Superunknown

I have just performed a little test using a sound meter and was not surprised to get the following readings:

At idle: 92db
At 4500rpm: 108db

Measured from .5 metre from exhaust.

My mates 2003 Impreza WRX with PPP measured:

AT idle:72db
At 4500: 92db

I guess i wont be going on any tracks with a 100db limit then!

SimonExtreme

I think you mean to say that you won't be doing ANY trackdays! Your only chance is tracks that do drive by and for you to short shift. If you are serious about trackdays, I think you need to do something.

Lew964

I've got a sound meter in the office so i'll do a test at 0.5m away from the exhaust to see what level i get.
Where in relation to the exhaust pipe tip do you hold the meter ?
What exhaust system are you running ?

Superunknown

I held it in line with the exhaust pipe .5m away.

I have a cat bypass and a cup pipe.

Most tracks have a limit of 105db so i may get away with it....

Lew964

Did you hold the meter at the same hight as the exhaust or at waist level ?
I've seen test carried out in different ways and just wanted to compare your reading with mine.

Superunknown

At exhaust level. If they read from waist level then i would hope that it might scrape in at about the 105 mark.

Take a reading from both exhaust and waist level to see if there is any difference and then post the results!

kgorman

Most tracks don't measure you .5m away. At Laguna Seca for instance, the sound booth is 20m off the track at least. Try 20m and see what you get, I would be interested.

Jamie Summers

[QUOTE=Superunknown]At exhaust level. If they read from waist level then i would hope that it might scrape in at about the 105 mark.[QUOTE]

Static noise tests are usually done at a 45 degree angle 0.5 from the exhaust, so waist height is not far off it. You will also get a slightly lower reading with the clutch in.

Standard wisdom has it that a 964 with de-cat and cup pipe is about 105db static.

If you want to do something about it look here.
http://www.pistonheads.com/gassing/t...8&t=359516&h=0

Jamie

SimonExtreme

Many tracks in the UK do!

The norm is for the meter to be held at about waist height. The testers don't want to bend down! The test meter normally has a 0.5m rod attached so that the distance is accurate and they simply hold it so the rod touches the rear pipe.

If you are lucky, there is only one person doing it and then you don't rev to the correct point! It gets difficult if somebody is watching the revs

911addict

Still not clear to me I'm afraid!!
Is the meter mike held 50cm away from the pipe? Or is Simon saying its held at the pipe?

Even at 50cm it will make a massive difference as to whether its vertically 50cm above or diagonally or horizontally. Is there a recognised and 'correct' way to do this?

SimonExtreme

Sorry if I have caused confusion but I had meant to convey that the reading is done at 50cm away from the outlet. To ensure consistancy in reading, most tracks attach a 50cm rod to the soundmetre, the sole purpose of which is to measure the 50cm and it has no other function. Then it is easy for the person taking the measurement. They ensure the rod is at the exhaust exit and take a reading. Because of the 50cm and the device is hand held, the angle made is about 45 degrees. So, if you have a short tester, the angle is less and a tall one.......you get the point!

As for whether the measurement is to the side or from behind, I think that there is really an elemnt of randomness in this. Some testers try to look at the rev counter at the same time which means that they are off to the side. Some trust you to rev to the right point and are more behind the car.

Simple fact is that if you are close to or at the limit, you are running a risk. Getting through at one circuit is no guarantee of doing so at another.

As an aside, my car was last tested at Oulton Park and made 105db @ 4200rpm (the tester wasn't watching the revs!) Since then, we found a hole in the cup pipe and replaced that and I have taped up the holes drilled in the filter case. The reduction in noise makes the car far nicer to drive on a daily basis without loosing the great Porsche soundtrack.

Bob Rouleau

At Lime Rock, Tremblant and others the test is 15 meters behind the car one meter off the ground, meter set to A scale and fast response. The limit is 92 DB on the A scale. Based on your measurement you can subtract 14 dB from your reading to match the above limits.

Regards,

SimonExtreme

But the guy is in the UK!!!

AFAIK, no UK track uses this meathod of testing. The alternative to a static test at 50 cm is usually a drive by test where the test equipemnt is set up on a section where the car is likely to be at higher revs. This is easy to get around as you know here it is and just short shift to keep the revs and noise down.

IanR

All tracks in the UK that I've been to do the static test at 0.5m 45 degrees from the tailpipe with the meter pointing at the tailpipe, and 3/4 max revs (4500-4700 for 964). Some tracks don't seem to bother (Silverstone, Brands), and others give you a second chance. At Bedford if you fail the static, they'll do a drive-by test and let you on if you pass that - a couple of 964s have got on there this way that I know of.

aeroman

I am confused as to the relevence of taking noise measurements at a distance to the source where no sane person would have their ear???

I have worked in Noise Certification for aircraft for years. In order to have any value the measurement point must be representative of where the listener is located. Static jet engine noise test (engine on test stand) the mics are 75-100 ft away and under little "hats" an inch off the ground.