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All 130 series array microphones are designed for use in a free field environment. A free field
environment is one without reflections. Anechoic rooms and outdoor spaces without structures
are good examples of a free field environment. The free field response is the voltage response
with respect to the pressure when exposed to a plane progressive sound wave. A free field
microphone has a flat frequency response with respect to any source whose primary direction is
collinear with the axis of the microphone.
Calibration of free field microphone occurs at a zero degree angle of incidence. This means that
the frequency response reported on the calibration certificate is valid when the microphone is
directed straight at the sound source. If the microphone is directed at an angle with respect to the
source the response may vary depending on the angle and the frequency of operation.
After completing the system set-up, turn on the the signal conditioner and allow 1 to 2 minutes
for the system to stabilize. If the system doesn’t appear to be functioning correctly check all
system connections and try to isolate and individually check functionality of all system
components, or consider replacing system components one at a time. If the system still does not
operate properly, consult a PCB Application Engineer.
Under normal conditions, microphones offer a very stable response. However, the microphone
output may be affected by harsh environments, such as moisture, dirt, mechanical shock, or other
unusual conditions. This may manifest itself in a number of ways, ranging from a loss in
frequency range to failure of the built-in microelectronic circuits. To assure sensors
characteristics are known PCB
®
recommends that a recalibration cycle be established for each
microphone. Customers should determine a calibration cycle best suited for their needs as the
cycle is based upon a variety of factors, such as frequency of use, exposure to harsh
environmentals, accuracy requirements, trend information obtained from previous calibration
records, contractual regulations, and risk associated with incorrect readings. PCB
®
recommends
12 to 24 month calibration intervals but as stated, this interval is at the discretion of the customer
and is based on customer needs. It is also best practice to perform verification both before and
after each test. PCB’s CAL 250 acoustic calibrator (sold separately) is a handheld calibration
instrument ideal for field or quick sensor operational evaluation purposes.
6.0 Service
See the supplemental sheet for information on our service, repair and return policies, procedures
and instructions. If an unexpected problem arises, call our 24-Hour SensorLine
SM
(716-684-
0001) to discuss your dynamic instrumentation needs with a PCB
®
Application Engineer.
7.0 Warranty
PCB’s 130 Series Microphones are covered by a limited warranty against defective material and
workmanship. Visit
http://www.pcb.com/terms_conditions
for a complete statement of our
warranty.
