Specifications

7. Display (-dB)

This control allow centering of the 1/3 octave display columns to compensate for the

approximate 16dB difference in signal level between vide-band pink noise out of the

generator and the signal level in each 1/3

octave band. True level readings in each 1/3

octave band may be obtained by adding the indicated level on the display to the

dB-SPL

switch setting and

SUBTRACTING

the setting of the Display (-dB) switch (assuming a

calibrated microphone is being used). This compensates for the level difference due to

band-limiting.

8. Display Range

The Model 140 has a display window of either 10dB in 1dB steps or 20dB in 2dB steps.

For coarse tuning or display of widely varying levels, the 20dB range should be used. For

fine tuning or display of only slightly varying levels, the 10dB range should be used.

Care should be taken to note which range is being used when absolute readings are being

taken.

9. Overload

The Overload lamp indicates when either the microphone pre-amplifier or the line

amplifier is clipping. If the lamp flashes when being used with a microphone, the

dB-

SPL

switch should be moved to the next higher position. If the signal level is beyond the

range of the microphone pre-amplifier, then the input signal level will have to be reduced.

See the Specification list for ranges of input voltages. Very occasional flickering of the

overload lamp will not cause spurious readings.