Electro-Voice T251i User manual

Description
The compact, trapezoidal-shaped Electro-Voice
T251i is a 400-watt, two-way, biampable, con-
stant-directivity speaker system. The system
combines professional-quality components,
arranged in a time-coherent vertical array,
with an unusually robust, installation-
friendly,ventedenclosure. The result is clear
and articulate, high-quality sound for per-
manent installation.
The enclosure is constructed of 13-ply void-
free,birch plywood. This high-strength shell
is painted with a textured, neutral, white
paint. Suspension hardware is preinstalled
and three eyebolts are included in the ship-
ping carton. Small rubber feet and mount-
ing screws are also included but not attached
to each system for the less likely situation
where the system will not be suspended.
The high-frequency section of the T251i uti-
lizes a 60° x 40° constant-directivity horn
driven by a wide-bandwidth, two-inch tita-
nium-diaphragm DH2T driver. This driver
uses a unique convex-drive phasing plug
structure for smooth and extended high-fre-
quency performance. The voice coil is
coupled to the diaphragm with EV’s exclu-
sive Resonant DriveTM technology. This in-
creases and smooths the high-frequency re-
sponse and reduces the amount of internal
equalization required for flat frequency re-
sponse.
EV’s self-resetting PROTM circuitis built into
the crossover network to guard the compres-
sion driver from damage. If input power to
the driver exceeds the nominal rating, the
PRO™ circuit is activated, reducing the
power delivered to the driver by 6 dB. The
system will remain in this mode of opera-
tion until input power is reduced to a safe
level.
Ring-Mode Decoupling (RMDTM)
The T251i controls both acoustical and
mechanical ring modes to provide dra-
matically increased intelligibility, using
techniques learned from the development
of the Electro-Voice X-Array™ concert
speakers. There is much less coloration
of the sound from resonating sources,
leaving only the intended sound to be
heard by the audience. The optimally
vented bass section of the T251i is designed
using Thiele-Small parameters for efficient
performance to below 50 Hz. The DL15ST
high-excursion 15-inch woofer features be-
ryllium copper lead wires with a low-mass,
extended-length, edge-wound voice coil and
high-temperature materials. EV’s unique
Thermo Inductive Ring (TIRTM) is placed on
top of the pole piece, where the extended-
lengthvoicecoilwouldnormally be exposed,
placing metal in close proximity to the coil
and providing a major heat-transfer path that
helps keep the voice coil cool.
Notes on Installation
Any suspension system is only as strong as
its weakest link. The installer must ensure
the top mounting points have sufficient load
bearingcapability to safely suspendthe cabi-
net. The initial support cables or chains
should be as close to vertical as possible and
never more than 30° from vertical. Once the
system is installed none of the chains or
cables should touch or rub against the cabi-
net. Local codes and regulations, if they
exceed Electro-Voice’s recommendations,
should be followed at all times.
Electro-Voice recommends that a safety fac-
tor of at least 8:1 be adopted. The
Electro-Voice HS-style suspension compo-
nents supplied in the T251i exceed this rec-
ommended safety factor when the system is
installed in compliance with Electro-Voice
recommendations.
T251i
Trapezoidal Speaker
System
• HS-style suspension hardware is
preinstalled, eyebolts are included
and may be suspended vertically or
horizontally
• Enclosure is paintable (supplied with
white textured paint)
• Ring-Mode Decoupling (RMDTM) for
increased intelligibility
• PROTM circuit provides HF driver
protection
• Rotatable constant-directivity
60° x 40° horn
• High-excursion, 400 W, DL15ST 15-in.
woofer
• Biampable, passive network in-
cluded

T251i Trapezoidal Speaker System
T251i Trapezoidal Speaker System
2
Itis the installer’sresponsibility toensure
thespeaker system has been installedcor-
rectly. Electro-Voice strongly recom-
mends that all suspended items be in-
spected at least once a year and any dam-
aged parts be replaced immediately.
All Electro-Voice HS- and HST- systems
follow the same principles. Put minimum
stress on the cabinet and make each cabinet
hang independently of any other device.
Suspending the Electro-Voice T251i
Speaker System
Part of the T251i’s versatility is that it can
be mounted either vertically or horizontally,
and has a rotatable horn. The mounting sys-
tem is conceptually very simple. Two alu-
minumtubespassverticallythrough the cabi-
net and each is secured via two oversize cast
brackets (threaded flanges). The enclosure
issandwiched between thefour (two on each
end) brackets. The enclosure is essentially
resting between the brackets.
When installing the T251i, two of the three
suppliedforged eyebolts are screwed intothe
uppertwo brackets. The third eyebolt should
be screwed into the appropriate T-nut on the
rear panel of the enclosure. When mount-
ing the enclosure vertically, use the lower
T-nut. When mounting the enclosure hori-
zontally, use the T-nut located in the center
of the rear panel of the enclosure. This is
necessary for aiming the system. The center
of gravity is arranged so the enclosure is di-
rected towards the ceiling. In order to pro-
vide a downward or horizontal projection
angle, the pull-up point must be used.
Ifmultiple cabinets are to be suspended,each
system requires its own rigging points. Sys-
tems should not be suspended from each
other. The eyebolts must be connected us-
ingsuitably rated chain withconnectors such
as shackles or threaded chain connectors, or
suitably rated aircraft cables to suspend and
aim the system.
Constant-Directivity Speaker System
The crossover frequency and speaker com-
ponentgeometries have been selected so that
the directional characteristics of the woofer
and constant-directivity horn match at the
crossover frequency (approximately 90° cir-
cular coverage patterns for each) to create a
special system type—the constant-directiv-
ity system. At higher frequencies the hori-
zontalcoverage pattern remains constant and
the vertical pattern smoothly transitions to a
40° angle above 4,000 Hz. Response within
the 60° x 40° rated coverage angle is uni-
form, which means dependable audience
coverage without hot spots or dead zones at
certain frequencies. The 60° x 40° disper-
sion characteristic also helps avoid early re-
flections from nearby floor or side wall sur-
faces which could degrade intelligibility.
The controlled directivity of the high- and
low-frequency transducers also eliminates
response irregularities caused by diffraction
off nearby enclosure edges and, in combina-
tionwithanessentiallyflat on-axis frequency
response, produces a total acoustic power
output that is uniform with frequency.
Enclosure Construction
A combination of dado-cut joints, tough ad-
hesives and proper bracing ensures a soni-
cally dead enclosure free from panel reso-
nances. The flying hardware is preinstalled
in the T251i. The exterior of the T251i is
covered with a white textured paint that is
also paintable if the installer desires.
Rotating the High-Frequency Horn
The T251i high-frequency horn may be eas-
ily rotated about its major axis, providing
coverage independent of enclosure orienta-
tion. First remove the enclosure grille, then
the horn. Both are affixed with #2 Phillips-
head screws. Rotate the horn 90° about its
axis and reinstall the components.
Connections
Biamped or passive crossover with Neutrik
Speakon®connectors. Pins 1+ and 1- are used
in passive crossover.
Biamped Operation
TheT251iis shipped from the factory in“full
range mode” with its passive crossover uti-
lized. If biamp operation is desired, this is
easily achieved. The input panel/crossover
assembly (on the back of the system) must
first be removed using a #2 Phillips screw-
driver. After removing the input panel/cross-
over assembly, notice the crossover instruc-
tion label on the side of the panel. There are
four automotive fuses on the printed circuit
board. These fuses are not functioning as
fuses, but rather are functioning together as
a four pole switch. To convert the T251i to
biamp operation, move each fuse over one
position. The fuses should, once again, all
be in one column and nearest the word BI-
AMP on the printed circuit board. Replace
the input panel/crossover assembly in the
enclosure and carefully replace the screws–
being careful not to strip the holes. To return
the system to full-range operation, repeat the
steps in a similar manner. Remember, all
fuses must be arranged in a vertical col-
umn for safe, proper operation.
Neutrik Speakon®connectors are used. Pins
1+/1– are wired to the low-frequency driver
and pins 2+/2– to the high-frequency sec-
tion. The high-frequency section incorpo-
rates a low-frequency blocking capacitor
with a 3-dB-down point of 800 Hz and
PROTM circuit auto resetting overload pro-
tection.
Frequency Response
The combination of a 15-inch woofer, wide-
bandwidth high-frequency driver and an
equalized crossover results in the wide and
smooth overall response shown in Figure 1.
The T251i’s axial frequency response was
measured in Electro-Voice’s large anechoic
chamber at a distance of 10 feet with a swept
sine-wave input of 4 volts. Figure 1 has been
averaged and corrected for 1 watt/1 meter.
Directivity
A unique feature of the T251i is the con-
stant-directivity dispersion provided by the
60° x 40° horn. The polar response of the
system at selected one-third-octave band-
widths is shown in Figure 2. These polar re-
sponses were measured in an anechoic envi-
ronment at 10 feet using one-third-octave
pink-noise inputs. The frequencies selected
are fully representative of the polar response
of the system. Beamwidth of the system uti-
lizing the complete one-third-octave polar
data is shown in Figure 3. Rθand directivity
index (Di) are plotted in Figure 4.

T251i Trapezoidal Speaker System
T251i Trapezoidal Speaker System
3
Power-Handling Capacity
To our knowledge, Electro-Voice was the
first U.S. manufacturer to develop and pub-
lish a power test closely related to real-life
conditions. First, we use a random-noise in-
put signal because it contains many frequen-
cies simultaneously, just like real voice or
instrument program. Second, our signal con-
tains more energy at extremely high and low
frequenciesthantypical actual program, add-
ing an extra measure of reliability. Third, the
testsignal includes not onlythe overall “long
termaverage” or “continuous” level—which
our ears interpret as loudness—but also
short-duration peaks which are many times
higher than the average, just like actual pro-
gram. The long-term average level stresses
the speaker thermally (heat). The instanta-
neouspeaks test mechanicalreliability (cone
anddiaphragmexcursion).Notethatthesine-
wave test signals sometimes used have a
much less demanding peak value relative to
their average level. In actual use, long-term
average levels exist from several seconds on
up, but we apply the long-term average for
several hours, adding another extra measure
of reliability.
Specifically, the T251i is designed to with-
stand the power test described in EIA Stan-
dard RS-426-A 1980. The EIA test spectrum
isapplied for eighthours. To obtain the spec-
trum, the output of a white-noise generator
(white noise is a particular type of random
noisewithequalenergyperbandwidthinHz)
is fed to a shaping filter with 6-dB-per-oc-
tave slopes below 40 Hz and above 318 Hz.
When measured with an analyzer having the
usual constant-percentage bandwidth (one-
third octave), this shaping filter produces a
spectrum whose 3-dB-down points are at
100 Hz and 1,200 Hz with a 3-dB-per-oc-
tave slope above 1,200 Hz. This shaped sig-
nal is sent to the power amplifier with the
continuous power set at 400 watts into the
5.175-ohm EIA equivalent impedance
(45.5 volts true rms). Amplifierclippingsets
instantaneous peaks at 6 dB above the con-
tinuouspower, or 1,600 watts peak (91.0 volts
peak).This procedure providesarigoroustest
of both thermal and mechanical failure
modes.
Architects’ and Engineers’
Specifications
The loudspeaker system shall be a two-way,
full-range design consisting of a 381-mm
(15-inch) woofer in a vented, trapezoidal-
shapedenclosure,ahigh-frequencycompres-
sion driver mounted on a rotatable 60° x 40°
constant-directivityhorn and a passive cross-
over/equalizer network. The loudspeaker
shall meet the following performance crite-
ria: frequency response of 50-16,000 Hz,
–3dB; power handling of 400 watts long
term and 1,600 watts short term with a
shaped random-noise input per EIA
Standard RS-426-A 1980;sensitivityof101
dB SPL at 1 meter with a 1-watt, 300-2,000-Hz
pink-noise input; 6-dB-down horizontal cover-
age angle of 60° ±10° in the 2,500-20,000-Hz
range; 6-dB-down vertical coverage angle of
40°±4° in the 3,150-16,000-Hz range;cross-
over frequency of 2,200 Hz; nominal imped-
ance of 8 ohms; and minimum impedance of
5.9 ohms. Input connections shall be two
paralleledNeutrik Speakon®connectors.The
enclosure shall be constructed of 13-ply
void-freeplywood, covered with a whitetex-
tured paint with a black steel grille. Hard-
ware required to suspend the system over-
head will be preinstalled. Suspension will
be accomplished by a total of three 3/8-in.
eyebolts (included). Two are mounted to the
topof the enclosure and one inthe back panel
for aiming purposes. Dimensions shall be
822 mm (32.35 in.) high x 476 mm (18.75 in.)
wide at front x 272 mm (10.71 in.) wide at
rear x 591 mm (23.25 in.) deep. Net weight
shall be 35.5 kg (78 lb), estimated.
The loudspeaker system shall be the
Electro-Voice T251i.
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 individualprod-
uct data sheet or owner’s 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.
Exclusions 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 individualprod-
uct data sheet or owner’s manual; (c) mal-
function 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
theproductbyanyoneotherthanElectro-Voice
orany ofitsauthorizedservice representatives.
Obtaining Warranty Service: To obtain war-
ranty service, a customer must deliver the
product, prepaid, to Electro-Voice or any of
its authorized service representatives to-
gether with proof of purchase of the product
in the form of a bill of sale or receipted in-
voice. A list of authorized service repre-
sentatives is available from Electro-Voice
at 600 Cecil Street, Buchanan, MI 49107
(616/695-6831 or 800/234-6831) and/or
Electro-Voice West, at 8234 Doe Avenue,
Visalia, CA 93291 (209/651-7777 or
800/825-1242). IncidentalandConsequen-
tialDamages Excluded: Productrepair or re-
placement and return to the customer are the
only remedies provided to the customer.
Electro-Voice shall not be liable for any in-
cidentalorconsequential damages including,
without limitation, injury to persons or prop-
erty or loss of use. Some states do not allow
the exclusion or limitation of incidental or
consequential damages so the above limita-
tionor exclusion may not apply toyou. Other
Rights: This warranty gives you specific le-
galrights, and you may alsohave 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
periodof five (5) years from thedate of origi-
nal purchase. The Limited Warranty does
notapply to burned voice coils. Electro-Voice
active electronics associated with the speaker
systemsare guaranteedforthree (3)yearsfrom
the date of original purchase. Additional de-
tails are included in the Uniform Limited
Warranty statement.
Service and repair address for this product:
Electro-Voice, Inc., 600 Cecil Street, Bucha-
nan, Michigan 49107 (616/695-6831 or
800/234-6831).
Specifications subject to change without
notice.

T251i Trapezoidal Speaker System
T251i Trapezoidal Speaker System
Figure 2—T251i Polar Response 5 dB per division
Figure 1—T251i Frequency Response
10 kHz 16 kHz
6.3 kHz
4 kHz
2 kHz1.25 kHz
800 Hz
500 Hz
250 Hz
HORIZONTAL
VERTICAL
4

T251i Trapezoidal Speaker System
T251i Trapezoidal Speaker System
Figure 4—T251i Directivity vs.
Frequency, Whole Space (anechoic)
Figure 3—T251i Beamwidth vs.
Frequency, Whole Space (anechoic)
Figure 5—T251i Impedance
5

T251i Trapezoidal Speaker System
T251i Trapezoidal Speaker System
6
SPEAKERS-Full Range/Install Part Number 534651 — 9750
600 Cecil Street, Buchanan, MI 49107
616/695-6831, 616/695-1304 Fax
©EVI Audio 1997 • Litho in U.S.A.
Specifications
Frequency Response, Measured at
10 Feet on Axis, Swept 1/3-octave,
Half-Space Anechoic Environment
(see Figure 1. Curve shown has been
normalized for 1 watt/1 meter) :
50-16,000 Hz
Low-Frequency 3-dB-Down Point:
50 Hz
Usable Low-Frequency Limit (10-dB-
down point):
45 Hz
Half-Space Reference Efficiency:
3.0%
Full range operation:
Long-Term Average Power-Handling
Capacity per EIA Standard RS-426A,
(see Power-Handling Capacity
section):400 watts
Biamp operation:
Recommended Crossover Frequency:
1,200 Hz
Crossover Slopes,
Recommended:
24 dB per octave
Minimum:
12 dB per octave
Long-Term Average Power-Handling
Capacity (see Power-Handling Test
section),
Low Frequency
(per EIA RS-426-A 1980):
400 watts
High Frequency (per AES2-1984/
ANSI S4.26-1984):
60 watts
Sensitivity (far-field SPL referred to
1 meter, 1-watt (2.83 volts) input,
anechoic environment, band-limited
pink noise),
Low Frequency (100-800 Hz):
98 dB
High Frequency (500-5,000 Hz):
112 dB
SPL at Full Power (far-field SPL at 1
watt/1 meter referred to full power,
anechoic environment, band-limited
pink noise), Long-Term Average/Peak,
Low Frequency (100-1,200 Hz):
124 dB/130 dB
High Frequency (1,200-5,000 Hz):
129 dB/135 dB
Impedance,
Nominal (low frequency/high
frequency):
8 ohms/8 ohms
Minimum (low frequency/ high
frequency):
6.0 ohms/6.3 ohms
Nominal Efficiency,
Low Frequency: 3.0%
High Frequency: 25%
General operation:
Nominal Coverage Angle,
Horizontal: 60°
Vertical: 40°
Beamwidth (angle included by 6-dB-
down points on polar responses,
indicated one-third-octave bands of
pink noise, see Figure 4)
2,500 to 16,000 Hz Horizontal:
60° (+12°, –1°)
500 to 16,000 Hz Vertical:
40° (+2, –12°)
Directivity Factor Rθθ
θθ
θ(Q), 500- to
16,000-Hz Median (see Figure 5):
18.0 (+8.7, –8.5)
Directivity Index Di, 500- to 16,000-Hz
Median (see Figure 5):
12.6 dB (+9.4 dB, –9.3 dB)
Distortion (4 W), 1% Rated Input
Power (on axis at 1 meter from
system),
Second Harmonic,
100 Hz: 0.3%
1,000 Hz: 0.4%
10,000 Hz: 1.3%
Third Harmonic,
100 Hz: 0.1%
1,000 Hz: 0.4%
10,000 Hz: 0.6%
Distortion Response (40 W), 10%
Rated Input Power (on axis at 1 meter
from system; see Figure 5),
Second Harmonic,
100 Hz: 0.7%
1,000 Hz: 1.0%
10,000 Hz: 10.0%
Third Harmonic,
100 Hz: 0.3%
1,000 Hz: 0.6%
10,000 Hz: 1.6%
Transducer Complement,
Low Frequency:
DL15ST 381-mm (15-in.)
woofer in a vented enclosure
High Frequency:
HP64M 60° x 40° horn
mounted to DH2T compression
driver
Enclosure Tuning Frequency:
55 Hz
Enclosure Internal Volume:
137 liters (4.84 cu. ft.)
Driver Protection, High Frequency:
(in biamp mode) blocking capacitor
with 800-Hz corner frequency and
6-dB-per-octave slope; (in biamp
and full-range mode) Solid-state
self-resetting circuit (PROTM circuit)
drops input 6 dB
Enclosure Materials and Color:
White, 13-ply void-free Russian
birch plywood covered with a
neutral white textured paint
Grille:
Black, powder coated steel, remov-
able
Dimensions, overall (w/o rubber feet
attached),
Height:
822 mm (32.35 in.)
Width at Front:
476 mm (18.75 in.)
Width at Rear:
272 mm (10.71 in.)
Depth:
591 mm (23.25 in.)
Side-Wall Draft Angle:
10°
Net Weight:
35.5 kg (78 lb) (estimated)
Shipping Weight:
41.5 kg (91 lb) (estimated)