Telex Speaker DL18MT User Manual

General Product Description  
DL18MT  
The DL18MT low-frequency reproducer is a 460 mm (18-inch), 8-ohm  
driver designed for professional high-level, high-fidelity monitoring and  
sound reinforcement. At the heart of this speaker is a carefully  
engineered drive system.Its design assures linear, low distortion output,  
high power capability and efficient heat transfer.  
Low-Frequency  
Reproducer  
Incorporated into the design are three exclusive Electro-Voice®  
innovations. PROTEF™ coating (U.S. patent #4,547,632), a Teflon®  
-based coating, is applied to the inside diameter of the top plate.  
Occasional violent power peaks of several seconds may expand a  
transducer’s voice coil into contact with the top plate, causing failure.  
PROTEF™ proides protection against such failure. The coating  
lubricates any rubbing contact and provides electrical insulation between  
the coil and the steel top plate.The Thermo Inductive Ring (TIR™) and  
Flux Demodulation Device (FDD™), also included in the DL18MT  
design, are aluminum castings fastened to the pole of the magnet.They  
provided a shorted turn to control inductance and provide a major heat  
transfer path from the voice coil, which improves power handling and  
reduces thermal, dynamic-range compression.  
Electrical Connections  
The voice coil itself is constructed of edge-wound rectangular copper  
wire, mounted on a rugged laminated polyimide former. The complete  
assembly is fabricated using the most advanced epoxies, insulations  
and materials available.  
The DL18MT is fitted with a pair of plated, frame-mounted connectors  
with color-coded ends. Electrical connection is made by pushing down,  
inserting wire completely through the rectangular slot and releasing  
pressure.One conductor of #9 stranded, #8 AWG solid, a pair of twisted  
#15 AWG stranded or a pair of #14 AWG solid conductors will fit.  
Great care was taken in the selection of diaphragm materials and  
construction to ensure smooth, musical upper-bass reproduction and  
accurate low-frequency shock capability (punch). The cone has a  
moisture-repellent treatment, allowing it to be used in harsh and humid  
conditions. (Do not expose the cone to direct water or sunlight.)  
Typical Amplifier Size  
400-800 watts per woofer is the optimal amplifier size. Amplifiers of this  
size will allow maximum output with minimal risk of speaker damage  
when properly used. Smaller amplifiers can also be used with excellent  
results.  
The DL18MT is a true high-fidelity woofer in every sense, being capable  
of high output, low distortion and solid bass response.  
Architects’ and Engineers’ Specifications  
The low-frequency woofer shall have a nominal diameter of 457 mm  
(18.0 in.), an overall depth of 188 mm (7.42 in.) and weigh less than 9.3  
kg (20.5 lb). The frame shall be constructed of strong,  
deformation-resistant die-cast aluminum. The magnet assembly shall  
incorporate PROTEF™ protection, a TIR™ (Thermo Inductive Ring)  
and FDD™ (Flux Demodulation Device) to reduce inductive coupling  
and increase power handling.The cone and dust dome should withstand  
use in damp and humid conditions.The voice coil shall have a diameter  
of 64 mm (2.5 in.), a winding depth of 20.3 mm (0.8 in.) and be made of  
edge-wound copper ribbon. The voice-coil former shall be made of  
aerospace-grade polyimide laminate and bonded with high-temperature  
epoxy adhesives. The performance specification of a representative  
production unit shall be as follows: measured sensitivity (SPL at 1 m  
(3.3 ft) with 1 watt input, 100- to 800-Hz pink noise) shall be in excess  
of 95 dB.The halfspace reference efficiency shall be at least 2.9%.The  
usable response shall be 30 to 3,000 Hz, and the nominal impedance  
shall be 8 ohms. The EIA rated power shall be 400 watts. The  
low-frequency transducer shall be the Electro-Voice DL18MT.  
Typical Enclosures  
The most extended bass, lowest distortion and best control is usually  
realized in properly designed vented enclosures. In such designs, the  
vent, or port, actually provides the lowest octave of output. The vent is  
driven to full acoustic output by a relatively small motion of the speaker  
cone itself, acting through the air contained within the enclosure. The  
excursion of the DL18MT at these frequencies is much reduced  
compared to sealed or open-back enclosures, directly reducing harmonic  
distortion and the possibility of speaker bottoming. Thiele-Small  
parameters are provided so designers can tailor the response to suit  
their needs.  
Normally Tuned Enclosures  
A 1.8 cubic-foot enclosure tuned to 55 Hz has a smooth extended  
response to below 50 Hz. The 1.1 cubic-foot enclosure “bumps up”  
above 70 Hz but has less extended low-bass output.  
Directional Characteristics  
The directional characteristics of the DL18MT in the 7.4-cubic-foot  
TL18-1 vented enclosure were measured in ElectroVoice’s large  
anechoic chamber. The test signal was one-third-octave filtered pink  
noise centered at the frequencies indicated. All directional information  
was measured at 20 feet. Figure 1 shows the horizontal and vertical  
beamwidths.Beamwidth is the angle at which the horizontal and vertical  
polar responses have decreased in level by 6 dB when compared to  
the axial frequency response. Figure 2 illustrates the total directivity of  
the DL18MT.The directivity factor Rq (Q) is the relative value, at a point,  
of the DL18MT when compared to an ideal spherical response. The  
directivity index, Di, is calculated by the formula: Di = 10 log10 Rq.  
Figure 1  
 

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