General Product Description
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.
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.
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.
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.)
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.
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.
DL18MT
Low-Frequency
Reproducer
Electrical Connections
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.
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.
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.
