Hi Rob,
Besides the (minor) potential errors due to reflections off the environment,
the distance does not matter for your calibration procedure. This is true as
long as you place the microphone and the SLM at exactly the same spot (and keep
the distance from the sound source fixed).
If you however wish to quantify the noise that is emitted by a particular sound
source, then it is important to specify also the distance (1 meter is a
commonly used value such measurements) because the sound level will of course
change according to that.
Regards,
Raimund
--- In Rob Danielson <> wrote:
>
> Hi Bob, Raimund, Greg and Prataps--
>
> For several reasons including the ones Bob notes, we know that mic to
> speaker distance will make a difference in the critical step of 64 dB
> amplitude calibration. I looked through three SLM manuals and
> couldn't find anything about what distance to measure isolated, loud
> sound sources. (In most applications, measurements are taken where
> background levels are perceived). Doesn't 1 meter replicate usual mic
> sensitivity test conditions? I looked for a while could not find a
> succinct specification, but the distances were all on the order of 1
> meter. At this short distance, if I place the sound source and mics
> at 7 feet above thick grass, reflection impacts should be negligible-
> especially considering my $50 Nady ASM-2 meter is +/- 2dB! I noticed
> that some of the more expensive meters we've discussed are +/- 1.5dB.
>
> It would also be interesting to play the same sound samples in one's
> sound studio (same speaker) at 1 meter just to see what differences
> crop up.
>
> Its #4 on my current test list. I was thinking of using AT4022's and
> my SD744T and record level "60.5 dB" at a distance of 1 meter if
> anyone wants to get started. Rob D.
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