Manufacturers' Specifications

Bruel & Kjaer 2238

Precision Sound Analyser

All our 2238 Sound Level Meters include the following modules

BZ 7126 - Basic Sound Level Meter Software
BZ 7125 - Enhanced SLM Software
BZ 7124 - Logging Sound Level Meter Software
BZ 7123 - Frequency Analysis Software

This web page lists the full technical specifications - to jump to a specific module, click on one of the links above. We also have a quick Summary Table

Common Specifications - all 2238 Mediator versions:

Standards: Conforms with the following:
BS EN 61672 - class 1
BS EN 60651 - class 1
BS EN 60804 - class 1

Microphone : Type 4188 pre polarized free-field 1/2” microphone
Nominal Sensitivity : -30 dB re 1 V/Pa or 31.6 mV/Pa
Frequency Range : 8 Hz to 16 kHz ± 2 dB
Capacitance :   12 pF at 250 Hz

Microphone Preamplifier : ZC 0026
Extension Cable : 3 m included. No re-calibration is required

Measurement Ranges :
Dynamic Range : 80 dB adjustable to give full scale readings from 80 dB to 140 dB in 10 dB steps
Max. Peak Level : 3 dB above full scale reading
Upper RMS Limit for Crest Factor = 10 : 17 dB below full scale reading
Pulse Range : 83 dB
Linear operating ranges - broadband : For the individual level ranges, at 1 kHz, the nominal upper boundary level minus the lowest sound pressure level measurable with a noise margin of 5 dB and with a Type 4188 microphone of nominal sensitivity;

Inherent Noise Level :
This is due to the combination of electrical noise and microphone thermal noise at 20 °C (68 °F). Typical values with supplied microphone of nominal sensitivity - in dB.

Display :
129 pixel x 64 pixel dot matrix display with back light

Auto-Start :
Mediator supports a total of four timers which allow setup of measurement start times up to a month in advance

Calibration :
Semi-automatic using and external Sound Level Calibrator
The initial factory calibration, sensitivity and microphone serial number is stored for comparison with later calibrations. when using the supplied microphone the maximum allowed deviation from the initial sensitivity is ± 1.5 dB. An unspecified microphone can be chosen during calibration, in which case calibration can be made with practically any sensitivity.
Stored Calibration History : 20 latest calibrations plus initial calibration.

Memory :
2 Mbytes. Up to 511 measurements can be stored by each loaded software module, including time stamp, complete setup and calibration data

Serial Printer :
Measurement data can be printed on the B&K 2318 printer or on an IBM pro printer compatible printer.

Clock :
Semi-automatic using and Real-time - calendar

Serial Interface :
Conforms to EIA/TIA 574 - RS-232, coupled as data terminal equipment, DTE.
Connector : D-type male 9-pin
Baud Rates : 4800 to 115200
Word Length : 8 bits, no parity, 1 stop bit
Handshake : hardwired, modem

Settling Time :
From power on < 10 s

Environmental Effects :
Storage Temperature : -25 to +70 °C (-13 to +158 °F)
Operating Temperature : -10 to +50 °C (14 to +122 °F)
Effect of Temperature : < 0.5 dB (-10 to +50 °C)
Effect of Humidity : < 0.5 dB for 30% < RH < 90% - at 40 °C, 1 kHz

Batteries :
Four 1.5 V LR6/AA alkaline cells
Lifetime at room temperature : Typically > 10 h and with filter set selected typically > 7 h

External DC Power Supply :
Voltage : Regulated 7 to 15 V
Power : Approximately 150 mA at 7 V and with filter set selected 210 mA

Weight and Dimensions :
Weight : 460g (1 lb 2 oz) with batteries
Dimensions : 257 x 97 x 41 mm

Specifications with BZ 7126 Basic SLM Software or see the 2238 Summary Table

Detectors :
Simultaneous detection of RMS and Peak with independent frequency weightings
RMS : Three selectable exponential time weightings - Fast, Slow Impulse - and a linear averaging detector. Selectable frequency weighting A, C or Lin
Peak : Selectable frequency weighting C or Lin
Overload detector : Monitors all the frequency weighted channels
Exchange Rate : 3 dB - in addition 4 or 5 dB can be selected
Criterion Level : Can be set in the range 70 - 100 dB
Threshold Level : Can be set in the range 0 - 100 dB

Sample Rate : 160 Hz

Display :
Measurement Display : Range and quasi-analogue bar, plus four measurement parameters that can be freely selected from all available parameters during measurements

Measurement Control :
Manual control, or pre-set measurement time in the range 11/2 s - 24 h with automatic storage of measurement

Aux 1 Output :
Connector : Lemo coaxial
AC Output Signal : Range adjusted AC output, unweighted or with the frequency weighting selected on the RMS detector - short circuit protected
Output : 1 Vrms corresponds to full scale indication
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω

Aux 2 Output :
Connector : Lemo coaxial
DC Output Signal : DC version of the signal on the RMS detector, delayed 0.8 s - Fast, Inst., short circuit protected
Output : 0 to 4.0 VDC, 50 mV/dB
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω

Measurements :

Legend :
V = Frequency weighting C or L
X = Frequency weighting A, C or L
Y = Time weighting F, S or I
Z = Time weighting F or S
Q = Exchange rate 4 or 5, additional to the 3 dB exchange rate

Specifications with BZ 7125 Enhanced SLM Software or see the 2238 Summary Table

Detectors :
Two detectors with independent frequency weightings. one detector is an RMS detector and the other can be set up as a Peak detector or an additional RMS detector, allowing two independently weighted RMS detectors in parallel, each providing three exponential time weightings in parallel.
RMS : Three simultaneous exponential time weightings, Fast, Slow, Impulse and a linear averaging detector. Selectable frequency weighting A, C or Lin
Overload Detector: Monitors al the frequency weighted channels
Exchange Rate : 3 dB - in addition 4 or 5 dB can be selected
Criterion Level : Can be set in the range 70 - 100 dB
Threshold Level : Can be set in the range 0 - 100 dB

Sample Rate : 160 Hz

Display :
Measurement Display : Range and quasi-analogue bar, plus four measurement parameters that can be freely selected from all available parameters during measurements. Where applicable, frequency and time weighting of selected parameter are selected by softkey. Separate display for back erase

Measurement Control :
Manual control, or pre-set measurement time in the range 30 s - 100 h with automatic storage of measurement
Measurement Sequences : Mediator can be set up to make a sequence of individual measurements - up to 99 - in immediate succession

Aux 1 Socket :
Connector : Lemo coaxial, can be used as an AC output or a DC input for an external signal
AC Output Signal : Range adjusted AC output, unweighted or with the frequency weighting selected on the RMS detector 1 - short circuit protected
Output : 1 Vrms corresponds to full scale indication
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω
DC Input :
Voltage Range : 0 to 4 V, max. -1 to 6 V
Resolution : 5 mV, 800 steps

Aux 2 Socket :
Connector : Lemo coaxial, can be used as a DC output, a DC input for an external signal, a trigger input or a trigger output
DC Output Signal : DC version of the signal on the RMS detector 1, delayed 0.8 s - Fast, Inst., short circuit protected
Output : 0 to 4.0 VDC, 50 mV/dB
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω
DC Input :
Voltage Range : 0 to 4 V, max. -1 to 6 V
Resolution : 5 mV, 800 steps
Trigger Input :
Voltage Range : 0 to 4 V, max. -1 to 6 V
Trigger Level : 2 V, duration > 12.5 ms
Trigger Output :
Level : 4 V
Duration : Throughout measurements

Measurements :

Legend :
V = Frequency weighting C or L
X = Frequency weighting A, C or L
Y = Time weighting F, S or I
Z = Time weighting F or S
Q = Exchange rate 4 or 5, additional to the 3 dB exchange rate

Note 1 : When both detectors are set to RMS, it is not possible to select the same frequency weighting for the two detectors
Note 2 : Time weightings F, S and I are available simultaneously
Note 3 : If the Aux 1 and Aux 2 sockets are used for input, the signals(s) can be displayed and stored
Note 4 : Values for statistics are sampled 40 times a second and are derived from the signal on the RMS detector with a pre-selected time weighting - F, S or I. The class width is 0.5 dB. Seven percentiles (L_XYN,T) are available during measurement at user selectable levels, 1% - 99%. A complete level distribution is stored

Specifications with BZ 7124 Logging SLM Software or see the 2238 Summary Table

Detectors :
Two detectors with independent frequency weightings. one detector is an RMS detector and the other can be set up as a Peak detector or an additional RMS detector, allowing two independently weighted RMS detectors in parallel, each providing three exponential time weightings in parallel.
RMS : Three simultaneous exponential time weightings, Fast, Slow, Impulse and a linear averaging detector. Selectable frequency weighting A, C or Lin
Peak : Selectable frequency weighting C or Lin
Overload Detector: Monitors al the frequency weighted channels
Exchange Rate : 3 dB - in addition 4 or 5 dB can be selected

Sample Rate : 160 Hz, statistics sampled at 40 Hz

Display :
Measurement Display, current log period : Range and quasi-analogue bar, plus four measurement parameters that can be freely selected from all available parameters during measurements.

Measurement Control :
Manual control, or pre-set measurement time with automatic storage of measurements

Aux 1 Socket :
Connector : 2 pin Lemo. Can be used as an AC output or a DC input for an external signal
AC Output Signal : Range adjusted AC output, unweighted or with the frequency weighting selected on the RMS detector 1 - short circuit protected
Output : 1 Vrms corresponds to full scale indication
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω
DC Input :
Voltage Range : 0 to 4 V, max. -1 to 6 V
Resolution : 5 mV, 800 steps

Aux 2 Socket :
Connector : Lemo coaxial, can be used as a DC output, a DC input for an external signal, a trigger input or a trigger output
DC Output Signal : DC version of the signal on the RMS detector 1, delayed 0.8 s - Fast, Inst., short circuit protected
Output : 0 to 4.0 VDC, 50 mV/dB
Update Rate : 160 times a second
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω
DC Input :
Voltage Range : 0 to 4 V, max. -1 to 6 V
Resolution : 5 mV, 800 steps
Trigger Input :
Voltage Range : 0 to 4 V, max. -1 to 6 V
Trigger Level : 2 V, duration > 12.5 ms
Trigger Output :
Level : 4 V
Duration : Throughout measurements

Measurements : Parameters logged and stored in each interval - when selected

Legend :
V = Frequency weighting C or L
X = Frequency weighting A, C or L
Y = Time weighting F, S or I
Z = Time weighting F or S
Q = Exchange rate 4 or 5, additional to the 3 dB exchange rate

Note 1 : When both detectors are set to RMS, it is not possible to select the same frequency weighting for the two detectors
Note 2 : Time weightings F, S and I are available simultaneously
Note 3 : If the Aux 1 and Aux 2 sockets are used for input, the signals(s) can be displayed and stored
Note 4 : Values for statistics are sampled 40 times a second and are derived from the signal on the RMS detector with a pre-selected time weighting - F, S or I. The class width is 0.5 dB. Seven percentiles (L_XYN,T) are available during measurement at user selectable levels, 1% - 99%.

Specifications with BZ 7123 Frequency Analysis Software or see the 2238 summary table

Detectors :
Simultaneous detection of spectrum and broadband parameters
Spectrum : 1/1 octave and 1/3 octave band filters with two exponential time weightings - Fast, Slow - and a linear averaging detector
Broadband : Two selectable exponential time weightings - Fast, Slow - and a linear averaging detector
Selectable frequency weighting : A, C or Lin
Overload Detector : Monitors all the frequency weighted channels
Sample Rate : 160 Hz

Display :
Spectrum : Bar graph display of current and averaged spectrum with cursor read-out plus broadband channel L_eq, L_Min and L_Max can be selected for graphic display and read-out
Broadband Measurement : Range and quasi-analogue bar, plus four measurement parameters that can be freely selected from all available parameters during measurements

Measurement Control :
Time/accuracy optimised scan time at three confident levels, 0.25, 0.5 or 1.0 dB, or manually selected dwell time in the range 1 s to 1 h
User selected number of scans, in the range 1 - 99, averaged into one resulting spectrum

Aux 1 Output :
Connector : Lemo coaxial
AC Output Signal : Range adjusted AC output, filtered through the currently selected band - short circuit protected
Output : 1 Vrms corresponds to full scale indication
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω

Aux 2 Output :
Connector : Lemo coaxial
DC Output Signal : DC version of the signal on the RMS detector, delayed 0.8 s - Fast, Inst., short circuit protected
Output : 0 to 4.0 VDC, 50 mV/dB
Max. Load : 10 kΩ // 1 nF
Output Impedance : Typically 100 Ω

Filter Set Specifications - ZT 0328 :

Standards :
Conforms to the following :
IEC/EN 61260 - 1995 - Octave and 1/3 Octave bands Class 1

Octave and 1/3 Octave Band Filters:
Nominal 1/1 Octave Band Centre Frequencies : 31.5 Hz, 63 Hz, 125 Hz, 250 Hz, 1 kHz, 2 kHz, 4 kHz and 8 kHz
Nominal 1/3 Octave Band Centre Frequencies : 20 Hz, 25 Hz, 31.5 Hz, 40 Hz, 50 Hz, 63 Hz, 80 Hz, 100 Hz, 125 Hz, 160 Hz, 200 Hz, 250 Hz, 315 Hz, 400 Hz, 500 Hz, 630 Hz, 800 Hz, 1 kHz, 1.25 kHz, 1.6 kHz, 2 kHz, 2.5 kHz, 3.15 kHz, 4 kHz, 5 kHz, 6.3 kHz, 8 kHz, 10 kHz and 12.5 kHz

Measurements :
Parameters measured in each frequency band :

Measurements :
Parameters measured in concurrent broadband measurement :

Legend :
X = Frequency weighting A, C or L
Z = Time weighting F or S