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®®
®
SentrySentry
Sentry
SentrySentry
®®
100A 100A
100A
100A 100A
Professional
Monitor System
••
Near-field monitor for post productionNear-field monitor for post production
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Near-field monitor for post production
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Near-field monitor for post productionNear-field monitor for post production
and live soundand live sound
and live sound
and live soundand live sound
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Wide, uniform coverageWide, uniform coverage
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Wide, uniform coverage
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Wide, uniform coverageWide, uniform coverage
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Extremely smooth frequency responseExtremely smooth frequency response
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Extremely smooth frequency response
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Extremely smooth frequency responseExtremely smooth frequency response
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High power handlingHigh power handling
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High power handling
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High power handlingHigh power handling
Descriptions
The Electro-Voice Sentry
speaker system is the direct result of “human engineering” with the broadcast/recording studio engineer in mind. This system has
high efficiency, extended low-frequency
range, and a uniform frequency response and
dispersion, in a compact, no-frills package.
The Sentry 100A employs a Super-Dome
tweeter capable of handling 25 watts of input power (most tweeters operate in the 5watt range), while faithfully reproducing the
program material with response out to 18,000
Hz and uniform dispersion (120° at 5,000
Hz). Never again will accidental, high-frequency blasts from tape head contact (in rewind/fast-forward mode) leave a curl of
smoke where a tweeter used to be. The lowfrequency section is an 8 in. direct radiator
woofer installed in an optimally vented enclosure with fourth-order Butterworth tun-
1
ing.
The optimally vented design is responsible for the unusual combination of small
size, extended bass response and high efficiency. Such performance is simply not available in other enclosures of similar size.
The Sentry 100A is housed in a utility cabinet wrapped in a special, scratch-resistant,
®
100A monitor
TM
matte black vinyl. The cabinet size is intentionally designed for rack mounting. When
coupled with the SRB-7 rack-mount/wallmount kit, the Sentry 100A can be integrated
into virtually any environment that demands
conservation of space, such as mobile recording studio facilities. The steel-reinforced
grille is covered with a custom gray cloth.
This provides maximum protection, acoustic transparency and a pleasing aesthetic
quality.
Loudspeaker Response Due To The
Acoustical Environment
Several factors must be considered when determining the overall response of a speaker
system in any listening environment: physical characteristics of the room itself, placement of speakers, and position of the listener.
As pointed out in several texts on room
acoustics, as the source-listener distance increased, the sound pressure level (SPL) decreased in the direct field at a steady rate (inverse square law: 6 dB drop for every doubling of distance) until a certain distance is
reached. This point is often called the critical distance (D
approaches a constant value (the reverberation field). The listening position in the sound
). Beyond this point, the SPL
C
field determines the amount of acoustic
power output of the speaker system needed
to produce a certain sound pressure level at
the engineer’s ears. Generally speaking, the
amount of power output needed from the
speaker/amplifier system decreases as the
room becomes smaller and/or more reverberant (shorter critical distance). In most
cases, the audio engineer will be working
well within the direct field. If indeed this is
the case, the amplifier power requirement is
entirely dependent on the loss in SPL due to
inverse square law.
The low-frequency response of the overall
system can be adversely affected by poor
placement of the monitor speakers themselves. The Sentry 100A was designed for
- to 1/2-space use. This requires that the
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speaker system be mounted as close as possible to floor/ceiling and/or wall surfaces.
Placement in loose cavities or resonant
mountings can also seriously degrade the
overall response.
___________________
1. A.N. Thiele, “Loudspeakers in Vented Boxes: Part 1,” J.
Audio Engineering Society, Vol. 19, No. 5, pp 386-387
(1971).
1
/
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Sentry® 100A Professional Monitor System
SpeakerPlacement For Good Stereo
Imaging
Results of testing by Electro-Voice and others, such as Juhani Borenious
2
, suggest a recommended listening angle y of 60° ±10° for
an optimum stereo image. Rather than measure an imaginary angle, exact positioning
can be obtained by placing the speakers so
that the ratio of distances h/b = 0.9 ±0.2. The
stereo image that results is further reinforced
by the uniform dispersant characteristics of
the Sentry 100A, particularly in the higher
frequency range, where the majority of stereo information lies. Off-axis degradation of
frequency response cannot be corrected by
supplementary equalization. It is therefore
critically necessary to use a speaker system
with uniform directivity as well as smooth
on-axis response.
Sentry® 100A Professional Monitor System
Power Handling Capacity
Power handling specifications are usually
meaningless because they fail to indicate the
nature of the test signal and/or how this test
signal relates to actual use. The 30-watt
specification for the Sentry 100A is based
on filtered random noise (FM interstation
noise and tape hiss are common forms of
random noise), which is fed to the speaker
for an extended time (more than 15 hours).
Random noise testing is used because, like
real music and speech program material, it
contains many frequencies at once. Low frequencies, which cause large excursions of
the woofer suspension, are present; and mid
bass frequencies, which contribute mainly to
woofer voice-coil heating, are present as
well. Thus the woofer is simultaneously
tested for mechanical fatigue and voice-coil
overheating. Similarly, the tweeter is tested
for both mechanical and thermal failure at
appropriate power levels.
There is no generally accepted standard for
testing loudspeakers for power capacity. At
Electro-Voice, we expect each speaker and
system to survive 15 hours continuous application of rated power without failure of
any component or permanent change in performance.
One noise test standard, the West German
D.I.N. 45573, specifies the random noise
2
spectrum. This spectrum agrees approximately with studies of voice and music spectra that appear in several textbooks on acous-
3,4
tics.
However, only a very small percentage of the power applied to a Sentry 100A
would be in the range of the tweeter using
this spectrum.
A study done by John P. Overley of Electro-
5
Voice
resulted in the more realistic spec-
trum.
The curve shows the relative levels in octave bands of average peak energy found in
many musical passages of a symphony orchestra. “Based upon peaks as short as a fraction of a second in duration . . . it represents
the approximate distribution of energy vs.
frequency under highest signal conditions . .
. exactly those conditions which should determine the power handling requirements of
audio components.”
6
The musical passages
were taken from disc recordings that were
played back on “carefully equalized high
quality transcription equipment.”
7
The test signal actually used in developmental testing of the Sentry 100A is shown in
Figure 9. It is an approximation to measured
spectra of the output of a lead guitar amplifier driven into heavy clipping, and represents a worst-cast situation. The Sentry 100A
will survive 30 watts of this input for at least
15 hours.
The power-handling specification applies to
long-term application of power; for short duration peaks, the loudspeaker system is capable of handling many times the rated
power. For example: for a few milliseconds,
the system will handle 10 dB peaks; if the
average input power level were 30 watts,
then it would handle peak power inputs on
the order of 300 watts.
Crossover Network
The integral crossover network is a 12-dB/
octave dual-section type, crossover occurring at 2,000 Hz. In addition, the Sentry 100A
has a continuously variable, shelf-type highfrequency control which allows adjustment
____________________
2. Juhani Boreniou, “On Loudspeaker Response in Sound
Control Rooms,” J. Audio Engineering Society, preprint
(1980).
3. H.F. Olson, PhD., “Acoustical Engineering,” D. Van
Nostrand Company, Inc., Princeton, New Jersey, p. 588
(1957).
4. L. Beranek, “Acoustics,” McGraw-Hill Book Company,
New York, p. 338 (1954).
for individual listening preferences, with
both boost and cut capability (+2 dB to –4
dB from nominally flat). The high-frequency
control is conveniently located on the front
panel for easy access.
SRB-7Rack Wall Mount Kit
One of the fundamental design requirements
for the Sentry 100A provided for the ability
to install the system in standard EIA 19 in.
racks. The hardware needed for this procedure is available as an optional kit. This same
kit provides for flush and angle wall-mounting as well. (Refer to the SRB-7 engineering data sheet for complete details.)
A second nameplate, which can be applied
over the original label, has been included
for those situations where mounting the Sentry 100A in an inverted position is preferred
(woofer nearer to ceiling).
warning:
Never mount the Sentry 100A by the back
panel or by only one of the other panels.
Failing to comply with this will cause the
panel to separate, resulting in the speaker
falling. For the safest method of mounting
the Sentry 100A, Electro-Voice strongly suggests using the Model SRB-7 rack/wall
mounting kit.
______________________
5. John P. Overley, “Energy Distribution in Music,” IRE
Transactions of Audio, Vol. AU-4, No. 5, Sept.-Oct.
(1956).
6. Ibid. p. 121.
7. Ibid. p. 121.
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Sentry® 100A Professional Monitor System
Limited Warranty
Electro-Voice products are guaranteed
against malfunction due to defects in materials or workmanship for a specified period,
as noted in the individual product-line
statement(s) below, or in the individual product data sheet or owner’s manual, beginning
with the date of original purchase. If such
malfunction occurs during the specified period, the product will be repaired or replaced
(at our option) without charge. The product
will be returned to the customer prepaid. Ex-
clusions and Limitations: The Limited
Warranty does not apply to: (a) exterior finish or appearance; (b) certain specific items
described in the individual product-line
statement(s) below, or in the individual product data sheet or owner’s manual; (c) malfunction resulting from use or operation of
the product other than as specified in the
product data sheet or owner’s manual; (d)
malfunction resulting from misuse or abuse
of the product; or (e) malfunction occurring
at any time after repairs have been made to
the product by anyone other than ElectroVoice Service or any of its authorized service representatives. Obtaining Warranty
Service: To obtain warranty service, a customer must deliver the product, prepaid, to
Electro-Voice Service or any of its authorized service representatives together with
proof of purchase of the product in the form
of a bill of sale or receipted invoice. A list
of authorized service representatives is available from Electro-Voice Service at 600 Cecil
Street, Buchanan, MI 49107 (800/234-6831
or FAX 616/695-4743). Incidental and
Consequential Damages Excluded: Product repair or replacement and return to the
customer are the only remedies provided to
the customer. Electro-Voice shall not be liable for any incidental or consequential damages including, without limitation, injury to
persons or property or loss of use. Some
states do not allow the exclusion or limitation of incidental or consequential damages
so the above limitation or exclusion may not
apply to you. Other Rights: This warranty
gives you specific legal rights, and you may
also have other rights which vary from state
to state. Electro-Voice Speakers and
Speaker Systems are guaranteed against
malfunction due to defects in materials or
workmanship for a period of five (5) years
from the date of original purchase. The Limited Warranty does not apply to burned voice
coils or malfunctions such as cone and/or coil
damage resulting from improperly designed
enclosures. Electro-Voice active electronics
associated with the speaker systems are guaranteed for three (3) years from the date of
original purchase. Additional details are included in the Uniform Limited Warranty
statement.
For warranty repair or service information, contact the service repair department
at: 616/695-6831 or 800/685-2606.
For technical assistance, contact Technical
Support at 800/234-6831 or 616/695-6831,
M-F, 8:00 a.m. to 5:00 p.m. Eastern Standard Time.
Specifications subject to change without
notice.
Sentry® 100A Professional Monitor System
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Sentry® 100A Professional Monitor System
FIGURE 1—Axial Frequency Response,
2 Volts/3 Feet
FIGURE 2—Dimensions
Sentry® 100A Professional Monitor System
43.8 cm
(17.25 in.)
FIGURE 5—Impedance vs Frequency
FIGURE 6—Polar Response
30.5 cm
(12.0 in.)
28.2 cm
(11.13 in.)
FIGURE 3—Directivity vs Frequency
FIGURE 4—Beamwidth vs Frequency
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Sentry® 100A Professional Monitor System
Specifications
Frequency Response, 1 Meter on Axis,
Anechoic Environment, Swept One-
Third-Octave Pink Noise ±3 dB:
45-18,000 Hz
Half-Space Reference Efficiency:
0.6%
Dispersion Angle Included by 6-dB-Down
Points, 10 Foot Microphone Distance,
Anechoic Environment, One-Third Oc-
tave Bands of Pink Noise,
Horizontal:
250-6,300 Hz (158° ±32°)
8,000-20,000 Hz (55° ±18°)
Vertical:
250-6,300 Hz (140° ±40°)
8,000-20,000 Hz (52° ±13°)
Maximum Midband Acoustic Output
Power:
0.18 watt
Crossover Frequency:
2,000 Hz
Sound Pressure Level at 1 Meter, 1 Watt
into Nominal Impedance, Anechoic Envi-
ronment, 300-2,000 Hz Average:
91 dB
EIA Sensitivity Rating (on axis measure-
ment):
41.8 dB
Long-Term Average Power Handling Ca-
pacity (above 40 Hz):
30 watts
Short-Term Power Handling Capacity (10
milliseconds) (above 40 Hz):
300 watts
Nominal Impedance:
6 ohms
Minimum Impedance:
4.5 ohms
Optional Accessory:
SRB-7 rack-mount/wall-mount
brackets
Dimensions (see Figure 2),
Height:
43.8 cm (17.25 in.)
Width:
30.5 cm (12.00 in.)
Depth:
28.2 cm (11.13 in.)
Net Weight:
12.7 kg (28 lb)
Sentry® 100A Professional Monitor System
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Sentry® 100A Professional Monitor System
Sentry® 100A Professional Monitor System
600 Cecil Street, Buchanan, MI 49107
616/695-6831, 616/695-1304 Fax
MONITORS—Professional Monitor System Part Number 532077—9943
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©EVI Audio 1999 • Litho in U.S.A.
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