from such regulations for years by no other reason than location (middle of nowhere and adjoined to an airport), when in fact with exhaust technology being what it is today, there is no performance loss to running a bit quieter.
 To further support the initiative, I would mention that on many occasions I have spoken with drivers that had no idea their car was about to fail due to the excessive noise they experienced while in the car; simply put, when you can hear what your car is doing, you are a better driver and you can extend the life of you car.

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9 hours ago, mcorrie said:

when in fact with exhaust technology being what it is today, there is no performance loss to running a bit quieter.

Yes! Quite the opposite!
Todays muffler tech (well anything post 1990) actually increases scavenging on open exhaust and can increase HP/TQ values.
Gone are the days that open headers are "the best" headers and the most HP. Tuning of exhaust is almost as important as tuning an intake!

Quote

Will testing be done in the pits? Drive by? or both?

I find questions like this curious.
One should assume that it will be a worst case scenario event. So full throttle, full load @ peak power, wherever that falls in your rpm range.

Having been to various tracks that have sound decibel limits, you have no opportunity for testing of your exhaust except on the test and tune day before the race event.
However, the mic does move from location to location so you may pass on test day, but not on race day.

Some tracks do have a microphone station and you can fleece the system with turndowns etc. but not actually lowering the sound limit.

96db @ 50' is quite loud in a general sense. It could be compared as the same noise level as standing immediately beside a running lawnmower.

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I have no problems with bringing in a noise limit, and am only curious of the testing procedure to get an idea of how how loud my car is now. Don’t feel like changing my exhaust if it’ll pass! If it’s close but over, I may just add another resonator, if it’s well over then a different muffler may be in order. Hard to know without doing my own testing, in which case my testing should try and replicate the method that will be used at the track.

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@Joose

There is a HPDE/Test n Tune event the Friday before the race school weekend (April 29th).
I have been told the sound meter will be active for folks to get a listen in on how their cars perform.

That is three weeks prior to Event 1

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First off, I fully understand the need and process for noise abaitment by modification of exhaust  there are many other sources produced by our cars. 

Tires, intake, turbos, driveline, etc. Even stock daily drivers can produce sound levels above your 96 db target. 

I am not saying we should scrap the effort but I believe the level is a bit of a pipe dream.

There are also other methods we have not discussed. Berms, vegitation, panel fencing even billboards can be strategically placed to reduce noise travel in certain directions.

It may not be enough nor the only way we can become "good neighbours".

If this is a true effort we should think about modifications to GMP as well to help reduce sound travel from ALL users.

We should also do  distance and direction noise level testing to find out exactly what our issues are and whom they affect. Look at what the direction of the wind has on sound travel.

We are after all operating beside an airport that does not live within these guidlines. Yes, I already hear the people saying but .....

and I agree, an effort, any and all efforts, are signs to the minucipality that we are being proactive. 

Natural barriers are signs of long term commitments.

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18 hours ago, Jim Eh. said:

There are also other methods we have not discussed.

Discussion:

there are 4 ways to treat this issue: 

  1. reduce at the source (discussed above)
  2. dissipate over distance (discussed above)
  3. barriers
  4. absorption

So, Part 1 of my post: Barriers

Hundreds of miles of highway barriers have been constructed along freeways in residential areas, so the subject has studied and engineered with great rigor. Barriers are considered a success when they reduce traffic noise by 5 - 7db, it basically works by causing sound to travel a longer distance, up over the barrier. But there are several problems:

  1. It really only reduces noise in the shadow area near the barrier (like 100 meters or so), sound waves ‘bend’ over the barrier and the farther you are from the barrier, the less effective it is. For our application, this is the coffin, what follows below are more nails in the lid. 
  2. the barrier has to have substantial mass, like made of 3” thick wood planks or concrete or berms; flimsy materials allow noise to travel through the barrier
  3. there can be no gaps, even 1” gaps will allow noise to travel through
  4. the highway barriers we’ve seen along freeways, when constructed to a height of 4 - 5 meters cost between U$2 - U$3 million per mile

TLDR: https://onlinepubs.trb.org/Onlinepubs/nchrp/nchrp_syn_87.pdf

 

Part 2: Absorption 

Shrubbery and trees do absorb sound if you have enough of the best kind:

  1. A deeper band of trees work better, 100’ deep band approx 6db reduction, 200’ deep band 10db reduction
  2. should extend the full length of the pit straight + some
  3. Requires a dense band of trees and shrubbery 
  4. deciduous trees reduce in effectiveness as they grow taller
  5. evergreen trees are better, but need to be 10’ tall or more, as they get older they lose lower branches and shrubbery should fill in the gaps
  6. trees don’t absorb lower frequency bass sounds well, much better with midrange or high frequency sounds
  7. more mature stands can be a substantial fire fuel source
  8. none of my research sources addressed the possibility that efficacy reduces as you travel out of the ‘sound shadow’ (as happens with barriers above).
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The problem with sound walls, either physical or natural, is that the club doesn't own the facility.
The club also doesn't control other user groups.

On 2/23/2022 at 6:45 AM, Jim Eh. said:

Tires, intake, turbos, driveline, etc. Even stock daily drivers can produce sound levels above your 96 db target. 

I am not saying we should scrap the effort but I believe the level is a bit of a pipe dream.

I guess we will find out if this is true! I have no clue if my vehicles will pass but I'll find out!

Castrol is 98db - they share the similar topography as Gimli. Airport, reasonably close vicinity to residents etc
Mission is 95db

To the "extreme", for normal SCCA/NASA events, Laguna is 90db. And yes, there is potential at that level for stock or showroom condition cars to pass the microphone and fail. In-fact, a list exists that shows the potential candidates that would fail off the showroom floor. But, even then, the suggestion is that they fail because of environmental conditions such as wind and clouds and not simply fail outright. At first glance, the list is mostly high power cars with OEM exhaust by-pass systems.

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  • 2 weeks later...

The decibel limit will be posted as part of the registration process on MSR, so anyone travelling from other tracks will be made aware of the limit when they sign up and register. 

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  • 1 month later...

I’m certainly interested by this. I’ve got a Subaru with a Tomei titanium exhaust, very nice, expensive, and exceptionally light turbo back, as well as an external wastegate that vents to atmosphere ( i can’t weld my stainless steel dump tube to my titanium downpipe lol) buy I am curious as to why this came into play this season compared to previous exceptions. 

 I do understand this, 94db @ 50 feet, which isn’t really that far in all honesty, and I’m going to assume mostly everyone that has a modified exhaust system won’t pass this, even certain cars like Porsche’s and Lambos probably won’t pass….. I mean heck when I was in highschool my band of 15 could reach upwards of 100db lol! 
 

And I mean my car tapped in 5th gear with the external gate is not exactly quiet, but it’s certainly an interesting proposal.

but having an Exception weekend for vintage cars is kind of redundant, technically speaking according to MPI a “vintage” car is a car that is 25 years old, my car is 20 years old, just interested and trying to start discussion because I’m just more less confused! 
 

 

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It is 96dB at 50ft; that is a significant difference.

Most cars can pass this sound level - there are tracks that have an even lower limit. Of course that means that you can't just have an open exhaust; it has to be built to be somewhat quiet. A modified exhaust doesn't have to be a very loud exhaust, as noise does not equate power. And as far as I know, there never were any previous exceptions because there never was a noise limit at GMP. Your point about Vintage cars is misconceived: a Vintage vehicle in racing is something different than what MPI considers a vintage car.

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On 4/17/2022 at 7:38 PM, Damon Nash said:

I’m certainly interested by this. I’ve got a Subaru with a Tomei titanium exhaust, very nice, expensive, and exceptionally light turbo back, as well as an external wastegate that vents to atmosphere ( i can’t weld my stainless steel dump tube to my titanium downpipe lol) buy I am curious as to why this came into play this season compared to previous exceptions. 

 I do understand this, 94db @ 50 feet, which isn’t really that far in all honesty, and I’m going to assume mostly everyone that has a modified exhaust system won’t pass this, even certain cars like Porsche’s and Lambos probably won’t pass….. I mean heck when I was in highschool my band of 15 could reach upwards of 100db lol! 
 

And I mean my car tapped in 5th gear with the external gate is not exactly quiet, but it’s certainly an interesting proposal.

but having an Exception weekend for vintage cars is kind of redundant, technically speaking according to MPI a “vintage” car is a car that is 25 years old, my car is 20 years old, just interested and trying to start discussion because I’m just more less confused! 
 

 

Your downpipe should be stainless. I have the exact same setup as you on my sti and will be recirculating the ewg into the downpipe. 

 

Let's face it, the ewg pulse setup on the subarus just sounds weird lol.

 

Lots of cars should have no issues with the 96 dB limit. It will just affect the top 10 % of cars out there that are overly loud.

Edited by Ianfromduff
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Having run 20+ events at Mission raceway with a 95db @50ft sound limit I have got my car below the Gimli limit thankfully. It did take me a few exhaust revisions to get to this point though. 
 

Another thing that we have found effects this is relative humidity and low cloud cover two things we had a lot of at Mission. I always carry a “Laguna” pipe tip just in case the car goes over due to a change in weather. 
 

Jeremy

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