They are all different unfortunately. Different distances/rpms and angles.

I also suspect some trackside numpties get confused between dB and dB(A) - I have tried to research this and have asked planty of testers/track advisors the exact criteria and they typically haven't got a clue.

Some tracks actually have permanent sound levels metres at track boundaries that are linked (by data modem) to the local authority, very similar to airport noise monitoring.

The most common test I have seen was 1 metre from tailpipe and at 45 degrees.

_________________
JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

mine was 1 meter at 45degree angle @ 5200rpm

the permanent sound meter at snetterton is one as you say from 20m away, i presume this is a track boundary.

thanks for all your replies! its interesting to read as i too wonder how much interference from outside sources is picked up

To answer your original question...
102.8 dB at 1 metre should measure 76.8 dB @ 20 metres. What I can't take in to account is the additional noise from higher rpm/full load you will get when the internal wastegate opens. External wastegates are nomally unsilenced and IMHO this is totally unnecessary. It should be possible to locate a small motorbike can to stick on the screamer.

I know it is a ball-ache with all these different noise regs at different tracks but I also believe as track day enjoyers we need to actually get behind the reduction of noise from our own vehicles to safeguard our enjoyment. The local authorities will not budge on requirements for noise emission from circuits.

It basically works that there is a limit to the total noise emission from the circuit over 1 year.
To give you an example of how it is calculated..
They have a limit of lets say 20 100dB days over that year set by the local authority (a number picked from thin air)

The circuit could therefore run over that year:-
5 106 dB days (probably a race day)
10 103 dB days (race or test day)
or 20 100 dB days
or 40 97 dB days
or a mix of 5 103 dB race days and 10 100dB trackdays.
For each extra 3 dB you add to your noise you are halving the number of days they can run.

A lot of the smaller circuits used for track days are struggling to be financially viable and the simple way to increase income is to increase the number of trackdays.

A lot of the circuits therefore have to limit the number of track days

_________________
JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

thats good news then, mine should be well below the limit, to be honest i dont know how it managed a 102.8 anyhow!

yeah i see what you mean on all the above, thank you for all the info, very informative.

but with regards to the drive by i always wonder how loud screamers are as surely say... a screamer pipe 1.5 feet long running the pressure off at 1.8 bar would only be as loud as a Lamborgini or a Ferarri at full throttle??

as these type of cars are hideously loud at full chat and surely just as loud as the said screamer pipe?

just wondering as i have been searching old posts of cars on snetterton and both of the above have appeared on the same 105db days with a 92db drive by.

unless the sound of the car alters the perception of the reader but surely the high pitched squeel of the ferarri would be more noticable at long range?

Unfortunately, as a nation we are becoming less tolerant. Human rights and blame/claim culture are taking over.
Once upon a time, if you didn't like noise you didn't go and live by a racing circuit / airport / etc. Nowadays houses are built next to existing noisy places, people move in then start complaining. We have lost many good venues over thw last few years.

To be fair, you can still make good power without noise so there is no need to annoy neighbours. Doing so is largely just being selfish.

_________________
If at first you don't suck seed, try drier grain.

You are right CDB. The problem is the demographic shift to the south which requries more homes. More houses need to be built and for some reason the countryside / farmers land is left and areas near to existing housing and industry are developed for residential habitation.

Every one wants to be near to centre of town/train stations/airports/motorways for ease but no one wants the associated noise of trains/planes/cars and industry. The two don't mix and IMHO should be kept seperate in areas designated for particular use (industrial estates and house should not be located next to each other) current noise policy for planning and nuisance is and always has been ill-conceived.
To obtain planning for a residential proposal you have to measure the outside noise levels and then demonstrate that the internal noise levels will be acceptable (stick some bloody good double glazing in and acoustic ventilation and you can build next to a train line - look at Woking train station). For noise nuisance you measure the noise level outside of the residential property full stop.

As such the new residential properties that have been granted planning permission based on high-spec double glazing etc and are located next to an industrial estate are already very likely to be subject to noise nuisance. It is the responsibility of the noise generator to quieten down. The 2 policies are totally seperate and not considered together.

In the event that the noise generation is produced by something that is considered to be for the general publics greater good (such as a new motorway/airport/trainline) then tough - you just have to put up with the noise.

Back to Dales point - IMHO screamer pipe noise is not predominantly engine noise but bloody high velocity air movement noise. Whilst wastegate size is dictated by turbo size and boost levels (more to control boost) I am often surprised by the small size of the WG considering how much of the exhaust gas will pass through it. Most seem to keep pipe size after wastegate the same as WG size yet stick on a bloody large exhaust.

_________________
JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

i see jp, so hence the high db noise measuring not just due to the exhaust gas but the speed in which it goes through the pipe. thanks!

but with regards to supercars as such, are these cars surely not as loud as our cars etc?

at donington 2 years ago a lambo got banned within 10 minutes of a 98db day.

Most cars are similar noise levels once you have stuck a performance exhaust on. The higher the BHP the more noise I expect is produced.

Oddities such as a screamer or ITBs on simple filters seem to ramp up noise by quite a margin.

I did a bit of noise monitoring on a dyno cell or two - strangely the Honda VTEC on cam and with a foam type filter induction kit was the loudest - much louder than a supercharged 6.2 V8

High frequencies are however easier to attenuate without losing much power at all.

_________________
JP
GT4DC Treasurer

Grey St185 RC
Silver BMW E46 M3
Multicolour yawn Honda VFR400
Silver Honda Civic Type-R

i can believe that for sure! our friend with his civic type-r is just stupid when it hits vtec, just the induction noise is silly loud!, same with our friends caterham r500, but that is all the time noisey on throttle.

i suppose we shall just have to see when we get to the track but at least i shall pass!