Electro-Voice T251i Product Information

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 in­cluded

Description

The compact, trapezoidal-shaped Electro-Voice
T251i is a 400-watt, two-way, biampable, con­stant-directivity speaker system. The system
combines professional-quality components,
arranged in a time-coherent vertical array,
with an unusually robust, installation­friendly, vented enclosure. The result is clear
and articulate, high-quality sound for per­manent installation.

The enclosure is constructed of 13-ply void­free, 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 ship­ping carton. Small rubber feet and mount­ing 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 uti­lizes a 60° x 40° constant-directivity horn
driven by a wide-bandwidth, two-inch tita­nium-diaphragm DH2T driver. This driver
uses a unique convex-drive phasing plug
structure for smooth and extended high-fre­quency performance. The voice coil is
coupled to the diaphragm with EV’s exclu­sive Resonant Drive

TM

technology. This in-

creases and smooths the high-frequency re­sponse and reduces the amount of internal
equalization required for flat frequency re­sponse.

TM

EV’s self-resetting PRO
the crossover network to guard the compres­sion 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 opera­tion until input power is reduced to a safe
level.

Ring-Mode Decoupling (RMDTM)

The T251i controls both acoustical and
mechanical ring modes to provide dra­matically 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 be­ryllium copper lead wires with a low-mass,

circuit is built into

extended-length, edge-wound voice coil and
high-temperature materials. EV’s unique
Thermo Inductive Ring (TIR
top of the pole piece, where the extended­length voice coil would normally 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
bearing capability to safely suspend the cabi­net. 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 cabi­net. Local codes and regulations, if they
exceed Electro-Voice’s recommendations,
should be followed at all times.
Electro-V oice recommends that a safety fac­tor of at least 8:1 be adopted. The
Electro-Voice HS-style suspension compo­nents supplied in the T251i exceed this rec­ommended safety factor when the system is
installed in compliance with Electro-Voice
recommendations.

TM

) is placed on

T251i Trapezoidal Speaker System

It is the installer’s responsibility to ensure
the speaker system has been installed cor­rectly. Electro-Voice strongly recom­mends that all suspended items be in­spected at least once a year and any dam­aged 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 sys­tem is conceptually very simple. Two alu-

T251i Trapezoidal Speaker System

minum tubes pass vertically through the cabi­net and each is secured via two oversize cast
brackets (threaded flanges). The enclosure
is sandwiched between the four (two on each
end) brackets. The enclosure is essentially
resting between the brackets.

When installing the T251i, two of the three
supplied forged eyebolts are screwed into the
upper two brackets. The third eyebolt should
be screwed into the appropriate T-nut on the
rear panel of the enclosure. When mount­ing the enclosure vertically, use the lower
T-nut. When mounting the enclosure hori­zontally, 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 di­rected towards the ceiling. In order to pro­vide a downward or horizontal projection
angle, the pull-up point must be used.

If multiple 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-

ing suitably rated chain with connectors 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 com­ponent geometries have been selected so that
the directional characteristics of the woofer
and constant-directivity horn match at the

crossover frequency (approximately 90° cir­cular coverage patterns for each) to create a
special system type—the constant-directiv­ity system. At higher frequencies the hori­zontal coverage 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 uni­form, which means dependable audience
coverage without hot spots or dead zones at
certain frequencies. The 60° x 40° disper­sion characteristic also helps avoid early re­flections from nearby floor or side wall sur­faces 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 combina­tion with an essentially flat on-axis frequency
response, produces a total acoustic power
output that is uniform with frequency.

Enclosure Construction

A combination of dado-cut joints, tough ad­hesives and proper bracing ensures a soni­cally dead enclosure free from panel reso­nances. 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 eas­ily rotated about its major axis, providing
coverage independent of enclosure orienta­tion. First remove the enclosure grille, then
the horn. Both are affixed with #2 Phillips­head 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
The T251i is shipped from the factory in “full

range mode” with its passive crossover uti­lized. 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/cross­over assembly, notice the crossover instruc­tion 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 BI­AMP 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 col­umn 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 sec­tion. The high-frequency section incorpo­rates a low-frequency blocking capacitor
with a 3-dB-down point of 800 Hz and

TM

PRO

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 band­widths is shown in Figure 2. These polar re­sponses were measured in an anechoic envi­ronment 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 uti­lizing the complete one-third-octave polar
data is shown in Figure 3. R
index (D

) are plotted in Figure 4.

i

and directivity

θ

2