Noise Testing

[luddites7]

I have just rented a digital noise meter from bookatrack, and was hoping someone could tell me the procedure many of the tracks use for noise measuring. I have pointed it towards the exhaust at 1 metre but the reading seems quite low.

[Jason Plato]

Normaly its 0.5m at 45 degrees at 4500rpm or sometimes 2/3 max rpm ( It only revs to 5000 honest wink.gif.

I was disgusted on sunday when the marshall at the curborough sprint tested me at just 93Db ............. tut tut call your self a seven owner !!! , I requested a retest which produced a much more sensible 102Db teeth.gif

 

Dave

 

Edited by - Dave J on 25 Jul 2001 20:24:11

[Mike Bees]

3/4 max rpm at Goodwood & Castle Combe.

 

Mike

[fast_cat]

I assume it is 45 deg from the centre line of the exhaust outlet ?

If so for a side exit exhaust where do they hold the meter ?

 

Rob

[Dave H]

Rob,

 

Tape/tie/strap the meter .5m along a piece of wood/ruler and line it up in the direction of the exhaust outlet. Now raise the wood/ruler until it forms an angle of 45 degrees to the ground (but with the end in the exhaust). Now take your readings.

 

I think Tony Isherwood will have the noise meters at Brooklands again on 15th September, for a small donation to LRF you can get it checked again.

 

Dave H

[Paul Ranson]

Now raise the wood/ruler until it forms an angle of 45 degrees to the ground (but with the end in the exhaust). Now take your readings.

 

Strictly for an MSA compatible test it is 45 degrees to the outlet at the level of the outlet.

 

Paul

 

[Dave H]

That was how I had mine done at Goodwood last time I was there - before the latest noise restrictions (Xflow - 106db @ 3500). I don't think it makes a huge amount of difference withthe side exit, its more to stop the overhanging body work getting between the meter and the exhaust, on those cars with overhanging body work.

 

Dave H

[Graham Perry]

JNessling, When you have done it you will still need to allow for different variables at different locations, I have even heard it said that Tarmac and concrete can cause different readings due to the differing way they reflect the sound off of the ground back towards the probe. I have lost count of the number od times my car has been done, but it always seems to be in a 99db to 105db window, which apparently is very wide.

[Dave H]

Too right 99 - 105 is a big range. The Db scale is logarithmic - +4Db is a doubling of volume, so someone doing your measuring must have had a seriously iffy meter, or not much of a clue what they were up to.

 

Dave H

[Graham Perry]

Exactly , that is why I have by doubts about the calibration of these machines

[luddites7]

I have tested the car and at 4500 I am getting a reading between 97.8 to 99 dB, I have found that on the way up to 4500 the meter reading does go above 103 dB. Also when dropping off the revs if I am not careful the reading jumps to 106 dB as the exhaust pops.

 

Does anyone know if they just take the 4500 reading, or does the testing include revving up to 4500 and back down again.

[Tony Martyr]

To get any sort of repeatability and accuracy the test has to be taken in a hemi-anechoic space. Which means that there must be no reflection of noise from any object above the ground level. The worst place to test is in a pit lane where the walls will bounce sound back to the meter. You can get a substancially reduced reading if the reflective waves are subtractive or a big increase if, by virtue of distance away, they are in sync - either way the reading are wrong. So insist that your exhaust is pointing towards nothing but open air and long grass before being tested because even a truck some distance away will reflect noise.

[Richard_E]

Having completed a track day at Castle Combe they tested at 4500 rpm.