Sound Level meter requirements

[John Pavlick]

Tony,
 This is all very interesting. Even in the short time I've spent looking at
these meters I noticed some questionable areas. That's why I asked if there
was a more specific set of test criteria / procedures. It seems to me, that
even under controlled conditions, a GOOD meter might not produce repeatable
results. It is of course very important to calibrate to a reference (i.e.
94dB / 1KHz), then measure. Without doing that you can't take accurate
absolute measurements. Also, Unless the spec. is written to allow for
tolerance of the meter (most of the ones I've seen are +/- 1.5dB), sometimes
you'll read (too) high and sometimes you'll read low, even with the same
source and a calibrated meter. It's probably more important to have an
accurate means of re-calibrating the meter rather than having a meter that
has a tighter tolerance. Taking reasonably accurate measurements relative to
a known reference should be acceptable, I would think. That's why a band
tunes to the keyboard if they don't have an electronic tuner handy. A modern
electronic keyboard can be considered an accurate reference for pitch.
John Pavlick
http://www.idseng.com



 -----Original Message-----
From: discussion-request at nsrca.org [mailto:discussion-request at nsrca.org]On
Behalf Of tony at radiosouthrc.com
Sent: Wednesday, February 16, 2005 7:25 PM
To: discussion at nsrca.org
Subject: Re: Sound Level meter requirements


  Del:
  The problem with all meters I know of is that they all change!  I was the
first one in the USA to work with the FAI in establishing how a db check
would actually be done in the field.  I did the first ones at the 1983 US
Team Selections in Rough River, KY right before the 1983 World Champs.  As I
was the assistant CD for the WC, AMA wanted me to gather the data and learn
how the system the FAI had designed would really work in the field.  We
found that even expensive db meters developed drift.

  The expensive versions used by AMA have to be adjusted about every 4
hours, as they can drift 1/2 to 1 1/2 db in that period of time due to
temperature changes.  That is the problem with any meter.  Unless you have a
calibrator to adjust the meter, it is really pretty worthless in getting an
accurate measurement.  As long as + or - 5 db is OK, you don't need to
worry.  However, if you are trying to meet any model noise requirement out
there, your really spinning your wheels.

  Tony Stillman
  Radio South
  3702 N. Pace Blvd.
  Pensacola, FL 32505
  1-800-962-7802
  www.radiosouthrc.com

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