Extech 407744 Sound Level Calibrator – 94dB (Review)

Extech Calibrators accommodate Sound Level Meters with 0.5” and 1” microphones. The Calibrator’s die-cast aluminum housing is built for ruggedness and durability. The 407744 provides a 94dB calibration output signal while the 407766 provides both 94dB and 114dB outputs. This professional calibrator, with proper care, will provide years of safe reliable service.

Output signals

407744: 94dB
407766: 94dB and 114dB

Output signal accuracy 407744: ± 0.5dB; 407766: ± 0.5dB (94dB), ±0.8dB (114dB)
Accuracy of output signal frequency ± 5%
Compatible microphones sizes 0.5” and 1” microphones
Total Harmonic Distortion (THD) <2%@94dB, <5%@114dB (407766)
Operating temperature 32 to 122oF (0 to 50oC)
Power supply Two (2) 9V batteries
Power consumption Approx. 10mA DC
Battery check Status LED
Dimensions 2.2” diameter x 5.7” length (50 x 145mm)
Weight 0.75 lbs. (340g)
Output signal frequency 1KHz sine wave


1. ½” Microphone adaptor
2. 407766: OFF-94dB-114dB switch, 407744: OFF-BATTERY TEST-94dB switch
3. 407766: POWER-ON / LOW-BATTERY status LED, 407744: BATTERY OK LED
4. Battery compartment cap
* To remove the ½” adaptor, pull straight down as shown in diagram below.



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).


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 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.

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