User Manual

407744 & 407766 - V5.1 – 04/10

Operation

Theory of Operation

The 407744 sound level calibrator generates a 94dB sine wave at 1 KHz. The 407766

generates a 94dB and a 114dB sine wave at 1kHz. When a microphone from a sound level

meter is inserted into the calibrator, the sound level meter picks up the signal and displays

the signal in dB (decibel) units. The sound level meter should be adjusted (if necessary) to

match the calibrator’s output signal as closely as possible (see diagram).

Procedure

1. Insert the microphone into the calibrator’s microphone cavity as

shown; ensure that it is fully inserted. Use the ½” microphone adaptor

(supplied attached to the calibrator) for ½” microphones. Remove the

adaptor (remove as shown in the Description section) for 1”

microphones.

2. On the 407744, slide the function switch to the ‘I’ (Power On) position.

As soon as the unit is powered, the calibration tone is generated. On

the 407766, slide the function switch to the 94dB or the 114dB

position as desired. The calibrator generates its signal as soon as the

switch is set.

3. Read the sound level meter’s display. The sound level meter should

read 94dB or 114dB depending on the calibrator’s setting. If the sound

level meter does not match the calibrator’s signal (within

specification), adjust it as explained in the Operation section (typically a front or side-

panel pot adjustment). Refer to diagram at right.

4. Slide function switch to the OFF position, and remove the microphone.

Battery Check

On the 407744, check the condition of the battery by moving the function switch to the

‘Battery test’ position. The Battery status LED should illuminate if the battery is OK. If it

does not light, replace the 9V battery. On the 407766, the POWER-ON / LOW-BATTERY

LED glows brightly when the battery is fresh and dimly when the battery is weak.

Battery Replacement

Lift off battery compartment cap (shown in the Description section) to access the two (2)

9V batteries. Remove the batteries and replace with new alkaline 9V batteries. Replace the

cap.