richardm6994
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| posted on 30/7/14 at 11:41 AM |
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trackday noise limits
does anyone know what frequency tracks take the noise measurement at?
The company I work for has many £££'s worth of acoustic labs and measuring equipment. Today they took a measurement off my car (0.5m from
exhausts @ 45degrees angle)......it's 106.2db @ 500hz or 99.5db @ 1000hz
Obviously this is critical to me because if they measure at 500hz...then I'm too loud for track days, but if they measure at 1000hz (which our
technical director seems to think would make sense) then I'm ok for trackdays.
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SteveWalker
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| posted on 30/7/14 at 11:59 AM |
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I would have expected it to be across a range of frequncies - most likely A-weighted.
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richardm6994
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| posted on 30/7/14 at 12:23 PM |
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Those reading were z-weighted.....the guys are going to convert to a-weighted which should bring my 500hz reading down.
irrespective of what the weighting is, surely they have a set frequency (most hand held devices such as the ones they use at tracks take all measure
at whatever frequency you set them at......it's just knowing what that frequency is!)
[Edited on 30/7/14 by richardm6994]
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richardm6994
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| posted on 30/7/14 at 01:30 PM |
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or if someone could kindly ask when they are next at a track event and see's the person with the db meter....that would be a massive help 
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matt_claydon
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| posted on 30/7/14 at 11:32 PM |
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A-weighting covers the full range of audible frequencies and is intended to represent how they are heard by the human ear. A trackday organiser should
be setting their meter to dB(A) and leaving the meter to do the rest - there is no frequency selection once you have chosen the weighting curve.
See http://en.wikipedia.org/wiki/A-weighting for the science...
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richardm6994
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| posted on 31/7/14 at 08:19 AM |
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quote:
Originally posted by matt_claydon
A-weighting covers the full range of audible frequencies and is intended to represent how they are heard by the human ear. A trackday organiser should
be setting their meter to dB(A) and leaving the meter to do the rest - there is no frequency selection once you have chosen the weighting curve.
See http://en.wikipedia.org/wiki/A-weighting for the science...
I think you've got the wrong end of the stick regards sound weighting.
The sound-weighting in its simplest explanation is just a correction curve to the db readings over a range of frequencies. You still have to tell the
db-meter what frequency you want to measure and so depending on what frequency you set it at and what sound-weight you are working to (also selected
on the db meter) the db-meter applies a correction value (as illustrated in the graphs) to the db reading it's measuring.
So at 100hz (A-weighted) the db meter will apply a correction value of -20db to that which it is measuring and at 1000hz it would apply a correction
value of 0db to that which it is measuring....different weights give a different correction curve but you must still know what frequency you are
measuring at ....and with most db-meters you can select between 31.5hz and 8000hz.
[Edited on 31/7/14 by richardm6994]
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JimSpencer
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| posted on 31/7/14 at 09:13 AM |
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1khz, according to some old notes.
But all of them vary anyway, been tested loads of times and I can't recall two the same.. 
Plus you have different ways of measuring it to, some places do drive by also.
So if in your opinion it's 'a bit OTT'  then fix it now - much easier than trying to argue (you'll lose) with an official
at a track.
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matt_claydon
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| posted on 31/7/14 at 09:27 AM |
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quote:
Originally posted by richardm6994
quote:
Originally posted by matt_claydon
A-weighting covers the full range of audible frequencies and is intended to represent how they are heard by the human ear. A trackday organiser should
be setting their meter to dB(A) and leaving the meter to do the rest - there is no frequency selection once you have chosen the weighting curve.
See http://en.wikipedia.org/wiki/A-weighting for the science...
I think you've got the wrong end of the stick regards sound weighting.
The sound-weighting in its simplest explanation is just a correction curve to the db readings over a range of frequencies. You still have to tell the
db-meter what frequency you want to measure and so depending on what frequency you set it at and what sound-weight you are working to (also selected
on the db meter) the db-meter applies a correction value (as illustrated in the graphs) to the db reading it's measuring.
So at 100hz (A-weighted) the db meter will apply a correction value of -20db to that which it is measuring and at 1000hz it would apply a correction
value of 0db to that which it is measuring....different weights give a different correction curve but you must still know what frequency you are
measuring at ....and with most db-meters you can select between 31.5hz and 8000hz.
[Edited on 31/7/14 by richardm6994]
It sounds like you know more about the instrumentation than me, so perhaps I have never fully understood. I carry out many noise tests for type
approval of vehicles at lots of different sites and using lots of different makes and models of sound level meter, and have never come across a need
to select a frequency. The legislation we use states only:
quote:
1.1. Acoustic measurements
The sound level meter or the equivalent measuring system, including the windscreen recommended by the manufacturer shall at least meet the
requirements of Type 1 instruments in accordance with IEC 651, second edition.
The measurements shall be made using the frequency weighting A, and the time weighting F.
When using a system that includes a periodic monitoring of the A-weighted sound level, a reading should be made at a time interval not greater than 30
ms.
There is no mention of frequency, other than the weighting, so my assumption is that once you select dB(A) on the meter, the measurement is made
across the full frequency range and weighted accordingly. Always happy to learn, if that's wrong though
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