Bose Panaray MA12 User manual

Professional Systems Division
Bose Corporation, Framingham, MA, USA
April 2002
Bose®Panaray MA12 Modular Array:
Technical Foundation & Discussion
Morten Jørgensen
Manager, Marketing and Product Planning
Kenneth Jacob
Chief Engineer

Bose®MA12™ Modular Array: Technical Foundation & Discussion
April 2002, © Bose Corporation, All Rights Reserved
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Bose®MA12 Modular Array:
Technical Foundation & Discussion
Morten Jørgensen and Kenneth Jacob, Bose®Professional Systems Division
Summary
THE Bose MA12™ modular array takes advantage of the properties of cylindrical
waves to meet customer requirements that until now could only be met with
loudspeakers flown and aimed in more elaborate and expensive designs. With only
two dimensions of dispersion rather than the three of the more common spherical
waves, the sound from cylindrical waves diminishes much more gradually with
distance from the source. As a consequence, listeners experience relatively little
change in sound level from far away from the MA12 to literally right next to it. The
same gradual change in sound with distance makes the MA12 less susceptible to
feedback from microphones in close proximity. The radiation pattern of the MA12 is
wedge-shaped: wide from side-to-side but sharply confined to the top and bottom of
the array. The vertical radiation virtually shuts off above and below the speaker. As a
result, much less reverberation is generated because almost no sound is radiated
upwards to distant surfaces in the upper part of the room. The result is noticeably
better clarity and intelligibility. The ultra-thin shape of the MA12 means it is easy to
hide; it may be the most unobtrusive speaker yet developed given its exceptionally
high output and full, balanced frequency response. The fact that the MA12 is placed
at ear level (so that listeners are confined within its wedge-shaped radiation pattern)
means that it can usually be installed for a fraction of the cost of more elaborate
‘flown’ loudspeakers and loudspeaker clusters. Finally, it can be matched to a low
frequency enclosure (Bose Panaray MB4) when extended bass performance is
needed. Taken together, these features and advantages result in a product that
represents an important new tool for satisfying the most basic and important customer
requirements in a wide range of common applications.

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INTRODUCTION
CUSTOMER requirements for a sound system are diverse and cover the areas of acoustics,
architecture, operation and service. Some of the most important requirements include the
following:
-Customers value a system that has the right balance of low, mid and high frequencies –
what is called ‘tonal balance’. Customers hear and complain about sound that is too
‘boomy’ or ‘shrill’ or ‘sibilant’, all examples of tonal balance problems.
-Asystem that plays at the right level is better than one that is too soft or too loud.
Customers routinely complain about both excessive sound levels or when the desired
impact can not be achieved because the system is unable to play loud enough.
-Asystem where the sound is perceived to come from the same direction as the action to
which it corresponds is better in many applications. When, for example, a talker is on
stage, a system whose sound is perceived to come from the stage is better than one
where the sound comes from above. Lack of eye-ear correspondence is disconcerting
and distracting.
-Asystem that delivers music with clarity, and speech with intelligibility, is better than
one where instruments are garbled and speech is hard to understand. No other single
customer requirement generates as many complaints as poor speech intelligibility. It
often impacts the fundamental purpose of a venue – the sermon or lecture at a house of
worship, or the announcement at the airport, for example.
-Customers are understandably concerned about the appearance of a sound system. They
usually value a system that blends into its environment, and is out of the way. And
when the system is visible, customers want it to be elegant yet unobtrusive.
- Finally, customers value a system that works reliably for long periods of time without
degradation or the need for service. But should a problem occur, they want prompt,
cost-effective service. No customer wants to shut down a facility in order to undertake
repairs.
These customer requirements exist on any given project to one degree or another. For
example, in a place of worship a customer might seek nearly ideal speech intelligibility. But
in another situation, the required speech intelligibility might be set lower – to meet a
government standard for an emergency announcement in a shopping mall, for example.
Therefore, the intensity of need in each dimension on a specific project must be determined
for each project.
Customer satisfaction occurs to the degree that the performance levels in these key areas of
customer requirements are met at a competitive cost. The better system is always the one that
meets customer requirements for the least cost.
The standard design approach for meeting these requirements is unofficially called the
‘hang-and-tilt’ approach. In this approach, speakers with controlled radiation patterns are

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April 2002, © Bose Corporation, All Rights Reserved
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hung in the air and tilted down. Hang-and-tilt has become the de facto standard for sound
reinforcement in virtually every kind of venue, from retail spaces, to atriums, churches,
schools, gymnasiums, auditoriums, city halls, airports, and sports facilities.
Manufacturers including Bose offer a wide range of speakers used in the hang-and-tilt
approach, and similarly, offer a wide range of tools to help the designer of these systems. As
a result, dealers, contractors, consulting engineers, and others have learned to deliver systems
that perform well in satisfying the major customer requirements using this approach.
The purpose of this paper is to show that the Bose MA12™ modular array represents a
significant and important extension to the hang-and-tilt approach. To do this, our strategy
relies on an explanation of the speaker’s unique sound radiation pattern, and how that
radiation pattern, and the thin line-shaped source necessary to produce it, often allows
designers to meet customer requirements better and at a lower cost than before. The argument
begins with a review of the fundamental assumption that first led the industry to the hang-
and-tilt approach and then moves on to explain the approach’s strengths and remaining
weaknesses.
THE HANG-AND-TILT APPROACH
Original assumption
WHAT led the industry to embrace the hang-and-tilt method and dedicate decades of research,
development and marketing effort to perfect it? Why do so many speakers end up in the air
and tilted down?
The answer can be traced to a fundamental property of the speakers used – specifically,
that the sound waves they radiate spread in all three dimensions: up and down, left and right,
in and out. These are called spherical waves because the sound radiates in all directions, like
a sphere. As a result, the sound intensity, or sound pressure level from spherical wave sources
decreases by 6 dB whenever the distance is doubled, as shown in Figure 1. (To be exact, this
is true beyond a certain distance from the speaker. At very close distances the behavior is
different.)
For example, if a listener is four meters from the speaker and the level is 78 dB-SPL, then
when the listener is eight meters away – twice the distance – the level is 6 dB less, or 72 dB-
SPL. And while a speaker often has different intensity levels at different angles (as is the case
with any directional speaker), no matter what angle is chosen, when the distance is doubled
along that same angle, the level decreases by 6 dB.

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Spherical-Wave Sources
90dB
1m
84dB
2m
78dB
4m
72dB
8m
Figure 1. Sound from spherical waves radiates in all three dimensions:
up and down, left and right, and front and back. As a result, the sound
level decreases by 6 dB whenever the distance is doubled. The reason
for a 6 dB drop (and not something else) is readily understood, and is
contained in a footnote on page 16.
If the 6 dB per doubling of distance behavior is ignored for the moment, and the only
consideration were convenience, the easiest place to put a speaker in a typical room would be
a position in the front of the room with the speaker aimed toward the audience, as shown in
Figure 2a.
This placement, however, has a problem. In the example shown in the figure, the closest
listener is one meter from the speaker, and the farthest listener is twenty meters, a ratio of
twenty to one. This corresponds to a 26 dB difference in sound level, a very large level
difference corresponding to a perception that the sound at the farthest location is perhaps four
or more times softer than the front.

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April 2002, © Bose Corporation, All Rights Reserved
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Figure 2a. A traditional speaker producing spherical waves and
mounted at ear height in the front of the room results in a 26dB
difference in direct field level when the distance ratio of near to far is
1:20. A listener in the back would report the loudness to be four or
more times softer than the front.
Thus while localization is good because the speaker is placed close to the visual activity,
the system does poorly in creating the desired sound level in the audience area. No matter
what volume setting is used, the sound is either too loud or too soft in most of the audience
area – it is simply impossible to establish the correct level for the audience with such a big
difference from front to back.
To achieve less variation in speaker-to-listener distances, and therefore less variation in
sound level, the speaker can be hung in the air and tilted down at the audience as shown in
Figure 2b. This is what is referred to unofficially as the ‘hang-and-tilt’ approach. The ratio in
this example is 2:1, corresponding to a sound level variation of only 6 dB. The hang-and-tilt
approach largely solves the level variation problem, which is why it was vigorously pursued
as a way to satisfy customer requirements.
Figure 2b. When the same speaker is mounted in the air and tilted
down, the level variation is reduced significantly – in this case to only 6
dB – which corresponds to a near-to-far distance ratio of 1:2.

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Of course, as with any engineering solution, the hang-and-tilt approach is not perfect. It has
its strengths and weaknesses as they relate to the goal of cost effectively satisfying the major
customer requirements. The details of these strengths and weaknesses are the subject of the
next section.
Strengths of the hang-and-tilt approach
THE strengths of a good hang-and-tilt system are that with it, excellent tonal balance,
consistent sound level, and speech intelligibility can be achieved. Moreover, because the
speakers are located up and out of the way, they rarely interfere with sightlines.
Over the years, Bose and others have developed a number of technological solutions
specifically designed to improve the quality of hang-and-tilt systems. For example, Panaray®
LT speakers are designed with very narrow sound radiation patterns so that designers can
carefully aim them only onto audience areas and avoid reflective walls and ceilings that can
produce the excessive reverberation responsible for diminished speech intelligibility. These
speakers also exhibit a very sharp rolloff of sound outside their primary radiation angles,
making it easier to combine two or more in such a way that they exhibit a minimum of the
inter-speaker interference that can lead to dropouts in sound.
Similarly, the Bose Panaray 502®A loudspeaker represents an important contribution to the
field of hang-and-tilt speakers because it delivers consistent coverage over substantially a full
range of frequencies using very natural sounding cone-type drivers in a very small package.
This speaker is used in literally thousands of venues around the world where customers say it
meets their needs elegantly and unobtrusively.
As a final example of the types of innovations that have led to better hang-and-tilt systems,
until very recently it was thought to be difficult or impossible to include control of the lower
frequencies in hang-and-tilt designs. This lack of control meant that bass sound waves were
more or less allowed to go anywhere within a venue, causing a lack of clarity in music and
some masking of speech (and therefore a reduction of speech intelligibility). Today solutions
exist to control bass frequencies in hang-and-tilt designs with very nearly the same degree of
precision as the higher frequencies, including a comprehensive technique developed by Bose.
These solutions, which employ advanced array theory, have led to noticeable improvements
in the sound quality of systems in which they have been used.
Weaknesses of the hang-and-tilt approach
THE hang-and-tilt approach also has some weaknesses. For example, the designer must
ensure that the sound radiation pattern from the speaker being considered is appropriate for
the purpose of covering the audience area. However, the choice of speakers is limited to only
a few, which differ according to their radiation patterns. It is purely coincidence and therefore
rare for the designer to find a perfect match between the available radiation patterns and the
audience area. In general, the speaker being considered will have more or less coverage than
what is needed.

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If the speaker’s radiation pattern is too wide for the audience, there is over-coverage as
shown in Figure 3a. In these situations, sound radiates to areas other than the audience where
it reflects off of surfaces and arrives at the ears of the listeners as reverberation, which causes
degradation in clarity and intelligibility.
Figure 3a. The effect of choosing a speaker with a radiation pattern
wider than the audience is shown. Sound striking surfaces other than
the audience causes unwanted reverberation and reduced musical
clarity and speech intelligibility.
If, on the other hand, the speaker’s radiation pattern is too narrow for the audience, as
shown in Figure 3b, people outside the main beam will hear a serious degradation in tonal
balance, level and clarity.

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Figure 3b. The effect of choosing a speaker with a radiation pattern
narrower than the audience is shown. People outside the main beam get
poor sound quality.
In situations where the radiation pattern from a single speaker is too narrow, another
speaker is usually added. When that is done, however, the same set of challenges is repeated.
Will the added speaker be able to just cover the area that was uncovered before? If it does, it
is coincidental. In general, the added speaker will again have coverage that is too wide or too
narrow.
Regardless, when two or more speakers are used to cover an audience area, their individual
radiation patterns must be overlapped in order to avoid a coverage hole between their
patterns. This interference zone, shown graphically in Figure 4, can result in significant and
audible dropouts of sound at some frequencies. Without careful selection of speakers, their
locations, and aiming angles within a cluster, there can be as much as 20-30 dB of energy
missing in the middle of the frequency range crucial for speech. These dropouts caused by
interference have a significant impact on clarity, intelligibility and tonal balance.

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Figure 4. The interference zone caused by the overlap of two speakers
is shown. Inter-speaker interference can result in major sound dropouts
– as severe as 20-30 dB – which harms tonal balance, clarity, and
intelligibility.
For these reasons and others, hang-and-tilt systems require a significant investment in
design time to achieve good coverage without excessive interference. To aid in this effort, the
designs are usually created using computer modeling programs, where creating the room
model, then selecting, positioning, and aiming speakers, and optimizing the design can take
anywhere from a day to weeks, or even months in the case of large projects.
Once designed, sophisticated rigging is often needed to ensure that the speakers are
properly and attractively installed. A professional engineer is often employed to implement
the exact aiming angles dictated by the design and to ensure mechanical integrity and safety.
Then the rigging hardware has to be purchased or fabricated and shipped to the site. The
installation requires a lift or scaffolding to hang the speakers in the right place. And finally
the installation often has to be reviewed by the local engineer to ensure that it meets code and
safety requirements. Rigging and installation costs can climb into the thousands of dollars.
Once the system is installed, another significant investment in engineering time is required
for system tuning and adjustment. Level matching the low to the mid and high frequencies
and setting time delays in a cluster takes time and requires a skilled field engineer. So does
setting time delays and matching levels from cluster to cluster and deciding on the overall
room equalization.
Thus designing, installing, and tuning a hang-and tilt design is time consuming and requires
a high level of skill in a variety of areas. These factors mean that hang-and-tilt systems are
often expensive to create.
Hang-and-tilt systems also suffer from compromised performance in the area of sound
localization. The visual activity is usually to the front of the listener, but the sound comes
from above where the speakers are located. This lack of eye-ear correspondence is

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disconcerting and creates an ongoing distraction. When given the choice, listeners prefer the
sound to come from the same direction as the action.
And finally, service and maintenance is difficult when speakers are hanging in the air.
Service usually requires that the floor area be cleared, and a lift or scaffolding employed.
This is in general inconvenient and expensive. Sometimes, a facility has to be closed for a
day or more in order to gain access to the speakers, or the work must take place late at night
when labor costs can be much higher.
Summary
INsummary, the hang and tilt method is effective in meeting customer requirements. But not
without some compromises in sound quality, usually due to reduced performance in the
overlap areas of speakers and in poor localization performance. Perhaps more important, the
process of creating and servicing a system is time consuming and requires a high level of
skill in a number of areas, both of which add significantly to the cost of these systems.
Can anything be done about these weaknesses? Or should we only look forward to more
incremental improvements to the hang-and-tilt approach – a new speaker with slightly better
radiation pattern control, or equivalent performance in a somewhat smaller package, or
somewhat easier rigging hardware, for example?
We believe there is a true extension to hang-and-tilt components – a tool for designers that
can often overcome the weaknesses that have been described. To explain why we have come
to this conclusion, we must return to and examine the fundamental assumption that originally
led the industry to the hang-and-tilt approach.

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THREE KINDS OF SOURCES
ASexplained, the hang-and-tilt approach evolved because of a fundamental property of the
speakers used. Namely, the speakers have sound waves that radiate in all directions, in and
out, up and down, left and right. And that means that the intensity of sound leaving the
sources falls off by 6 dB per doubling of distance. We call these spherical-wave sources. To
provide consistent sound levels over a widely distributed audience, listeners must be nearly
equidistant to the speaker, and hence the need to raise the speaker into the air over the heads
of the listeners.
The obvious question is whether this fundamental 6 dB per doubling of distance property is
true for all sources. The answer is no. There are other kinds of sources that produce different
kinds of sound waves with very different behavior.
Plane waves
FOR example, we generate plane waves to measure the performance of compression drivers
in the lab. These waves diverge in only one dimension: out, but not up and down or left and
right. As a result, the intensity of a plane wave does not fall off at all with distance1, as shown
in Figure 5. In other words, the distance can be doubled and the sound level is the same. Such
a source, therefore, could produce the same sound pressure level in all seats – what would be
considered ideal coverage.
1This is an ideal description. In reality, any sound wave, whether spherical or planar, is affected by
environmental effects, such as humidity, temperature and wind.

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Figure 5. A plane wave diverges in only one dimension: out, but not up
and down, or left and right. As a result, the intensity does not drop off
at all.
Plane waves, however, are difficult and impractical to create outside of the laboratory. To
create plane waves in the open air requires an unusually large surface area – one at least one
meter by one meter square – to have any chance of creating plane or plane-like waves over a
reasonably wide range of frequencies. And by unique mechanical inventions this source
would have to be pistonic, meaning that the whole surface moved at the same magnitude and
phase at all times. To our knowledge, no such source has been attempted much less achieved,
even in prototype form.
Yet even if such a source could be realized – and if it were only driven at frequencies
where the wavelength is much smaller than its dimensions – there would be no sound outside
the source area, as shown in Figure 6, because the plane, or plane-like waves are only
radiated out but not to the sides, or up or down. A one-meter by one-meter source, therefore,
would have extremely limited, if any, application because it would only cover listeners
located within a one-meter by one-meter projection. To cover a typical audience, a plane
wave source would have to be much larger. It would need to be the same width and height as
the audience. Even if mechanically possible, which is extremely unlikely, it would obviously
also be completely impractical because of its size.

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April 2002, © Bose Corporation, All Rights Reserved
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Figure 6. What makes plane waves impractical is the fact that there is
no sound outside the physical size of the source.
Cylindrical waves
ATthis point, two kinds of waves have been described: spherical waves that radiate in three
dimensions and whose intensity drops off by 6 dB per doubling of distance, and plane waves
that radiate in one dimension and fall off by 0 dB per doubling of distance. A natural question
is, therefore: “Is there a third kind of wave that radiates in two dimensions and falls of
somewhere between 0 and 6 dB per doubling of distance?” The answer is yes. And these are
called cylindrical waves. To understand their behavior, it is helpful to return to the one-meter
by one-meter source that created plane waves. Looking down on the plane-wave source, it is
clear that the sound is confined to the width of the source (Figure 7, top right). Looking from
the side of the source, the sound is similarly confined to the height of the source (Figure 7,
bottom right).

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Figure 7. As we look down on the plane-wave source, we see that the
sound is confined to the width of the source (top right). If we look from
the side, the sound is confined to the height of the source (bottom
right).
Again looking down on the source, now imagine that the horizontal dimension of the
source (currently one meter) was reduced to only a few centimeters. The result is shown in
Figure 8. The vertical radiation pattern does not change because the source retains the same
vertical dimension (bottom of figure). The horizontal radiation pattern (top of figure) changes
drastically because the much smaller source size corresponds to a much wider radiation
pattern. (Note that the same physics explain why a 2" (5 cm) driver has a much wider
radiation angle than a 12" (31 cm) driver, assuming both are operating at the same
frequency).

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Figure 8. If we reduce the horizontal dimension of the source, the
radiation pattern gets wider and starts to spread out (top). The vertical
radiation pattern does not change because the vertical dimension of the
source has not changed (bottom).
If the horizontal and vertical radiation patterns of Figure 8 are combined into a three-
dimensional radiation pattern, the result is waves that are cylindrical in shape. To be more
exact, the radiation pattern is wedge-shaped, or like a piece of a cylinder, as shown in
Figure 9. The shape of the source responsible for this wedge-shaped pattern is slim and long:
in other words, it is line shaped. Thus a line-shaped source where all parts of the line move
with equal magnitude and phase produces a wedge-shaped radiation pattern. The sound
radiates in and out and to the sides, but not up and down.

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Figure 9. The radiation pattern of a long, thin source is wedge-shaped.
The sound radiates in two dimensions: in and out and left and right, but
not up and down.
How does sound intensity fall off as a function of distance for such sources and such
waves? The answer lies halfway between spherical waves and plane waves, as shown in
Figure 10. The spherical source radiates in three dimensions and falls off as 6 dB per
doubling of distance, the cylindrical wave radiates in two dimensions and falls off as 3 dB
per doubling of distance, and the plane wave radiates in one dimension and falls of as 0 dB
per doubling of distance.2
2For the reader interested in understanding the underlying physics of these differences, imagine a sound-
intensity-meter ten feet in front of a source producing each kind of wave: spherical, planar, and
cylindrical. Furthermore, imagine that at this distance, each source produces the same level. Now,
consider a small area of the sound wave at the location of the meter.
-As the spherical wave spreads out, the wave must expand over the surface of a sphere. When the sphere
doubles in diameter, the small area of the sound wave must expand over a proportionately larger area at
the doubled distance. As a result, the intensity of the original area of sound diminishes. Since the area of
a sphere increases as the square of the radius, increasing the distance from the source by a factor of two
(doubling the distance and therefore the radius) means reducing the sound intensity by a factor of four
(two squared). A factor of four in sound intensity corresponds to 6 dB.
-As the cylindrical wave spreads out, the wave must expand over the surface of a cylinder. When the
cylinder doubles in diameter, the small area of the sound wave at the closer distance must spread over a
proportionately larger area at the doubled distance. As a result the intensity of the original area of sound
wave is reduced. Since the area of a cylinder increases proportionately with only the radius (rather than
as the square of the radius as in the case of a sphere), increasing the distance from the source by a factor
of two (doubling the radius) means reducing the sound intensity by only a factor of two. A factor of two
in sound intensity corresponds to 3 dB.
-As the plane wave progresses, the wave does not expand. When the wave reaches a distance that is
double the original, the small area of the sound wave at the closer distance has not spread at all, and as a
result the intensity of the original piece of sound wave is the same. A factor of zero in sound intensity
corresponds to 0 dB.

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Figure 10. The intensity of a spherical wave falls off by 6 dB per
doubling of distance, a cylindrical wave by 3 dB, and a plane wave by
0 dB per doubling.
(For completeness, it is important to note that only a line source that is infinitely long,
perfectly thin, and equal in magnitude and phase at all points along the line will produce a
cylindrically shaped wave for all frequencies and all distances. However, the behavior of
even a one-meter line source can be better described using the basic properties of cylindrical
waves than by any other means considered.)

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APPLYING LINE SOURCES TO SOUND SYSTEM DESIGN
THE 3 dB per doubling behavior of cylindrical waves is of special interest in sound system
design because it is so much more gradual than the 6 dB per doubling behavior that
motivated us to hang and tilt speakers. On the other hand, so was the 0 dB per doubling
behavior of plane waves, but unfortunately, producing them was impractical in real life. Is it
more practical to produce cylindrical waves? Or are there problems that will rule this out too?
If such a source can be realized, would it really do a good job at meeting customer
requirements?
Source shape and sound output capability
TObegin, a source that produces cylindrical waves does not have to be rejected for the same
reasons a plane-wave source was rejected. A cylindrical-wave source must be as tall as the
audience, but not as wide, since the wide horizontal radiation pattern can be relied on to
cover an audience distributed side to side; a tall, slim source, resulting in wide side-to-side
radiation, can cover a typical audience.
Second, with modern transducer technology, there is no reason that a line source can not
produce a balanced frequency response at the kind of output levels required in many
applications. Major improvements in transducer technology (including many introduced by
Bose) mean that it is no longer true that the small transducers needed to fit into a slim line-
shaped source lack the correct balance of frequencies or necessary output capacity. A full,
balanced frequency response and very high output is now possible from speakers no larger
that a tea cup. Therefore, concerns about frequency response and output are also not reasons
to reject the line source.
Meeting the primary customer requirements
INprincipal – in other words without regard to the specifics of any particular implementation
– would a line-shaped source radiating cylindrical or near-cylindrical waves be a good choice
for meeting the major customer requirements listed earlier?
Re-examination of the side view of the radiation pattern of a line source, shown in Figure
11, reveals that sound does not radiate up and down, but rather is confined to a region
between a plane perpendicular to the top of the array and one perpendicular to the bottom.
When such a source is placed in a room, it means that sound will not radiate up and down and
therefore will not radiate to the ceiling and upper walls, where reflections contribute to the
amount of reverberation and therefore to the degradation of music clarity and speech
intelligibility. Such a source would be therefore ideally suited to environments with longer
reverberation times such as churches, auditoriums, airports, hallways and so on.