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BDR noise test


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So static noise test is 85db at 4875 revs at 50cm. Bit of a pleasant surprise.

However. What do we think (guess) it will be in the following circumstances, at dedicated test centre:

6 Speed box, third gear, standard Ford 711M block 169 bhp:

30 MPH drive to a white line, full throttle (WOT) for 10 metres,

Microphones at 5 metres of the ten, set each side 7 metres back from the centre line.

Known as the moving noise test as complied with by all modern cars.

Measured as the average of three passes.

Guess (estimate) what you think the Dba level will be? Please?

Seems to me that if 85 at nearly 5,000 it won't be anything like that at 30 in third with wot - as long as no backfire. Side exit of course.

I will be running a test in our car park.. :-)

Regards to all.



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I remember my first Caterham, a 40th Anniversary with a VX XE on DCOEs with a 6 Speed and a Raceco.  Static noise was never a problem but drive by always caused problems.  There were so many factors beyond the car itself the most memorable one was humidity.  If it was a cold misty morning there was no point going out for a track session, I knew I was going to be black flagged.  Waiting until the day warmed up was the only option. 

Don't think I can give a number, but I will "play my cards right" and say higher than your static. 

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Just to urge some caution with Apps for measuring noise.  I spent my career working in acoustics (although not in the automotive industry), and as part of that, ran some tests on various apps to see if they were any good.  The bottom line was:

  • As Jonathan says, they are better for relative measurements rather than absolute. 
  • They are more consistent on Iphones than other devices because the microphones have broadly the same sensitivity as they come from the same supplier.
  • There is a big difference between dB and dB(A) – not all measure the dB(A) level (the level expressed in dB(A) will always be lower).  Also, some tests require averaging over time (to measure the LAeq) which is an added complexity some apps cant deal with.
  • They are very sensitive to wind noise so not ideal for measuring out of doors
  • The microphones in phones are directional so how you point the phone is important.  The phone case can also make a difference.  A professional sound level meter will have an omni-directional microphone so is much less affected by direction (important if you are doing a drive-by test).
  • Its very difficult to calibrate a phone – protocols for noise measurements almost always require the noise meter to be calibrated before and after use with a standard sound source that fits over the microphone.

The test we ran in a semi-controlled environment gave a range of +/- 20dB(A) from a mix of different phones and software packages.  That’s a big variation.


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