James Winey, President and also firm’s research and development engineer of Magnepan (White Bear Lake,MN,USA) introduced in 1971 the first full planar-magnetic loudspeaker of the world. This speaker, named Tympani, was formed by three screens for each side, two for mid-bass section and one for high frequencies, every one measuring 16"×71"×1" .

In 1973, Magnepan released the MG II, produced in different version until to 1987.The MGII has only one panel (for each side) (22”x71”x2”),containing the mid-bass and tweeter section.

In 1976 was introduced the MGI, the smaller and less expensive version of MGII loudspeaker (22”x60”x2”). Both the MG II and MGI were produced until to 1987.

The Planar-magnetic driver

It consists in a large planar magnetic area of permanent magnetic field with a very thin (.0005”) film diaphragm (mylar) stretched over it. To the low mass mylar diaphragm are attached two long aluminum wires (one of more large diameter for mid-bass section and the other of lesser diameter for the high section). The wires are oriented in a vertical zig-zag pattern. “As the audio current passes through  the wires, the interaction between the magnetic field around the conductors and the permanent magnetic field causes the entire diaphragm to move. The movement of the diaphragm creates sound waves which are accurate reproductions of the input waveforms.” (from the original Magnepan brochure)

The direction of force on a positive charge or a current is determined by the right-hand rule.

The right-hand rule is a common mnemonic for understanding notation conventions for vectors in 3 dimensions. It was invented by British physicist Ambrose Fleming in the early 1900s. Hold the thumb, index and middle fingers at right angles to each other. Make sure that the thumb and index finger form an "L" or a gun shape. Thus, if the thumb represents the direction of the current and the index indicates the magnetic field, then the middle finger represents the direction of the movement.

The waveforms are radiated alternately front and back (the so called di-polar radiation) which is completely different from the bi-polar radiation of two conventional cone speaker located front and rear in a same box, where the front and back work against each other.  

MGII

(1973)

Panel covered off-white or black. No fuse. Impedance (purely resistive) : 6 Ohms

MGII Improved

(1975 ?)

Same characteristics but the speaker input has the protective fuse (3A,normal-blo).

MGII A

(1978)

This new version presents the same speaker connections of the previous MGII improved.

MGII B

(1981)

Panel covered off-white or black. New speaker inputs for bi-ampli operation. 3A normal fuse.

MGII C

(1987)

Increased both mid-bass (500”) and tweeter (68”) section. Impedance : 5 Ohms (instead of 6 Ohms). The speaker input are similar the MGII C. Same dimensions.

(Sorry, no pictures are available)

MGI Series

(1976-1987)

Magnepan released this speaker in 1976, as less expensive and reduced in size model. Various versions were produced until to 1987.

MGII Series

* Increased mid-bass and tweeter section

Are available on request the MGII C manual, the MGI brochure and schematics of MGII A/ MGII C.

Back

Torna alla mia collezione hi-fi