Active Audio StepArray Series Manuel utilisateur

manual

L ' a c o u s t i q u e a c t i v e

StepArray

CONTENTS

Contents

Contents 2

I StepArray: tutorial for recommandation 4

1 Sound reinforcement in large spaces 5

2 Overview of the StepArray system 9

3 Choosing the right installation set-up 12

4 Column positionning rules 14

5 Options 16

6 SAdrive software 16

7 CAD modeling 17

References 18

II StepArray technical reference 20

8 Installation of the columns 21

9 Wiring 22

10 Test before powering up 25

11 SAdrive software 26

12 Advanced functions 27

13 Troubleshooting 30

14 Hardware speciﬁcations 32

15 Acoustical data 37

List of Tables 44

List of Figures 44

CONTENTS

Foreword

StepArray is a versatile line-array system designed for speech reinforcement in large spaces. It offers excellent

sound intelligibility, slim design, external electronics, security systems compatibility and more.

This reference manual is intended to be a user manual for StepArray based systems, as well as a complete reference

with all the technical speciﬁcations and details about the StepArray system.

How to use this manual

This reference manual is divided in two parts:

• The ﬁrst part is a tutorial for recommandation. It deals with StepArray design and principles, introducing

the acoustic background necessary to understand sound reinforcement in large space, and how StepArray

can help to achieve good intelligibility in these places.

• The second part is a technical reference describing the full range of StepArray products. It covers installa-

tion, wiring, maintenance, and tuning. Extensive technical data is found there.

Last update: December 23, 2010 3

Part I

StepArray: tutorial for recommandation

Table of Contents

1 Sound reinforcement in large spaces 5

1.1 General issues with public address in large spaces ..................... 5

1.2 Loudspeaker arrays ..................................... 7

1.3 DGRC: The StepArray system ............................... 8

2 Overview of the StepArray system 9

2.1 StepArray system example .................................. 10

2.2 StepArray column models .................................. 11

2.3 StepArray speciﬁcity: shared electronics .......................... 11

3 Choosing the right installation set-up 12

3.1 Columns ............................................ 12

3.2 Processors ........................................... 13

3.3 Ampliﬁers ........................................... 13

3.4 Cables ............................................ 14

3.5 Subwoofers .......................................... 14

4 Column positionning rules 14

5 Options 16

5.1 Microphone (MIC) ...................................... 16

5.2 Sub-bass Output (SUB) ................................... 16

5.3 Sound Security System (SSS) ................................ 16

6 SAdrive software 16

7 CAD modeling 17

References 18

Introduction

This is a tutorial for StepArray recommandation.

Section 1presents general issues about public address in large spaces (1.1) and explains how loudspeaker arrays

can be a good solution to these issues (1.2). StepArray is introduced as the last point of this section (1.3).

The following parts are a step by step introduction to the StepArray system:

• Section 3explains the rules to follow when designing a StepArray system,

• Column positionning is described in section 4,

• The different options are described in section 5,

• SAdrive software, serving both as a simulation and tuning software, is described in section 6,

• CAD modeling tools are presented in section 7.

1 Sound reinforcement in large spaces

1.1 General issues with public address in large spaces

Speech reinforcement in large and reverberant rooms is made difﬁcult by several causes, namely reverberation,

ambient noise, and architectural constraints.

Reverberation

In all rooms, sound transmission from a loudspeaker to a listener can be divided in two parts (ﬁgure 1):

• Direct sound, which depends on the loudspeaker-to-listener distance and on the loudspeaker directivity.

• Reverberated sound, which depends on the geometry of the room, and the acoustical properties of the walls.

In large spaces (church, railway station), the reverberation can be very important and plays a negative role

on speech intelligibility (Note that the energy of the reverberated sound is constant throughout the room).

Direct sound

Reverberated

sound

Figure 1: Direct sound increases speech intelligibility, reverberated sound impairs it.

Intelligibility rule #1:

Direct sound increases speech intelligibility, reverberated sound impairs it.

Last update: December 23, 2010 5

1.1 General issues with public address in large spaces

Ambient noise

Ambiant noise reduces intelligibility. For example, the loud noise produced by trains in railway stations could prevent

the listener from understanding a message properly. Also, the noise level can change drastically over time: in this

case, the public address system must adjust its diffusion level according to the noise level.

Intelligibility rule #2:

The public address sound system should emit at least 10dB above the ambient noise level.

Architectural constraints

Loudspeakers positionning is often restricted by architectural or practical constraints. Because loudspeakers are

not always welcome in places where aesthetics are important, they should be made discreet and as few as possible

should be used.

Speech intelligibility in large spaces

As seen above, speech intelligibility1depends on:

• Reverberation time. This is a caracteristic of the room acoustics and depends on the material of the wall and

the geometry of the room.

•Direct Sound

Reverberated Sound energy ratio. This depends on reverberation time, room volume2, loudspeaker to listener

distance, and loudspeaker directivity.

•Signal

Noise ratio. This depends on the ability of the sound system to emit enough energy to «cover the noise».

In large spaces, changing the reverberation time involves changing a signiﬁcant portion of the wall material, and

most of the time, this is not possible.

Providing a strong signal to noise ratio is also important, but it is not enough to ensure intelligibility.

Therefore, in large and reverberant rooms, the most important parameter the public address must affect is the

Direct Sound

Reverberated Sound ratio. It is necessary to privilege the direct sound energy and avoid putting energy in the reverberated

part of sound. This can be achieved either by moving the loudspeaker close to the listener, or by using highly

directional loudspeakers.

In a large and highly reverberant room, it is necessary to privilege the direct sound energy for good

intelligibility results.

In large spaces, if the loudspeakers are to be placed close to the listeners, many loudspeakers are required. This

is not practical in such places because ﬁxing loudspeakers can be difﬁcult (very high ceiling, etc). Also, in many

cases, this will not give good intelligibility results because only the loudspeakers close to the listener contribute to

the direct sound, while all the loudspeakers contribute equally to the reverberated sound.

1Several indexes have been proposed to measure speech intelligibility. The most widely used of them is the Speech Transmission Index (STI).

Value 0 corresponds to extremely poor intelligibility, and value 1 corresponds to perfect intelligibility. It is generally considered that intelligibility is

correct above STI=0.55.

2Energy of the reverberated ﬁeld is proportionnal to the ratio Reverberation time

Room volume .

1.2 Loudspeaker arrays

Using many non-directional loudspeakers often leads to poor intelligibility: all loudspeakers contribute to the

reverberation, while only a few contribute to direct sound.

Using highly directionnal loudspeakers is an easier solution in large spaces because only few diffusers are needed.

In addition to improved acoustic performance and reduced cost, it minimizes the aesthetical impact of the public

address system.

Sound quality

Intelligibility is not enough for good perceived sound quality. Another very important aspect is that every listener has

an adequate sound pressure level (SPL), which implies that the public address system provides an even coverage

of the audience area. This can be acheived with an accurate control of the loudspeaker directivity.

Acoustic comfort also implies a wide frequency bandwidth and low harmonic distortion.

The most important goal of a public address system is to provide a strong and constant direct sound over the

entire audience area, and minimize the energy emitted elsewhere.

1.2 Loudspeaker arrays

Loudspeaker arrays are often the best solution to providing strong and constant direct sound over the audience.

Indeed, although a distributed public address system might yield a relatively constant SPL over the audience using

a large number of loudspeakers, it is usually not able to provide satisfactory speech intelligibility when reverberation

in the room is high. In addition, it usually has a rather negative impact on the visual aspect of the room.

In contrast, high speech intelligibility can be obtained with a limited number of loudspeaker arrays (often only 1 or

2) in a large and highly reverberant room with minimum impact on the aesthetics of the room.

It is easy to calculate the shape of the wave front that should be radiated by a loudspeaker array in order to yield

constant SPL over the entire audience area, and minimize sound energy emitted elsewhere. A J-shape wave

front is obtained, in which the local curvature depends on the focal distance, as illustrated on ﬁgure 2. In order

to generate such a wave front, one can align loudspeakers along the J-shape as in geometric arrays (ﬁgure 3a

on the following page) [C-HEIL], or place loudspeakers on a vertical line and rely on the ﬁltering of each individual

loudspeaker as in electronic arrays (ﬁgure 3b on the next page) [DSP directivity]. The latter case corresponds to

column loudspeakers, which can be ﬂush mounted on a wall. Advantages and disadvantages of both array types

are discussed in [DGRC-Arrays].

Wave

front

x1x2

Listening plan

Figure 2: J-shape wave front required in order to radiate constant SPL over the listening plan.

Last update: December 23, 2010 7

1.3 DGRC: The StepArray system

The main characteristic of an array is its range, which corresponds to the minimum and maximum distance (from the

column) where the SPL is constant (with a given tolerance). The range of a column is proportional to its height. An-

other important characteristic of an array is the spacing between loudspeakers. Good rejection of secondary lobes

at high frequencies is obtained with a short spacing. At high frequencies, geometric arrays generally use waveg-

uides that radiates like an isophase vertical slit. Aligning several of these waveguides yields a semi-continuous “line

source”, which greatly reduces undesired secondary lobes.

Signal

Wave

front

(a) In a geometric array, loudspeakers are aligned

along the shape of the wave front to be generated,

usually a J shape.

Signal

Wave

front

(b) In an electronic array, loudspeakers are aligned vertically, and

the wave front is synthesized by adequate ﬁltering by ﬁlters Fi, de-

lays Di, and gain Giassociated to each loudspeaker.

Figure 3: Electronic and geometric arrays

1.3 DGRC: The StepArray system

The StepArray columns implement the DGRC line-array principle (Digital and Geometric Radiation Control) which

is a synthesis of geometric and electronic arrays patented by Active Audio. The principle is illustrated in ﬁgure 4 on

the facing page.

The key idea is to split the desired wave-front into sections and move them back on a vertical line, much like what is

done in the Fresnel lenses used in optics. Then electronic delays are used to compensate sound propagation delay

between the sections. It was shown in [DGRC-Arrays] that with this delay setting there is no diffraction at the edges

of the saw-tooth shape. As a result of this principle, the number of DSP and ampliﬁcation channels is independent

of the number of loudspeakers, so that a dramatically reduced number of channels is achieved.

Wave

front

Input

signal

Figure 4: The DGRC principle used by StepArray columns. The wave front is controlled both by the positioning and

orientation of the loudspeakers, and by ﬁlters Fi, delays Di, and gain Giof each channel.

The main advantages brought by the DGRC principle used in StepArray columns are:

• The column is vertical and can be ﬁtted close to the wall.

• Reduced number of electronic channels, both for DSP and ampliﬁers. For example, model SA250P which is

2.5mhigh uses only 6 channels for 30 loudspeakers. This can make a big cost difference.

• Power is uniformly distributed to all loudspeakers. This way they can all be used at their maximum capabilities,

enhancing overall performance and sound pressure level.

• The number of channels does not depend on the number of loudspeakers. Therefore, many small full-range

loudspeakers can be used to obtain perfect sound quality in the treble range and reduce secondary lobes at

higher frequencies.

2 Overview of the StepArray system

The StepArray range consists of several column models dedicated to speech diffusion and to mid-power music

diffusion in large and/or reverberant enclosed spaces. The different models allow coverage of ﬂat or tilted audience

area ranging from 15m to 68m with perfect speech intelligibility and high sound quality.

Last update: December 23, 2010 9

2.1 StepArray system example

StepArray columns use external electronics. They are controlled by the UT26 digital signal processor (DSP) and

• Possibility to use a single UT26 processor controling several columns, yielding a large cost reduction

(see section 2.3 on the next page).

• Possibility to use several ampliﬁers for a single column in order to increase security: failure of one ampliﬁer

would only affect some of the channels, but the column continues to diffuse messages. For example, when

using 2 columns and 2 ampliﬁers, ampliﬁer 1 can be connected to channels 1, 3, 5 of both columns, and

ampliﬁer 2 to channels 2, 4, 6 of both columns.

• Easier maintenance: all electronics can be easily accessed in the technical room.

• Electronics can be placed in a ﬁreproof room, with uninterruptible power supply (UPS).

The operating parameters of the UT26 processors are tuned with the SAdrive software through RS232 serial

communication. UT26 processors feature ﬁltering functions such as the control of directivity, equalization, delay,

and high level functions.

In addition, the StepArray system features a set of options such as subwoofer output (SUB), active gain control

(AGC), and security system supervision (SSS).

2.1 StepArray system example

Figure 5is an example of a complete StepArray installation.

The audio signal is fed into the UT26 processors which then supply DGRC compatible signals to the MPA6150

ampliﬁers. A UT26 can also provide sub-bass output when equipped with the SUB option. The settings are made

with the SAdrive software through an RS232 serial bus.

RS232

BAN

2x UT26

3x MPA6150

Audio input

SA12-SWA

SA250PSA250P

4x SA100P

Figure 5: Example of StepArray system

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