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Noise
iiyama - 22/4/09 at 04:54 PM

Failed the re-test today on noise, passed everything else. Need some ideas as Im out of em. Stuck another baffle into the exhaust and have placed sound mat on the floors, back of the cockpit panel and along the inside of the offside engine panel. Sound reading has increased by 6db over the original reading!!

Help! Its getting expensive, SVA cost, £38 re-test and now another £38 becuse of noise.

iiyama - 22/4/09 at 05:34 PM

Interesting. He only used the one meter, didnt get close to pulling another one out. It mystifies me though as to the 6db increase as that is a hoooooooooge amount!

matt_claydon - 22/4/09 at 05:49 PM

quote:
Originally posted by robocog
I really wanted to question the second meter's accuracy since he had just twiddled a calibrated instrument in front of us,


Noise meters should be calibrated before each use using a sound generator (creates a fixed frequency sound at a pre-set level) that is attached to the microphone. An adjustment screw is then turned to make sure the meter reads the same as the expected output of the calibrator (usually 94db). Note: you wouldn't be able to hear the calibrator but would see a (usually cylindrical) object on the business end of the meter where the wind shield would normally be.

They are also calibrated in a laboratory annually across a whole range of levels and frequencies.

Obviously I can't say if this is definitely what he was doing, however!

INDY BIRD - 22/4/09 at 06:02 PM

Hi

do you have a noise meter yourself that you are testing with, ???

if not can borrow mine if helps

is this a dax exhaust you are using or another system pics would help??

sean

mistergrumpy - 22/4/09 at 06:29 PM

I wrapped my exhaust from the collector pipe up to the end of the can mainly to cover the lambda plug and to help with warming the CAT up. First test without the wrap my noise was 102 dB, afterwards it was 96 dB!

nstrug - 22/4/09 at 07:35 PM

So is there any requirement for the meters at VOSA to be correctly calibrated? If I asked to see the official calibration certificate, would they actually have one?

It really seems like there is a problem at Northam - going from 103dB to 109dB after baffling, soundproofing, damping etc just doesn't seem conceivable.

Nick

iiyama - 22/4/09 at 08:21 PM

I know that Nick ^^^^ has had the similar problems to me.

Exhaust is not a Dax item, but Im not sure the noise issue is an exhaust problem if that makes sense! Think Im getting a resonance problem, however I do think it strange that after fitting the exhaust exit with one of these:- http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250391607443 and then slapping sound material in various places increase the sound by 6db. Considering that this is a logarithmic scale, 6 is hooooooooooooooooge!

Edited to add that there was a cylindrical item placed on the front of the meter before we went outside and I asked him if that was to calibrate it, he said that it was. However what I forgot to ask was if they zero the meter against back ground noise as I thought this was meant to happen??

[Edited on 22/4/09 by iiyama]

INDY BIRD - 22/4/09 at 09:47 PM

hi i fitted one of those db killers and it took 4 db of the noise so not sure whats going on,

are you running a std airbox if not may be a good idea to get one as this cuts induction noise big time,

and yes insulate like mad had same issue on my dax pannel resonating like mad,

good luck if need a meter just ask

sean

iiyama - 23/4/09 at 06:43 AM

Thanks for the offer bud but Ive got a meter sorted. Hopefully I can get some idea of whats going on now.

Kriss - 23/4/09 at 09:15 AM

What engine, and can combo are you running?I would try and get my hands on a big boy exhaust can with plenty of well packed packing. My gosh, if a busa lump with a sausage filter like my mates passed DB at the SVA then most cars should. Can you not borrow a bigger can from someone?

iiyama - 23/4/09 at 11:00 AM

The Simpson can I have is much bigger but there is no cat fitted in it. The can I have on there is a bodge just to get through emissions come SVA/MOT and its passed that test. Wanted to put the SImpsons can on yesterday at SVA for the noise but tester said that if I did he would re-test emissions........