BRUEL & KJAER 4952 Quick start guide

Sound & Vibration Measurement A/S
Outdoor Microphone Type 4952
Notes for Use
General
Outdoor Microphone Type 4952 consist of 3 major parts:
• An upper part, UA-1679, with windscreen and bird spike
• A base with thread for pole mounting
• An internal transducer part, consisting of the microphone cartridge and a preamplifier
No cable is included with Type 4952.
The connector on the microphone’s transducer part is a male 7-pin LEMO 1B connector.
For connection to Brüel & Kjær standard LEMO Microphone Input Connectors, Cable AO-0414 should be used. Its order
number is:
• Up to 99.9 m: AO-0414-D-nnn, where nnn denotes the length in decimetres
• Above 99.9 m: AO-0414-M-nnn, where nnn is the cable length in metres.
For connection to Brüel & Kjær Type 2260 and 2250 Sound Level Meters, Cable AO-0645 should be used. Its order number is:
• Up to 99.9 m: AO-0645-D-nnn, where nnn is the length in decimetres
• Above 99.9 m: AO-0645-M-nnn, where nnn is the length in metres
The preamplifier in the transducer part is equivalent to Brüel & Kjær Microphone Preamplifier Type 2669-C. Details on dynamic
range of the preamplifier with various loads are given in Brüel & Kjær Microphone Handbook, Volume 2 (BE1380-12),
Chapter 8. The Microphone Handbook can be viewed from the Literature section of the Brüel & Kjær Internet Site
www.bksv.com.
For Brüel & Kjær Sound Level Meters and Noise Monitoring Terminals supporting Outdoor Microphone Type 4952, the
recommended connecting cables and the maximum cable length are stated in their Technical Documentation.
Mounting and Assembling
Outdoor Microphone Type 4952 is designed to operate mounted vertically with the bird spike pointing upwards. The microphone
should not be mounted outdoors with other orientations.
The base of Outdoor Microphone Type 4952 has an inner thread that fits on the thread of normal 1” opening diameter water
pipes (ISO 228-1 G1). The transducer part and the upper part of the microphone are mounted on the base with bayonet
couplings. The microphone can be mounted on a tripod with Tripod Adaptor DB-4024. The adaptor fits into the thread of the
base.
The cable (not included with the microphone) must be led through the base.
Fix the base to the mast or tripod before you mount the transducer part in the base. In this way you avoid twisting the cable.
Connect the cable to the transducer part and mount the transducer part in the inner bayonet by placing it in the flanges and
turning it clockwise until it locks.
The upper part is mounted on the base with the transducer part in a similar matter.
The upper part as well as the transducer part is removed by turning it anticlockwise until it stops and then pulling it upwards.
The sensing point of the microphone is marked with a groove in the windscreen, that is, the microphone height should be
measured from the ground to the groove.
Acoustic Calibration
When calibration is needed, the upper part must be removed, and remounted after calibration.
With the Upper Part UA-1679 removed, an acoustical calibrator can be placed on the transducer part for calibration.
Recommended calibrators are Brüel & Kjær Sound Calibrator Type 4231, Pistonphone Type 4228 or Multifunction Calibrator
Type 4226.
A correction must be added to the sound pressure of the calibrator in order to obtain the calibration value for the Sound Level
Meter or Noise Monitoring Terminal used with the microphone. The corrections are given in the table below.
Frequency 250 Hz 1 kHz
Correction 0.0 dB −0.17 dB
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For example, if the sound pressure of the calibrator at 1 kHz is 94.0 dB, the sound level meter without the Response
Linearisation Filter (see below) should be adjusted to a reading of 94.0 dB −0.17 dB = 93.83 dB.
Note, that the correction is automatically taken care of in the calibration routines of Brüel & Kjær Sound Level Meters and Noise
Monitoring Terminals supporting Outdoor Microphone Type 4952.
Remote Verification with CIC
The preamplifier in the transducer part of Outdoor Microphone Type 4952 is designed with Brüel & Kjær’s patented Charge
Injection Calibration facility, CIC. With CIC the complete signal path with the microphone can be remotely verified.
Details on verification with the CIC technique can be found in Brüel & Kjær Microphone Handbook, Volume 1 (BE1447-11),
Chapters 4 and 6. The Microphone Handbook can be viewed from the Literature section of the Brüel & Kjær Internet Site
www.bksv.com.
Maintenance
Outdoor Microphone Type 4952 is designed for unattended outdoor use for long periods of time. In periods where the
microphone is used unattended, it is recommended that it is verified regularly with CIC, see above. Once calibrated in a setup,
the CIC gain at 1 kHz should not change by more than 0.2 dB.
In aggressive environments like cities with heavy traffic, chemical industry plants, near railway or near coasts (salt water) the
likelihood of corrosion is large as compared with normal outdoor environments. If used in such environments, it is recommended
that the microphone is initially inspected at short intervals, say, every two to four weeks. When it is clear that the microphone
does not corrode, the interval can be increased.
The grid on the transducer unit may become discoloured with time, especially in aggressive environments such as those
mentioned above. This does not affect the performance of the microphone as long as the diaphragm – partially visible below the
grid – does not appear to be damaged.
At least once per year the microphone should be inspected and calibrated. Preferably, the frequency response and system
noise should also be verified. Calibration and verification services are available from Brüel Kjær Service Centres and include
replacement of the windscreen.
Note
The windscreen should never be removed, except when it is being replaced.
Replacement of the windscreen is recommended whenever needed and at least once every 24 months.
Spare windscreens are available as UA-1700 and UA-1701 (pack of 6 windscreens)
Response Linearisation Filter
In order for Outdoor Microphone Type 4952 to have a flat frequency response as specified in the Product Data for reference
directions 0° and 90°, a frequency weighting filter as defined below must be used.
Brüel & Kjær offers different solutions with the appropriate frequency weighting.
Note, that Brüel & Kjær does not assume any responsibility for the combined response of Type 4952 and filters not made by
Brüel & Kjær.
Recommended Filter Responses
Frequency Filter, dB Frequency Filter, dB
Hz 0° 90° Tol. Hz 0° 90° Tol.
20 0.00 0.00 ±0.15 4000 -1.00 1.05 ±0.15
250 0.00 0.00 ±0.15 4500 -1.00 1.40 ±0.20
315 -0.05 0.00 ±0.15 5000 -0.90 1.85 ±0.20
400 -0.10 0.00 ±0.15 5600 -1.00 2.25 ±0.20
500 -0.15 0.00 ±0.15 6300 -1.10 2.10 ±0.30
630 -0.20 0.00 ±0.15 7100 -1.30 1.70 ±0.40
800 -0.40 0.00 ±0.15 8000 -1.60 1.50 ±0.50
1000 -0.50 0.00 ±0.15 9000 -1.80 1.20 ±0.50
1250 -0.70 0.00 ±0.15 10000 -2.10 1.20 ±0.60
1600 -0.85 0.00 ±0.15 11200 -2.30 1.50 ±0.80
2000 -0.90 0.00 ±0.15 12500 -1.20 3.10 ±1.00
2500 -0.95 0.05 ±0.15 14000 0.70 5.10 ±2.00
2800 -0.95 0.10 ±0.15 16000 0.90 4.80 ±5.00
3150 -1.00 0.30 ±0.15 18000 -0.20 3.00 ±10.00
3550 -1.00 0.68 ±0.15 20000 -3.30 -2.00 ±15.00
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