As i remember from my degree we should be using db(A), other measurements are db(m) and db(w) which relate directly to the power in watts.

Reading off my V5C document for a September 2004 WRX UK sourced it reads


stationary db(A) 81
engine speed (min-1) 4200
drive by db(A) 70

I should imagine if I fiited an aftermarket exhaust that was indeed far louder than 81, I would get nicked.....

I would also assume it won't be long before all V5's have noise limits....

Cheers Gary; Id been wondering why I chose an Arts & Humanities degree and now Im sure I made the right choice.....

:)

From the site I mentioned earlier, dBs relating to pressure are 10log(p2/p1), so if you double the pressure it equates to 10log(2) = 3.01dB (which is where the approximation of 3dB = double the noise comes from).

Apparently microphones (and presumable sound meters) measure the sound pressure, so this 3dB rule of thumb makes sense.

It will be very, very interesting to learn what sound meter the police used, and how they did it!!!

Does this mean that Im vindicated Iain? :)

You speak the truth!

My mate (who works on weapons systems and know a bit more about dBs than I do) says there's another rule of thumb that says perceived loudness only doubles for every 10dB (though this is purely subjective and very dependant on how good yer lugs are), which is perhaps what the police are alluding to in their letter...

A guy at work used to be a traffic cop, so I asked him.

He said that the law can refer either to altering a component (eg by drilling holes or knocking out baffles) or changing the system (or parts of the system) that result in it being noisier. Which isn't exactly good news. :mad:

He had to rush off today, but I'm going to ask him tomorrow about noise meters and whether they're standard issue etc etc.

Gary C - you are correct that it should be using db(A) as this is the dB scale "weighted" to reflect human hearing. The SVA test definitely talks about dB(A).

IIRC as well (degree in physics, but seems a long while ago), sound intensity increases as the sqaure root of sound pressure - therefore ~3dB is doubling of pressure, but ~6dB is doubling of intensity. Perceived volume links to intensity, so will double approx every 6dB. I'm happy to be proved wrong if my memory is failing. ;)

Iain - I think that traffic cop in question is only stating his opinion. I have heard from other respected sources the complete opposite, which would make sense to me. Otherwise, a Kwik-fit exhaust fitted to a quiet car at +1dB could be much quieter than most new cars on the road, and yet technically illegal. People of limited expertise such as us could speculate all day, but it sounds to me like a job for a proper lawyer to confirm.

Yep, is my 03sti PPP illegal.
Would be nice to know if I'm pulled by Mr traffic cop.

Dipster

If it's not legal, then where does it say this in the documentation?

Dipster

I'd like to know the situation as well (particuarly as I'll be in the Inverness area in a few months time and could do without a £30 holiday fine.. :/ )

Theres two things we need to be fully certain of

1) The section of legislation in question (and to be fair I wouldnt hold judgement for that point alone on an ex traffic cops view given the complexity of the situation- after all thats what information the nice Mr Plod has already told you :()

2) Then following on from that, the actual noise level of the car under formal test conditions.

I reckon the key thing is to get the car correctly sound tested, in line with how the procedure should be carried out, by an appropriate expert. Any ideas who to approach for that?

Once you've got that, great if it's less than the noise should be the police wont have a leg to stand on- problem solved. If however it's more you'd then have to start to dig further into the legality of the application of the legislation.

I too would be very interested to hear the outcome. I have a MY'05 WRX with PPP and use it everyday (Less than 2 years old and just had 60K service). If I am pulled over, I would like to know how to handle it.

I would also like to hear if your dad gets the case overturned which in my view, he should. :)

Don't you mean an MY03? MY05 would be brand new wouldn't it?

I'd be interested in the outcome of this too though...

He is lurking on here at the moment.

Someone give him a nudge ;)

Sorry, yes I mean MY'03. I am easily confused! :cuckoo:

Surely anyone getting tugged for having a std PPP fitment on their car needs swift recourse from Subaru (UK) - it is being implied that Subaru (UK) & Prodrive are selling an illegal product.

You would have full rights to claim back damages arising from them as it would be their fault in effect for selling this part illegally and not informing you.

*If* as a previous poster said, the PPP tailpipe is E marked then they (plod) haven't got a leg to stand on, as it has been officially homologated for legal use on the EU/UK.

Now anybody with a ninja/hyper dragger mega loud exhaust I can understand, as these really are antisocially loud - which I suspect is what this police force in question is trying to eradicate - but to fail a manufacturer supplied 'E' marked part - they are cruising for a fall!

Someone from Subaru (UK) phoned him yesterday to request copies of all correspondence to date. They thought it would be very difficult to get the police to change their minds...no surprise there though.

As has been said though - it's in their interests as much as anyones. How much would it cost them to recall their PPP-spec'd cars and fit a standard exhaust???

Very good point.

Thing is though this applies to the whole aftermarket exhaust industry, it isnt just Prodrive products and it's not just Subarus it relevant to. How many non OEM exhausts are sold every year in the UK?

We really need to get this issue properly understood and clarifed before it starts to become a serious problem for all of us.

How does this law apply to imports where the exhaust obviously isn't going to be E-Marked?

I'm now getting paranoid about getting a tug in my Legacy B4 (H&S backbox) and getting it compared to the closest UK model which would be a non-turbo 2 litre model.

Hopefully it'll just be a case that there will be no data available so they can't do anything.

Those of you with JDM STIs could be in for an interesting time, they should just be down as "Impreza WRX STI" without the "Type UK" bit, but you may want to get your log books updated to be sure.

News from Subaru!!!
 

Subaru have been in touch with my dad.

They are going to take his car down to Bedfordshire, to an independant testing center, and conduct noise tests based on the following:

Static and drive-by tests with his car (as per current legislation).
Same with a new PPP exhaust system fitted.
Same with a standard WRX exhaust fitted.

They're then going to remove the PPP and run all the tests again. This will give a definative set of results that says which component adds what to the sound output.

They've written to Northern Constabulary asking for their sound-testing procedures (LOL) :thumb:

While all this is going on they're supplying a replacement car.

Now that's customer service!!!

Will keep you all posted.

Iain

:) good on you for not lying down and letting the police take the ****.

Top marks for Subaru! :)

I don't think you could ask for more help than that from Subaru. Great stuff :)

top notch to subaru:notworthy ,lets hope they dont have to do this too often :thumb: :luxhello:,and to the other side :hjtwofing .lets hope that subaru prove the case and stupid incidents like this are deterred in the future,

goodluk

Visited Inverness in March, top roads and drive up. Plod must have been hiding under a rock, had a Ninja on the Classic wagon. Will be up again soon in the WRX with WR Sport back box. I'll see what the outcome from Subaru is first!!!!

Err, not quite right actually. 3dB is a doubling of power, 6dB is a doubling of volume. So 79dB to 88.7db (9.7db) is a tripling of volume.

Have a look at :

http://www.phys.unsw.edu.au/~jw/dB.html

Great News, Fantastic service from Subaru

I am looking forward to hearing the outcome !

Big thumbs up for Subaru ! I am pleased that they are taking this so seriously !

Very pleasantly surprised that Subaru are taking this seriously. It bodes well for the outcome, as presumably Subaru will have some legal beagles who really know their stuff. Hopefully this will be resolved in such a way so that we know where we stand with aftermarket exhausts.

Police up there must be really bored.