Voigt Mains Energised drive unit

The Voigt Mains Energised drive unit was first available with a single-cone diaphragm from Edison Bell in 1931. This unit had a high electro-acoustic efficiency of between 25-35%.

Weight: 31 lbs

Flux density: 16,000 - 17,500 gauss under working conditions

Magnet gap: 2mm

Field consumption: 40 watts (approximately)

Field energising voltage: 8 voltage ranges

Voigt was granted a patent in July 1934 for the design of his twin-cone diaphragm. This new design extended the frequency response from the previous upper limit of 4 KHz to above 12 KHz.

The cost of the Mains Energised unit in 1936 was £14-10s-0d (single diaphragm) or £15-0s-0d (twin cone).

Voigt Permanent Magnet drive unit

The Voigt permanent magnet drive unit made its debut in 1949. This was the culmination of a patent application entitled "Improvements in magnets" which was lodged in March 1947 and granted in June 1949.

This driver utilised a massive centre block of Ticonal, which gave a flux density of 18,000 gauss in a 1.5 mm gap. This drive unit could be supplied with either the standard twin diaphragm in a 2 mm gap at £36, or the light coil twin diaphragm in a 1.5 mm gap for £40.

Later units were fitted with a 1mm air gap and had a 22,000 gauss density. In 1951 an improvement on the light coil twin diaphragm was made, which resulted in the "re-matched diaphragm". This had a different speech coil with a two-layer winding, which made it Smaller and lighter.