I
I
Microphone Characteristics
The microphone used in the 21.5 Sound i.eveJ M_ter is a Shtlro
type d01 ceramic omnidirectionalunit Overalldiameter is 1.126
inches(2.8G cn'0.Typicalsensitivityis59 dB below I veilper micro-
bar measured at dO0 Hz. l;'igurc5 isa diagnml of typicalnlierophoms
responsetarhath pc,rpendicalaralldrandom ineidcliee,
+I0
• "o
+'5 Porpond+c,_lar_ e+++
! '°°'"°a+°"i"' _._._j..-
° \
'.: ,qandam
-5 (and70o[nc[dal_co}
_,o I I ]
20 50 lOP _OO '_1I 2K 5K 7KIOK
Frequency- Hz
Figure5. Type401 MicrophoneResponse- PerpendicularandRandomIncidence
INTERNAL ELECTRICAL NOISE
Table 1 on tile next page shows tileinternalnoiselevelof tile
215 mater with the meter set at "C" scale weighting, The noise h+vals
are typical and are determined by subtracting the readings shown
from the reading or the meter _tt fun scal_ d(_necLion, The figtlres m'e
shown for each Josition of the dB RANGE selector switch =it each
octavo land and at broad l)aild {all passb Noise levels on "A" weight-
ing are further r_duc:orl because of its attenuation characteristic, The
internal noise is alway_ .t least 27 dB below the full scale reading and
all reading_ .an thus be made without excessive noise prol_loms.
OPERATING PROCED Uff.E
GOIIORI|
']'0 el)Lain relldillgS of nlaxJlllllm accuracy, ]lo[d thr, illstrumellt
away from you Ilt an mlgle of zq)proxinlately 70° from the llorizon.
tal, Under cartain conditions slightly lass ace[l]I[|tl + readings may re-
suit from pointing the mierol_hone directly at tha noise+source,. This
callbe noted frmn tileMicrophone Itosponse elmrI.
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