Instruction manual

113
Technical Notes
Frequency Weighting Network
The NA-27 provides a choice between "A", "C" and "Flat" frequency weighting. The elec-
trical characteristics of the weighting circuitry are as shown below.
The volume impression (loudness) of a sound depends not only on the sound pressure
level, but also on the frequency. At high or low frequencies, a sound is felt to be less loud
than a sound of equal level in the midrange. The "A" weighting curve compensates for this
effect and produces measurement results which are close to the actual impression of loud-
ness. For this reason, this type of frequency weighting is widely used for purposes such as
sound pressure level evaluation.
With the "Flat" characteristic, frequency response is linear, which is suitable for straight
sound pressure level measurements and for using the sound pressure level meter output
for frequency analysis.
The "C" weighting curve produces almost flat response, but with a rolloff below 31.5 Hz
and above 8 kHz. This is suitable for sound pressure level measurements in situations with
unwanted low-frequency or high-frequency components.