Noise testing at Snetterton race meetings

[DaveW]

In an effort to improve the efficiency of noise testing at race meetings, discussions have been taking place with the circuit management in respect of the noise test area at Snetterton.

For those competitors present on the 24th June, please note in the Final Instructions that the area of the paddock next to the current test area needs to be kept clear. You will also be given further details of the revision when you sign on - please make sure that you are aware of the change.

This change is just to improve the procedure and hopefully reduce the congestion that can occur as vehicles are tested prior to entering the assembly area. There is NO change to the actually noise test or limits.

If your vehicle passes the noise test a sticker will be affixed to the vehicle, in addition to the scrutineering ticket, indicating it has passed. Vehicles will not be allowed onto the circuit without both.

It may take a few meetings to arrive at the best solution for both the circuit and the organising clubs, so competitors cooperation and feedback will be most appreciated.

[Al Weyman]

Hopefully they will not test us just as we are about to line up giving us no time to make adjustments to get the noise down. Why not do it at scrutineering and include as part of the criteria for getting the pass ticket?

[DaveW]

Al, firstly the test is, as has always been the case, carried out before entering the assembly area. This is why competitors are always advised to leave enough time and the assembly marshals usually call competitors in good time before their practice session.

Secondly, the noise testing needs to be carried when the engines are warm but it is difficult to scrutineer cars with warm engines. If the noise test was carried out first, then the engines allowed to cool, it would significantly increase the time required for scrutineering. It would also mean subjecting the engine to another heat cycle which, particurlarly with full race engines, is unlikely to be appreciated.

As I mentioned, the actual test and limits (as laid down by the MSA) have not changed, so unless the engine or exhaust system keeps changing there shouldn't be significant problems. It is perhaps worth mentioning that limits imposed by circuits for testing can vary whereas at race meetings the limits should be consistent.

Ultimately, the changes to the noise test area have been considered to allow it to be quicker and easier, improving the process for competitors and officials alike. Hope that helps.

[Al Weyman]

I knew there must be a logical reason, thanks for explaining it. We are down Snett later in the year with my IROC which failed Brands testing once (but past twice oddly enough at meets earlier in the year!) now fitted with an extra exhaust silencer box so hopefully for now it will be quiet enough, if not me mate will have to do his quick SuperTrapp fitting again in the assembly up area (never leave home without them!) :-).

[Tim Falce]

I was wondering how you get away with fitting a Supertrap as temporary fittings are prohibited, but don't tell anyone I said so

[Al Weyman]

When it is fitted with two big screws how is it temporary, you could say that about any part of the whole system. Its either that or I go home and if they are that bloody minded I would never come back. Typical MSA Blue book gooblydegook, what is and isn't temporary.

[R59]

As you can easily "tweak" the supertrapp, by adding/removing plates, is it therefore "adjustable for noise", and therefore not legal......

Arrrgggghhhh

I also assume that following vehicles on the way into the assembly area will be kept back to the distance prescribed in the blue book in relation to the space that must be clear around the car, without obstacle, etc.. to enable accurate measurements to be taken....

[Al Weyman]

Not adjustable if the nuts are tack welded on though is it and thats soon done, its not exactly a five minute job either to remove the discs I did just that at the weekend and the special nuts and bolts they are assembled with required the use of a vice and a lot of strenght and took me about an hour to do the two. You could drop a silencer out the system and replace it with plain tube in minutes so would that then be considered adjustable, its a nonsense. I would look at the term adjustable to beone of those instant cutouts that are like a big butterfly valve in the system I do not see a supertrapp in the same light and in fact nor did the scrut at Brands who let me and Gerald Faber (another Camaro) race with Supertrapps and quite right too. At the end of the day the goal is to get the car on the track and running below the legal decibles and anything you can do on the day surely must be OK.

[DaveW]

Firstly, the test is done at 0.5m so that reflected sound from other vehicles, walls etc. does not become a factor.

Then the area we are proposing to use is slightly further back from the entrance to the assembly area than previously. If your car is unfortunate enough to fail there will be sufficient room to move away from the noise test area without blocking access to the assembly area. It will not be possible to enter the assembly area and then work on your exhaust as you would not be able to get back out to be re-tested.

As far as additional silencing is concerned (and hopefully any scrutineers reading this can verify) I think if it's securely fixed to the vehicle, such that it can't come off in use, and that any silencing material(s) can't be ejected, hence altering the efficiency of said silencing, then it is likely to be allowed. For this reason that's why Al doesn't/shouldn't have a problem with the Supertrapp. It might be adjustable but not whilst running and it is unlikely that it is going to be done in the assembly area just before a practice session.

Finally, bear in mind that the scrutineers or clerk can ask for a vehicle to be retested so "adjusting" the system after passing the noise test for seem to be a foolhardy thing to do.

[Al Weyman]

Thanks Dave that seems very sensible.

[midgetman]

>>>>>>Firstly, the test is done at 0.5m so that reflected sound from other vehicles, walls etc. does not become a factor.

Is that really so? I well remember when my standard road car was only just below the noise limit at a sprint at Combe. It was tested in a queue. At all other events it was tested on its own and was under 90dBa. So I don't believe that.

Unless of course the Combe noise meter was inaccurate and we know that would never happen because standards across the country are completely uniform, aren't they boyz'n'gurlz ;-)

>>>>>>>>and that any silencing material(s) can't be ejected,

Again at Combe, some years ago a chap with a Camaro silenced his car with Coke cans up the tailpipe. How do I know they were Coke cans? Well, we found one embedded in my car when he left the line and fired them out like mortars :-) Not you was it Al?

[MGDavid]

[QUOTE=DaveW]Al, firstly the test is, as has always been the case, carried out before entering the assembly area. This is why competitors are always advised to leave enough time and the assembly marshals usually call competitors in good time before their practice session......

==== so why have I always had a noise test at Silverstone on the exit from the scrute bay?!?

[DaveW]

[QUOTE=MGDavid]

Originally Posted by DaveW

Al, firstly the test is, as has always been the case, carried out before entering the assembly area. This is why competitors are always advised to leave enough time and the assembly marshals usually call competitors in good time before their practice session......

==== so why have I always had a noise test at Silverstone on the exit from the scrute bay?!?

We're not talking about Silverstone, or what happens at any other circuit for that matter, just Snetterton.

As I said in my original posting, this Saturday 24th June is the first time the new arrangement will have been tried and the area is not yet marked up permanently but, if it works as intended, should improve the process. And again, the specific procedure of noise testing has not changed because that is laid down in the Blue Book.

[Paul V]

Originally Posted by midgetman

>>>>>>Firstly, the test is done at 0.5m so that reflected sound from other vehicles, walls etc. does not become a factor.

Is that really so? I well remember when my standard road car was only just below the noise limit at a sprint at Combe. It was tested in a queue. At all other events it was tested on its own and was under 90dBa. So I don't believe that.

Unless of course the Combe noise meter was inaccurate and we know that would never happen because standards across the country are completely uniform, aren't they boyz'n'gurlz ;-)

>>>>>>>>and that any silencing material(s) can't be ejected,

Again at Combe, some years ago a chap with a Camaro silenced his car with Coke cans up the tailpipe. How do I know they were Coke cans? Well, we found one embedded in my car when he left the line and fired them out like mortars :-) Not you was it Al?

I have trouble with the first statement - the difference between 90db & 105db (assumption) is huge.
What revs were both tests done at, hot or cold engine?

The Combe owned meters have a valid certificate and are calibrated at least once a day - you are welcome to see the log.

The temporary parts rule is to attempt to stop the more silly fixes that get presented for test. The standard phrase is 'no coke cans/wire wool or jubilee clips please'. Still get some tho'
Within reason, extra parts if properly clamped/fixed are not likely to be rejected.

Al - Testing after scrutineering is not always possible due to circuit curfews.

[Al Weyman]

Thats how I thought a sensible scrutineer would act after all like the chap at Brands he only wanted to get me and Gerald out to race and did really put himself out even coming round to the paddock to inspect the SuperTrapp fitment, can't really be any fairer than that.

Oh and no it was not me with the Coke cans.

[Anuauto]

I've never seen a local resident with his or her ears 0.5 metres from the exhaust outlet.
That actually is a serious comment as a former (rally) Clerk of the Course. Experience suggests that older 2 valve per cyl engines suffer more in this particular option of noise testing than modern multi valve/cam "turbines" but perceived noise when actually competing may be no different.

[Paul V]

Originally Posted by Al Weyman

Oh and no it was not me with the Coke cans.

I should hope not too.
Anyway the record I know of is held by a mighty Porsche 935, twin turbos, shed loads of bhp represented with 2 coke cans stuffed up the exhaust ends.

Turned it on and blipped it - it shot the cans 50ft.
Was a while ago now but it is fondly remembered.

[DaveW]

Originally Posted by Anuauto

I've never seen a local resident with his or her ears 0.5 metres from the exhaust outlet.

Maybe not, but the test can be carried out at 0.5m, 2m or 8m with different pass levels for each distance, such that the 105 dB(A) at 0.5m equates to 93 dB(A) at 2m. The problem is that for a 2m test you need 10m with no "large reflecting objects" which means a huge area has to be kept free.

It is true to say that on some vehicles the induction noise can be more noticeable than the exhaust but, as yet, nobody seems to have suggested this be tested, possibly because there may be inherent difficulties in doing it.

[R59]

One of the biggest difficulties in the issue of noise, is the perception of how loud something really is.

The dB scale is logarithmic, for audio levels, a perceived increase of double the sound level, is 10dB, requires TEN times the power to produce it.

The fall-off in the level, based on distance, is known as the "Square rule", where the level of fall is the square of the distance, ie: twice the distance = sound level is four times less, 10 times the distance = 100 times less, etc..

But don't forget, it's a logarithmic scale, so 4 times less power is 6dB(A) - so at 0.5m you have 105dB(A), at 2m, which is 4 times the distance, and therefore 16 times less power, that's 12dB(A) ie: 93dB(A) as Dave says.

Go from 2m to 8m, and another 12dB(A) comes off.

Another factor is the effectiveness of the calibrators used. While I do not disbelieve that scrutineers test their meters regularly, using the supplied calibrators - which is usually a 1kHz tone generator that creates a 100dB(A) signal as perceived by the microphone on the meter. That's OK, providing the filter's response is correct. The (A) scale is supposed to simulate the human ear's frequency response. The simple single frequency calibrator cannot perform that test.

A "flat" response, or using the dB(C) filter, could see more cars fail that currently pass.

However, frequency response is the key here, and different frequencies are attenuated/absorbed/reflected by our surroundings, which affects the levels that we perceive. Low frequencies are often absorbed, which is why many big V8's sound quieter at distance compared to a small 4 pot which may produce a lower reading on the sound meter at 0.5m. High frequencies bounce off solid objects much better (or worse if that's your point of view!), making small screamers sound even louder.

The legislating body has to set an arbitary level which is clear cut. As most people do not understand the vagaries of frequency response, viz-a-viz environmental attenuation, especially nearby residents who don't like hearing people enjoying themselves over the hedgerow, between periods of annoying their own neighbours with their best 2-stroke strimmer, garden vac, or similar noisy annoying contraption.

A very very thorny subject.

Rob.

[DaveW]

Very informative Rob and noise is an issue/topic that could be discussed for ever, particularly in the current climate.

The purpose of my original post was to advise drivers coming to Snetterton, starting this Saturday, of the organisation and operation of a new noise test area (slightly ahead of where it used to be) with a view to improving the current setup.

This is likely to be trialled over a few meetings and all we would ask is for your cooperation and feedback as to how it works.

[Bob Pearson]

I presume cars in garages will be tested in the pit road if tested at all

[midgetman]

Paul V wrote: I have trouble with the first statement - the difference between 90db & 105db (assumption) is huge.

My point exactly. That's how I knew something was wrong. But it was a long time ago and it really doesn't matter now.

Don't want to go any further down this route, just wanted to demonstrate that I don't believe the contention that there's no effect from reflected noise. Only based on my own personal experience, no scientific principals.

I once saw a Supertrapp that was welded on the end of a side-exit exhaust that set fire to the fibreglass body skirts! LOL

[DaveW]

Originally Posted by Bob Pearson

I presume cars in garages will be tested in the pit road if tested at all

Bob, as far as this Saturday (BRSCC) everything will be tested in the noise test area, not the pitlane. I suspect that you may be there on Sunday with BARC and whilst I can't be certain would expect you to be tested in the same area. It certainly is not the usual practice to be tested in the pit road.

It is also normal with other clubs as well, because even those cars allocated garages usually have to go to the assembly area for practice so that a) they can be noise tested and b) the assembly marshals can ensure that all vehicles have passed scrutineering.

If you check my earlier postings you'll see that it is not a huge change from what you may have had in the past at Snetterton, just an attempt to improve the process for drivers and scrutineers.

[Barry Pomfret]

MSV circuits seem to be tightening up on noise readings. We had a Formula Ford Zetec out testing at Oulton today and during a static noise test they told my team that we were on the limit! This is very surprising as it has passed numerous noise tests previously with the same exhaust sytem and engine. Perhaps they were a little over zealous so as not to upset the neighbours?

[Anuauto]

Originally Posted by DaveW

Maybe not, but the test can be carried out at 0.5m, 2m or 8m with different pass levels for each distance, such that the 105 dB(A) at 0.5m equates to 93 dB(A) at 2m. The problem is that for a 2m test you need 10m with no "large reflecting objects" which means a huge area has to be kept free.

It is true to say that on some vehicles the induction noise can be more noticeable than the exhaust but, as yet, nobody seems to have suggested this be tested, possibly because there may be inherent difficulties in doing it.

As I made clear, I am well aware, from previous experience, of the options - and I do not acccept that, in most cases, a "distance" test is impracticable. It is not a criticism of any particular venue, more the general acceptance and lack of complaint about the 0.5 m test.