Прочие устройства — Line Magnetic LM-555

The LM-555 is a field-coil compression driver from the Foshan horn-unit range of Line Magnetic, listed by the maker as the LM-555 Alto Drive and also sold under the Analog Sound name as the 555.W. It reproduces the Western Electric No. 555, the unit that Bell Labs added in 1933 as the midrange driver of its two-way divided-range loudspeaker of 1931, which made it the first commercial compression driver. Line Magnetic states that the outer shape keeps the original size and that the diaphragm is reproduced to the original dimensions. Its price is USD 3,995.56.

Key specs that matter

The factory rating is 600 Hz to 7 kHz with a power handling of 6 W. The field coil needs a DC supply of 7 V at 1.5 A, and there is no permanent magnet in the motor. On the 22A horn the working band extends from 100 Hz to 6 kHz. Measured nominal impedance is about 12.8 ohm. The driver is heavy for its size, at roughly 10 kg per unit.

Engineering and use context

Inside is a large-format diaphragm on a phenolic suspension, the arrangement used for mid-frequency coverage in the original design. Because the magnetic field comes from a coil, the driver produces nothing until its excitation supply is switched on, and the field strength depends on the supplied voltage. Line Magnetic makes suitable supplies. The valve-rectified PR-5 can feed one LM-555 from its low terminal or two from its high terminal, the PR-12 is a transistor low-voltage unit, and the PR-4144 is an adjustable valve supply suited to this driver. On a mid-frequency horn the horn and driver resonance showed as an impedance peak at 190 Hz and output fell away quickly at the top of the band. Given its power rating, the LM-555 is meant for low-power amplification in a high-sensitivity horn system rather than for public-address duty.

Pairing

From the same range, the LM-22A alto horn is listed by the maker as compatible with all drivers and covers 150 Hz to 13 kHz. Above the range of this driver a tweeter such as the Line Magnetic HT-70Cu or LM-597 takes over, and the low end needs a separate bass unit such as the TA-4151. That power limit points to a low-power single-ended valve design as the driving amplifier.

Alternatives

The Line Magnetic LM-597 is a field-coil driver from the same horn-unit range, rated from 2 kHz to 30 kHz at 24 ohm.