Fig. (6)
This sound level calibrator from Extech (Model 407744) provides a 94 dB ± 0.5 dB (SPL) acoustic reference signal at 1000 Hz. More information on this unit is available at
http://www.extech.com/ resources/407744_407766_DS-en.pdf
.
Image Credit
:
http://www. extech.com/407744/
.