Casella CEL CEL-393 - Manual (Page 94)

14) The recommended windscreen has negligible effect at frequen-
cies <12.5kHz.
15. The instrument should be calibrated with either a CEL-284/2
electroacoustic calibrator or an RFT 05001 pistonphone.
16. For maximum accuracy the operator and instrument case
should be more than 1m behind the microphone.
17. The CEL-393 is designed to be used only with its own internal
filter set. Models containing filters are designated CEL-393B
and CEL-393D.
18. The electrical impedance of equipment attached to the log DC
or conditioned AC output connectors should be >3k3 Ohms.
Digital outputs are available for CEL-238 Secondary Proces-
sor or CEL-433 Serial Interface.
19. The reference frequency is 1kHz.
20. The reference range is '70' ('60' on C and D versions).
/90. 393 Handbook