Close-up: Midax Horn

Rear view of a Goodmans Midax "mid range" horn

A Midax horn and crossover installed in a Beatle cabinet

4 uf , 150 volt oil filled Aerovox crossover capacitor

The story of Goodmans Midax horns in Vox speaker cabinets is tied into the English production of the AC-50 and AC-100 amp heads. While the 30 watt AC-30 (especially the "top boost" models) had an abundance of treble, these amps were no longer loud enough. Vox needed to develop higher powered and louder amps that maintained the characteristic brilliant Vox tone.

However, to achieve the power outputs Vox wished to reach, the EL-84 power tube that powered the AC-30 and AC-15 was not practical. Vox needed to use higher powered output tubes (valves), and none seemed more perfect than the big brother to the EL-84, the EL-34.

The use of the EL-34 tube created a problem. While it could easily provide 50 watt RMS power in a pair, or 100 watts when used in a quartet, the EL34 had much less treble than the EL-84. Even when coupled to the most brilliant "top boost" tone circuitry from the AC-30, the characteristic bright Vox tone was missing.

Vox chose to audition a number of different horns to add to the speaker cabinets that would be sold with the AC-50 and AC-100 heads. Goodmans, a British manufacturer of loudspeaker components, offered two horns that might solve the treble problem. The Goodmans Trebax and Midax horns were popular in home stereo installations and had sufficient power handling capacity to allow them to work in a guitar amp. The Trebax, with frequency response in excess of 12,000 hz, sounded scratchy and distorted. The Midax horn, on the other hand, worked well in a guitar amp. The Midax would respond in the desired 2,000 to 4,000 hz frequency range when fitted with the appropriate crossover capacitor, making it ideal for guitar use. The AC-50 and AC-100 cabinets were fitted with the Goodmans Midax horn, and this solved the problem of the treble defiency in the Vox EL34 powered amplifiers.

When Thomas Organ developed their own solid state amplifier heads in 1966, there was an abundance of treble available in the tone circuitry. No horns would be necessary or needed. However, to stay faithful to the UK Vox designs, Thomas Organ decided to install Midax horns in the US equivalent amplifiers to the AC-50 and AC-100. The Royal Guardsman and Super Beatle were fitted with Goodmans Midax horns.

When Goodmans went out of business in 1977, the Midax horm, along with its replacement repair diaphragm disappeared from the market place. As modern speaker manufacturers do not commonly produce "mid range" horns, no functional replacement for the Midax exists. Treble horns, while commonly available, do not sound the same as the Goodmans Midax.


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Photos and editorial content courtesy Gary Hahlbeck, North Coast Music

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