Напольная акустика — Line Magnetic LM-755A

The LM-755A is a console loudspeaker from Line Magnetic that takes the Western Electric 755A as its starting point. The company duplicated that classic driver as a brand new unit and adapted it to a field coil motor, which is energised by the separate Line Magnetic PR-3 power supply. The model belongs to the maker's retro loudspeaker range, where it sits next to the LM-69 full-range console model, the LM-812 horn system and the LM-222 coaxial speaker. Line Magnetic also sells the 755 driver family on its own as bare components in its horn unit catalogue.

Key specs that matter

The maker lists a frequency range of 70 Hz to 13 kHz, a sensitivity of 92 dB and a nominal impedance of 8 ohm. Rated power is 10 W and the resonance frequency of the driver is 68 Hz. Excitation of the coil requires 200 V DC at a current of 50 mA, so the speaker cannot work from an amplifier alone.

Engineering and use context

The PR-3 that feeds the coil is itself a valve unit built around 300B triodes, which links this speaker directly to the brand's amplifier technology rather than to a solid-state supply. Among the bare components, Line Magnetic offers two versions of its 8 inch 755 unit. The field coil LM-755 shares the console model's excitation requirement and impedance, with a 6 W rating. The LM-755A driver with a cobalt magnet needs no external supply and runs at 4 ohm, and for it Line Magnetic points to its own work on paper cones and paper pulp. The console speaker therefore uses the field coil approach of the first unit while carrying the 755A name. Its published frequency limits, sensitivity and resonance are identical to the values given for both bare 8 inch drivers, while the finished speaker carries a higher power rating than either of them.

Pairing

Its modest rating calls for a small single-ended triode amplifier. Line Magnetic's own AM-2 and AM-3 mono power amplifiers are built around the 300B triode, the same valve type used in the PR-3 supply, so an owner can run an all-300B chain. The catalogue also includes an HT-70Cu tweeter and a TA-4151 field coil woofer, both sold as separate units for systems that extend the band beyond the quoted limits.

Alternatives

Line Magnetic's LM-69 is another floorstanding console design from the same retro range, using a single 6 x 9 inch oval cone.