The LFT-6 Planar Magnetic Reference Loudspeaker

The Eminent Technology LFT-VI is a full-range, push-pull, dynamic planar loudspeaker. In a sense, it is the magnetic equivalent of a push-pull electrostatic loudspeaker, differing in that it requires no step-up transformer or bias voltage, and that the audio signal is applied directly to its diaphragm.
LFT-VI General Specifications:
Power Requirements:           100 watts minimum               

Sensitivity                   83 dB (pink noise, 20-20 kHz)   
                              at 1 watt/1 meter (2.83 V)      

Frequency Response            38 Hz-20 kHz ±4 dB (typical     
                              room, close-mic measurement)    
                              -10 dB at 35 kHz                

Phase Accuracy                ± 20° 100 Hz-31 kHz             

High Frequency Level          Flat, -6 dB, -12 dB at 20 kHz   
                              smooth rolloff                  

Impedance                     6 Ohm rating                    

Maximum SPL                   105 dB at 1 meter               

Magnet type                   Ceramic 8                       

Diaphragm Area                420 in2 (front)                 

Harmonic Distortion           Less than .04%, 100 Hz-20 kHz,  
                              90 dB, 1 meter                  

Dimensions                    18" wide by 78" high by 1"      

Shipping Weight               95 lbs. each                    

Foil thickness                .00033"                         

Mylar thickness               .0005"                          

Laminate Adhesive Thickness   .00015"                         

Gap Between Conductors        .03"                            

Peak-to-Peak Diaphragm        .4" Woofer  .035 Tweeter        

Warranty                      3 years parts, 1 year labor     

Finish                        Oak standard                    
                              Walnut and other painted        
                              finishes optional               

Music                         All of the above done for the   
                              enjoyment of music.             

Designers                     David Collie and Bruce Thigpen  

To fully understand the strengths of the LFT design, one must first consider the design and operation of this speaker's three most notable antecedents: the push-pull electrostatic loudspeaker (ESL); the traditional, single-ended planar magnetic loudspeaker, and the ribbon loudspeaker.

By applying such new techniques to planar loudspeaker construction, Eminent Technology has been able to eliminate many of the flaws inherent in earlier designs. The use of a welded channel-and-crossbar frame dispenses with the need for perforated sheet metal (an ìoff-the-shelfî material presumably used for reasons of economy and ease of manufacture.) thus greatly improving dispersion, especially at high frequencies.

Since it is now possible to have a powerful, precisely aligned magnet structure on both sides of the diaphragm, true push-pull operation has been achieved: Regardless of the degree of excursion the diaphragm undergoes, the voice element is always optimally positioned within the magnetic field. The result is extremely linear performance throughout the audible range, with a profound increase in dynamic range and an absolute minimum of distortion.

Each LFT-VII has five individual driver panels. The outside portion on each panel is divided into separately driven bass and (line-source) midrange areas, with the former operating from 400 Hz down, and the latter operating from 400 Hz up to 10 kHz. The tweeters operate as a line source from 10 kHz up to and beyond 20 kHz. The midrange and tweeter sections are distinguishable by their thinner magnet structures.

All three panels operate as woofers, from 400 Hz on down. Actually, all of the panels, including the woofers, are physically capable of operating to beyond 20 kHz, but would exhibit undesirable diffraction effects and poor dispersion if allowed to do so, which is why the panels are segmented into different sections for different portions of the frequency range. The use of a flat panel design maintains excellent phase response throughout the audible range.

LFT Impedance

The LFT-6 can be made to operate at almost any impedance; our present choice of a nominal 6-Ohm impedance has been made in the interest of maximizing efficiency and amplifier compatibility. Because of the large surface area of the panels and the resulting good heat dissipation (a function also of the material choice for the voice grid), the LFT-6 can handle tremendous amounts of power before any risk of damage.

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