Ribbon Tweeter RSL1

The RSL1 ribbon loudspeaker, manufactured by Kelly Acoustics, Ltd., and distributed by Thermionic Products, Ltd., was introduced recently at trade exhibitions in August 1955 and is claimed to represent a radical advance in the development of high-frequency reproducing units.

The diaphragm consists only of a special duralumin foil 0.0003" thick operating in an intense magnetic field. The alternating voice current moving through the foil results in a magnetic field being generated which interreacts with the permanent field and the magnetic force resulting from this reaction is applied uniformly over the whole ribbon.

Therefore, unlike conventional moving-coil type tweeters where the force is applied only at the point of contact between the voice coil and the diaphragm the whole of the moving system vibrates with equal force and in phase, contributing to a remarkably smooth response free from resonance.

The ribbon is coupled to the air by a specially designed catenoidal horn which gives high coupling efficiency at frequencies from 3-20 kc/s and attenuates considerably all frequencies below about 1,000 c/s. The unit is supplied complete with its own matching transformer for 15-ohm lines. As with all tweeters, the unit must be fed from either a high pass filter with a cutoff frequency between 1,500-3,000 c/s., or from a specially designed high-frequency transformer, again with a response only in excess of 3 kc/s. Low-frequency signals below 3,000 c/s. must not be applied to the tweeter or damage will result.

Specifications

• Frequency response: 3-20 kc/s
• Power handling capacity: 10 W;
• Impedance: 15 Ω

See the later version Decca Kelly Ribbon Tweeter DK30 R

Thermionic Products, Ltd. also manufactured a cabinet for the RSL1.

Here you find 7 models, 7 with images and 1 with schematics for wireless sets etc. In French: TSF for Télégraphie sans fil.
All listed radios etc. from Kelly Acoustics Ltd.; Enfield