Natural Science Forum / Physics / Acoustics / January 2006

Leq as rigorously defined does not include use of any exponential time
weighting such as slow.  However, some meters will sample a slow or fast
response level and compute an Leq from that.  In most circumstances the
results should be essentially the same.  If a meter offers two different
options that appear to be the same, I would look closely at the definitions.
The "average" Lp may be defined by the manufacturer differently from the
Leq.  Check the instrument manual.

Use 'Slow' time weighting:
1. When standards so state
2. For the measurement of steady state noises such as fans or compressors

Use 'Fast' time weighting:
1. When standards so state
2. For the measurement of variable or fluctuating noise levels such as
traffic

In "Slow" mode, about 10 data averaging within 10secs.  I believe,
Lp(instaneous,Slow) result is similar to Leq(10sec,Slow) result if and only
if the noise source is relatively steady.

CSLL

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