Rohde & Schwarz UPD Installation and operating instructions

Loudspeaker measurements
with Audio Analyzers
UPD or UPL
Application Note 1GA16_1L
replaces 1GPAN16L Subject to change
M. Schlechter 07.97
Products:
Audio Analyzer UPD
Audio Analyzer UPL

1GA16_1L.DOC ROHDE & SCHWARZ1
Content
1 INTRODUCTION 3
2 PREPARATIONS 3
2.1 HARDWARE AND SOFTWARE REQUIREMENTS 3
2.2 SOFTWARE INSTALLATION 4
2.3 STARTING THE APPLICATION SOFTWARE 4
2.4 CONFIGURING THE APPLICATION 4
2.4.1 SETUP AND CONFIGURATION FILES 5
2.4.2 PRELIMINARY CONFIGURATION OF SETUP FILE 5
2.5 CONVERTING THE SETUP FOR SOFTWARE UPDATES 6
3 OPERATING CONCEPT 6
3.1 OVERVIEW 7
3.2 SOFTKEY LEVELS 7
3.3 SOFTKEYS COMMON TO ALL LEVELS 7
3.4 ENTRY OF PARAMETERS 7
3.5 COMMON SOFTKEYS FOR POST-PROCESSING 8
4 MEASUREMENT MODES 9
4.1 MODES OF FREQUENCY RESPONSE ANALYSIS 9
4.2 FREQUENCY SWEEP 10
4.2.1 ADVANTAGES 10
4.2.2 SETUP AND PROGRAM SETTINGS 10
4.3 FFT NOISE 10
4.3.1 ADVANTAGES, LIMITS AND MAIN FIELDS OF APPLICATION 11
4.3.2 SETUP AND PROGRAM SETTINGS 11
4.4 SWEPT BURST MEASUREMENT 12
4.4.1 ADVANTAGES AND MAIN FIELDS OF APPLICATION 12
4.4.2 PROGRAM SETTINGS 12
4.5 GO/NOGO TESTS 12
4.6 SELECTING THE MEASUREMENT MODE 13
5 MEASUREMENTS 13
5.1 IMPEDANCE AND ASSOCIATED PARAMETERS 14
5.1.1 TEST SETUP 14
5.1.2 SPECIAL NOTES ON ENTRY OF PARAMETERS 15
5.1.3 DC IMPEDANCE 15
5.1.4 IMPEDANCE FREQUENCY RESPONSE 16
5.1.5 RESONANCE FREQUENCY AND RESONANCE IMPEDANCE 17
5.1.6 ABSOLUTE MINIMUM AND MAXIMUM IMPEDANCE 17
5.1.7 TUNING FREQUENCY 17

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5.1.8 Q FACTOR 18
5.1.9 EQUIVALENT VOLUME 18
5.1.10 GO/NOGO TEST 19
5.2 SOUND PRESSURE MEASUREMENTS 19
5.2.1 TEST SETUP 19
5.2.2 ADJUSTING THE OUTPUT POWER 21
5.2.3 ENTRY OF MICROPHONE AND ROOM PARAMETERS 22
5.2.4 SELECTING THE SOUND PRESSURE UNIT 22
5.2.5 SENSITIVITY MEASUREMENT AND RADIATION ANGLE 23
5.2.6 FREQUENCY RESPONSE OF SOUND PRESSURE LEVEL AND TRANSMISSION RANGE 24
5.2.7 SELECTING THE COMBINED NEAR/FAR-FIELD MEASUREMENT 26
5.3 PHASE AND ASSOCIATED PARAMETERS 27
5.3.1 TEST SETUP 27
5.3.2 FREQUENCY RESPONSE OF PHASE 28
5.3.3 LINEARITY DEPARTURE AND GROUP DELAY 29
5.4 POLARITY 30
5.4.1 MEASUREMENT FUNCTION POLARITY FOR ELECTRICAL SYSTEMS 30
5.4.2 POLARITY CHECK BY COMPARISON TO REFERENCE PHASE MEASUREMENT 30
5.4.3 POLARITY CHECK BY COMPARISON TO REFERENCE SOUND PRESSURE CHARACTERISTIC 31
5.5 DISTORTION 32
5.5.1 SPECIAL FEATURES OF THD+N MEASUREMENT (WITH POST-FFT) 33
5.5.2 SPECIAL FEATURES OF ZOOM FFT 33
6 COMBINING SEVERAL MEASUREMENTS 33
6.1 MACRO OPERATION 34
6.1.1 RECORDING A MACRO 34
6.1.2 RUNNING A MACRO 34
6.1.3 PREDEFINED MACROS 35
6.2 CREATING AND USING DIFFERENT CONFIGURATION FILES 36
6.3 LABELLING OF MACRO AND CONFIGURATION MEMORY LOCATIONS 36
7 PROCESSING OF MEASUREMENTS 38
7.1 CHANGE OF TASK APPLICATION/USER INTERFACE 38
7.2 PRINTOUT 38
7.2.1 PRINTOUT AT USER INTERFACE 39
7.2.2 PRINTOUT DURING RUNNING APPLICATION 39
7.3 RESTART 39
7.3.1 RESTARTING A MEASUREMENT 39
7.3.2 RESTARTING THE APPLICATION 39
8 TERMINATING THE APPLICATION 39
11

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1 Introduction1 Introduction
Audio Analyzers UPD and UPL with their large variety of functions provide practically all measurement
procedures required in audio technology. Thanks to the Universal Sequence Controllers UPD-K1 and
UPL-B10, which are available as options, the user is able to considerably expand the range of functions to
suit his particular requirements. It is possible, for instance, to add complete measurement functions - eg
measurement of ohmic resistance - and to read out, convert or reload sweep results or to add new scale
labelling (eg group delay). Another example is the analysis of sweep curves and the display of results in a
window next to the curve. As far as softkey labelling and functions are concerned, operation of the
sequence control programs is analogous to the softkey control of the UPD/UPL graphics display.
This application contains a BASIC program permitting automatic measurements of loudspeaker
parameters with the aid of the features described above. The program can be run on UPD with UPD-K1
and on UPL with UPL-B10. The application software supports the following measurements or
measurement sequences:
• Measurement of impedance characteristic with calculation of tuning frequency, resonance frequency
and resonance impedance, DC resistance, minimum and maximum impedance, Q factor and
equivalent volume.
• Measurement of sound characteristic with calculation of transmission range as well as measurement
of sensitivity and peak sound pressure.
• Measurement of intermodulation products at fixed frequencies or of harmonic distortion as a function
of frequency using a variety of measurement procedures and displays
• Measurement of phase linearity and group delay as well as
• Various methods for checking the polarity
The software not only yields highly accurate results for the development of loudspeakers but also
supports measurements in production testing:
• Impedance- and frequency-response curves can be referenced to a "golden unit" so that a GO/NOGO
decision can be made for each tested device.
• Control of measurement sequences can be stored (learned) by the program so that whole sequences
can be performed by a keystroke without any further intervention being required. Thus several
measurements can be combined to a series of measurements (macro operation).
The measurements and calculations described in this Application Note are in line with DIN IEC 268,
part 5.
22 PreparationsPreparations
22.1.1 Hardware and Software RequirementsHardware and Software Requirements
The accompanying floppy disk holds BASIC program modules and one complete setup (SPEAKER.SCO),
so that the application software can be run immediately under the UPD/UPL universal sequence controller
(UPD-K1 or UPL-B10). As regards the hardware, an UPD/UPL of basic configuration will be sufficient. An
external keyboard is required for operating the automatic sequence controller.
The following software requirements must be met:
• UPD software version 3.03 or higher, UPL software version 1.01 or higher,
• Universal Sequence Controller UPD-K1 or UPL-B10,
• configuration 3 (64-Kbyte program and 32-Kbyte data memory), for very long sweeps (more than 400
sampling points) or combined near/far-field measurements possibly configuration 5 (64-Kbyte data
memory).
Note: UPD and UPL are configured with the aid of service programs UPDSET and UPLSET,
respectively.

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22.2.2 Software InstallationSoftware Installation
Same as the UPD/UPL software, the application software is installed with the aid of the installation
program APPINST.BAT:
• quit UPD/UPL (press SYSTEM key or Ctrl F9,
• insert the supplied floppy disk,
• select floppy disk drive (A:),
• call up the installation program (APPINST).
The installation program creates a subdirectory with the name SPEAKER (if not yet available) and then
copies the BASIC program modules and setups required for the application into this subdirectory.
After the installation, the SPEAKER.SCO setup can be adapted to specific user requirements and to the
external hardware (printer, monitor). See also section 2.4.2, Preliminary Configuration of Setup File.
22.3.3 Starting the Application SoftwareStarting the Application Software
The application software is loaded and started under the universal sequence controller. So the device
software has to be started first (either by switching the instrument on or by calling up the UPD/UPL at
DOS level) and then the universal sequence controller is selected with key F3 (external keyboard).
Note: Before selecting the universal sequence controller make sure that the logging mode is switched
off ("logging off" displayed at the very right of the command line) as otherwise commands
entered in the manual mode are added to the application program and this might cause the
BASIC program memory to overflow. The logging mode is switched on and off by means of key
F2.
The application software must be started from the path
⇒ \SPEAKER
as it searches for all program modules in the current path. Therefore, either the path has to be changed or
the application setup \SPEAKER\SPEAKER.SCO be loaded.
The path can be changed in one of the following ways:
• in the device software under "Working Dir" in the FILE panel
• in the automatic sequence controller with the BASIC command line
⇒ UPD OUT "MMEM:CDIR '\SPEAKER'".
Note: UPL OUT and UPD OUT are synonymous, the BASIC program always uses UPD OUT.
• at the DOS level with CHDIR (via the SHELL of the automatic sequence controller)
The BASIC program SPK.BAS can now be loaded and started. To do so the following entries have to be
made:
• press the LOAD softkey,
• enter SPK (confirm with "return"),
• press the RUN softkey.

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22.4.4 Configuring the ApplicationConfiguring the Application
2.4.1 Setup and Configuration Files
The application software uses two different sources for device setting:
SPEAKER.CFG: Configuration file holding all user entries (see section 3.4, Entry of Parameters) or
default values on initial call-up. When the application is started, this file is loaded; when the application
is left using the EXIT softkey (see section 7, Terminating the Application) the file is stored with updated
values so that the entries made by the user during the last run are reinstated on starting the application
again. If as an exception user entries should not be stored, the application should be quit with CTRL
BREAK.
SPEAKER.SCO: Setup file used as the basis for all commands of the application software. Most of the
settings in this file have to remain unchanged or are overwritten by the application software. A few
settings only may be (or have to be) updated by the user. The program reads the setup but does not
change it. The final version of the setup may be protected against inadvertent overwriting by assigning
the attribute READ ONLY.
Note: Alternative configuration files can be stored and loaded under the menu item UTILITY ->
CONFIG. This capability is particularly important when macros are used (see section 6,
Combining Several Measurements).
The SPEAKER.SCO setup also includes settings that are identical for all procedures and measurements:
FIG 1: Generator, analyzer and display panel of SPEAKER.SCO setup

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2.4.2 Preliminary Configuration of Setup File
The following modifications of the SPEAKER.SCO setup file are permissible:
• selection of printer interface (SCREEN HARD COPY in OPTIONS panel),
• defining a maximum generator voltage for protecting DUTs,
• driving an external monitor (Extrn Disp in OPTIONS panel),
• changing the X axis from log to linear (Spacing LIN POINTS in GENERATOR panel and X-AXIS-
>Spacing LIN in DISPLAY panel),
• changing the Y1 axis from lin to log (TRACE A->Spacing LOG in DISPLAY panel), applies to
impedance measurements only,
• selection of commands to be displayed in the status panel ("tick off"),
• comments in plain text in the graphics display (DISPLAY panel) and info text (FILE panel)
• comments in plain text for printout (dialog box of hardkey HCOPY),
• defining tolerance curves/values and checks (LIMIT CHECK in DISPLAY panel).
The application software is tailored to the audio range, ie to the 25-kHz generator and a 22-kHz analyzer.
In the UPD instruments for higher frequencies may also be selected but in this case the following aspects
have to be considered:
• the lower limit frequency of the analyzer is higher,
• the resolution of the 8k FFT is only 41.67 Hz (100-kHz analyzer) or 125 Hz (300-kHz analyzer),
• the measurement speed is lower.
With the preliminary configuration terminated, the setup has to be stored (as complete setup) under the
same name and may be assigned the attribute READ ONLY.
IMPORTANT: Only the listed settings may be modified, as otherwise proper function of the software
cannot be guaranteed.
22.5.5 Converting the Setup for Software UpdatesConverting the Setup for Software Updates
If the device software is updated, the SPEAKER.SCO - and all other setups - may require to be
converted. This is done automatically when the setup is loaded but to avoid unnecessary delays during
loading, SPEAKER.SCO should be stored as converted setup. This can be done in two ways:
• at the DOS level by calling up the batch converter:
⇒ UPD_CONV \SPEAKER\SPEAKER.SCO or
⇒ UPL_CONV \SPEAKER\SPEAKER.SCO,
• at the UPD/UPL level by loading and storing SPEAKER.SCO.
IMPORTANT: with setups set to READ ONLY, the "r" attribute has to be deleted at the DOS level:
⇒ ATTRIB -r \SPEAKER\SPEAKER.SCO

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33 Operating ConceptOperating Concept
33.1.1 OverviewOverview
The application is operated by means of softkeys which are organized in 4 hierarchical levels. When the
application software is started, the first (highest) softkey level is displayed; pressing a softkey triggers an
action and/or causes another softkey level to be entered. Each level may have up to eight active softkeys;
unassigned softkeys are blank. Same as in the UPD/UPL device software, function keys F5 to F12
correspond to softkeys #1 to #8.
Each time a softkey is pressed, the displayed softkey are cleared. No entries can be made while the
application program carries out setting sequences or calculations or waits for the end of a measurement.
The softkeys are blank. Only after the softkeys have been assigned new (application) functions can
further entries be made.
33.2.2 Softkey LevelsSoftkey Levels
Functions of the four hierarchical softkey levels:
• Level 1 (main level): selection of measurement; implicit loading of a specific measurement module
• Level 2: selection of measurement mode (frequency sweep or FFT noise; see section 4, Measurement
Modes) with implicit (re)-loading of SPEAKER.SCO setup;
• Level 3: entry of parameters and start of measurement;
• Level 4: post-processing and restart of measurement.
DRUN
EXIT
BACK
BACK
BACK START
START
(RE)ZOOMGOTOUPDHARDCOPY
IMPEDANCSOUNDPHASE
FFT RANDFRQSWP
VOLTAGEFREQRNGSWPPNTS
Veq/Vb
RUNAWAYS
THD
D
FIG 2: Operation of application software via softkey menus
33.3.3 Softkeys Common to all LevelsSoftkeys Common to all Levels
Two of the altogether eight softkeys are assigned the same function at all levels and are always located at
the same position:
• the lefthand softkey (#1, F5) is used for returning to the next higher level (BACK); at the top level the
application is quit (EXIT; see section 7, Terminating the Application),
• the righthand softkey (#8, F12) is only active at levels 3 and 4 and used for starting the measurement;
at the end of the measurement the application is always at level 4.

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33.4.4 Entry of ParametersEntry of Parameters
All parameters are entered at level 3 and initiated by softkeys. Strings, integer and floating-point numbers
are entered in a dialog, a 1-out-of-N selection is made at another softkey level.
For dialog entries the following applies:
• The designation of the parameter (eg voltage) is displayed in the entry line, possibly together with the
unit (eg V).
• The currently set value is displayed at the right of the cursor. It may be overwritten or confirmed by
means of the RETURN key.
• Floating-point numbers are entered in the specified unit; only the value is entered.
• If the permissible upper or lower limit is exceeded, the entry is limited to this value or a new entry is
requested.
For 1-out-of-N entries the following applies:
• Selecting a 1-out-of-N entry opens up a 1-out-of-N selection level at which selectable values are
assigned to the softkeys.
• When the desired softkey is pressed the selected value becomes valid immediately and the 1-out-of-N
selection level is closed.
Since the parameters to be entered in this way are the same for most of the measurements, they will be
explained in brief below. Special parameters shall be dealt with together with the respective
measurement. The mentioned measurement modes FFT noise and frequency sweep are explained in
detail in section 4.
- VOLTAGE (F6, level 3): total voltage (FFT noise) or sinewave voltage (frequency sweep), at the same
time DC voltage for measuring the DC resistance.
- FREQ RNG (F7, level 3): Lower Freq (in Hz) and Upper Freq (in Hz): frequency range within which
sinusoidal lines are generated (FFT noise) or sweep points set (frequency sweep). With FFT noise
mode, reducing the frequency range also reduces the number of sinusoidal lines and therefore
shortens the time required for generating the noise signal. If frequency sweep is used the resolution is
improved (constant number of sweep points).
- SWP PNTS (F8, level 3): number of sweep points (frequency sweep only). Reducing the sweep points
shortens the sweep time, an increase improves the resolution.
- FFT SIZE: number of FFT lines determining the FFT resolution and therefore the FFT noise. Reducing
the lines causes the resolution to deteriorate but shortens the time for generating the noise signal and
the FFT measurement time.
33.5.5 Common Softkeys for Post-ProcessingCommon Softkeys for Post-Processing
The softkeys for post-processing are at softkey level 4. Some of them are available for all measurements
and always assigned the same function (and label):
• Softkey #2 (F6): o <--> O changes from partial to full graphics display and vice versa.
• Softkey #3 (F7): GOTO UPD changes temporarily to the UPD operating software (see section 7.1,
Change of Task Application/User Interface)
• Softkey #4 (F8): HARDCOPY outputs the screen content to a printer or file (see section 7.2.2, Printout
during Application Run)

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44 Measurement ModesMeasurement Modes
44.1.1 Modes of Frequency Response AnalysisModes of Frequency Response Analysis
Measuring the frequency response of various parameters is particularly important in development and
production testing. Such parameters are for instance:
• electrical transfer function of crossover units,
• acoustic transfer function of loudspeakers,
• impedance characteristic,
• sound pressure characteristic,
• phase characteristic and group delay,
• distortion.
These parameters can be measured by the frequency sweep of a sinewave signal and displayed in a
tabulated or graphical form. Each curve may contain of up to 1024 single measurements with linear or
logarithmic scaling as required.
Frequency sweeps are very time-consuming because of the generator setting time, DUT settling time,
measurement time and, for acoustic measurements, the signal travel time involved. Particularly at low
frequencies, settling time and measurement time may be too long when it comes to alignments or
production testing.
All measurements based on voltage measurements may also be carried out with a noise generator and an
FFT analyzer. The (quasi)-noise generator of the UPD/UPL uses discrete sinusoidal lines and may be
synchronized to the FFT, ie the sinusoidal audio signals produced by the generator are of the same
frequency spacing as the FFT (called FFT noise in the text below). Consequently the measurement signal
at the display edges of the FFT can be continued without any transitions that no window function is
required for suppressing the FFT continuation error and an optimum frequency and level accuracy of the
FFT is obtained.
Measurement time and frequency resolution depend on the selected FFT size or on the frequency
stepwidth of the noise generator.
The smallest step of the 25-kHz generator is 5.86 Hz. This is therefore the maximum permissible
resolution for the FFT analyzer although a much better resolution could be obtained in the analyzer (with
the aid of ZOOM FFT). It is advisable to use 8 k FFT where the measurement speed still allows several
measurements per second to be made. The measurement speed can be further increased by reducing
either the frequency resolution or the FFT size.
At the generator side, generation and phase optimization of the noise signal involves much more
computation work than the generation of a simple sinewave signal. If all available sinusoidal lines are
used, the noise signal is available after about 1 minute. However, this time is only required once and any
number of highly accurate measurements can be carried out thereafter. By reducing the FFT size
(analyzer) or the frequency range (generator) the number of discrete sine tones can be reduced and the
signal generation time drastically shortened.
Note: The highest resolution (2.9296875 Hz at 8 k zoom FFT) makes only sense in the UPL, as the
UPD is not able to track a resolution of < 5.859375 Hz because of its higher internal generator
clock rate.
The frequency sweep and the FFT noise mode each have their pros and cons so that both modes are
employed (as far as possible) for the measurements described in the Application Note.

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Another measurement mode implemented particularly for transmission range measurements is the swept
burst measurement. The measurement time is longer than in the normal (sinusoidal) sweep mode, but
above a room-dependent lower frequency limit, echofree measurements can be performed outside
anechoic rooms.
44.2.2 Frequency SweepFrequency Sweep
4.2.1 Advantages
• Logarithmic frequency scaling is possible so that a very good frequency resolution is obtained at low
frequencies. FFT uses linear scaling only.
• The frequency resolution can be improved without any restrictions by reducing the frequency range;
with FFT the smallest step is fixed to 5.86 Hz (UPD) or 2.93 Hz (UPL).
• The generator setting time for each sweep point is very short while a time-consuming noise-signal
generation is required with FFT noise.
• Frequency sweep is possible with all measurements, FFT noise can be used for voltage
measurements only.
4.2.2 Setup and Program Settings
When selecting the frequency sweep mode (see section 4.6, Selecting the Measurement Mode) the
SPEAKER.SCO setup with the following settings becomes active:
FIG 3: Example of SPEAKER.SCO setup for frequency sweep mode
Values for start, stop, points and voltage are generated from user entries or taken from the
SPEAKER.CFG configuration file.

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44.3.3 FFT NoiseFFT Noise
4.3.1 Advantages, Limits and Main Fields of Application
• The pure measurement time - without signal generation time - is very short (online response).
• An increase (doubling) of the frequency resolution increases the measurement time only
insignificantly.
• Up to 3712 measurement points - 7424 in the UPL - are possible (1024 in the sweep mode) so that a
higher frequency resolution is possible over the entire sound frequency range with linear scaling.
In the present application the FFT noise mode can be used for measuring the impedance and sound
pressure characteristic. Main fields of application are:
• production testing (go/nogo tests),
• adjustments,
• sound level measurements in not completely anechoic rooms.
4.3.2 Setup and Program Settings
Selecting the FFT noise mode (see section 4.6, Selection of Measurement Mode) activates the
SPEAKER.SCO setup with the following settings:
FIG 4: Example of SPEAKER.SCO setup for FFT noise mode
The values for Lower Freq, Upper Freq, VOLT RMS and FFT size are generated from user entries or
taken from the configuration file SPEAKER.CFG.
Remarks:
• If an entry is made in the GENERATOR panel which requires a regeneration of the noise signal, the
generator starts the very time-consuming noise signal computation (GEN BUSY in the status display).
Noise-signal generation can be aborted by a keystroke in the case of manual control but this is not
possible when the universal sequence controller is used.
• "Window RECTANGULAR" switches off the window function.
• "Zooming ON" (with zoom factor 2) is only possible in the UPL, as the UPD generator is not able to
set frequency resolutions below 5.8584 Hz.

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44.4.4 Swept Burst MeasurementSwept Burst Measurement
In this mode, not a continuous but a burst sinewave signal is swept, ie varied in frequency. A whole
number of periods is measured, the burst duration is one period longer than the measurement time. This
mode is used for measuring the transmission range as with this measurement reflections in the room can
be eliminated by simple means.
Between the echo signal delay and the signal delay only the direct measurement signal is present at the
microphone. This period defines the lower frequency limit for an echofree operation: all frequencies with a
shorter signal period can be measured without any echoes. The procedure is described in detail in section
5.2.6, Frequency Response of Sound-Pressure Level and Transmission range.
4.4.1 Advantages and Main Fields of Application
• Echofree measurements above a certain lower frequency limit also outside anechoic chambers
• the measurement is not impaired by the echo of the preceding sweep point
• short burst pulses are easier to support than continuous sinewave signals.
Because of the longer measurement time compared with those of other modes and the susceptibility to
interference, this mode can only be used in development laboratories.
4.4.2 Program Settings
Since the burst sweep cannot be directly selected as a mode in the device software, each sweep point
has to be set by the application software:
• Select SINE BURST as a generator signal.
• Set analyzer to a special RMS mode (TRIGGERED) where the measurement is automatically triggered
on detection of the signal level.
• Same as with the sinewave sweep, vary the frequency depending on the values set for start, stop,
points and spacing.
• The measurement time is a multiple of one period, but at least one period. Towards the upper end the
number of periods is limited such that the measurement is terminated before the first echo arrives.
• The burst duration is one period longer than the measurement time and also an integer (to avoid DC
components).
• The burst-on delay is constant and should compensate the internal measurement delay.
• The input level range is fixed and maintained for all sweep points. An automatic routine defines the
level range so that the reference frequency (SNS FREQ) is optimally driven.
• The trigger threshold at which the RMS measurement is started can be selected (TRGLEVEL softkey).
The threshold should be selected so that it is exceeded by all sweep points but sufficiently away from
ambient noise. Values around 1% are recommended.
44.5.5 GO/NOGO TestsGO/NOGO Tests
For applications in production, the impedance characteristic and transmission range of a reference
loudspeaker can be recorded, tolerance values defined and DUTs checked for compliance with set
tolerances (GO/NOGO tests).
The measured characteristic of this "golden unit" is stored as a trace and loaded into the display panel as
a reference trace for the DUTs. The tolerance curves are then displayed as horizontal lines at a specified
distance above and below the 0-dB line. The advantage of this method is that deviations from the ideal
trace (0-dB line) can be directly read in dB. An ideal DUT would produce a horizontal line of exactly 0 dB.

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If the DUT is within the specified tolerances (limits), "DUT passed" is displayed. If at least one measured
value is out of tolerance, "DUT failed" is displayed. If a macro is used, the macro is stopped and the
instrument waits for a keystroke.
At the end of the measurement, the reference curve is stored by pressing the STO REF softkey and
entering a file name. The reference curve can be called up and tolerance limits entered with the REF SPK
softkey.
44.6.6 Selecting the Measurement ModeSelecting the Measurement Mode
The measurement mode is selected at softkey level 2.
Impedance measurement:
• Softkey #2 (F6, FFT RAND) selects FFT noise and
• Softkey #3 (F7, FRQ SWP) the frequency sweep for determining the impedance characteristic.
Sound measurement:
• Softkey #2 (F6, FFT RAND) selects FFT noise and
• Softkey #3 (F7, FREQ SWP) the frequency sweep for determining the transfer function.
• Softkey #4 (F8, SNS RAND) selects FFT noise and
• Softkey #5 (F9, SNS SNGL) a fixed frequency for determining the sensitivity.
• Softkey #6 (F10, BRST SWP) selects the burst sweep for determining the transfer function.
Phase measurement:
• Softkey #2 (F6, SINGLE) selects a fixed frequency and
• Softkey #3 (F7, FRQ SWP) the frequency sweep for determining the phase.
THD(N) measurement: ZOOM FFT
• Softkey #2 (F6, THD TOTL) selects the THD measurement forall harmonics (d2 to d9) for determining
the distortion; display as a BARGRAPH (for single measurements) or sweep trace.
• Softkey #3 (F7, THD d2) selects the THD measurement for thefirst harmonic for determining the
distortion; display as a BARGRAPH (for single measurements) or sweep trace.
• Softkey #4 (F8, THD d3) selects the THD measurement of thesecond harmonic for determining the
distortion; display as a BARGRAPH (for single measurements) or sweep trace.
• Softkey #5 (F9, THD+N) selects the THD+N measurement (harmonics+noise) for determining the
distortion; display as a BARGRAPH (for single measurement) or sweep trace.
• Softkey #6 (F10, POST FFT) selects also the THD+N measurement, but every test point is displayed
numerically or as an FFM spectrum.
• Softkey #7 (F11, ZOOM FFT) sets the FFT measurement function and permits all available FFT sizes
and zoom factors to be entered. Each test point is displayed as an FFT spectrum.
Upon this selection, SPEAKER.SCO is (re-)loaded and required settings are made. The data in the
configuration file and user entries made in the application program since program start (see section 3.4,
Entry of Parameters) are taken into account.
User entries made during post-processing (see section 7.1, Change of Task, Application/User Interface)
are overwritten.

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55 MeasurementsMeasurements
The SPEAKER application software covers a variety of loudspeaker measurements which are displayed
in the softkey line (softkey level 1).
• IMPEDANC for measuring all relevant impedance values and corresponding frequencies and for
determining associated parameters.
• PHASE for measuring phase linearity and detecting polarity reversal.
• SOUND for measuring sound pressure characteristics and loudspeaker sensitivity.
• THD for measurement and display of THD+N, THD total, d2, d3, or similar
Pressing the START softkey (F12) triggers the selected measurement and the described measurement
procedure.
55.1.1 Impedance and Associated ParametersImpedance and Associated Parameters
The impedance curve of a loudspeaker chassis or system gives information on important parameters
which sufficiently characterize the response at low frequencies. The parameters include the quality factor
Qt, resonance frequency frand equivalent volume Veq. Equations used in this Application Note are in line
with DIN IEC 268, part 5.
Since UPD and UPL comprise a DC generator and a DC measurement function, the DC impedance can
be measured without any additional equipment being required.
The impedance measurement is selected with the IMPEDANC softkey (F6).
5.1.1 Test Setup
For measuring the magnitude of the (complex) impedance of a loudspeaker array or system, the latter is
connected to the XLR outputChannel 2 of the generator (+ and -) and the voltage drop V1 is measured at
the generator output (via GEN coupling).
FIG 5 Test setup for impedance measurement

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The open-circuit generator voltage Vqbeing known, the following voltage ratio is obtained:
Uq/ Z+R = U1/ Z
Because of the complex impedance, the equation cannot be solved for Z, but the generator may be used
as a current source for Z<< R
Iq= Uq/ R
so that the following applies:
Z= U1/ Iq
For impedances in loudspeakers, the condition Z<< R is fulfilled if a generator with a source impedance
of 600 is selected. Since this source impedance is only available at the XLR outputs, the BAL outputs
have to be used.
If the value for
Iq= Uq/ 600
is entered as reference value for the RMS or DC measurement and V/Vr is selected for the display, the
measured value for Z can be directly read off in .
5.1.2 Special Notes on Entry of Parameters
With the aid of the RUNAWAYS softkey (F9, level 3) it can be determined how many outliers (runaways)
are tolerated by the algorithm for extreme value determination (resonance and tuning frequency).
In this case the relative maximum or minimum values have to be determined. For instance, when
searching for the maximum it may happen (particularly with very flat impedance curves) that a lower value
is measured although the curve slightly rises. To avoid misinterpretations, the algorithm responds only if
the following N RUNAWAYS show a decrease.
N is recommended to have a value of 2. Higher values extend the search time and may even mask
runaways. In the case of frequency sweeps lower values may be sufficient (even 0) but this has to be
determined empirically.
Under the REF SPK softkey the GO/NOGO test mode can be switched on and off, the trace of the
reference unit loaded and tolerances entered. With this softkey, OFF (no GO/NOGO test), TRACE A
(GO/NOGO test only) or TRACE B (impedance curve on trace A, GO/NOGO test on trace B) can be
selected.

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5.1.3 DC Impedance
The DC impedance RDC is required for calculating the quality (see section 5.1.8, Q Factor). The
measurement is carried out with the DC function.
The offset which can be set with almost all generator signals is used as the DC signal; the AC signal level
is set to 0. The low-distortion generator has to be switched off for the offset function to become active. A
DC voltage of, for instance, 6.0 V yields a current of 10 mA which is entered as reference value in the
analyzer panel.
FIG 6: Settings for DC impedance measurements
5.1.4 Impedance Frequency Response
The impedance frequency response is required for documentation and for determining all subsequent
parameters (see sections 5.1.5 to 5.1.9). According to DIN IEC 268 it is to be determined at least in the
range from 20 Hz to 20 kHz. Either logarithmic frequency sweep or (linear) FFT noise may be used for the
measurement. Results should in any case be displayed logarithmically. If there are no special reasons for
selecting FFT noise (eg online response), frequency sweep should be given preference that in this case a
smaller number of measurement points is required because of the logarithmic scaling and uncertainty of
the noise signal at higher frequencies. Furthermore, the small number of sweep points reduces the
program running time for subsequent search procedures.
For obtaining the maximum measurement speed, the frequency measurement is switched off.
Measurements are made in 1 channel only and the (faster) function generator is selected (low-distortion
generator not active). The measurement time can be further reduced by selecting AUTO FAST (however
with a certain loss in accuracy).

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FIG 7: Impedance characteristic and evaluation of a multi-path loudspeaker
(Trace B shows the impedance characteristic referenced to a "golden unit")
5.1.5 Resonance Frequency and Resonance Impedance
The resonance impedance Zris the first main maximum in the impedance curve at the resonance
frequency fr. The two quantities can be directly read from the impedance curve with the aid of a graphics
cursor. In the program they are obtained by scrolling up through the obtained impedance value array. The
maximum is considered found if N RUNAWAYS +1 (see section 5.1.2, Special Notes on Entry of
Parameters) are found in successive values in the descending order.
5.1.6 Absolute Minimum and Maximum Impedance
The absolute maximum of impedance Zmax is normally not identical with the resonance impedance.
Using softkeys
⇒ Cursor --> set to --> max A
the (active) graphics cursor is set to the maximum and the impedance and associated frequency can be
read from the display. Correspondingly, the absolute minimum is determined with softkeys
⇒ Cursor-->set to-->min A
This method is also used in the program.

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5.1.7 Tuning Frequency
The tuning frequency is the frequency at which the impedance curve shows the first minimum after the
resonance frequency at increasing frequencies. It can be read directly from the impedance curve with the
aid of the graphics cursor. In the program it is obtained by scrolling up through the impedance data array,
starting at fr; the minimum is considered found if N RUNAWAYS + 1 (see section 5.1.2, Special Notes on
Entry of Parameters) are found in successive values in the increasing direction.
5.1.8 Q Factor
The quality factor Qtis derived from the impedance curve according to the following formula (BASIC
syntax):
Qt=Fr/(F2-F1)/R0*SQR(R0^2-R1^2)/SQR(R1^2-1)
where
Zr, Fr= Resonance impedance and resonance frequency (see section 5.1.5)
Zt, Ft= Tuning impedance and tuning frequency (see section 5.1.7)
R0 = Resonance impedance standardized to RDC (see section 5.1.3, DC Impedance)
R0=Zr/RDC
R1 = Impedance standardized to RDC between Zrand Zout (see section 5.1.7, Tuning Frequency);
R1=SQR(R0)
F1 = Frequency below the resonance frequency at which impedance Z1=R1
*RDC
F2 = Frequency above the resonance frequency at which impedance Z2=R1
*RDC
Rdc
Zr
frf
Z(f)
f1f2
Z1~Z2
Zt
ft
FIG 8: Parameters of impedance curve for determining Qt

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5.1.9 Equivalent Volume
The equivalent volume Veq of a loudspeaker array defines the air volume, the compliance of which is
equal to that of the loudspeaker array.
First the impedance measurement is carried out with the loudspeaker array open. The loudspeaker is then
accommodated in a small, rigid housing without any further openings and additional insulation and a new
measurement is started with the Veq/Vbsoftkey (F11, level 4). With the newly determined resonance
frequency Fb(>Fr) the equivalent volume Veq/Vbreferred to Vb is obtained with the formula
V
Vf f
eq
b
b
r
=



−
2
1
Vbbeing the internal volume of the loudspeaker housing less the volume of the loudspeaker array.
5.1.10 Go/Nogo Test
At the end of a sweep the impedance characteristic of a reference loudspeaker can be stored as a
reference trace (softkey STO REF) and is then available as a "golden unit" for further measurements. To
measure further DUTS, the stored reference characteristic is loaded with softkey REF SPK and the
tolerance range specified. One of three display modes can be selected:
• TRACE A: the relative impedance characteristic is displayed.
• TRACE B: the relative impedance characteristic is displayed as trace B while the absolute impedance
characteristic is displayed as trace A (see Fig. 7).
• OFF switches the reference off so that only the absolute impedance characteristic is displayed.
55.2.2 Sound Pressure MeasurementsSound Pressure Measurements
Sound pressure variations versus frequency allow conclusions to be drawn on the tone quality of a
loudspeaker. Without this information dimensioning of crossover units is not possible. Furthermore, the
sound pressure characteristic of a system provides information on possible polarity reversals in the
loudspeaker system provided the sound pressure curve of a correctly poled reference system is available
(see section 5.4.3, Polarity Check by Comparison to Reference Sound Pressure Characteristic).
With sound pressure measurements at a fixed frequency, the maximum sound pressure of a loudspeaker
(at nominal power) and the sensitivity (at 1 W) can be measured at a distance of 1 m. The measured
sensitivity (in dBspl at 1 W and 1 m distance from the microphone) may be stored as a reference value in
the measurement of frequency response (see section 5.2.5, Sensitivity Measurement and Radiation
Angle).
Sound pressure measurements (measurement of sensitivity and sound-pressure frequency response) are
selected by means of the SOUND softkey (F7).