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Discussion Starter · #1 ·
Hey guys, bought myself a new toy, had a play yesterday.

Over here in the UK, they test your car at 3/4 of your max rpm (5250). They test from 500mm/20" away at a 45 degree angle. Not sure for the rest of the world. Levels vary from track to track, with most at or around 102db, some at 105db, and some very strict at 99db.

When I went to Brands Hatch, the limit is 105db, the guy who tested me told me not to 'rattle the windows on the way out of the pits!' Which to me told me I was over but he let me through. When I went to Cadwell Park, I arrived late and didn't get tested, and also didn't get flagged during the day, so I was happy.

Anyway my findings are a little scary, bare in mind that an increase of 3db is TWICE as loud!

Cold idle 101.3db!!!
Warm idle 79.2db
Warm @ 5250rpm 108.3db!!!!!

Now remember thats at a static 5250rpm, not under load when screaming through the rev range! Well all I can think of is they must like the noise.... ;)

If anyone has any requests for testing, I'll try my best. If you live near enough, we can meet up and I'll test your car, or if you are going to the Dyno day at evolve in June, I'll be taking it there with me.
 

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whats road legal,i have h&s back boxes and mmmmm love the roar..the neighbours maybe not.
wouldnt mind oneday getting mine tested,im not mega far away other side of bury st edmunds.
 

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Discussion Starter · #3 ·
whats road legal,i have h&s back boxes and mmmmm love the roar..the neighbours maybe not.
wouldnt mind oneday getting mine tested,im not mega far away other side of bury st edmunds.
I don't think there is a limit legally on the road, but I know someone has been done for 'noise pollution' before. Give us a shout if you wanna meet up.
 

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Discussion Starter · #5 ·
Just googled it apparantly its 101db, but where I go for an MOT it really wouldn't matter ;)
 

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Sound level meters certainly do have their uses.....


Don't worry to much if your meter indicates a slight over-read; most of the simple SLMs over read by a few dB. Also, one thing to check is the frequency weighting that you are using - this will appear as 'A', 'C', or 'Lin' on the meter. You want it set on 'A' which reflects the frequency response of the human ear; 'C' and 'Lin' will give higher readings.


You are entirely correct that a 3dB change is equivalent to a double or halving of sound energy, but our ears have a unique set of gain controls that mean we detect a 3dB change as being just noticeable. A 10 dB change is detected by us as being a doubling or halving of loudness, whereas it is actually a change in sound energy by a factor of 10.


I'm going to the dyno day so I'll happily bring my meter for you to compare yours against if you like, and to extend the offer of free testing to anyone that wants it. The meter I use is more accurate than the ones most race tracks use.
 

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Discussion Starter · #9 ·
Sound level meters certainly do have their uses.....


Don't worry to much if your meter indicates a slight over-read; most of the simple SLMs over read by a few dB. Also, one thing to check is the frequency weighting that you are using - this will appear as 'A', 'C', or 'Lin' on the meter. You want it set on 'A' which reflects the frequency response of the human ear; 'C' and 'Lin' will give higher readings.


You are entirely correct that a 3dB change is equivalent to a double or halving of sound energy, but our ears have a unique set of gain controls that mean we detect a 3dB change as being just noticeable. A 10 dB change is detected by us as being a doubling or halving of loudness, whereas it is actually a change in sound energy by a factor of 10.


I'm going to the dyno day so I'll happily bring my meter for you to compare yours against if you like, and to extend the offer of free testing to anyone that wants it. The meter I use is more accurate than the ones most race tracks use.
Thanks Dave, I knew a bit about the whole human perception of sound but didn't want to sound stupid trying to explain it! You done a much better job! I was on 'A' which is human ear if you like. I will be good to compare, thanks.
 

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I don't think there is a limit legally on the road, but I know someone has been done for 'noise pollution' before. Give us a shout if you wanna meet up.
There is a limit :

Motor vehicles with trailers: permissible sound level

In France, they can control your "noise" level and they can force you to put back the original exhaust (with a control afterwards :D). On my grey card (car registration document), it is said that the sound level of the M5 is 85dB, so I'm an "Outlaw" :D
 

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whats road legal
This is not my area of work, but from what I remember, there are a few elements to it:

New cars. The current limit for petrol engined road cars with less than nine seats is 74 dB(A). I believe that the measurement procedure changed in 2007, and I am not familiar with the new method. The old measurement procedure was not straight forward and depended on the number of gears and type of gearbox fitted. The measurement was taken over a 20m distance under full throttle with the microphone being a perpendicular 7.5m from the mid point of that 20m run. In an M5, the run would start in third gear at 31mph or 50 km/h. This rather strange method of measurement lacks much real world validity and is open to abuse. Some Ferraris and the like have exhaust valves that open to increase noise level at higher revs; this increase in noise level often happens just after the test would have finished, coincidentally...

MOT time - it is down to the tester to decide whether the car produces 'excessive' noise. Rather subjective then.

Modified exhausts: As far as I know, it is actually against the motor vehicle regulations to modify the exhaust of a road car so that it produces a higher noise level than measured at type approval for that model.
 

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Discussion Starter · #14 ·
Modified exhausts: As far as I know, it is actually against the motor vehicle regulations to modify the exhaust of a road car so that it produces a higher noise level than measured at type approval for that model.
Could this be another one of those stupid laws in the UK where they are allowed to sell them, but we are not allowed to use them? Its the same with all the blue lights you can buy that are 'for show purposes only'ouich
 

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Thanks Dave, I knew a bit about the whole human perception of sound but didn't want to sound stupid trying to explain it! You done a much better job! I was on 'A' which is human ear if you like. I will be good to compare, thanks.
Most things to do with acoustics are a pig to explain; I've just had a bit of practice.

Sound decays very quickly with distance from the source, so it is often difficult to compare one race tracks noise limit to another; some take it at differing distances, some with a static car and some as a drive-by.
 

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Could this be another one of those stupid laws in the UK where they are allowed to sell them, but we are not allowed to use them? Its the same with all the blue lights you can buy that are 'for show purposes only'ouich
Pretty much, yes. I believe this regulation still stands.
 

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Discussion Starter · #17 ·
What is it you do then Dave?
 

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Discussion Starter · #19 ·

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What is it you do then Dave?
I'm a noise consultant. I work with housing developers, industry, commerce, entertainment venues and the like, solving their acoustic problems and doing noise surveys in support of planning applications, for example. Pretty varied work; I take on most types of acoustic jobs and it is generally rewarding.

Tomorrow I should be with a board member who owns a Nowack N500. If we have chance, I'll measure both our cars using the static method and let you know the result - mine is mechanically standard.
 
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