Напольная акустика — Line Magnetic LM-3 Field Coil Loudspeaker

The LM-3 Field Coil Loudspeaker is a three-way horn system from the Foshan division of Line Magnetic Audio, built around replicas of vintage Western Electric components. Its midrange horn and the compression driver behind it copy the Western Electric 22A and 555W, and every driver in the field coil version is energised by an external supply instead of a permanent magnet.

Key specs that matter

Line Magnetic specifies the system by its parts. The tweeter is the HT-70Cu, a copper and aluminium field coil unit with a range of 3 kHz to 30 kHz, 106 dB sensitivity and 15 W handling. The midrange combines the LM-22A horn, rated from 150 Hz to 13 kHz with dispersion of 20 degrees horizontally and 40 degrees vertically, and the LM-555 driver, which covers 600 Hz to 7 kHz, handles 6 W and needs DC 7 V at 1.5 A for its coil. Bass comes from the TA-4181 18-inch field coil woofer. A TA-7376 network divides the signal, and the PR-22 unit provides excitation. System sensitivity is given as 105 dB. The complete speaker is 900 mm wide, 2080 mm tall and 690 mm deep.

Engineering and use context

For the 18-inch woofer, Line Magnetic analysed materials taken from surviving vintage units and used modern digital engineering methods to rebuild a design that it says survives only in very limited numbers, aiming to recreate the classic Western Electric result. The PR-22 excitation unit follows the Western Electric WE4144 circuit, uses valve rectification with four EL-6C or EQ1-6/0.325 tubes and has panel meters for setting the output current. It offers one low-voltage output of DC 10 V to 24 V and two outputs of DC 3 V to 10 V, each adjustable from 0.5 A to 2 A, and it runs on either 220 V to 240 V or 100 V to 120 V mains. The supply alone measures 485 x 320 x 450 mm and weighs 39 kg, and Line Magnetic lists two TA-4181 woofers and 555 drivers among the loads it can feed.

Pairing

With its very high system sensitivity the LM-3 is aimed at low-power single-ended valve amplification. Line Magnetic's own single-ended integrated amplifiers include the LM-845IA with 845 output valves and 22 W per channel and the LM-805MK II with 805 valves and 50 W per channel. The owner also has to plan floor space for two cabinets more than two metres high and a spot close to them for the PR-22 supply.

Alternatives

The LM-3 Constant Magnetic Barrier Speaker from Line Magnetic is the permanent magnet counterpart of this floorstanding horn design and needs no excitation unit.