BRUEL & KJAER 4720 Guide

Technical
Documentation
HEADQUARTERS: Brüel & Kjær Sound & Vibration Measurement A/S ·DK-2850 Nærum ·Denmark
Telephone: [phone] ·Fax: [phone] ·www.bksv.com ·[e-mail]
Local representatives and service organisations worldwide
Echo Speech Source Type 4720
English BE 1866– 11
User Manual
ËBE-1866---MÎ
BE1866-11_Cover.fm Page 1 Wednesday, December 18, 2013 11:22 AM

BE 186611 December 2013
Echo Speech Source
Type 4720
User Manual

Copyright 2013, Brüel & Kjær Sound & Vibration Measurement A/S
All rights reserved. No part of this publication may be reproduced or distributed in any form, or
by any means, without prior written consent from Brüel & Kjær Sound & Vibration Measurement
A/S, Nærum, Denmark
Safety Considerations
This apparatus has been designed and tested in accordance with IEC/EN 61010 – 1 and
ANSI/UL 61010 – 1 Safety Requirements for Electrical Equipment for Measurement,
Control and Laboratory Use. This manual contains information and warnings which must be
followed to ensure safe operation and to retain the apparatus in safe condition. Special note should
be made of the following:
Safety Symbols
The apparatus will be marked with this symbol when it is important that you refer to the
associated warning statements given in the manual.
Protective Earth Terminal Hazardous Voltage
Explosion Hazard
The equipment is not designed to be used in potentially explosive environments. It should not be
operated in the presence of flammable liquids or gases.
Warnings
• Switch off all power to equipment before connecting or disconnecting their digital interface.
Failure to do so could damage the equipment
• Whenever it is likely that the correct function or operating safety of the apparatus has been
impaired, it must be made inoperative and be secured against unintended operation
• Any adjustment, maintenance and repair of the open apparatus under voltage must be
avoided as far as possible and, if unavoidable, must be carried out only by trained service
personnel
• Do not dispose of electronic equipment or batteries as unsorted municipal waste
• It is your responsibility to contribute to a clean and healthy environment by using
the appropriate local return and collection systems
• Hazardous substances in electronic equipment or batteries may have detrimental
effects on the environment and human health
• The symbol shown to the left indicates that separate collection systems must be used
for any discarded equipment or batteries marked with that symbol
• Waste electrical and electronic equipment or batteries may be returned to your
local Brüel & Kjær representative or to Brüel & Kjær Headquarters for disposal

Table of Contents
CHAPTER 1
Introduction......................................................................................................... 1
1.1 Before First Use ................................................................................................... 1
CHAPTER 2
Overview.............................................................................................................. 3
2.1 Control Panel and Loudspeaker .......................................................................... 3
2.2 Battery Compartment........................................................................................... 5
2.3 Tripod Mounting Plate.......................................................................................... 5
CHAPTER 3
Installation........................................................................................................... 7
3.1 Installing the Echo Speech Source Software....................................................... 7
3.2 Batteries............................................................................................................... 7
3.3 Mains Power Supply ............................................................................................ 8
CHAPTER 4
Operation............................................................................................................. 9
4.1 Basic Measurement ............................................................................................. 9
4.2 High Background Noise ..................................................................................... 10
4.3 Intermittent versus Continuous Noise ................................................................ 10
4.4 Voice versus Noise ............................................................................................ 11
4.5 Public Address Sound System Measurement.................................................... 11
4.6 Using an External Signal.................................................................................... 12
CHAPTER 5
Calibration, Certification and Troubleshooting ............................................. 13
5.1 Calibration.......................................................................................................... 13
Calibration Check............................................................................................... 13
Certification ........................................................................................................ 14
5.2 Troubleshooting ................................................................................................. 14
CHAPTER 6
Specifications ................................................................................................... 17

1
Chapter 1
Introduction
Thank you for purchasing Brüel & Kjær’s Echo Speech Source Type 4720. This manual
contains important information for correctly and safely operating Echo Speech Source. Please
take the time to read this manual and familiarise yourself with the advanced features.
1.1 Before First Use
Check for any noticeable damage. Every Brüel & Kjær Echo Speech Source is tested and
inspected before leaving the factory and should arrive in perfect condition. If it has been
damaged in shipment, notify the shipping company immediately. Only the consignee may
institute a claim with the carrier for damage incurred during shipping. Be sure to save the
carton and packing materials for the carrier's inspection.
NOTE: Save the carton and packing material: Always use the original packing materials for
shipping.
For the best results and unit longevity:
• Read the operating and safety instructions applicable to you.
• Keep this manual for future reference.
• Heed all warnings.
• Follow all instructions.
• Do not use this unit near water. Do not spill water or other liquids into or on the unit. Do
not operate the Echo Speech Source while it is wet or immersed in liquid.
• Clean only with a dry cloth.
• Install the unit in accordance with the instructions.
• Do not operate the Echo Speech Source near any heat-producing devices such as radiators,
heat registers or stoves.
• Only use accessories specified by the manufacturer.
• Unplug the apparatus during lightning storms or when not in use for long periods of time.
• Remove batteries when not in use for long periods of time.

Echo Speech Source Type 4270 – User Manual2
• Refer all servicing to qualified service personnel. Servicing is required when the apparatus
has been damaged in any way, such as:
– Liquid has been spilled into the unit
– The unit has been exposed to rain or moisture
– The unit does not operate normally
– The unit has been dropped or the enclosure damaged
• Do not disassemble the unit. There are no serviceable parts inside and disassembly may
void the warranty.
• An experienced user should always supervise this professional audio equipment,
especially if inexperienced adults or minors are using it.

3
Chapter 2
Overview
Echo Speech Source Type 4720 is a small active loudspeaker box that provides calibrated
acoustic signals for speech intelligibility measurements for use with DIRAC Room Acoustics
Software Type 7841.
Echo Speech Source is typically placed at a human speaker position. The received signal at a
listener position is then picked up by a microphone and analysed in DIRAC to arrive at an
accurate qualification of the speech intelligibility through parameters such as Speech
Transmission Index (STI). Echo Speech Source runs on four AA batteries or an external mains
power supply and can be mounted on a standard tripod.
2.1 Control Panel and Loudspeaker
Fig.2.1 Control panel and loudspeaker of Type 4720
1) Raised Level Speaker button (yellow LED): Plays the internal signal through the
loudspeaker (13) at a raised level. The raised level state only applies to the internal MLS
signals (4) and (5), and not to the internal voice signal (6), while in this state the BNC
input (8) is disabled and the BNC output signal (9) is not affected.
12 V 5 00 mA
130731
1
2
3
6
7
8
5
4
12
11
10
13
9

Echo Speech Source Type 4270 – User Manual4
2) Reference Level Speaker button (yellow LED): Plays the internal signal through the
loudspeaker (13) at an A-weighted output level of 60 dB, at a distance of 1 m in front of
the loudspeaker. In this state the BNC input (8) is disabled.
3) Off button (yellow LED): Stops internal signals playing through the loudspeaker (13), and
enables a signal from the BNC input (8) to be played through the loudspeaker. The BNC
output signal (9) is not affected.
4) Continuous Noise button (yellow LED): Selects the internal continuous MLS signal for
the loudspeaker (13) and the BNC output (9).
5) Intermittent Noise button (yellow LED): Selects the internal intermittent MLS signal for
the loudspeaker (13) and the BNC output (9).
6) Test Voice button (yellow LED): Selects the internal test voice signal for the loudspeaker
(13) and the BNC output (9).
7) Input LED (red): Lights up with an overload of the BNC input, and flashes briefly if the
input signal is too low for more than 22 s while the Echo Speech Source is in the Off
state (3) (see also section 4.6).
8) Input Signal BNC socket: External signal input.
9) Output Signal BNC socket: Provides the selected signal type (4), (5) or (6). Not affected
by the loudspeaker level selection buttons (1), (2) or (3). Maximum voltage is
approximately 1.5 Vpeak.
10) External Power Supply socket: Connect a mains power supply with a DC plug accepting a
2.1 mm centre pin (see also section 3.3 and Specifications).
11) Power On/Off button: toggle button.
12) Power On LED (green): illuminated if the power is turned on and briefly blinks if the
demanded power exceeds the available power from the batteries or external power supply.
While blinking, the loudspeaker is muted.
13) Loudspeaker

CHAPTER 2
Overview 5
2.2 Battery Compartment
Fig.2.2 Battery compartment of Type 4720
14) Battery cover.
15) Battery cover lock: To open: With the handles facing away, push the locking strip to the
right and lift the cover.
16) Batteries: AA batteries, all with the positive pole pointing towards the control panel, as
indicated at the bottom of the compartment (17).
17) Battery orientation diagram.
18) Serial number label: Your Speech Source’s unique serial number.
2.3 Tripod Mounting Plate
Echo Speech Source Type 4720 has a 1/4-20 UNC screw thread on the bottom, which is
compatible with many standard camera tripods.
130732
AA AA
14
15
16
17
18

Echo Speech Source Type 4270 – User Manual6
Fig.2.3
Tripod mounting plate
130733
Made in the Netherlands

7
Chapter 3
Installation
This chapter frequently references section 2.1 and section 2.2. The numbers in brackets refer to
the number call-outs in Fig.2.1 and Fig.2.2 and their descriptions in the text.
3.1 Installing the Echo Speech Source Software
Echo Speech Source Type 4720 comes with a USB memory stick containing installation
software for use with DIRAC Room Acoustics Software Type 7841. To install the Echo Speech
Source software, insert the USB memory stick into a USB port on your PC and run the
ECHO SETUP.MSI file from the stick.
3.2 Batteries
Echo Speech Source Type 4720 can be battery operated, using four AA batteries – 1.5 V
alkaline or 1.2 V rechargeable, such as NiMH batteries.
To remove the battery cover, push the centre of the locking strip (17) towards the cover center.
To insert batteries, align them with the polarity symbols shown at the bottom of the battery
compartment, all pointing towards the control panel.
To remove batteries, lift the batteries at +poles (16) using a thin plastic tool, such as the
included battery-removal tool, which can be stored on top of the batteries, under the cover.

Echo Speech Source Type 4270 – User Manual8
Fig.3.1
Battery removal tool
and battery removal
When the batteries are get low (Power Low condition), the green Power On LED (13) starts to
flash and the loudspeaker is muted. The Power Low condition may disappear due to temporary
battery recovery but will resume and remain (longer) as the batteries are increasingly depleted.
If the Power Low condition persists longer than 5 s, Echo will shut down. Depleted batteries
have to be removed or replaced.
NOTE 1: A measurement interrupted by a Power Low condition is invalid, which is also
visible by an increased noise level in the resulting impulse response.
NOTE 2: A battery charger is not supplied with the Echo Speech Source.
NOTE 3: Rechargeable batteries have to be charged separately from the Echo Speech Source.
NOTE 4: Incorrectly placed (polarity reversed) batteries are ineffective and harmless to the
Echo Speech Source, but might eventually damage a battery.
3.3 Mains Power Supply
Echo can also be mains operated using the included mains power supply, which delivers 12 V.
Echo Speech Source has been approved to meet the EMC safety standards using this particular
mains power supply (or four batteries).
NOTE 1: Functionally, Echo will operate from a regulated DC power supply with an output
voltage ranging from 6 – 8 V and 6 W of available power.
NOTE 2: A mains power supply delivering too little power may cause Echo behave as if it
were running on low batteries (section 3.2).
NOTE 3: Avoid a power supply voltage exceeding 18 V because this might eventually damage
the Echo Speech Source.
130734
AA
AA

9
Chapter 4
Operation
This chapter frequently references section 2.1. The numbers in brackets refer to the number
call-outs in Fig.2.1 and their descriptions in the text.
4.1 Basic Measurement
This section contains instructions for a typical auditorium speech intelligibility measurement
using the Echo Speech Source and DIRAC.
1) Place Echo Speech Source Type 4720 on a camera tripod at the speaker position in an
auditorium.
2) Place a hand-held analyzer at a listener position.
3) Connect the hand-held analyzer’s AC output to USB Audio Interface ZE-0948 and the
interface to a PC running Room Acoustics Measurement Software DIRAC Type 7841 (see
the respective product manuals for their set-up information).
4) Start DIRAC and open the Measurement window.
5) On the Preset tab, select ECHO.
This results in the following measurement settings:
–Source Signal: External, ECHO Source, 10.9 s, other options disabled
–Receiver: Single Omnidirectional, Pre-Average = 1
6) On the Gain tab calibrate the microphone input level using Sound Calibrator Type 4231
(see DIRAC Room Acoustics Software Type 7841 User Manual (BE 1685) or on-line help
for calibration instructions). Now the DIRAC level meter shows the A-weighted sound
level.
7) Turn on Echo Speech Source (Power On/Off button (11)) – resetting the Off (3) and
Intermittent Noise (5) states.
8) Press the Reference Level Speaker button (2). In this example, the A-weighted level
meter in DIRAC shows an increase of 20 dB (over the situation with no active Echo), so
the Signal-to-Noise Ratio (SNR) exceeds 15 dB and the chosen speaker level is ok (4).

Echo Speech Source Type 4270 – User Manual10
9) The estimated reverberation time (RT) is 2 s, so the product, SNR*RT = 40 dB. Because
this is below 120 dB, Intermittent Noise (5) is the proper stimulus type to be selected
according to the rule of thumb described in section 4.3.
10) In DIRAC start the measurement. DIRAC automatically detects the Echo Speech Source
settings.
NOTE: Do not make loud noises until DIRAC finishes recording and starts processing the
recording.
11) Save the resulting impulse response file, containing the auditorium impulse response in
channel 1 and the background noise in channel 2.
From this file, speech intelligibility related parameters are obtained in DIRAC through the
Parameters menu or the Graph/Statistics button.
12) Repeat steps 7 and 8 for the other receiver and source positions of interest.
Positions close to the source may require another source level (1) or (2) than positions at a
greater distance. DIRAC supports statistical analysis over multiple measurements.
4.2 High Background Noise
If the SNR is substantially lower than 15 dB at the reference speaker level, the resulting
impulse response in channel 1 may become very noisy, and the derived parameters less
reliable. This can be improved by pressing the Raised Level Speaker button (1) on Echo
Speech Source Type 4720 or by increasing the Pre-Average value in DIRAC.
On the other hand, if the SNR exceeds 15 dB, raising the level may not in all cases lead to a
further reduction of the noise in the impulse response because the inherently higher distortion
at the raised level will also add some noise that might dominate a low background noise level.
The obtained relative noise level in a measured impulse response can be judged through the
Impulse response-to-Noise Ratio (INR), which can be viewed in DIRAC as a Level parameter
in the Parameter menu or the Graph window. The INR should preferably exceed 20 dB in each
octave frequency band from 125 Hz through 8 kHz.
4.3 Intermittent versus Continuous Noise
The use of an intermittent stimulus enables DIRAC to determine the noise level separately
from the impulse response measurement, thereby minimising mutual influences and
maximising derived parameter accuracy. This is particularly true if, in the silent part of the
stimulus, the level of the reverberation tail is negligible with respect to the background noise
level, which translates into the following rule of thumb:
• SNR*RT < 120 dB – select Intermittent Noise
• SNR*RT > 120 dB – select Continuous Noise
In DIRAC an Intermittent Noise measurement produces a dual-channel impulse response file
containing the impulse response (plus noise) in channel 1 and the background noise in
channel 2.

CHAPTER 4
Operation 11
A Continuous Noise measurement produces a single-channel impulse response file. The
background noise level is then derived from the noise in the impulse response tail. This method
may be effective if the measurement has been performed with a chosen Pre-Average value of 1
in DIRAC, while the time variance and the distortion of the system are negligible. In general,
however, more reliable results are obtained if you choose a Pre-Average value aimed at
maximising the INR, and measure the octave band background noise levels separately using
DIRAC or a hand-held sound level meter (SLM).
The background noise levels can be entered into the measured impulse response files, thereby
forcing DIRAC to use these values instead of the noise in the impulse response tail and arrive
at more accurate speech intelligibility parameters.
To enter noise (or signal) values separately, in the Impulse Response window select
File >Properties >Speech, in the Speech Window select Properties or in the Parameters dialog
select one or more files and then choose Edit >File Properties >Speech.
NOTE: SNR values and MTF graphs shown in DIRAC are not affected by user entered signal
or noise values and always reflect originally measured impulse responses.
4.4 Voice versus Noise
Echo Speech Source Type 4720 contains a test voice signal. This signal is based on a standard
male spectrum according to IEC 60268–16 and also has a known spectral relation to the
measurement stimuli (the intermittent and continuous noise signals). Therefore, after using the
test voice to set the proper sound system level by auditive judgement, the measurement stimuli
allow DIRAC to objectively and accurately measure the speech intelligibility through the
adjusted sound system.
The test voice is also suitable for a subjective judgement of the speech intelligibility in a room.
4.5 Public Address Sound System Measurement
To measure the speech intelligibility through a sound system, Echo Speech Source is either
placed at the speaker position in front of a microphone, or connected electrically from the
Output Signal BNC socket (9) to the sound system input. The raised speaker level is normally
not applicable here, as a sound system should enable normal speech to overrule the background
noise.
To adjust the acoustical output level of the sound system, select the Test Voice (Te st Voice
button (6)). When played through the sound system, this test voice should sound as loud as a
typical male voice during normal operation of the sound system. Adjust the level as follows
before starting the measurements:
1) Turn on Echo Speech Source (Power On/Off button (11)) – resetting the Off and
Intermittent Noise states. The selected signal is now output through the Output Signal
BNC socket (9).

Echo Speech Source Type 4270 – User Manual12
2) Select the Test Voice (Te st Voice button (6)) and, if the Echo Speech Source is placed in
front of a microphone, also select Reference Speaker Level (Reference Level Speaker
button (2)).
NOTE: With the test voice signal selected, the Raised Speaker Level is disabled.
3) Set the sound system to an acoustical output level that is also heard during normal use.
4) Switch from Test Voice (Test Voice button (6)) to Intermittent Noise (Intermittent Noise
button (5)) or Continuous Noise (Continuous Noise button (4)) (see Section 4.3) and
perform the measurements.
4.6 Using an External Signal
You can connect a custom signal to the input BNC socket (8). This signal is directed to the
loudspeaker (unequalised), but not to the output BNC. The input sensitivity is 15 mVrms (pink
noise, 60 dB SPL, 1 m in front of the loudspeaker).
The input is enabled if Echo Speech Source is in Off state and the signal exceeds 40 mVpeak. If
the input signal is too low for more than 22 s, the input is switched off and the red Input LED
flashes briefly.
The maximum operational input voltage is 600 mVpeak, above which the Input LED (7) is
illuminated, indicating an overload situation.
If enabled, the input has an impedance to ground of 10 k, and 52 kotherwise. To attenuate
the input voltage or to increase the input impedance, a special attenuator cable, containing an
RC-network, can be inserted.

13
Chapter 5
Calibration, Certification and Troubleshooting
This chapter frequently references section 2.1. The numbers in brackets refer to the number
call-outs in Fig.2.1 and their descriptions in the text.
5.1 Calibration
After installing the included software, Echo Speech Source Type 4720, in conjunction with
DIRAC Room Acoustics Software Type 7841 version 6, provides a calibrated system to
measure speech intelligibility in compliance with IEC 60268–16. The nominal A-weighted
sound level at a distance of 1 m in front of the loudspeaker equals 60 dB at the Reference
Speaker Level and 72 dB at the Raised Speaker Level. These levels are exclusive of the pauses
in the intermittent stimuli and the test voice.
The sound level spectrum of the test voice signal is not critical because it is used only to adjust
the output level of a PA system based on subjective assessment. Therefore, its level spectrum is
specified by design and tested during production but does not require maintenance.
The stimuli are noise signals with a pink third-octave frequency band spectrum from 100 Hz
through 10 kHz. Because all calculated signal-to-noise ratios affecting speech intelligibility are
based on these stimuli, their level spectra have been calibrated. You can roughly verify this
calibration or have the unit fully certified by Brüel & Kjær, as described below.
5.1.1 Calibration Check
1) In a free field, such as in an anechoic room, place an SLM 1 m to the front of the
loudspeaker (13).
2) Set the SLM to measure an LAeq,10 of 60 dB.
3) Turn the Echo Speech Source on, select Continuous Noise (Continuous Noise button (4))
and Reference Level Speaker (Reference Level Speaker button (2)). The read-out SLM
value should be approximately 60 dB.
4) Select Raised Speaker Level (Raised Level Speaker button (1)). The read-out SLM value
should be approximately 72 dB.

Echo Speech Source Type 4270 – User Manual14
NOTE 1: The check values are nominal values, based on the third octave band levels used for
the calibration during production or certification. Deviations may arise due to measurement
system errors or parasitic reflections if the calibration check is not carried out in an anechoic
room or free field. In general higher levels will be found in the presence of reflections.
5.1.2 Certification
You can have the calibration of your Echo Speech Source certified by Brüel & Kjær.
The calibration is checked in a anechoic room, with a calibrated microphone placed 1 m to the
front of the Echo Speech Source, which is producing continuous noise (MLS). From the
recorded microphone signal the third-octave frequency band spectrum is measured.
If necessary, the unit will be recalibrated.
5.2 Troubleshooting
If your Echo Speech Source seems faulty, use the following checklist.
The unit cannot be turned on
There is not sufficient power. Check the batteries, including their orientation, or the mains
adapter.
Intermittent signal from the loudspeaker, but no intermittent noise selected
If the green LED blinks during the silent parts, there is not sufficient power available. Check
the batteries or the mains adapter or reduce the demanded sound level if possible.
Green Power On LED blinks sometimes during silent part of intermittent noise
The intermittent noise is probably irregular, and continuous noise will be irregular as well.
There is not sufficient power available. Check the batteries or the mains power supply, or
reduce the demanded sound level if possible.
Red Input LED suddenly starts to flash briefly
Indicates that the input signal has become low. The Speech Source received an input signal 22 s
before the LED started to flash. This could be caused just by a touch of the centre contact of the
input BNC socket or connecting a cable.
Signal on Input BNC socket not coming through or dropping out
The input signal is (sometimes) too low for more than 22 s. Increase the input level to at least
40 mVp.
Signal on Input BNC socket very noisy
Increase the input signal level in order to improve the signal-to-noise ratio. If the level would
then become too high, insert, for example, a –20 dB attenuator cable (section 4.6).