Electro-Voice T251i Trapezoidal Speaker System

Product Overview

The Electro-Voice T251i is a compact, trapezoidal-shaped, 400-watt, two-way, biampable, constant-directivity speaker system designed for professional, permanent installations. It combines professional-quality components in a time-coherent vertical array with a robust, installation-friendly, vented enclosure, delivering clear and articulate sound.

The enclosure is constructed from 13-ply void-free birch plywood, finished with a textured, neutral white paint. It features preinstalled suspension hardware and includes three eyebolts for mounting. Small rubber feet and mounting screws are also provided but not attached, for flexibility in installation.

Key Features

• HS-style suspension hardware preinstalled, with included eyebolts for vertical or horizontal suspension.
• Paintable enclosure, supplied with white textured paint.
• Ring-Mode Decoupling (RMD™) technology for increased intelligibility.
• PRO™ circuit for High-Frequency (HF) driver protection.
• Rotatable constant-directivity 60° x 40° horn.
• High-excursion, 400 W, DL15ST 15-inch woofer.
• Biampable design with an included passive network.

Technical Details

High-Frequency Section

The high-frequency section utilizes a 60° x 40° constant-directivity horn driven by a wide-bandwidth, two-inch titanium-diaphragm DH2T driver. This driver features a unique convex-drive phasing plug structure for smooth and extended high-frequency performance. The voice coil is coupled to the diaphragm using EV's exclusive Resonant Drive™ technology, which enhances and smooths the high-frequency response while reducing the need for internal equalization. EV's self-resetting PRO™ circuit is integrated into the crossover network to protect the compression driver from damage by reducing power by 6 dB if input power exceeds the nominal rating.

Ring-Mode Decoupling (RMD™)

The T251i incorporates Ring-Mode Decoupling (RMD™) to control both acoustical and mechanical ring modes, resulting in dramatically increased intelligibility. This technology, developed from Electro-Voice's X-Array™ concert speakers, minimizes sound coloration from resonating sources, ensuring only the intended sound is heard. The optimally vented bass section is designed using Thiele-Small parameters for efficient performance below 50 Hz. The DL15ST woofer features a high-excursion design with beryllium copper lead wires, a low-mass, extended-length, edge-wound voice coil, and high-temperature materials. EV's unique Thermo Inductive Ring (TIR™) is placed on the pole piece to provide a major heat-transfer path, keeping the voice coil cool.

Constant-Directivity Speaker System

The crossover frequency and speaker component geometries are optimized to match the directional characteristics of the woofer and the constant-directivity horn. This creates a constant-directivity system with approximately 90° circular coverage patterns at the crossover frequency. At higher frequencies, the horizontal coverage pattern remains constant, while the vertical pattern smoothly transitions to a 40° angle above 4,000 Hz. The uniform response within the 60° x 40° rated coverage angle ensures dependable audience coverage without hot spots or dead zones. The controlled directivity also minimizes diffraction off enclosure edges, contributing to a uniform acoustic power output.

Enclosure Construction

The enclosure is built using dado-cut joints, strong adhesives, and proper bracing to ensure a sonically dead construction free from panel resonances. Flying hardware is preinstalled. The exterior is covered with a white textured paint that can be repainted if desired. A black, powder-coated steel grille is also included.

Connections

The system supports biamped or passive crossover operation via Neutrik Speakon connectors. For biamp operation, the input panel/crossover assembly on the rear must be accessed to reposition fuses, which act as a four-pole switch. Pins 1+/1- are wired to the low-frequency driver, and pins 2+/2- to the high-frequency section. The high-frequency section includes a low-frequency blocking capacitor (800 Hz corner frequency) and a PRO™ circuit for overload protection.

Installation and Safety

It is the installer's responsibility to ensure the speaker system is installed correctly and safely. Electro-Voice strongly recommends that all suspended items be inspected annually, with any damaged parts replaced immediately. Systems should be suspended with minimum stress on the cabinet, and each cabinet should hang independently.

When suspending the T251i, two of the three supplied forged eyebolts are screwed into the upper brackets, and the third is screwed into the rear panel T-nut for aiming. The pull-up point is used for downward or horizontal projection angles. For multiple cabinet suspensions, each system requires its own rigging points; systems should not be suspended from each other. Use suitably rated chain or aircraft cables for connection. Support cables or chains should be as close to vertical as possible (never more than 30° from vertical) and should not touch or rub against the cabinet. Local codes and regulations must be followed, and Electro-Voice recommends a safety factor of at least 8:1.

Rotating the High-Frequency Horn

The high-frequency horn can be rotated 90° about its axis for coverage adjustment independent of enclosure orientation. This is done by removing the enclosure grille and the horn, rotating them, and then reinstalling.

Specifications

General

• System Type: Trapezoidal Speaker System, Two-Way, Biampable, Constant-Directivity
• Power Handling: 400 W (Long-Term, EIA RS-426-A), 1600 W (Short-Term Peak)
• Frequency Response: 50 Hz - 16,000 Hz (-3 dB)
• Low-Frequency Limit: 45 Hz (10-dB-down point)
• Sensitivity (1W/1m, Anechoic): 98 dB (Low Freq.), 112 dB (High Freq.)
• Nominal Coverage Angle: 60° Horizontal, 40° Vertical
• Impedance: 8 ohms nominal, 5.9 ohms minimum
• Crossover Frequency: 1,200 Hz (Recommended for Biamp)
• Enclosure: 13-ply void-free birch plywood, vented, trapezoidal
• Finish: White textured paint
• Grille: Black, powder-coated steel, removable
• Suspension Hardware: HS-style, preinstalled, includes three 3/8-in. eyebolts

Transducer Complement

• Low Frequency: DL15ST 381-mm (15-in.) woofer
• High Frequency: DH2T 2-inch titanium-diaphragm compression driver on HP64M 60° x 40° horn

Dimensions & Weight

• Height: 822 mm (32.35 in.)
• Width (Front): 476 mm (18.75 in.)
• Width (Rear): 272 mm (10.71 in.)
• Depth: 591 mm (23.25 in.)
• Net Weight: 35.5 kg (78 lb)
• Shipping Weight: 41.5 kg (91 lb)

Graphical Data Descriptions

Figure 1: Frequency Response
This graph displays the speaker's frequency response measured at 10 feet on axis in a half-space anechoic environment. The response is relatively flat from approximately 100 Hz to 16 kHz, with a slight peak around 5 kHz and a gradual roll-off at higher frequencies. The curve is normalized for 1 watt/1 meter.

Figure 2: Polar Response
This series of polar plots illustrates the speaker's directivity at various frequencies (250 Hz, 500 Hz, 800 Hz, 1.25 kHz, 2 kHz, 4 kHz, 6.3 kHz, 10 kHz, 16 kHz). The plots demonstrate the consistent 60° horizontal and 40° vertical coverage angles, showing how the dispersion pattern changes with frequency.

Figure 3: Beamwidth vs. Frequency
This graph shows the speaker's beamwidth (the angle included by 6-dB-down points) in degrees as a function of frequency. It indicates that the coverage angle narrows at higher frequencies.

Figure 4: Directivity vs. Frequency
This graph presents the speaker's directivity index (DI) in decibels as a function of frequency, providing a measure of its directional control across the audio spectrum.

Figure 5: Impedance
This graph illustrates the speaker's impedance in ohms across the frequency range. It shows typical impedance characteristics for a 15-inch woofer system, including peaks and valleys related to the driver's resonance and the crossover network.

Limited Warranty

Electro-Voice products are guaranteed against malfunction due to defects in materials or workmanship for a specified period, beginning with the date of original purchase. If a malfunction occurs during the warranty period, the product will be repaired or replaced at Electro-Voice's option, without charge. The product will be returned to the customer prepaid.

Exclusions and Limitations: The warranty does not cover exterior finish or appearance, specific items noted in product literature, malfunctions resulting from improper use or operation, misuse or abuse, or repairs performed by unauthorized personnel.

Warranty Period: Electro-Voice Speakers and Speaker Systems are guaranteed for five (5) years from the date of original purchase. This warranty does not cover burned voice coils. Active electronics associated with speaker systems are guaranteed for three (3) years.

Service and Repair: For warranty service, customers must deliver the product, prepaid, to Electro-Voice or an authorized service representative with proof of purchase. The service and repair address is: Electro-Voice, Inc., 600 Cecil Street, Buchanan, Michigan 49107.

Specifications are subject to change without notice.