Larson Davis CAL291 Product manual

I291.01 REV B
Larson Davis
CAL291
Technical Reference Manual

Copyright
Copyright 2006, 2007, 2008 and 2010 by PCB Piezotronics, Inc. This manual is copyrighted, with all
rights reserved. The manual may not be copied in whole or in part for any use without prior written
consent of PCB Piezotronics, Inc.
Disclaimer
The following paragraph does not apply in any state or country where such statements are not
agreeable with local law:
Even though PCB Piezotronics, Inc. has reviewed its documentation, PCB Piezotronics, Inc. makes no
warranty or representation, either expressed or implied, with respect to this instrument and
documentation, its quality, performance, merchantability, or fitness for a particular purpose. This
documentation is subject to change without notice, and should not be construed as a commitment or
representation by PCB Piezotronics, Inc.
This publication may contain inaccuracies or typographical errors. PCB Piezotronics, Inc. will
periodically update the material for inclusion in new editions. Changes and improvements to the
information described in this manual may be made at any time.
Recycling
PCB Piezotronics, Inc. is an environmentally friendly organization and encourages our customers to
be environmentally conscious. When this product reaches its end of life, please recycle the product
through a local recycling center or return the product to:
PCB Piezotronics, Inc.
Attn: Recycling Coordinator
1681 West 820 North
Provo, Utah, USA 84601-1341
where it will be accepted for disposal
Product Warranty
Refer to our website, www.larsondavis.com, for a copy of our product warranty.

I291.01 REV B

CAL291 Technical Reference Manual Table of Contents i-i
Table of Contents
Chapter 1 Introduction 1-1
About This Manual......................................... 1-1
Features ........................................................ 1-2
Applications ................................................... 1-2
Unpacking and Inspection ............................. 1-3
Accessories ................................................... 1-3
Chapter 2 Description ...................................... 2-1
General Description....................................... 2-1
Microphone Ports .......................................... 2-2
End Plate ....................................................... 2-3
Connectors ............................................................. 2-3
Input ........................................................................................... 2-3
Power ......................................................................................... 2-3
Chapter 3 Operation .........................................3-1
Powering the CAL291.................................... 3-1
Input Signal.................................................... 3-1
Microphone Placement.................................. 3-2
Pressure\Residual Intensity Measurement.... 3-3
Amplitude/Phase Normalization .................... 3-4
Appendix A Technical Specifications ............ A-1
Standards ...................................................... A-1
Input............................................................... A-1
Acoustical Output .......................................... A-1
Mechanical Characteristics............................ A-2
Power ............................................................ A-2

CAL291 Refernce Manual About This Manual 1-1
CHAPTER
1Introduction
The Larson Davis Model CAL291 Residual Intensity
Calibrator satisfies the residual intensity test device
specifications of both IEC 1043:1993 and ANSI S1.9-1996.
About This Manual
This manual has 3 chapters and 1 appendix covering the
following topics:
•Chapter 1 - Introduction: Orients the user to the contents
of this user manual and the features, functions and
measurement capabilities of the CAL291. It also
includes instructions on unpacking the CAL291.
•Chapter 2 - Description: Provides a physical description
of the CAL291.
•Chapter 3 - Operation: Describes the setup and
operation of the CAL291.
•Appendix A- Specifications: presents the technical
specifications of the CAL291.

1-2 Features CAL291 Refernce Manual
Features
The Larson Davis Model CAL291 Residual Intensity
Calibrator has the following features:
• Applies the same signal with zero phase difference to a
pair of 1/2” or 1/4” microphones
• Can be driven by external signal generators such as the
following:
- Larson Davis Model SRC20 Signal Source
- Analog or digital signal generator modules available
for the Larson Davis Models 2800, 2900, 3000+ and
3200 portable real-time analyzers.
• Built-in amplifier provides sound pressure levels to 122
dB
Applications
• Generation of signals for verification of the amplitude/
phase accuracy of multi-channel acoustic measurement
systems
• Amplitude/Phase Normalization: The digital filters of the
Larson Davis analyzers provide both amplitude and
phase, permitting the measurement of the complex
transfer function between two measurement channels,
including microphones, in the 1/3 octave frequency
bands. By using the CAL291 to excite both microphones
simultaneously, the amplitude and phase differences
between the two measurement channels can be
determined as a function of frequency. From this
information, a correction function can be generated
within the analyzer to correct for any amplitude and
phase errors which may have existed between channels
prior to the normalization.

CAL291 Refernce Manual Unpacking and Inspection 1-3
Unpacking and Inspection
Your CAL291 has been shipped in protective packaging.
Pleaser verify the package contains the items listed below
and retain the shipping container for safe shipment at a
future date. Report any damages or shortage immediately to
Larson Davis, Inc. at 801-375-0177.
If you have not already done so, please record your
instrument’s serial number (located on the bottom of the
instrument) and the purchase date. You may be asked to give
this information in future communications with Larson
Davis.
Accessories
The CAL291 is delivered with the following standard
accessories:
• PSA004 100 - 240 VAC to 12 Vdc 2.5A Switching AC
Power Adaptor
• Two ADP038 1/2” to 1/4” microphone adaptors
• User Manual (Larson Davis part number I291.01)
• Calibration Certificate

1-4 Accessories CAL291 Refernce Manual

CAL291 Refernce Manual General Description 2-1
CHAPTER
2Description
The physical description of the CAL291 is presented in
this chapter. Operational information is presented in
Chapter 3 “Operation” on page 3-1
General Description
The CAL291 has a flat shape factor for optimal use on a
table or desktop. In use, the sound intensity probe of the
intensity measurement system to be evaluated is laid flat on
the table with the two microphones inserted into the
microphone ports of the CAL 291 as shown in Figure 2-1.
FIGURE 2-1 CAL291, General View

2-2 Microphone Ports CAL291 Refernce Manual
Microphone Ports
The microphone ports are on two opposite faces of an
aluminum block mounted on one end of the CAL291, as
shown in Figure 2-2.
FIGURE 2-2 Aluminum Block with Microphone
Ports

CAL291 Refernce Manual End Plate 2-3
End Plate
The power switch, electrical input connector, DC power
connector and fuse are located on the end plate, as shown in
Figure 2-3.
FIGURE 2-3 CAL291 End Plate
Connectors
Input
BNC Female
Power
2.5 X 5.5 mm coaxial connector, center positive
Power Switch
Power Connector
Fuse
Input Connector

2-4 End Plate CAL291 Refernce Manual

CAL291 Refernce Manual Powering the CAL291 3-1
CHAPTER
3Operation
This chapter presents a detailed description of the
operation of the CAL291.
Powering the CAL291
An LED in the center of the top
surface of the CAL291 is illuminated
when the CAL291 power is On.
The CAL291 is powered by the Larson Davis PSA004,
which is supplied as a standard accessory. Connect to the AC
power cable to main power and the DC output to the power
connector on the end plate of the CAL291. Press the upper
portion of the power switch (I) to switch on the CAL291 and
press the lower portion (O) to switch it off.
Input Signal
The CAL291 was designed to work
optimally with the analog and digital
signal generators available with the
Larson Davis Models 2800, 2900,
3000+ and 3200 portable real-time
Analyzers.
Connect the output from the external signal generator
capable of generating pink noise to the BNC input on the
end plate of the CAL291.

3-2 Microphone Placement CAL291 Refernce Manual
Microphone Placement
In most cases this CAL291 will be used with a dual channel
sound intensity probe, although it can also be used with two
separate microphones mounted on the microphone
preamplifiers.
• If using a sound intensity probe, separate the two
microphones as described in the operating manual for the
probe, remove the space, and spread the microphones far
enough apart that they can be placed over the
microphone port block. Do not remove the microphone
grid caps. Slide them firmly into the two ports as shown
in Figure 3-1.
FIGURE 3-1 Microphone In Place Inside
Microphone Ports of CAL291
• If using separate microphones, insert each firmly into the
microphone ports. It may be necessary to place support
beneath the preamplifiers so that they are aligned parallel
to the center line of the microphone port openings.

CAL291 Refernce Manual Pressure\Residual Intensity Measurement 3-3
Pressure\Residual Intensity Measurement
The CAL291 can be used to determine the pressure-residual
intensity index of either the sound intensity probe or the
complete sound intensity measurement system.
With the probe microphones inserted into the microphone
ports as described in “Microphone Placement” on page 3-1,
excite the CAL291 with pink noise at a low voltage level
using the signal generator.
Table 3-1 shows the recommended maximum input voltage
level to the CAL291 for several different frequency bands,
and the corresponding sound pressure levels which would be
produced at the microphone diaphragms.
To maintain the total harmonic distortion less than 1%, the
sound pressure level at the microphones should be kept
within the range of 25 dB- 121 dB (1 kHz). Adjust the signal
generator output to obtain a sound pressure level at the
microphones within this range and the amplitude level
difference between the two microphones will be < 0.1 dB
(@ 1kHz). The phase angle between the acoustic signals will
be zero.
Table 3-1 Output Level and Maximum Input Voltage
The signals applied to the microphones will no be as
required for the measurement of the pressure-residual
intensity index.
ANSI S1.9-1997 and IEC1043:1993 call for the
measurement of the pressure-residual intensity index in 1/3
octave bands (1/1 octave bands for the instrument providing
only 1/1 octave analysis). The user is directed to refer to the
Frequency
(Hz)
Output SPL
(dB re. 20Pa)
Maximum Input Voltage
(dBV)
250 124 128
630 122 127
1000 121 128
1600 121 127
2000 118 128
2500 119 121
6300 112 113

3-4 Amplitude/Phase Normalization CAL291 Refernce Manual
appropriate standards for further details on performing these
measurements as specified.
Amplitude/Phase Normalization
For sound intensity measurements, it is essential to have the
best possible amplitude and phase match between
measurement channels in order to meet the minimum
pressure-residual intensity index cause stipulated by the
standards. Both the ANSI and IEC standards include
provisions for phase compensation in the measurement
system.
Because a residual intensity testing device is being used as
the acoustic source for both microphones, we know that they
are exposed to equal amplitude signals with zero phase
difference between them (within the limits of the device).
Thus, any variation of the magnitude of the transfer function
between channels from unity (0 dB) and of the phase from
zero is the result of errors in the measurement system which
includes the microphones, intensity probe electronics and
the analyzer.
Some instruments, such as the Larson Davis Models 2900B,
3000+ and 3200 can not only measure the complex transfer
function between channels in the 1/3 octave frequency
bands, but they can also use the measured transfer function
to generate a correction function to correct for some of the
errors and decrease the pressure-residual intensity index of
the system. For further details on the implementation of this
normalization technique, see the operators manual for the
instrument being used.

CAL291 Refernce Manual Amplitude/Phase Normalization 3-5

CAL291 Reference Manual Technical Specifications A-1
APPENDIX
ATechnical Specifications
The technical specifications in this chapter are subject to
change without notice. Please refer to the calibration and test
results for data on a specific unit.
Standards
Meets the residual intensity test device specifications as pre-
sented in IEC 1043:1993 “Instruments for the measurement
of sound intensity” and ANSI S1.9-1996 “Instruments for
measurement of sound intensity”.
Input
Input Connector
BNC with impedance of 1M
Acoustical Output
• Sound Pressure Level (1% harmonic distortion): 25 - 115
dB @ 1kHz
• SPL difference between channels: < 0.1 dB 1 kHz
• Maximum pressure-intensity index: > 27 dB
• Output Level and Maximum Input Voltage for < 1% dis-
tortion: as specified in Table A-1 on page A-2

A-2 Mechanical Characteristics CAL291 Reference Manual
Table A-1 Output Level and Maximum Input Volt-
age
Mechanical Characteristics
Length
25.6 cm (10.3 in)
Width
10.0 cm (4.0 in)
Height
5.3 cm (1.1 in)
Weight
1.0 kg (2.2 lb)
Power
D.C. Power: 9 -16 Vdc, 400 mA provided by PSA004 DC
Power Supply (included) 90 - 240 VAC @ 50- 60 Hz
Frequency
(Hz)
Output SPL
(dB re. 20Pa)
Maximum Input Voltage
(dBV)
250 124 128
630 122 127
1000 121 128
1600 121 127
2000 118 128
2500 119 121
6300 112 113

CAL291 Reference Manual Power A-3