2.5 W Loudspeaker F.2.500

Type F.2.500, Electromagnet Loudspeaker.

This speaker is of the moving-coil type, with a 2,500 ohms field winding, rated for a current of from 40 mA. to 70 mA.

A low-resistance moving coil is fitted and drives a small diameter buckram cone, while the transformer is of such ratio that the average primary impedance is about 4,000 ohms, the correct value for a PX4 valve.

A good, and rather unusual, point is the fitting of a hum-bucking coil, so that smoothing of the field supply is unnecessary. This, of course, is not an essential feature of a speaker for use with the Monodial, but its presence is in no way harmful, and it renders the speaker more generally useful.

A 7" diameter hole is required in the baffle board or cabinet. The speaker has been tested with a Monodial AC Super and proved capable of excellent results. The bass is well reproduced, and without marked resonance, while the high-frequency response is well maintained, although at a somewhat lower level than usual, for the high-frequency resonances normally found with paper cones appear to be less marked. Speech is clear cut and distinct, and free from any "boomy" effect, and the tone of the music is well balanced.

In spite of its small size, the power handling capacity is high, and it shows no sign of strain when dealing with the full 2,500 milliwatts output of a PX4. The efficiency is also high, for the volume to be obtained with a given input is noticeably greater than usual.

In view of its satisfactory performance, this speaker can be confidently recommended for use with the Monodial AC Super; it is listed as type F.2.500, and at the price of 35s., complete with transformer, it represents excellent value.

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Elenco delle radio e altri apparecchi della British Rola Co. Ltd.; London