Vox VOX-01 User manual

Operating manual
IEC 60268-16 rev. 4
IEC 61672 Class 2 / ANSI S1.4 Type 2
SPEECH INTELLIGIBILITY TESTER
VOX
SPEECH INTELLIGIBILITY TESTER
VOX
Specialized Fire Products
SPEECH INTELLIGIBILITY TESTER
VOX
VOX-01

2 VOX-01 Operating Manual
Contact information and support
The VOX-01 is designed and manufactured in the Netherlands and supplied by
SDi, USA.
You can contact SDi at the following address:
Updates of the system’s firmware and documentation are released online :
www.sdifire.com/support/#productsoftwareupdates
NOTE: Screenshots and product pictures shown in this manual correspond to the VOX-01
hardware platform 1.8 running firmware version 1.8. Once you update the firmware, the
screenshots may not fully correspond to what is being displayed on your device’s screen.
© SDi, 2017. All rights reserved.
SDi and VOX Speech Intelligibility Tester are registered trademarks.
Document version 2.0, release date October 2017. Applies to model(s): VOX-01.
SDi,
3535 Route 66, Building 6
Neptune, NJ 07753
Tel: [phone]
Fax: [phone]
Email: [email protected]
Web: www.sdifire.com
See page 46 for new
features added in V2.0

3
Contents
Contact information and support 2
1. Introduction 4
2.General use and safety precautions 5
Safety precautions when charging 5
Safety precautions related to connectors 6
3. Getting started 7
4. Using the VOX-01 8
Quick STIPA 8
STIPA pro 11
SPL meter 14
Real-Time Analyzer (RTA) 16
Fast Fourier Transform Anazlyzer 18
Reverberation Time Meter (RT60) 20
LAEQ Logging 26
5. Power and charging 38
Charging instructions 38
Power saving recommendations 39
Use of power banks and external battery packs 39
6. Cleaning, maintenance and calibration 40
Battery disposal 40
7. Product warranty 41
8. Firmware updates 43
9. Technical specifications 44
10. Troubleshooting 45
VOX-01 Operating Manual
Oscilloscope 30
USB Audio Device Mode 31
Settings 32
Calibration 34
Status 36
Accessing saved measurements from a PC 36
Accessing saved measurements from a PC 37
11. New in Update 2.0 46

4
Class 2 / Type 2
microphone
Power button
Status LED
USB charge &
data port
Touch screen
1. Introduction
Congratulations on purchasing the VOX-01 STIPA meter, the most advanced instrument for
measuring the Speech Transmission Index ever built, designed and manufactured
by the inventors of STIPA. The VOX-01 is also a fully compliant Class 2 / Type 2 Sound
Pressure Level meter, a 1/1 and 1/3 octave Real-Time Analyzer, a Fast Fourier Transform
Analyzer, a Reverberation Time Meter, an Oscilloscope, and much more. Its wide range of
measurement options cater to a variety of different acoustic measuring needs.
Using the VOX-01 is quite easy, thanks to its touch-screen operation and intuitive menu
structure. Most users will get the hang of doing measurements with the VOX-01 without
spending much time with this manual. Nonetheless, we strongly recommend that you do
read through this manual before starting to use your VOX-01, in order to get acquainted with
the various features of the device and the procedures for charging and maintaining your
device.
Tripod mount
Hook for
carrying cord
Serial number
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2. General use and safety precautions
The VOX-01 is a sophisticated electronic measuring instrument that should be used,
maintained and stored with care:
• We recommend that you always use a lanyard to secure your device against
dropping, by suspending it around your neck or wrist. If you use a tripod
to mount the device during measurements, we recommend that you use a
sturdy model with a sufficiently wide base.
• Do not expose the device itself, the measuring microphone or charger to
rain, moisture or liquids of any kind. Take special care to prevent liquids to
permeate into the device through the connectors or along the display bezel.
• Do not operate at ambient temperatures over 35°C/95°F
• Do not use close to flames or open fire.
• Do not use in environments where flammable or explosive materials are
used.
• Do not keep the device powered on while unattended for prolonged periods
of time.
• During transportation and storage, keep the device in a suitable casing or
container – preferably its original case. The device needs to be protected
from shocks and vibration (due to transportation or falling), excessive
temperatures, liquids and moisture, and any other external conditions that
could do damage to the device. Care should be taken that other objects cannot
come into direct contact with the display during transportation.
• Make sure that the device is switched off before transportation and storage.
Safety precautions when charging
The VOX-01 is a battery-powered rechargeable device, with an internal low self-discharge
NiMH battery pack. This battery pack is designed for many years of operation, and therefore
cannot be swapped out by the user. Recharging takes place through the mini USB
connector found on the left side of the device.
The VOX-01 is charged through the USB connector using high currents of
up to 1500 mA. While being charged, the device will heat up. DO NOT
CHARGE THE DEVICE WHILE IT IS INSIDE A CLOSED CON-
TAINER (BOX, BRIEFCASE, ETC.). Please make sure that the device
can shed excess heat while charging.
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The supplied charger includes adapters for use worldwide, and operates on
a wide AC-voltage range of 100 – 240V. Do not use the charger if the casing
appears cracked or broken, or if it has been exposed to fluids or moisture.
Contact with components inside the charger while this is plugged in may
result in serious injury or death.
Safety precautions related to connectors
The VOX-01 features a USB connector and an XLR connector (to which the
microphone is attached). If you connect external devices to these connectors,
please ensure that these connections are protected against over-voltage
and power surges. The voltage supplied to the USB port should not exceed
5.5V. As the USB power circuitry is connected to the battery pack, excessive
voltage applied to the USB port may cause the battery pack to catch fire or
explode.
The XLR connector supplies 48V phantom power to the microphone. This
phantom voltage can be switched on and off through the hardware settings
menu. IMPORTANT: connecting equipment not designed for 48V phantom
power to the VOX-01 connector (with phantom power switched on) will
permanently damage the connected device. The manufacturer explicitly
denounces responsibility for any damages to third-party hardware resulting
from exposure to the VOX-01’s phantom power.
VOX-01 Operating Manual

STIPA
pro
quick
STIPA
SPL
meter
settings calibra-
tion status
main menu
100%
SPEE CH INT ELLIGIBILITY TESTER
VOX
Specialized Fire Products
3. Getting started
You should receive your VOX-01 with sufficiently charged batteries to start the device and
get acquainted with its features. We do recommend that you fully charge the device using
the supplied charger before starting your first real measurement session.
The device is powered on by pressing the red power button once.
Note: the power button can also be used to power the device off. If you press the button
while the device is in operation, you will see a dialog window asking confirmation before
powering off. If the power button is kept pressed for 10 seconds in the “power on” state,
the device will be forced into the “off ” condition. This can be used to reset the device if it
becomes unresponsive (keep pressed to 10 seconds to switch off, then press again to restart).
The VOX-01 will boot into the main menu. You can launch its different modules from this
STIPA pro : module that gives you access to all STI measurement details
Quick STIPA : simple module to quickly do STIPA measurements
SPL meter : Sound Pressure Level meter module
Settings : change the system’s hardware configuration
Calibration : calibrate the VOX-01 and its microphone
Status : general information on the measurement system
All modules will be explained in detail in the following sections of this manual. Apart from
these modules, the VOX-01 has two specific operating modes: charging via USB, and data-
transfer via USB. These modes will also be explained further on in this manual.
menu.
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4. Using the VOX-01
The Quick STIPA module is intended to do simple and straightforward STI measurements
using the STIPA test signal. A comprehensive explanation of the STI method is beyond
the scope of this device manual; there are several online and offline resources that provide
guidance and information on doing STI measurements. In this manual, we will briefly
explain how to set up your equipment for measuring the STI. The Quick STIPA module
makes the process as simple as possible.
For any STI measurement, you need a source of the STIPA test signal as well as an STI
analyzer. In your case, the analyzer is your VOX-01. What the signal source is, depends on
what kind of measurement you aim to carry out.
The Embedded Acoustics reference STIPA test signal is included with the VOX-01 (on a USB
flash drive) and can also be downloaded from the SDi website, free of charge. This is a fully
IEC-60268-16 rev.4 compliant test signal, compatible with all STIPA meters that conform
with the standard.
STI measurement screen of the Quick STIPA module, in digit mode (left) and bar mode (right)
In order to carry out an STI measurement, complete the following steps:
• Power on your VOX-01 and go to Quick STIPA
• Now start playback of the STIPA test signal through the channel or system
which you intend to test. Note that the STI that you will now measure, will
characterize all parts of your transmission path, from playback device up to
the microphone of your VOX-01.
Quick STIPA
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• Tap “Start” on the VOX-01
• Wait for 25 seconds while the measurement takes place. Make sure that signal
playback is not interrupted, and that the acoustic environment is stable and free
from impulsive sounds (such as door slams).
• You will see that the STI on your screen stabilizing towards its end value.
• Optionally, you can press “save” once the measurement is finished to store
the data, to be browsed or downloaded to PC later. A measurement number
is assigned to each saved measurement. This number is displayed at the
bottom right of the screen (preceded by a “#” character), above the battery
indicator.
That is really the entire procedure. If you are new to STIPA measurements, please consult
tutorials and standards to make informed decisions about the STIPA signal playback level,
measuring positions, number of repeated measurements, etc.
The Quick STIPA module also shows some additional measurement information:
• The A-weighted sound pressure level
• The qualification band (a letter between A and U) that is used in some
standards and defined in IEC 60268-16 rev. 4.
• A label (“bad”-”excellent”) the characterizes intelligibility based on the STI
The arrows in the blue bar on the top of the display van be used to navigate through the
different screens for each module. The Quick STIPA app has three screens: “STI”, “settings”,
and “browse measurements”.
“Settings” screen and “browse measurements” screen. The latter screen is nearly identical to the
STI measurement screen, but with previous/back buttons instead of start/stop and save buttons.
The “settings” screen give you some options to control the appearance of your measure
ment results:
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• Choose between presentation of the STI in large digits or as a bar plot
• Choose whether or not you want to see the qualification bands displayed
The “browse measurements” screen allows you to review earlier (saved) measurements
without having to download your data to a PC first.
• Use to blue buttons at the bottom of the screen to scroll back and forth
through your saved measurements.
• Note that the measurement number displayed above the battery indicator
corresponds to the measurement currently shown on the screen.
Interpreting larger numbers of STIPA measurements by using the “browse measurements”
screen will be inefficient; we recommend downloading the data to a PC for this.
Please take note of the following features of the Quick STIPA module:
• On the bottom left of the screen, a red “recording dot” is displayed when-
ever a measurement is running. Below this red dot, the progress of the cur-
rent measurement is indicated by a progress bar.
• The “save” button is only operational when new (unsaved) measurement
data is available from a finished measurement. If this is not the case, the
save icon is colored gray.
• The VOX-01 calculates a heuristic reliability metric for each STI measure-
ment. If the measurement is found to be unreliable (e.g. due to disturbance
by impulsive sounds), then a red cross is displayed across the STI value.
Crossed-out STI values are often seen at the beginning of measurements,
when the calculation has not ran long enough to compute a reliable STI. As
soon as the cross disappears, the STI value can be trusted to be within the
usual STI measurement error of 0.03.
A crossed-out STI value means that the measurement is not (yet) sufficiently reliable
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STIPA pro
The STIPA pro module is also used to measure the Speech Transmission Index, but unlike the
quick STIPA module, it also comprises features that allow you to analyze and manipulate your
measurement data in greater detail.
“STI and spectrum” and “measurement details” screen in the STIPA pro module
The STIPA pro module has five screens:
STI and spectrum : display measured STI, octave spectrum and dBA level
Measurement details: display all measurement details including the MTF
Settings : configure the STIPA pro module
Additive noise: enter and enable/disable a noise spectrum to add to data
Browse measurements: review saved measurements
Measurements are usually started from the “STI and spectrum” or the “measurement
details” screen. STI measurements are set up and started in the same way as when using the
Quick STIPA module (see above). However, in the STIPA pro module, more details about
the measurement are shown, and the user has more elaborate options to configure the
measurement. Measurements are started, stopped and saved in the same way as with the
Quick STIPA module (by using the buttons at the bottom of the screen).
The “STI and spectrum” screen shows not only the current STI value and the A-weighted
sound pressure level, but it also shows an octave band spectrum of the measured signal in
the 7 octave bands from 125 Hz to 8 kHz. The STI analysis is carried out in these octave
bands. The scale of the octave band spectrum plot can be modified by tapping on the
triangualar arrows to the left of the plot.
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The “measurement details” screen shows all the diagnostic details of an individual STI
measurement:
• OCT: The octave center frequency (Hz)
• REL: The octave band levels relative to the STIPA signal spectrum (this is
effectively the frequency transfer function of the tested channel in octaves).
• MTI: Modulation Transfer Index. This quantifies the contribution to the
overall STI from each octave band.
• mr: the m-values (modulation transfer function in octave band OCT for
modulation frequency mf). These m-values are uncorrected, not adjusted
for masking effects and additive noise. Since the STIPA signal features two
modulation frequencies per octave band, there are also two m-values per
octave band. The modulation frequencies are also shown (mf)
• TI: the Transmission Index per octave band for each modulation frequency
These measurement details will enable more experienced operators to determine not only
the speech intelligibility of the tested channel, but also the causes of intelligibility reduction
induced by the channel.
Settings screen (left) and additive noise screen (right)
The settings screen gives the user three options:
• Choose whether or not to display STI qualification bands (A-U) as standardized
in IEC-60268-16. These bands are used in certain applications.
• Choose to enable or disable the level dependent model features: level
dependent masking and the speech reception threshold. For standard measure
ments, these features should be turned ON. Only when all-electric transmission
chains are tested (without any acoustics involved) should these features be turned
off, since there is no acoustic level reference in those cases.
• Choose whether or not to (computationally) add noise to the measurement.
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There are two ways to include the influence of background noise in your STI measure-
ment:
• Simply do your measurement in the actual noise environment. The STI
method is designed to incorporate the effects of any noise present during
the measurement representatively in the measured STI. This approach
works well if the noise field is stable and free from fluctuating and impulsive-
components.
• If you have the option to physically “turn the noise off,” then it is often
more accurate to add the noise computationally in a so-called post-hoc calculation
The VOX-01 does this for you, if you enter the noise spectrum in the “additive
noise” screen and change the setting to “Noise included in displayed STI
If you wish to add noise computationally, the screen “additive noise” should be used to en-
ter the noise spectrum. Note that the noise spectrum that you enter is only used if you also
select the corresponding option in the settings menu.
You can browse through all measurements saved earlier in the “browse measurements”
screen.
The following tips and pointers may be useful to remember when browsing STI measure-
ments with Quick STIPA and STIPA Pro:
• Measurements saved in Quick STIPA can be browsed in STIPA pro, and
vice versa. The measurement numbering range is shared between these
modules. This means that you can use STIPA pro to investigate measure-
ments done with Quick STIPA in more detail using the browsing screen in
STIPA pro.
• The settings you choose in STIPA pro (additive noise, level dependent
masking) affect the current measurement, but also affect which data is
shown in the measurement browser. This means that you can always enter
a noise spectrum and see how this affects measurements you did earlier
on. Similarly, you can go back later on and see what affect level dependent
masking has for a certain measurement.
• This implies that all data for each measurement is always saved - including
any data not actually shown during the measurement itself.
• Measurements can also be retrieved over USB; please refer to the section
“accessing saved measurements on a PC” for further instructions. For larger
numbers of measurements, processing of these saved data files (e.g. through
worksheet software) may be more efficient than inspection through the
measurement browser.
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SPL meter
The VOX-01 is also Sound Pressure Level meter (also known as SPL meter or SLM) that
complies with IEC 61672 Class 2 and ANSI S1.4 Type 2. In fact, the VOX-01 electronics far
exceed the requirements for a Class 2/Type 2 device.
The layout and buttons of the SPL meter app are similar to the STIPA module, featuring three
screens: SPL measurements, settings and browse measurements.
SPL measurements screen
The following sound pressure level measurement settings are supported:
• Time weighting: Fast (F) and Slow (F)
•Frequency weighting: Z (linear, unweighted), A-weighted, C-weighted
• Max hold (holds and displays the maximum level during the measurement interval;
used with either Fast or Slow time weighting)
• Equivalent continuous (EQ): computes the time-integrated level over the
measurement interval; the level shown corresponds to the level of a contin -uous
signal containing the same amount of energy as the measured signal.
•Peak values (PK): the highest instantaneous value within a measurement interval.
Once a measurement has started, each combination of the above settings is measured
simultaneously. However, not all of these combinations are displayed: only two level
measurements are displayed at the same time.
Each of these two levels is shown in its own bar graph and its own digit field. The red graph
corresponds to the red field, the blue bar graph to the blue field. You are free to select which
level to display in each of the two fields. Tap the “set” button in the level field to choose
time weighting, frequency weighting, max hold and time integration settings for the
corresponding field.
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The settings screen in the SPL module allows you to set the measurement time. Once
you press start, the measurement will run for as many seconds as you choose here. You may also
choose to let measurements run continuously; you then determine the measurement time
manually, by choosing the moment you press “stop.”
The SPL meter module also features are measurement browser, that lets you review previously
saved sound pressure level measurements.
A few things to note about SPL measurements and the SPL meter module:
VOX-01 Operating Manual
• By definition, “max hold”, “EQ” and “PK” are mutually exclusive settings.
•The elapsed measurement time is shown above the progress bar. If the
measurement interval is set to “continuous,” the measurement will run un-
til it is manually stopped. Note that, in practice, the maximum measuring
time is limited by:
•The battery. When measuring continuously, the battery is drained
relatively quickly (within 3-4). For longer measurements, we rec-
ommend using the charger or an external power bank.
•Internal data storage, especially if you are recording all measure-
ment audio (per the option in the “Settings” module). When re-
cording audio, the internal storage fills up in about 5 hours.
•When you press “save,” data from the current measurement is stored. Re-
sults based on all time and frequency weightings are saved; not just the
results that are currently displayed. However, as remarked above, since the
instantaneous levels fluctuate throughout the measurement, these cannot
be saved as a single number representing the entire measurement interval.
So for each saved measurement, just the maximum level (max hold) and
equivalent continuous level (EQ) and Peak level (PK) are saved.
•As a logical consequence, the measurement browser can only display Max
Hold, EQ and PK results from earlier measurements. If you set a display
field to show instantaneous values, the measurement browser will leave this
display field blank.
•You can use the measurement browser to go back to earlier measurements,
and see what the level is with different time- and frequency weightings
applied.
•The measurement numbers form a separate consecutive series for each
module. That means that the same measurement number might occur
multiple times (once for each module; e.g. number #0002 might exist for
SPL as well as RTA, STIPA, etc.)

20 Bedrock SMxx operating manual
Real-Time Analyzer (RTA)
The RTA module has two main modes of operation: as a 1/1 octave band analyzer (span-
ning the octave bands from 31 Hz to 16 kHz) and as a 1/3 octave band analyzer (25 Hz
through 20 kHz).
The operation is generally similar to the SPL module, but instead of just the overall signal
level, a frequency analysis (into 1/1 or 1/3 octave bands) is also shown.
RTA main measurement screen (1/3 octave band mode)
The RTA module has the ability to present two different spectral views at the same time,
differing in frequency weighting (A, C or Z) and time averaging and integration (FAST,
SLOW, MAX, or EQ). The main spectrum is presented in red bars, while a second (auxil-
iary) spectrum is shown in blue lines. The corresponding broadband levels are also shown,
to the right of the spectrum.
While the spectrum graph already gives a first impression of the spectral content of the
measured signal, you may wish to read the exact value in each band. This is done by placing
the cursor (dashed line) over the band of interest. The cursor can be moved left and right
by pressing on the left or right side of the frequency axis (or the area of the graph above
the axis). The values for the selected band are shown in the grey field on the top left of the
screen (main weighting shown in read, aux weighting in blue - same color as the spectrum
bars).
The “measuring time” screen can be used to set the duration of a measurement to a fixed
value. The measurement can also be set to run until stopped manually. The “settings”
screen allows you to switch between 1/1 and 1/3 octave band resolution, and to change the
weightings for the main and auxiliary spectrum views.
16 VOX -01 Operating Manual

© Embedded Acoustics BV, 2016
By pressing the “save” ( ) button in the main measurement screen, you store the current
measurement on the devices internal storage, using the measurement number indicated
above the battery indicator.
Some remarks about the RTA module:
• By definition, “max hold” and “EQ” are mutually exclusive settings.
•The elapsed measurement time is shown above the progress bar. If the
measurement interval is set to “continuous,” the measurement will run un-
til it is manually stopped. The progress bar itself is not used when measur-
ing continuously.
•Measurements saved as 1/1 octave cannot be retrieved as 1/3 or vice versa.
However, data recalled through the measurement browser are shown with
the frequency weightings selected at the time the measurement is recalled
- even if these are different from the settings that were in effect during the
measurement. This allows you to inspect the effect of frequency weightings
on all measurements saved previously
•Note that the spectrum and its corresponding broadband level are affected
by the same time- and frequency weightings. In other words, if the main
spectrum is A-weighted, then the level shown in the red field is also A-
weighed (and vice versa). If you wish to display a Z-weighted spectrum and
an A-weighted level at the same time, you need to display these in different
channels (main and aux).
•The measurement numbers form a separate consecutive series for each
module. That means that the same measurement number might occur
multiple times (once for each module; e.g. number #0002 might exist for
SPL as well as RTA, STIPA, etc.)
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22 Bedrock SMxx operating manual
Fast Fourier Transform Analyzer
The FFT module allows you to perform spectral analyses with a much higher frequency
resolution that the RTA module. This is very useful if you are looking to identify the exact
frequency and level of certain signal components, or if you want to study the harmonic
structure of sounds.
The maximum frequency resolution of the FFT analysis, with supported window sizes of
up to 32768 samples, approaches 1 Hz. This means that the analysis contains more data
and more detail than can be shown on the display at once. In order to deal with this, the
FFT module features a zoom function to zoom in on part of the spectrum. Also, the full
details of every measurement can be retrieved through USB by saving measurements.
FFT measurement screen
The general “look and feel” of the measurement screen is similar to the RTA module, but
with a few differences. First of all, in line with the normal conventions, frequency weight-
ings are not supported by the FFT module. Secondly, a button at the top right-hand
side of the graph can be tapped to reveal a small keyboard with zooming options:
These controls are used to zoom in or zoom out along the frequency axis, and to center
the display around the current cursor position. By pressing “hide” the zoom controls are
collapsed again. The zoom controls are used together with the cursor to focus on any region
of interest in the spectrum.. The cursor, shown as a vertical red line, can be moved by
tapping the arrows below the frequency axis or by tapping directly on the graph.
18 VOX -01 Operating Manual

© Embedded Acoustics BV, 2016
The minimum and maximum frequency that can currently be displayed are indicated at
the top of the screen, as well as the exact frequency at the cursor position and the level at
the cursor position.
The second screen of the FFT module allows you to set an integration time for the FFT
analysis. If the integration time is set to “infinite,” then the instantaneous spectrum is
shown. The graph on the display will show rapid fluctuations. In general, the longer the
integration time that is chosen, the more accurate the spectrum.
The third screen of the FFT module (“settings”) is where the parameters of the FFT algo-
rithm are controlled.
The window size determines the frequency resolution of the FFT analysis. The number
of spectral lines is exactly half the window size. At the maximum window size (32768),
the audible frequency range is analyzed in16384 spectral lines. Shorter windows offer less
detail, but the analysis runs quicker allowing for shorter integration times to arrive at the
same accuracy.
The type of window to be applied can also be set in the graphics screen. Each type of win-
dow (blackman, hamming, rectangular, etc) is associated with a specific set of advantages
and disadvantages relating to the FFT analysis. We recommend studying the literature on
spectral analysis, or one of the many available online resources, to choose the window that
best suits your application.
For most non-critical applications, the settings selected by default (hamming window with
a window size of 8192 samples) are a suitable choice.
Some remarks about the FFT module:
•The elapsed measurement time is shown above the progress bar. If the in-
tegration time is set to “continuous,” the instantaneous spectrum will be
shown.
•The FFT module is recommended whenever a high frequency resolution
is needed. To obtain standardized spectral measurements, where the exact
levels at standardized frequencies are of prime interest, 1/3 or 1/1 octave
band measurements through the RTA module are the best choice.
•Saved data can be retrieved over USB and imported in MS Excel or any
other program capable of dealing with .csv formatted data. This is the same
as all other modules. However, the FFT module is capable of producing
much more data (up to 32768 data points and frequencies for a single meas-
urement). Not all spreadsheet programs may be able to import that many
columns, which is why the data is organized in rows rather than columns.
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24 Bedrock SMxx operating manual
Reverberation Time Meter (RT60)
The reverberation time (or RT60) is among the most commonly specified acoustic
measures. Unfortunately, reverberation time measurements are also among the most
complex to carry out accurately. RT60 measurements are prone to errors, which cannot
always be detected by the measuring device.
If you are new to measuring reverberation times, we recommend that you read
this section of the manual carefully, and preferably also consult external literature
and training materials on reverberation time measurements.
Standardized procedures for measuring the reverberation time of a room are specified in
ISO-3382-2. Generally speaking, there are two different ways to measure RT60: the impulse
response method and the interrupted noise method. Both methods are standardized through
ISO-3382-2.
The impulse response method uses a carefully controlled, known test stimulus of short
duration (sweeps, chirps, pseudo-noise sequences or gunshot-like impulsive sounds). By
normalizing the recorded sound in a room relative to the source signal, the impulse
response of the room is obtained. From this impulse response, the RT60 is calculated. The
impulse response method is currently not supported by the VOX-01. Of the two available
methods, it is more likely to produce invalid results for the following reasons:
• The impulse response method requires that very specific, known test signals
are used. Any difference between the test signal that was really used on the
one hand, and that test signal that the measuring instrument expects on the
other hand, may produce greatly distorted results.
• Depending on the type of test signal, even the slightest movement of the
microphone during the test may render the measurement inaccurate. The use
of a tripod is absolutely necessary.
The interrupted noise method, as supported by the VOX-01, measures the decay of the
sound field if a sound source is suddenly switched off. This method is more robust
against slight inaccuracies or inconsistencies in the placement of sound source and
microphone. In small rooms, no other tools than the VOXBOX talkbox and the VOX-01
may be needed. In larger rooms, a larger (spherical) loudspeaker and amplifier will be
needed. Either way, the procedure requires the following steps to be taken in preparation:
• Place a source of continuous sound (preferably pink noise) in the room for
which the RT60 needs to be measured.
• Place the VOX-01 at some distance from the source (stay clear from walls
and other flat surfaces)
20 VOX -01 Operating Manual