Lightning
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| posted on 17/2/05 at 08:30 PM |
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Noise
I'm going to borrow a noise meter from the very nice lads at SWTOC as I want to do a track day next month at Keevil.
My car only just passed the SVA (shouldn't really only rev'd to 6K). It has to be under 100 DB at 0.5m.
I have a blade with an MK exhaust.
If it's to loud will restuffing reduce the noise and if so which material and where?
Ive got 'till the 14th March.
Anyone else going?
Steve
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Jon Ison
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| posted on 17/2/05 at 09:03 PM |
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If you re-pack be carfull you dont put to much in, you want it to soak up the noise not bounce it about, if you pack it too tight its like claping
your hands in a "ginnle" it sounds louder. Most track days are "drive by" rather than a static test (a lot do say they will
test it static on forms but don't)
You can get one of them "decible eaters" cheap as chips on ebay stuffed up exhaust and held in with one bolt, but ive found them not too
work for me unless iv'e shoved soom wire wool up 1st and used the "decible eater" to hold it in there, all that said sort it before
you go, nothing worse than turning up for a couple of laps then black flag, was at Donnington Sunday, they where keen 98dba drive by with plenty of
black flags to be seen.
what rev counter you got ? Iv'e sneaked thru static noise tests by altering the number of clys setting on a rev counter, making it read 6000rpm
when its actually doing less, crafty but it works....
[Edited on 17/2/05 by Jon Ison]
[Edited on 17/2/05 by Jon Ison]
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Northy
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| posted on 17/2/05 at 10:21 PM |
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The noise monitor at Donington is one of ours! 
It's not sited in the best place though which makes it worse. 
Graham
Website under construction. Help greatfully received as I don't really know what I'm doing! 
"If a man says something in the woods and there are no women there, is he still wrong?"
Built 2L 8 Valve Vx Powered Avon
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Hellfire
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| posted on 18/2/05 at 01:13 AM |
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Ours at 7000RPM was 104db - not good, equivalent setup. Chances are the wire wool jobby will blow out and/or restrict it to much. Better to reduce the
bore of the exhaust but this also has the same effect as a brick under the LOUD pedal... May be worth repacking but as the Isonmaster says - too much
will act as no packing at all. Too little and the same effect... good luck. Sounds like trial and error to me...
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Jon Ison
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| posted on 18/2/05 at 07:14 AM |
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Northy, go get it sorted...
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Lightning
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| posted on 18/2/05 at 11:11 AM |
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Yep just had it tested 104DB at 7700 revs
That being 3/4 of max revs ish.
Steve
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Lightning
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| posted on 18/2/05 at 11:21 AM |
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Just had a word with Performance exhausts at Collumpton, will go up there and see what they can offer. I want to get a boss put in anyway for a Lambda
sensor for rolling road tests.
Steve
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NS Dev
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| posted on 18/2/05 at 01:34 PM |
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Some years ago I had a play around my old Opel Manta (with 16v XE engine on throttle bodies) with a sound meter..................the exhaust was
consistently around 100dbA, (2.5" system with two big silencers) but the induction noise was over 103dbA!!!!!!!!!
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Northy
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| posted on 18/2/05 at 06:18 PM |
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quote:
Originally posted by Jon Ison
Northy, go get it sorted...
What do you want me to do!???
It because of where it it (on the pit straight). Sound bounces off all the nice hard surfaces around it and back to the microphone!
Graham
Website under construction. Help greatfully received as I don't really know what I'm doing!
"If a man says something in the woods and there are no women there, is he still wrong?"
Built 2L 8 Valve Vx Powered Avon
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Northy
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| posted on 18/2/05 at 06:23 PM |
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quote:
Originally posted by Dave Ashurst
I think drive-by noise measurement is quite different to the SVA exhaust noise test. Just wondering, are the results comparable?
I mean, I wouldn't want to spend much on silencing the exhaust (and retuning the engine to suit) if it wasn't necessary.
ISTR in a drive-by noise test there's an array of microphones? parallel to track, 3.5m from vehicle?
Don't they measure combined noise from:
tyre/road
wind
intake
exhaust
mechanical noise (e.g. whine from a straight cut gearbox can be significant)
screaming passenger..
etc
I suppose 104dBA at 500mm from the exhaust would be less at 3.5m?
Is it worth checking that first?
[Edited on 18/2/05 by Dave Ashurst]
Nah, just look out for one of these:
 
Rescued attachment 243_4a.jpg
Graham
Website under construction. Help greatfully received as I don't really know what I'm doing!
"If a man says something in the woods and there are no women there, is he still wrong?"
Built 2L 8 Valve Vx Powered Avon
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Northy
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| posted on 18/2/05 at 06:24 PM |
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Or one of these:
 
Rescued attachment nmt_1.gif
Graham
Website under construction. Help greatfully received as I don't really know what I'm doing!
"If a man says something in the woods and there are no women there, is he still wrong?"
Built 2L 8 Valve Vx Powered Avon
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Northy
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| posted on 19/2/05 at 09:35 AM |
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quote:
Originally posted by Dave Ashurst
Aha, I see.
I probably won't understand the answer! but sticking a microphone up in the air on a pole seems a bit random; what does it measure?
How do you know from that how loud any given car is? Isn't distance from the source an important part of the calculation?
If there are 2 or more sources of noise doesn't that confuse the reading?
Hi Dave,
First of all I'm an electronic engineer, not an acoustition, but I'll try and answer what I can. I'll ask the clever acoustics guys
when I get back to work.
I can't remember what they measure, probably what they do at SVA, Fast time weighted maximum.
When you say how does that measure how loud the car is and distance effects etc, I don't think they're really bothered how loud the car
is, all there interested in is not pi*ing off the people living nearby. Yes the distance will effect the measurement, but this is probably taken into
consideration.
2 or more sources will be measured together as a single measurement, but I think they look out for say multiple cars going down the straight at
once.
Just for info, these poles are all over the world also on plane flight paths, measuring the noise home owners are subjected to. Usually fitted to
schools and office blocks.
With each microphone capsule cost many hundreds of pounds, it would be very expensive to set up an array of microphones.
Hope that helps, any more questions just ask.
Graham
Website under construction. Help greatfully received as I don't really know what I'm doing!
"If a man says something in the woods and there are no women there, is he still wrong?"
Built 2L 8 Valve Vx Powered Avon
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