Community M4 white paper

M4
A White Paper
An In-Depth Look At The Community M4 Midrange Driver
by Pat Brown
M4
A WHITE PAPER
by Pat Brown
TABLE OF CONTENTS
M4 - A DEVICE FOR THE CRITICAL MIDRANGE ......................................................................... 1
THE REBIRTH OF THE COAXIAL HORN ..................................................................................... 7
VOICE-ONLY SYSTEM DESIGN USING THE M4 .......................................................................... 8
3-WAY SYSTEM DESIGN USING THE M4 .................................................................................... 9
M4 APPLICATIONS ................................................................................................................... 10
M4 INSTALLATION PROFILES ................................................................................................... 11
BIBLIOGRAPHY ........................................................................................................................ 25
C O M M U N I T Y P R O F E S S I O N A L L O U D S P E A K E R S
333 East Fifth Street
Chester, PA 19013-4511 USA Phone (610) 876-3400 Fax (610) 874-0190
© 1997, Community Light & Sound, Inc.
M4
TM
A Device for the
Critical Midrange
The purpose of this investigation is to describe a device
that has been designed specifically for the frequency band
that extends from about 200 Hz to 2000 Hz, which is commonly referred to as the "midrange." It shall be put forth that
this decade is critical to sound reproduction since it contains
the majority of audio information for speech and music. Support for this assumption will begin with an overview of the
basic information from which it is drawn.
The human hearing system is sensitive to modulations,
or ripples, in the atmospheric pressure that surrounds us.
This pressure can be "rippled" anywhere from less than once
per second to many thousands of times per second. The typical human ear/brain system is sensitive to frequencies between 20 and 20,000 cycles per second, or Hertz (Hz). The
purpose of a sound reinforcement system is to reproduce
this spectrum with sufficient acoustic power to produce a
desired level at some listener distance. The human ear, as
marvelous a device as it is, does not cover the entire spectrum with equal sensitivity. In fact, the human ear/brain system is optimized for reception of the middle portion of the
entire passband, most likely due to our dependence upon
speech in our day-to-day lives. This middle portion, which
we will call the midrange, contains the most critical information for the human receiver. With this in mind, it is interesting that this critical band has long been overlooked in the
design and implementation of sound reinforcement components and systems. One purpose of this paper is to put forth
the idea that the midrange is the most critical part of the
spectrum, and that superior reinforcement systems can be
constructed if developed around the midrange decade.
The first step of this investigation is to determine the requirements for an optimum transducer for coverage of the
middle decade of the audible spectrum. Such a transducer
would serve as a complement to the already existing variety
of excellent transducers for the other two decades of the
audible spectrum. While there are many approaches to component design, perhaps the best course is to allow such a
device to define itself based upon the physics of the sound
that we wish to reproduce. This approach will discourage
any temptation to take an existing transducer and stretch its
parameters to include the middle decade, a common practice in the audio industry. As with the other two decades in
the audible spectrum, the requirements are clearly defined
by the physics of the sound that we wish to reproduce.
The essential requirements for optimum midrange reproduction shall include, but not be limited to:
High Efficiency
Low Distortion
High Power Handling
Durability
Let us first describe the desired passband of such a device based on the essential parameters of wavelength and
distortion.
The response of all transducers is frequency dependent.
This simply means that they do not and cannot behave the
same at all frequencies, due to the physical characteristics of
sound waves. In everyday life, the physical size of something nearly always determines how we handle it. The same
is true for sound waves. Since sound propagates at a velocity
that is not frequency dependent, the physical size of a sound
wave is directly related to its duration and velocity. This can
be understood by considering that a single cycle of a 1000Hz
tone lasts for about 1ms. Since this wave is traveling at approximately 1130 feet per second (344 meters/sec), distance
(or length) is equal to the product of time and velocity, the
length of the wave will be:
λ =
1130
f
= 1.13 ft or
344
= 0.344 m
f
where:
f is the frequency in Hertz
Audible Spectrum
Lower Decade
20Hz - 200Hz
10
100
Middle Decade
200Hz - 2kHz
1000
Upper Decade
2kHz - 20kHz
10K
100K
A 100Hz tone has a period of about 10ms, and since it
travels at the same speed as the 1000Hz wave (but lasts
longer) its physical length becomes about 11 feet(3.44 m).
The common term used to describe the physical length of a
wave in free space is "wavelength." Since wavelength is inversely proportional to frequency, as the frequency goes
lower, wavelengths get longer. And, as wavelengths get longer,
the physical attributes of the transducers that reproduce them
must be altered accordingly.
1
Since we are defining the characteristics of an optimal
midrange device, the passband of such a device should be
considered in terms of wavelength. While such a description will clearly define the physical dimensions of a pattern
control horn, it will also serve to define the size and other
physical properties of the piston that shall ultimately drive
such a horn. Our optimum midrange device must be capable of generating large amounts of acoustic power from
250Hz to 2500Hz, and the waveguide must provide directional control for the corresponding wavelengths ranging from
about 6 inches to 6 feet.
to Olson's work in the 1930's and 40's. Viewing transducers
as ladder networks of resistive and reactive components leads
to an understanding of the inherent signal delay properties
of such systems. It is the energy storage characteristics of the
devices reactive elements that cause phase (time) anomalies. The clever transducer designer understands that these
are present and accounts for them in the design.
V.C Inductance
Phase Plug
Air Compliance
V.C Resistance
Moving Mass
of Diaphragm
EIN
Horn EOUT
100
Suspension
Suspension and
other losses
50
30
Phase Plug
Air Mass
Wavelength in Feet
10
A more revealing depiction would be a mechanical
model, as shown below:
5
3
1
0.5
Diaphragm
0.3
Constant Speed
Spring Effect of
Inductance
Horn
0.1
10
30
50
100
300
500
1K
3K
5K
10 K
Frequency in Hz
Amplifier
Voice Coil Shock Absorber
Nomograph showing the relationship between wavelength and frequency.
Speech vs. music
It may be demonstrated that the requirements for speech
systems are unique, and are not necessarily met by systems
that are favored for music reproduction. Music is an inherently non-linear event, meaning that there is often no exact
criteria by which to evaluate it, and that colorations that
were not present in the original are often tolerated or even
desirous in reproduction. We may conclude that music
systems are best evaluated by listeners and not test instruments.
Research has shown that speech is not so subjective, and
that many of the artifacts that are considered acceptable or
even desirable in music systems cannot be tolerated in speech
systems. The reverb and delay added to a singer's voice suddenly becomes unacceptable when the person stops singing
and begins speaking. Unfortunately, many loudspeaker systems have this same "Jekyll and Hyde" personality.
Design of a Midrange Driver
The circuit in the following figure depicts a simplified
electrical equivalent circuit of a compression driver, and the
analysis of it yields a series of useful equations for driver
parameters. These are set forth in several texts, dating back
Suspension
Notice that the only thing that stands between the amplifier and the diaphragm is the mechanical resistance REM,
which simplifies to:
R EM =
B2 VVC
p
where:
VVC is the volume of the voice coil
p is the resistivity of the voice coil wire
B is the flux density
This simple relationship tells us that the higher the field
intensity and the larger the volume of the voice coil, the greater
the efficiency (due to lower losses in R EM).
The M4 maximizes both of these important parameters,
making the M4 the most efficient loudspeaker on the market to date. Let us look deeper into the anatomy of the M4
and examine why it stands alone as the optimum driver for
the critical midrange.
2
What is Acoustic Power?
The concept of acoustic power is not readily considered
by most people, due in part to the industry's preoccupation
with sound pressure. To put it simply, sound pressure is the
result of sound power. Sound power is the cause, sound
pressure is the effect. The goal in driver design is to maximize
the amount of acoustic power available from the device,
given the constraints and trade-offs between the available
parameters. Once the acoustic power has been realized,
we then turn our focus to pattern control devices (horns)
that will channel this power to a smaller unit area, increasing
the sound intensity for that area, increasing the sound
pressure (at a given listening position) beyond what it would
have been if no pattern control was used.
In many conventional cone-type transducers, it can take
as much as 100 electrical watts to produce one acoustical
watt, yielding an efficiency of about 1%. At the other extreme, a perfectly efficient transducer (that unfortunately does
not and cannot exist) would produce one acoustic watt with
the application of one electrical watt. The M4 comes closer
to this ideal than any other driver available today, producing
nearly one-half watt of acoustic energy from a single watt of
electrical energy.
One acoustic watt is equivalent to 107.5 dBSPL at four
feet from an omnidirectional source. A device's directivity
can be described with a term called "Q" which is an indication of its ability to confine the applied energy to a smaller
unit area. Q, therefore, is a parameter of the horn, not the
driver. If we take one acoustic watt and couple it to a horn
with a Q of 2 (hemispherical), the intensity and therefore
the pressure will increase by a factor of 2 to 1 in the area
covered by the device. This is quite useful, since it allows
more energy on the audience and less on the walls and ceiling. It is common practice to convert the Q rating into decibels by the formula:
By considering Q in terms of the Directivity Index, the
increased sound pressure provided by increasing Q beyond
unity (Q = 1) is readily apparent. Let's look at the numbers
and get a feel for what a large source of acoustic power and
a high Q horn can do for a system design (see figure below).
When you consider that a 3dB difference in efficiency represents a two-to-one power ratio, the benefits of the M4
become very apparent. Also consider that the M4 is more
efficient in its passband than some conventional mid/hi frequency drivers are in their passband. This means that it can
require several high-frequency drivers for each M4 in the
system, for flat power response.
Power Capacity
With 200 watts of electrical power applied, the M4's
power output at 250Hz is 100 acoustic watts. This output
increases as frequency increases, due to lower excursion requirements. While electrical power handling capability is a
much more common specification, it tells nothing about how
much sound comes out when that power is applied to the
device. It only indicates how much amplifier power can be
applied to the device without damage.
The electrical power capacity of a loudspeaker is determined primarily by two factors: its excursion limits and its
thermal limits (caused by voice-coil heating). Since both vary
with frequency, the actual power capacity of a loudspeaker
is said to be frequency dependent, therefore being a complex function of frequency.
The power capacity of the M4, by the AES standard, is
200 watts. This 200 watt rating primarily describes M4's thermal limits. At low frequencies, below 300Hz, M4's power
capacity will be primarily excursion limited. For voice or musical program material, the 200 watt rating describes the M4's
power capacity accurately.
D I = 1 0 log Q
where DI i s the directivity in dex
How much sound can you get from one electrical watt?
SPL at 4 feet
Source of Acoustic
Power
% Efficiency
Acoustic power
from 1 electrical
watt
Cone
Loudspeaker
3%
2" Mid/Hi
Driver
M4
With omni horn
Q=1
With 90x40 horn
Q=10
With 60x40 horn
Q=16
With 40x20 horn
Q=50
0.03
93dBSPL
103dBSPL
105dBSPL
110dBSPL
35%
0.35
103dBSPL
113dBSPL
115dBSPL
120dBSPL
43%
0.43
105dBSPL
115dBSPL
117dBSPL
122dBSPL
3
Achieving Efficiency
Efficiency is a measure of how much acoustic power results from an application of electrical power.
In the early days of audio, transducer efficiency was a
prime consideration, mainly because the largest amplifiers
were able to produce only a few watts of power. High efficiency meant that most of this power could be converted
into sound. With the advent of solid state electronics, amplifier power became quite economical. These days, amplifiers in the thousands of watts are readily available and (at
least compared to the old days) inexpensive. So why would
we continue to be concerned about efficiency?
The answer lies in what a transducer does with the electrical power that it receives. Each watt drawn by the transducer is converted into one of two types of energy: sound or
heat. While sound is what we are after, it is inevitable that
heat will also be produced, and heat is a main culprit for
many transducer failures in high-level systems.
While a frequency response specification is useful, it may
be misleading at high frequencies due to high-frequency
beaming, a phenomenon that occurs as the wavelength being reproduced by a driver becomes small when compared
to the diameter of the driver. Even though the on-axis response is flat, the pattern has narrowed and there is less offaxis coverage. Power response is best measured on a constant-directivity horn or plane wave tube, which gives a better representation of these two parameters. Simply stated, a
highly efficient transducer produces more sound and less
heat.
Efficiency in a transducer is proportional to the amount
of magnetic flux that can be concentrated into a magnetic
field gap. This magnetic field gap should be made as narrow
as possible, yet not so narrow as to allow the voice coil to
rub as it moves through the gap.
The M4 achieves a highly concentrated magnetic field
by using a unique focused geometry and an added flux stabilizing ring. This combination helps keep the magnetic field
from varying under high power inputs.
This voice coil and magnetic assembly, when combined
with other design features, result in an amazing 43% efficiency rating for the M4. This means that 43% of the incoming electrical energy is actually converted into acoustical
energy, and only 57% is converted into heat. The following
chart shows the typical efficiency ratings for various types of
transducers. The high efficiency of the M4 means that it will
be less prone to heat related problems, such as power compression, and therefore much more reliable than other devices.
Power compression results from the tendency of voice
coil impedance to rise as temperature increases. This causes
less power to be drawn from the amplifier, and hence a reduction in acoustic output. The power compression in many
devices can be several dB. Due to the M4's efficiency, virtually no power compression occurs.
Transducer Efficiency
100
90
80
70
60
50
40
30
20
10
Cone-Type
Loudspeaker
Typical Mid/Hi
Compression
Driver
M4
Composite Diaphragm
A large diaphragm is essential for a 4-inch midrange driver
capable of producing 100 acoustic watts. The diaphragm of
an M4 is a full 6.65" (16.89 cm) in diameter and has an
effective piston area of about 40 in2 (258 cm2). This is due in
part to the use of the outer suspension as part of the piston.
The phase plug throat area of 8 square inches with this 40
square inch (258 cm2) diaphragm results in a compression
ratio of about 5:1. The M4's maximum diaphragm excursion
is +/- 0.1 inches (2.54 mm), rivaling that of some woofers.
All loudspeaker diaphragms begins to break-up at some
high frequency. This is the point where the diaphragm is no
longer acting like a piston. The design goal of the M4 was to
extend high-frequency response to beyond 2000Hz. Originally this was accomplished by the development of a sandwich diaphragm with 2.0 mil aluminum "skins" and a rigid,
low-density foam core. To further reduce breakup, the outer
edge of the diaphragm was rolled, greatly increasing it's stiffness.
The M4 uses a carbon fiber diaphragm to raise the frequency of the first
breakup mode out of the devices passband.
4
The result was a lightweight, extremely strong and stiff
diaphragm that maintains a smooth frequency response to
about 2200Hz.
Carbon Fiber
Although the original diaphragm proved very successful
and was produced for a number of years, a new diaphragmhas
been developed that is now used in all M4s. It takes advantage
of newer strutural materials being made of a composite of
carbon fiber and rigid foam bound with a resin compound.
With the same mass (15 grams) and formed to the same
shape as the original, this material considerably increases the
diaphragm’s tensile, flexural, and impact strength. The
inherently high internal damping of the carbon fiber material
helps reduce breakup at higher frequencies. This material
has also stretched the mechanical limits of the diaphragm to
a point where even extreme physical abuse is unlikely to
cause it damage.
Voice Coil
The M4 voice coil is edge-wound aluminum which is
copper-flashed to allow proper solder joints on the beryllium copper lead-in wires. It is placed on the inside of an
aluminum former. This in turn is fastened to the aluminum
lower skin of the diaphragm. The consistent use of aluminum throughout the voice coil yields tremendous thermal
conductivity, and conducts heat away from the voice coil
area. Since voice coil impedance rises with heat (and less
amplifier power is drawn), the M4 's impedance remains
stable, even at full amplifier power. Power compression is
less than 1 decibel at full rated power (200 watts).
The voice coil design of the M4 uses some innovations that optimize it for
its passband. Trying to "stretch" a devices passband to include more than
one decade involves compromises that reduce fidelity and reliability.
Throat Distortion
Distortion is a prime consideration for our middle decade
device, especially so since the existing array of commonly
used devices (12 and 15-inch woofers, 2-inch com.
pression drivers) have inherently high distortion levels due to
operation at the fringes of their optimum passband
Throat distortion, for a given horn flare, acoustic power
level, and frequency, is inversely proportional to the square
root of the throat area. This means that as throat area decreases, distortion increases. The true "throat area" of a compression loudspeaker, however, is not the area at the throat
of the horn (the exit of the driver). It is the area at the entrance to the phase plug, that is, the combined area of all
the phase plug slits as seen by the diaphragm. This "phase
plug throat" area, because it is smaller than the horn throat
area, is the area that must be considered for the control of
distortion and acoustic power output.
The M4's phase plug throat area is about 8 square inches.
The phase plug throat area of a popular 2-inch exit driver (2inch horn throat, that is) is about 1.25 square inches. Considering just this one factor, phase plug throat area, it would
take more than six of this popular 2-inch driver to equal
M4's acoustic power output and distortion level.
Phase Plug
In a compression driver, the sound radiating area of the
diaphragm is much larger than the throat area of the horn.
The sound from the diaphragm area must be collected and
"compressed" down to the size of the horn throat while maintaining the complex phase relationships of the program material. The phase plug performs this function, and its design
is critical to the fidelity of the transducer.
By careful design, the resonant cavity formed by this phase
plug can be used to actually boost the driver's response over
some narrow band of frequencies. The price paid is that the
high-frequency response falls off much faster above the frequency of resonance, and that radical phase shift occurs over
a very narrow band. The M4 does not resonate this cavity,
and as a result exhibits a more natural response in the critical articulation region surrounding 2kHz.
5
Magnetic Assembly
A unique feature of M4's magnetic assembly is its position relative to the diaphragm and phase plug. On a conventional mid/high-frequency compression driver, the magnetic assembly is in front of the diaphragm and phase plug.
Forcing the sound through the narrow opening in the pole
piece contributes to throat distortion. In addition, this opening actually behaves like a short horn section whose flare is
only randomly matched to the primary horn. On the M4,
the magnet is behind the diaphragm and phase plug.
This placement avoids both the distortion and horn mismatch problems and allows the M4's throat size and other
parameters to be selected without regard to the size of the
opening in the pole piece.
A survey of commercially available ferrite magnets shows
that a 9.6 in O.D. (24.3 cm), 1.2 in (1.27 cm) thick ferrite
magnet (approximately 5.2 kg) could be used to supply a
4.5 in (11.4 cm) diameter, 0.24 in (6.1 mm) high and 0.055
in (1.4 mm) wide airgap with 17.2 kilogauss. This approaches
the highest flux density possible from a commercially available magnet, using good magnetic engineering practice. The
final magnet design (patented) is shown below. The thick
top and bottom plates reduce fringing and make this extremely powerful magnet structure a manageable weight of
approximately 30 pounds.
Providing Pattern Control
Once a high level of efficiency and acoustic power have
been achieved from a transducer, the next design problem
becomes delivering that acoustic power to the audience.
This is accomplished by confining the acoustic energy to a
defined unit of area, via a pattern control device, such as a
horn.
Our attention now shifts back to the wavelength problem that we discussed earlier. Sound waves have a physical
size, which is inversely proportion to frequency. Since our
midrange device is reproducing a lower frequency than a
conventional 1" or 2" driver, the associated horn must be
much larger to allow pattern control.
The PC1500 series horns are designed to channel the
immense acoustic output of M4 to a defined area, the audience. This provides increased direct sound level for listeners, and reduces energy delivered to the reverberant sound
field. Directivity control, or "Q", is one of the most valuable
tools available to the system designer, often allowing for sound
system solutions to room problems. Maintaining dispersion
control down to 250Hz may tame an otherwise hostile acoustic environment. The clever system designer will utilize the
absorption of an audience along with well defined coverage
patterns to reduce excitation of a very reverberant space,
making both intelligible speech and natural music reproduction possible.
M4/Horn Specifications (200 Hz - 2k Hz Pink Noise)
Sens.
(1W/1M)
Q
Directivity
Index
PC1594M
110.5
16
12
PC1594M-EXT
110.3
17
12
PC1564M
112.2
25
14
PC1564M-EXT
112.0
24
14
PC1542M
113.8
44
16
PC1542M-EXT
113.4
42
16
SH1894M
108.9
10
Pattern-Control Horn
Cross-section of the patented M4 magnet structure
Impedance
The impedance of a transducer is the complex load that
it presents to the amplifier. Since all voice coils are made up
of lengths of coiled wire, their impedance will have a reactive component that is frequency-dependent. The lowest impedance that a transducer can have at any frequency is the
DC resistance of the voice coil. The M4 rated impedance is
8 ohms.
10
above 800Hz
6
The Rebirth of the Coaxial Horn
Obviously part of the definition of a coaxial is that two
loudspeakers share the same axis. But, if they do share the
same axis, do they have the same acoustic origin? And what
about the acoustic centers? For a coaxial device to work properly, all of these questions must be resolved.
The concept of placing one horn inside another has been
attempted in past decades, most notably by Blattner in the
1930's, Community (FRC, For Real Coaxial) in 1972, and
Frazier in 1975.
Unfortunately, since both horns are radiating from a
unique point in space, the resulting pressure wave was severely distorted in the region of crossover due to phase cancellation. The horn within a horn was doomed until crossover and delay technology advanced to the point where the
needed corrections in time and bandpass could be realized
and implemented.
In 1987, consultant Jim Young of Ruston, Louisiana approached Dr. Eugene Patronis, a physics professor at the
Georgia Institute of Technology. He needed assistance in
reducing the size of an array he was designing for a church.
Dr. Patronis suggested the concept of a horn within a horn,
utilizing the components Mr. Young had hoped to use in the
array.
The M4 with pattern control horn was the midrange device of choice. It's high acoustic output and low distortion
made it ideal for the installation. Dr. Patronis added an EV
HP640 horn with an EV DH1A driver inside the Community
horn to convert it to a coaxial unit. Next, a 24dB/octave
crossover was added, and the optimum corner frequency
was determined to be 1250 Hz. This solved the bandpass
problems, but the offset acoustic origins remained. A KlarkTeknik 20-microsecond/step delay reconciled the origins, and
provided a true mid/hi range device with excellent pattern
control and smooth response. The rebirth of the horn within
a horn was complete, and many companies rushed to develop similar products.
On-Axis
10 deg off-Axis
20 deg off-Axis
30 deg off-Axis
7
Voice-only System Design Using the M4
Voice-only applications, such as paging and warning systems, are often required to operate in difficult environments
or over very long distances. The characteristics of the M4
make it ideal for these applications. Let us consider the design parameters for such a system.
A human voice has the highest power output in the 500Hz
octave band. Consonants of speech (essential for articulation) are centered in the 2kHz octave band. A good voice
device should provide high acoustic output and pattern control over a passband that extends to either side of these two
critical octave bands.
The unequalized response of the M4 is from 200Hz to
2000Hz. Given the M4's robust construction, this can be
equalized within 3dB of flat response out to 4kHz, extending its response through the articulation range for human
voice. Used with the proper horn, M4 completely satisfies
the requirements for a high-level, voice-only system. The
chart shows the levels that can be delivered by a single M4
at various distances with two typical horns. As always, these
are conservative estimates based on the M4's capabilities at
the lower limit of its passband. With proper equalization,
M4 can typically exceed these levels by 3dB.
Contribution to articulation at one-third octave centers
Power spectrum of the human voice
20kHz
M4 as a Voice-Only Device
High
Frequency
With 90x40 Horn
(Q=10)
DI=10dB
With 60x40 Horn
(Q=16)
DI=12dB
@4'
138dBSPL
140dBSPL
@ 30'
120dBSPL
122dBSPL
@ 100'
109.5dBSPL
111.5dBSPL
2kHz
(1) M4 Driver
100 Acoustic Watts
LW = 140dB
Midrange
200Hz
Low
Frequency
20Hz
8
3-Way System Design Using the M4
Let us now turn our attention to designing a full-range
reproduction system using the M4. A full-range system should
be capable of delivering the same acoustic power at each
octave throughout its bandpass. If we use this criteria to design our system, we can begin by noting that the acoustic
output of a single M4 can be up to 150 acoustic watts in the
middle of its bandpass. To be conservative, we will base our
estimates on the M4's output at 200Hz, the lower frequency
limit of its pass band. At 200Hz, the acoustic output power
of a single M4 is:
W
out
= 200(.5) = 100 acoustic watts
at 50% efficiency and full input power
How many low-frequency devices will be necessary to
deliver the same 100 acoustic watts into the environment?
Assuming a 200 watt power rating and 5% efficiency (both
very typical specifications), our required number of bass
speakers will be:
Wout = 200 (.05) = 10 acoustic watts each
# devices =
100
= 10 bass speakers
10
How many high-frequency devices will be necessary to
deliver the same 100 acoustic watts into the environment?
Let us assume that our high-frequency driver can handle
100 watts from 2000Hz up, and that it is 25% efficient in
this passband. Our required number of drivers will be:
Wout = 100(.25) = 25 acoustic watts each
# devices =
100
= (4) high - frequency drivers
25
At this point it becomes apparent that the massive output capability of a single M4 can dwarf the output capabilities of the other devices needed to complete the passband.
One solution is to relax the acoustic output of the system to
a practical working level, which will mean that the M4 will
be operating with a large amount of headroom, not a bad
idea for the critical midrange. It should also be pointed out
that a few assumptions have been made in our design problem. The same directivity factor has been assumed for each
device. This means that bass horns or special arraying techniques must be used to provide directivity that extends into
the bass region. Remember that wavelengths get larger as
frequency goes lower, so the required pattern control devices can become quite large. Also, it should be emphasized that this is a very conservative and worst case estimate
for the M4, whose typical acoustic output is closer to 150
acoustic watts through most of its passband. But, it never
hurts to be conservative, and this approach results in an extremely reliable system.
Equal Acoustic Power
Per Decade Approach
Extra Midrange
Headroom Approach
20kHz
High
Frequency
(4) High-Frequency Drivers
@ 25 Acoustic Watts each.
(2) High-Frequency Drivers
@ 25 Acoustic Watts each.
(1) M4 Driver
100 Acoustic Watts
(1) M4 Driver
50 Acoustic Watts
(10) LF Drivers
10 Acoustic Watts each
(5) LF Drivers
10 Acoustic Watts each
2kHz
Midrange
200Hz
Low
Frequency
20Hz
9
M4 Applications
Outdoor Stadiums
Inherent to stadium sound reinforcement systems are very
long throw distances, often hundreds of feet. Projecting sound
over these distances requires that the source generate a very
large amount of acoustic power, since the spherically expanding wavefront will drop in level 6dB each time the distance from the source doubles (inverse-square law). In addition, the noise levels in stadiums can often exceed 90 dBA,
driven by large crowds and noise from the event itself. This
requires the sound reinforcement system to routinely provide levels of 100 dBA to all seats for speech communication. The M4 is ideally suited for such an application, since it
can generate more acoustic power per watt than any device
on the market. This fact, along with the M4's inherent high
power handling, provides the designer with a tool to reach
the masses. Used in conjunction with the proper waveguide,
the M4 can not only provide adequate level, but has the
high reliability necessary for such applications.
Arenas
When a sound system is used indoors, it must compete
with high levels of noise from crowds, HVAC equipment,
machinery, etc. The problem is compounded by energy storage from the room itself. The reverberation times of typical
arenas are often 4-5 seconds in the 2 kHz octave-band, and
even longer at lower frequencies. Throw distances often
approach 150 feet, rivaling stadium systems. To overcome
such environments, the best tools available to the system
designer are pattern control and high efficiency. Pattern control allows the energy from the sound system to be confined
to audience areas, reducing excessive excitation of the room
itself. High efficiency means that the available amplifier power
produces the maximum possible amount of acoustic power
with the least amount of heat. The M4 driver, used with the
proper pattern-control horn, provides the system designer
with the best available specifications in both pattern control
and efficiency. Control of these vital parameters can be more
effective than room treatment in providing intelligible speech
in such spaces.
Houses of Worship
Sound systems for worship spaces are faced with a different set of requirements than the previous examples. Typical spaces have very low ambient noise levels, making even
moderate degrees of distortion audible. Since both speech
and music are reproduced, the system must provide intelligibility while retaining the ability to sound musical, two often conflicting parameters. The system must be able to reproduce the subtleties of a violin or guitar, and yet have the
available headroom and linearity to reproduce a clap of thun-
der for a musical production, or a mic inside a kickdrum.
Pattern control extending into the mid-bass region is necessary for sufficient gain-before-feedback. The lack of it can
mean excessive notch filtering and its audible by-products.
No device on the market today addresses all of these needs
like the M4. For this reason, the M4 has become a very
popular device for church sound systems.
Touring Systems
Touring companies utilize the M4 for many reasons, one
of which is that it provides the highest level of acoustic power
per watt available today. When you consider that a 3dB increase in efficiency can mean halving the number of midrange
amplifiers needed for a touring group, it becomes apparent
that a device that can provide both fidelity and efficiency is
what this market demands.
Voice Warning
Research has shown that the most effective emergency
warning systems should be capable of reproducing both voice
messages and warning signals. This means that robust
midrange reproduction is what is required. Massive areas
must be covered with sound, and reliability can mean life or
death to those involved. The M4 has found widespread use
in such applications, due to its efficiency and reliability.
Studio Monitors
From the earliest days of recording and playback technology, engineers have realized that the midrange is the key
band for accurate music reproduction. It is in this region
that the human ear/brain system is most sensitive to abrupt
shifts in the phase of the acoustic signal. Critical monitoring
applications require a device that can reproduce an entire
decade, beginning at about 250Hz and extending to about
2200Hz, without the nonlinearities produced by crossovers
and multiple devices. The M4 provides the accuracy that
engineers demand, and has found a home in some of the
top control rooms in the world.
Cinema Systems
The audio reproduction requirements of modern motion pictures are some of the most demanding in the sound
reinforcement world today. Movies require exemplary voice
reproduction in order to convey the dialog (and the plot) to
the audience. In addition to level and bandpass, the phase
response of the loudspeaker is critical to providing accurate
localization of on-screen dialog and effects. The M4 does
not require crossovers in the voice range (and their inherent
phase nonlinearities) making it an excellent choice for cinemas. It also has the power handling and transient response
needed for accurate reproduction of special effects.
10
A Multi-purpose Arena System
Built Around the M4
Two-years of abuse and no failures
Large indoor arenas are often plagued with severe
acoustical problems. Noise levels tend to be high,
reverberation times very long, and concave roof surfaces can
cause focused reflections that create severe intelligibility
problems. A possible solution is the use of extensive acoustical
treatment. A better solution is to implement a carefully
designed, well-controlled sound reinforcement system.
The Pepsi Coliseum of Indianapolis, IN is used for hockey,
public skating, equestrian events, tractor pulls, and exhibits.
The original system had very poor intelligibility when the ice
was in the arena, and insufficient level during tractor pulls.
The M4-based array solved both problems completely. Even
with a 4.5 second mid band reverberation time and strong
focused reflections, Percent Alcons scores are about 7% at
distant seats with no audience present. Improvement from
audience absorption brings intelligibility scores to the
excellent range.
Figure A is a TEF TDS measurement of the M4, PC1564
horn, and a coaxially mounted high-frequency horn/driver.
Both magnitude and phase are shown. While the magnitude
response is smooth and broad band, the phase response
reveals that these two devices are properly synchronized and
truly behave as a single device. This combination is capable
of delivering a direct sound-pressure level of 108dB at the
farthest seat in the venue (150 feet).
The main cluster in this arena consists of six of these
devices. Figures B, C and D show measurements made during
a performance test two years after the original installation.
The devices are extremely similar, with no failures during
that period, even though the system experienced almost
constant use. Sound personnel at the arena say that there
has never been an event that the system could not handle.
Figure A. Magnitude and phase response of the M4 CoAx system. The
1200 Hz crossover point is difficult to discern.
Figure B. Overlaid measurements of two M4 CoAx systems (two devices
from the same cluster)
Figure C. Overlaid measurements of three M4 CoAx systems (three
devices from the same cluster)
11
The First Baptist Church
of Orlando, FL
Three M4 Arrays provide high-level, low-distortion sound reproduction
for a 6200 seat house of worship
Sound reinforcement for worship spaces is one of the
most challenging tasks for the system designer. The needs of
the First Baptist Church of Orlando, FL. were as follows:
High-level voice and music reproduction
Very low distortion
Smooth full-range coverage of over 6000 seats
A stereo sound field for as many seats as possible
Pattern control to 250 Hz to minimize acoustic feedback
With these goals in mind, system designers Jim Carey,
Bill Thrasher and Phil Allison chose the M4 driver as the
nucleus of the system. This would assure that voice reproduction would be the best possible. By designing around
the midrange, the bandwidth of the system could then be
extended for full-range reproduction.
The system utilizes three (3) arrays containing six (6) M4
CoAx systems each. The arrays are arranged in a left-rightcenter arrangement, providing stereo reproduction for music and a point-source configuration for speech. M E is a measure of increased gain-before-feedback that can be achieved
with device directivity, and is very frequency dependent.
Large devices are required to extend ME down to the bass
region. The M4 pattern control horns provide an "ME factor"
that extends down into the 250 Hz region, resulting in excellent gain-before-feedback. The coaxial design provides a
smooth transition between the mid and high-frequency devices. Total electrical power is over 26,000 watts (approximately 35 horsepower), the vast majority of which is used
on the subwoofer and woofer systems.
The loudspeaker clusters were arrayed using a laser aiming system that projects the orientation of each device from
a single point in space. This arrangement best approximates
a common wavefront of spherically expanding sound with
minimal phase distortion due to device overlap, and has
become well accepted as an optimum method for arraying
horns.
The M4 CoAx systems used in these arrays received some
proprietary modifications from the system designers/installers. Bill Thrasher explains that for this application, the performance of the horns were improved by reducing the spacing between their acoustic centers (apparent apex). This
served to provide a better transition between the mid and
high frequency devices, and gave the smoothest attainable
coverage across the full coverage pattern of the device.
The spherical arraying technique developed by the system designers has
become an accepted method of arraying horns.
12
The Houston
Astrodome
A near twenty second low-frequency reverberation time made the management of
energy emitted from the sound system of prime importance.
When the Harris County Domed Stadium (better known
as the Astrodome) opened in Houston in 1965, it was the
first domed stadium in the world. Along with all of the benefits offered by an indoor arena of this magnitude came
acoustical problems that presented the system designers with
quite a challenge.
The original distributed loudspeaker arrays were stateof-the-art for the mid 1960's, and served the dome for an
almost unbelievable 25 years. System designer David Klepper
(then of Bolt Beranek and Newman) used many innovations
to make the system work, including tape delays for synchronization of the distributed arrays.
Acoustical studies of the venue revealed what everyone
had known for a long time, that the Astrodome was an acoustical nightmare. The reverberation time at 2kHz was in excess of 4 seconds, and it continued to rise for each lower
octave band to a high of 17.6 seconds at 63Hz. It was decided early in the process that acoustically treating the Astrodome would be too expensive for Harris County to consider in the foreseeable future. The sound system would have
to tame this harsh environment and provide intelligible
speech to all seating areas. In addition to the acoustic prob-
lems, strict budget and weight limitations were placed on
the project, and the maximum budget was set at $1 million.
It was known that the Community M4 driver could take
an enormous amount of power, was very efficient, and had
a proven track record in large system installations. Ford Audio/Video installed (10) M4 drivers on PC1542 horns for the
central array.
Another reason for using the M4 were the weight constraints placed on the system. The dome was already near its
maximum load capacity, and the prospect of suspending a
huge full-range array from the center was quickly ruled out.
The final design was a hybrid system, utilizing the M4 central cluster in conjunction with (12) circumferential loudspeaker clusters. This shortened the required throw distances,
distributed the loudspeaker load, and seemed like the best
overall compromise for the design.
The project proved to be a success, and the Astrodome
was tamed with innovative sound system design, well-controlled devices, and adherence to the most basic principle of
speech intelligibility: Preserve the integrity of the critical
midrange.
(10) Ten M4 drivers are at the core of this massive hybrid sound system.
13
Pegasus Studios
When Dave Engelke was called upon to outfit a state-of-the-art studio, he built the
proprietary monitors around the critical midrange.
Pegasus Studios of Tallahassee, Florida can handle virtually any project, from the recording of albums to the scoring
of motion pictures. Studio owner Butch Trucks, who gained
fame as drummer for the Allman Brothers Band, hired Dave
Engelke to update the original design of George L. Augspurger.
Engleke became a key player in revamping the studios interior to meet the latest in acoustic standards.
"Monitoring was a paramount consideration when we
built Studio A's control room, so we literally built the room
around the
speakers,"
Engelke revealed. "Our
goal was to
have a system
which was accurate, and
provided a
true representation of the
actual sounds
in the studio.
For that reason, we went
to great lengths
to create a
physical envir o n m e n t
which would
be conducive
to
proper
acoustical presentation, and
were highly selective about which components went into
the cabinets themselves."
After producing a series of prototype monitors, Engelke
settled upon a proprietary 4-way design he named E IV/D.
Standing 45 inches tall and measuring 38 inches wide by 24
inches deep, the cabinets each weighed 600 lbs. Not your
average square box by definition, the cabinets, like the shape
of the control room itself are highly geometric with many
angular planes. Power for the cabinets is provided by five
Crown amplifiers, while the crossover network was provided
by Creative Electronics of Nashville.
Engelke relates that he chose the M4 because of its strong
midrange performance, intelligibility, low distortion characteristics, and power handling capabilities. "We selected the
M4 because, in my estimation, the midrange section is too
often ignored when choosing the proper components for a
loudspeaker system," says Engelke. "I think people tend to
ignore the midrange because they are so preoccupied with
high-end response and low-end bass. As a result, when you
listen to some monitors, you find that the midrange band
simply isn't accurate in its representation of sound, especially with snare drums or the male vocal range. To illustrate
my point, try running a signal off of a snare drum into a
woofer. Without question, you will not obtain true reproduction of sound. Conversely, the same thing will occur when
you try to run sound from a low-end component into a high
frequency driver. Over the years, it became obvious to me
that something had to be done to get accuracy back into the
midrange spectrum, and that's where the M4 comes in. When
you look at the M4's total response, the midrange frequencies between 200 and 2000
Hz are just about as optimum as you can get for accurate performance."
For low frequency reproduction from 120Hz to
400Hz, a Crown Micro-Tech
1200LX powers twin TAD
15-inch woofers in each
cabinet. At 400Hz, the signals are crossed over into the
M4s, which are driven by a
Crown PSA2. At 1600Hz the
signals are routed to a TAD 4001 coupled with a Community SH864 horn, which can theoretically carry them up to
22kHz using the Crown PS400 amplifier.
The use of the M4 at Pegasus Studios helps to dispel the
myth that this device is only for large stadium arrays and
very long throw distances. Low distortion is one of the M4s
most appealing features, which makes it ideal for any application that requires exceptional fidelity in the critical
midrange.
14
The Orange Bowl
An experienced design/build team and the M4 driver bring the dreams for a new
sound system for the University of Miami to reality.
When the Miami Dolphins moved from the Orange Bowl
to Joe Robbie Stadium, one of the reasons cited was that a
better sound system was needed. The Joe Robbie system
was built around the M4 midrange driver, and became one
of the best examples to date of how to cover a large stadium
from one end zone. The success of that system gave birth to
a new system at the Orange Bowl. While there are many
differences in the system, the critical midrange was reinforced using the same proven device, the M4 driver.
Due to scheduling constraints, only two months were
available for the design and installation of the Orange Bowl
sound system. The project was financed by the University of
Miami, and $300,000 was allocated to ensure a professionally designed and installed system. Florida Sound completed
the design/build project in record time, drawing from their
turnkey capabilities and long-term experience in sound reinforcement. L.W. "Mac" McGowan and his crew carried the
project from the start, from generating the AutoCad drawings to calibration of the last amplifier level control.
The nucleus of the system is the M4 midrange driver.
Ten of these devices are used to cover the frequency band
extending from 260Hz to 1800Hz. The M4s are coupled to
the environment via ten (10) PC1542M 40x20 horns. The
bandpass from 1800Hz and up uses 38 PC442 horns, each
An excess of 3-to-1 ratio between high-frequency and
mid-frequency devices was required to produce
similar acoustic outputs.
driven by a single JBL 2245 driver. This 3.8 to 1 ratio between the number of high frequency and mid frequency
devices is not uncommon, and is a testimony to the massive
acoustic output of the M4. To round out the long-throw section of the array, Community VB664 bass horns are used,
and are loaded with (40) JBL 2226H drivers.
"Everything arrived on-site as planned," says McGowan,
"and out of hundreds of devices delivered, there were no
defects. Excuses wouldn't have helped me on game day, and
all of my suppliers helped make sure that I didn't have to
make any."
Is it possible to complete such a massive project in a
two-month time window? The powers that be at the University of Miami think so, who commented "It sounded like
they had been working on it for months, and not just weeks."
The Orange Bowl system, as viewed from the top and front
15
Cincinnati Music Hall
Cincinnati, Ohio
Low distortion was a main criteria in the design of a system for this
historic performing arts facility.
The Cincinnati Music Hall is a historic and architecturally impressive facility with a worldwide reputation for acoustical excellence. But even with fine acoustics, sound reinforcement is needed for many of the productions at the facility. Such a setting presents some difficulties for system
designers, who must balance fidelity and aesthetics in providing a workable system for the client.
A state-of-the-art sound system was needed to replace
the 15-year old column loudspeaker system in this historic
venue. Manager of the Music Hall, David Curry, explains,
"We were looking for the best quality system we could get
with the funds we had available, approximately
$160,000.00."
The new system had to solve some ongoing sound problems in the Music Hall, including poor coverage, poor frequency response, lack of definition and intelligibility, high
distortion and insufficient loudness. In addition, the system
had to keep up with the orchestra, which was producing
100dB average levels at the front edge of the balconies.
With these criteria in mind, system designer Charles C.
Baxley chose the M4 driver as the cornerstone of an elaborate array of constant directivity horns. This format would
allow well-defined coverage of the audience with minimal
overlaps in coverage between adjacent devices.
The main array consists of two long-throw Community
CB594 bass horns (60Hz - 250Hz) loaded with 18" JBL woof-
ers, five large format PC1542M pattern control horns and
two PC1564M pattern control horns, all loaded with the M4
driver (250Hz to 1250Hz), and seven CLS small format constant directivity horns with JBL drivers which are mounted
coaxially in the midrange horns. Additional front bass fill is
provided by one CLS CB594 dual 15-inch pattern control
reflex cabinet.
Why were such large horns necessary? According to
Baxley, "These devices have the pattern control needed to
achieve the extremely high intelligibility desired in this reverberant space. The Pops runs nominally at about 85dBSPL
with crescendos averaging 100dB, so we also needed a sound
system that could keep up with the high sound levels. If a
vocal or instrumental soloist performs, they need reinforcement against the full orchestra. We had to have a system
capable of reaching those same levels while maintaining the
low distortion required."
How does the system work? David Curry comments, "We
have been very pleased with the result. Usually after a show
we would have a fair number of complaints from people
who just couldn't hear well. Since the installation of the new
sound system, we've had no complaints whatsoever and I
am sure we won't in the future." Even performers have commented on its quality, he says, adding, "I believe we probably have the finest sound system anywhere."
A perfect example of an array design driven by
the physics of sound and the basic requirements of the
human ear/brain system.
16
Pro Player Stadium
(formerly Joe Robbie Stadium)
The reinforcement system for the home of the Miami Dolphins
is built around the M4 driver
The 75,00 seat Pro
Player Stadium of Miami,
Florida is host to one of
America's favorite football
teams, the Miami Dolphins.
After 21 successful years at
the Orange Bowl, the
Dolphins required a venue
with some additional
facilities, including a better
sound system.
Suitable loudspeaker
locations for outdoor stadiums are difficult to come by.
Distributed and central cluster systems aren't practical since
there is no ceiling structure from which to suspend
loudspeakers. Locating loudspeakers in several locations can
result in severe delay problems, since these locations can be
hundreds of feet (and milliseconds) apart. The solution for
Pro Player Stadium was to attempt coverage from a single
location high above an end zone, requiring massive acoustic
power generation to overcome the extremely long throw
distance. Large-format pattern control horns would serve to
deliver this acoustic energy equally to all seating locations.
The elaborate system was designed and specified by
Christopher "Topper" Sowden. The three-way main
loudspeaker system consists of twenty (20) low-frequency
enclosures operating from 60 Hz to 300 Hz, ten (10)
Community M4 midrange drivers with PC1542M patterncontrol horns operating from 300 Hz to 3 kHz, and thirtynine (39) JBL high-frequency horn/drivers to extend the
frequency response from 3 kHz to 16 kHz.
The end-zone cluster provides the powerful, clean sound
that is necessary for playback of full-range music and highlevel speech reinforcement over the extreme levels of crowd
noise present at a typical Dolphins game, while exhibiting
the durability and reliability needed to withstand the harsh
south Florida climate.
The massive end zone array is located above the scoreboard in an
80 x 16 x 10 foot room.
17
The Georgia Dome
Twenty-two distributed loudspeaker arrays are built around the M4 driver, making
communication with 75,000 people possible in this massive space.
The 75,000 seat Georgia Dome of downtown Atlanta
was built with all of the known acoustical problems inherent
in domed stadiums. Long reverberation times and crowd
noise levels in the 90dBA range meant that the sound system would play a crucial role in the usability of the space.
One of the primary goals of this type of system is maximizing the direct-to-reverberant energy ratio at each listener
seat. When considering the energy from the sound system,
this means that directivity (Q) must be used to focus the
energy into the audience. A live audience has an absorption
coefficient of about .7, meaning that 70% of the energy that
strikes it will be absorbed and only 30% returned to the environment. This means that the direct sound energy can be
reduced by about 6dB before being reflected into the space
and causing reverberation.
The massive design project was placed in the hands of
consultant Ron Baker, who used his experience and computer modelling to arrive at the optimum design for the dome.
Baker determined that 22 distributed loudspeaker clusters
would be required to generate the high SPL's required. Each
cluster would be a three-way design, utilizing a dual 15inch direct radiator enclosure for the lows, large-format horn/
driver combinations for the midrange, and a high-frequency
horn/driver combination to match the coverage pattern of
the midrange.
Given all of the requirements of the project, Baker chose
the M4 driver as the heart of the system. "The Community
large-format midrange horn enhanced the speech clarity in
the Georgia Dome's reverberant space to a great degree,"
Baker said. "We have used it in several indoor and outdoor
facilities with success, and continue to think of it as a special
product for these types of applications."
The arrays are located about 130 feet above the lower
audience seating areas, and are separated from each other
by roughly 50 feet along the sides of the dome, and about
30 feet on the ends.
The system was installed by Ancha Electronics of Norcross,
Georgia and was completed in time for the Atlanta Falcons
football season in September. Operating in mono, the system provides intelligible speech as intended, along with music
quality approaching full-blown concert-level systems. "We
didn't intend to get 115dB out of the system," says Baker,
"but in the end it could easily produce 105 to 110dB peaks.
Directivity control can be more useful than acoustical
treatment in such spaces, and the M4 allows the absolute
optimum performance possible for the midrange, providing
the needed SPL's with low distortion, using the smallest possible amount of amplifier power and producing the least
amount of heat.
The arrays for the Georgia dome are suspended from
catwalks, and tower 130 feet over the lower audience area.
18
The Pennsylvania
Convention Center
This multi-purpose ballroom utilizes M4 CoAx systems in the main cluster.
Convention centers are especially challenging to the system designer. Not only must the system work for many types
of events, each performer expects the system to operate as
though it were designed specifically for their use. This requires the system designer to balance many criteria when
combining excellent performance with versatility.
The Pennsylvania Convention Center is just such a multipurpose facility. It's 30,000+ square-foot ballroom hosts
many types of events, from concerts to corporate parties.
The ballroom stage is located on a long wall of the rectangular venue. A full-range loudspeaker array is located over the
stage, and is called upon for reinforcement when acoustic
localization to the stage is required.
Stephen Siegel of Acentech explains that the ballroom
can be subdivided into two smaller rooms by a moveable
partition wall. When this occurs, the main array is isolated
from the smaller section, and the distributed overhead system is used. When an event utilizes the stage, the main array is used because it provides sufficient level and coverage
to handle about any event that requires sound reinforcement.
The main array consists of three (3) M4 CoAx systems,
and four (4) dual-fifteen inch bass enclosures, located in an
elaborate support truss. The three Coax systems provide a
full 180 degrees of horizontal coverage.
Pattern control and reliability were the main reasons for
choosing the M4-based system, and, according to Siegel,
the powers that be at the Pennsylvania Convention Center
are very pleased with the choice.
Design and drawings by Washington Professional Systems,
Mt. Laurel, NJ
19
Jacobs Field
The M4 brings the game to the fans of the Cleveland Indians, in their newly constructed 42,400 seat "baseball only" stadium.
Jacobs Field, a 42,400 seat "baseball only" facility, is the
home of the Cleveland Indians. When the time came to
outfit the facility with sound, the call went to WJHW of Dallas, a well-known audio and acoustical consulting firm affectionately known within the industry as "The Radio Station."
Ron Baker of WJHW is an industry leader in designing sound
reinforcement systems for such facilities, his success being
attributed to his ability to repeatedly design reliable systems
that get the job done.
The audio requirements for Jacobs Field were not unlike
those of the other large, outdoor sports facilities in existence. They needed a full-range reinforcement system that
could generate high SPLs over long distances with good
speech intelligibility. To meet these design goals, Baker designed an elaborate distributed loudspeaker system. He chose
to build the system around the midrange, the M4 compression driver being the device of choice. The M4's, coupled to
PC1542M horns, were installed in openings within the up-
per deck canopy about 40 feet apart. From this location they
effectively provide coverage to the first 12 rows of lower
level seating.
Upon its introduction, the M4 provided the professional
sound industry with a tool that has led to the development
of new design philosophies for stadiums and other applications. Systems simply sounded better when the proper attention was given to the critical midrange decade. In summing up the performance of the M4 design employed at
Jacobs Field, Baker states that "the balance of the main loudspeaker system is very good. Particularly with the way that
the M4s firing from the canopy blend in so well with the
more localized enclosures. Upper deck volume levels are
well under control."
Installing contractor Ed Simon adds, "Reliability is crucial, because when you're making a service call 250 feet in
the air in 30 degree weather with a 25 mph wind, while
standing on an eight-inch beam, the best service call is one
you don't have to make."
Indians fans expect only the best in audio and video entertainment at the
Indians home games. Sound system designer Ron Baker chose the M4
driver to be the heart of this state-of-the-art stadium system.
The arrays are located about 40 feet apart, and are suspended from the
canopy of the upper deck. Due to the precarious location, reliability was a
key factor in choosing system components.
20
Concert Audio
Bellville, South Africa
"The basic system we have, is to say the least, very impressive. It handles 6000 people
with loud rock program, no problem!"
Chris Rossouw
Concert sound systems must provide the fidelity and performance that superstars demand and expect, and they must
do so consistently and reliably. In this highly competitive end
of the audio business, poor devices identify and disqualify
themselves very quickly.
Concert Audio of Bellville, South Africa has built their
touring systems around the M4 driver. The M4's ability to
deliver high SPLs with excellent efficiency has made it an
optimum choice for this application. Since the M4 runs cooler
than any other driver in its class, efficiency in this case means
that there are fewer component failures. Even at a torturous
250Hz low-frequency crossover point, the M4 performs its
task of low distortion midrange performance.
Concert Audio has experimented with many configurations of its Unibell concert system, each utilized to provide
various degrees of coverage as the application demands. This
"building block" approach allows the systems coverage to be
modified as needed through various arrangements of devices.
This method of coverage adaptation is one of the few
tools that the touring system designer has in order to adapt a
system to a particular arena. Full-range cabinets are not nearly
as versatile, since the various components cannot be as closely
coupled due to the constraints from the box itself. With the
modular approach of the Unibell system, the lows, mids and
highs can be packed individually, resulting in better pattern
definition.
The bottom system (pictured at right) is capable of producing greater than 120dB at 25 meters. Note the ratio of
mid to low-frequency devices, and the mid to high-frequency
devices. Even at these levels, the M4 is operating well below
its maximum output capability.
Low-Frequency
Section
Midrange Section
(M4 Driver)
High-Frequency
Section
Standard full-range configuration (Total amplifier power 6400WRMS)
Narrow horizontal and vertical pattern for long-throw
applications.(24kWRMS)
Wide horizontal pattern and narrow vertical pattern. Excellent when
arrays must be placed at stage level. (24kWRMS)
21
Paramount Studios
Theater
A cinema system utilizes the M4 to reproduce the critical midrange for
motion picture soundtracks
The accurate reproduction of a motion picture soundtrack
can require the accuracy of a studio monitor, but at much
higher output levels. Many products are available that can
provide the needed levels, but when low distortion and
smooth phase response are required, the field narrows
quickly.
Speech reproduction is especially important for motion
picture soundtracks. For moviegoers to fully experience the
motion picture, they must be able to follow the dialog. The
speech must be intelligible, and it must provide proper localization to the correct area of the screen. Since localization is highly dependent upon the phase response of the
transducer, crossovers (and their inherent nonlinearities)
should be avoided in the speech decade. Oddly enough,
the search for the optimum device led studio personnel to a
transducer that was widely used in stadium and arena reinforcement.
In an effort to implement the required accuracy into their
studio theater, Paramount Pictures chose the M4 driver as
the device of choice to reproduce the critical midrange. The
M4 provided the high levels, low distortion and smooth phase
response that the theater demanded. Dialog reproduction
was the main factor in choosing the M4, and the rest of the
system was designed around this key component.
The system consists of five (5) full-range loudspeaker ar-
rays spaced evenly behind the projection screen. All devices
are from Community Professional Loudspeakers, and are
bandpassed as follows:
High Frequencies 1300 - 16kHz
Mid Frequencies 280 - 1300Hz
Low Frequencies 60 - 280Hz
Sub Bass 25 - 60Hz
The center array uses a 90 x 40 pattern control horn,
while the side arrays utilize 60 x 40 dispersion. This configuration was chosen to help keep energy off of the side walls.
Paramount Studios is quite pleased with their choice of
the M4, as the system works quite well. As the understanding of the need for accurate midrange reproduction increases,
the M4 will certainly become a standard part of cinema systems worldwide.
The Paramount Studio Theater system consists of
five four-way arrays spaced evenly behind the
projection screen.
22
Busch Stadium - St. Louis, Mo
Busch Stadium is an excellent example of how the architecture of the space should drive the design of the loudspeaker arrays. A proprietary design was used for the circumferential loudspeaker system, allowing coverage of the
under-roof and open-air seats from a single under-roof location.
In this innovative approach the M4 driver and horn are
coaxially mounted with the low-frequency device, yielding
the best approximation of a true full-range point-source possible.
Wading River High School
Shoreham, NY
The Shoreham Wading River High School's 6,700 squarefoot, 800 seat auditorium needed a new sound system that
would provide coverage for the middle section of the seating area and improve intelligibility overall. For this application, the two M4 drivers are mounted on Community
SH2064M midrange horns, providing a more compact array
that could be recessed into the ceiling.
According to school officials, the sound system now offers low distortion and improved vocal clarity, as well as the
ability to project over the entire seating area.
Kezar Municipal Stadium
San Francisco, CA
Directivity for the seating area was optimized by using
18 Community horn/drivers distributed in groups of nine at
promenade level on each side of the playing field from end
zone to end zone. "The horns are PC1594Ms, while the
drivers are M4s," explains project manager Jim Thielemann.
"They are mounted atop 40-foot poles and aimed down at
the stands. The resulting performance is strong, highly intelligible, and features tight pattern control, which is what was
intended to keep sound out of the surrounding areas."
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Chapel Hill Harvester Church
With a 200 member choir, 50-piece orchestra, and the
Cathedral singers, the Chapel Hill Harvester Church required
a sound system that would prove to be a prototype for the
church of the nineties. The 7000 seat Cathedral of the Holy
Spirit demanded a state-of-the-art system to meet its needs.
This was provided with the installation of a central cluster loudspeaker system built around the M4. The 3-way coaxial system has met all of the demands placed on it by the
church.
According to the staff, "Even when sound pressure levels
are hovering around 112dB during music programs, the system distortion is almost imperceptible."
Bellville Sport Complex
Bellville, South Africa
The field, track and outer perimeter of this large, outdoors sports complex are covered by a three-way loudspeaker
array. The roof-mount cluster is comprised of two CB594
bass horns, three PC1542 horns (M4 loaded) and three
PC242 high-frequency horns.
To protect against the harsh South African sun, all of the
Community fiberglass horns were coated with a white ultraviolet-reflecting topcoat resin.
The Target Center
Minneapolis, MN
NBA games in the nineties are multimedia events, and
demand massive audio and video systems to deliver the event
to large, noisy crowds.
The home of the Minnesota Timberwolves has been
served well by its 3-way loudspeaker system built around
the M4 driver. The circumferential cluster circles the
scoreboard, and provides speech and music reinforcement
to crowds exceeding 18,000 people.
The combination of high fidelity and "acoustic muscle" is
ideal for such venues, and makes the M4 the first choice of
arena design consultants worldwide.
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Bibliography
Sound System Engineering, Don and Carolyn Davis, Second Edition 1987 Howard W. Sams and Company
"Horns: Their Function, Measurement, Arraying and Alignment Workshop" Syn-Aud-Con Tech Topic supplement to
Newsletter Vol. 20 No. 2, by Don and Carolyn Davis
A High-Efficiency, One-decade Midrange Loudspeaker, by Bruce Howze and Clifford Hendrickson
"The Revival of a Horn Within a Horn" by Don Davis, Sound and Communication Vol. 38 No. 2
"Cincinnati Music Hall's New Sound System" by Lisa J. Ford, InView Fall 1990
"Joe Robbie Stadium" by Allan R. Carlson, Sound and Video Contractor Nov. 1987
"No Second Chances at the Orange Bowl" by Gregory A. Detogne, Sound and Video Contractor April 1991
"School of the Arts Features Artistic Sound" by Gregory Detogne, Sound and Video Contractor Jan. 1991
"Chapel Hill Harvester Church" by Bob Ditzler, Sound and Communications March 1992
"The Target Center" by Henry Sanford, Sound and Video Contractor Nov. 1990
"The Bellville Sports Complex" by Greg Detogne, Sound and Video Contractor April 1990
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