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Sentry® 100A Professional Monitor System
Sentry® 100A Professional Monitor System
2
SpeakerPlacement For Good Stereo
Imaging
Results of testing by Electro-Voice and oth-
ers, such as Juhani Borenious
2, suggest a rec-
ommended listening angle y of 60° ±10° for
an optimum stereo image. Rather than mea-
sure 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 ste-
reo 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.
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 fre-
quencies, 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 ap-
plication of rated power without failure of
any component or permanent change in per-
formance.
One noise test standard, the West German
D.I.N. 45573, specifies the random noisespectrum. This spectrum agrees approxi-
mately with studies of voice and music spec-
tra that appear in several textbooks on acous-
tics.
3,4 However, only a very small percent-
age 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-
Voice
5 resulted in the more realistic spec-
trum.
The curve shows the relative levels in oc-
tave bands of average peak energy found in
many musical passages of a symphony or-
chestra. Based upon peaks as short as a frac-
tion of a second in duration . . . it represents
the approximate distribution of energy vs.
frequency under highest signal conditions . .
. exactly those conditions which should de-
termine 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 developmen-
tal testing of the Sentry 100A is shown in
Figure 9. It is an approximation to measured
spectra of the output of a lead guitar ampli-
fier driven into heavy clipping, and repre-
sents 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 du-
ration peaks, the loudspeaker system is ca-
pable 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 occur-
ring at 2,000 Hz. In addition, the Sentry 100A
has a continuously variable, shelf-type high-
frequency control which allows adjustmentfor 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 proce-
dure is available as an optional kit. This same
kit provides for flush and angle wall-mount-
ing as well. (Refer to the SRB-7 engineer-
ing 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 Sen-
try 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 sug-
gests 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. ____________________
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).
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Sentry® 100A Professional Monitor System
Sentry® 100A Professional Monitor System
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Limited Warranty
Electro-Voice products are guaranteed
against malfunction due to defects in mate-
rials or workmanship for a specified period,
as noted in the individual product-line
statement(s) below, or in the individual prod-
uct data sheet or owners manual, beginning
with the date of original purchase. If such
malfunction occurs during the specified pe-
riod, 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 fin-
ish or appearance; (b) certain specific items
described in the individual product-line
statement(s) below, or in the individual prod-
uct data sheet or owners manual; (c) mal-
function resulting from use or operation of
the product other than as specified in the
product data sheet or owners 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 Electro-
Voice Service or any of its authorized ser-
vice representatives. Obtaining Warranty
Service: To obtain warranty service, a cus-
tomer must deliver the product, prepaid, to
Electro-Voice Service or any of its autho-
rized 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 avail-
able from Electro-Voice Service at 600 Cecil
Street, Buchanan, MI 49107 (800/234-6831
or FAX 616/695-4743). Incidental and
Consequential Damages Excluded: Prod-
uct repair or replacement and return to the
customer are the only remedies provided to
the customer. Electro-Voice shall not be li-
able for any incidental or consequential dam-
ages including, without limitation, injury to
persons or property or loss of use. Some
states do not allow the exclusion or limita-
tion 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 againstmalfunction due to defects in materials or
workmanship for a period of five (5) years
from the date of original purchase. The Lim-
ited 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 guar-
anteed for three (3) years from the date of
original purchase. Additional details are in-
cluded in the Uniform Limited Warranty
statement.
For warranty repair or service informa-
tion, 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 Stan-
dard Time.
Specifications subject to change without
notice.
