The A.J.S. Horn Loudspeaker

Background
 Right from the word go the A.J.S. Wireless and Scientific Instruments department manufactured loudspeakers for use with their receivers. Initially horn loudspeakers were produced but by 1925 the product range included more modern moving iron models.

There were two basic types of horn loudspeaker, the 'Junior' and the 'Standard'.

The cheapest and smallest model was the 19" high 'Junior Loudspeaker' with a metal horn. It came in a black crystalline or grained wood finish. The version with a wood grained finish initially sold for £1.17s.6d., and the black crystalline version initially sold for £1.15s.0d.

The largest and more expensive model was the 24" high 'Standard Loudspeaker' with either a metal or wooden horn. The metal horn came in either a matt black or grained wood finish and the wooden horn was available with oak or mahogany flares. The matt black metal horn version sold for £4, the wood grained metal horn sold for £4.5s.0d. and the wooden models were £4.15s.0d. The loudspeakers were also built into the A.J.S. 'Pedestal' receivers and the 'Consol' receiver.

The sound quality is poor when compared with a modern loudspeaker due to lack of sensitivity, a limited frequency range and lack of dynamic range due to their inability to handle large signals without distortion. The sound quality from the models with a wooden horn is supposedly better, probably more mellow due to the acoustic properties of the wood.

 


A 'Standard' model with a metal horn.
 Circuit Diagram
The loudspeaker uses a metal diaphragm that is suspended above two pole pieces that are attached to a horseshoe magnet. A coil is wound around each pole piece so that a current flowing through it will vary the magnetic field. The magnetic field attracts the thin diaphragm which bends towards the magnet. When the field is varied by the current in the coils the diaphragm moves. When an audio signal is applied to the coils the diaphragm moves up and down in sympathy.

The amount of movement is quite limited and so volume levels are low when compared with modern loudspeakers.
This assembly opposite is mounted directly under the diaphragm and bolted through the hole on the right-hand side to the base casting. The bolt on the extreme left passes through a hole in the casting and has the adjusting screw attached to it.

If the screw is tightened, the assembly is raised. By this method the gap between the pole pieces and the diaphragm is adjusted for optimum sound quality.
The inside of the loudspeaker showing the horseshoe magnet, pole pieces and coils.
The base casting with the adjusting screw at the front.
The top of the range model with wooden flares.

We would also like to add technical details of other A.J.S. loudspeakers. If anyone has any information please email the webmaster.

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