DESCRIPTION

The TD-4001 successfully achieves all the design objectives we set
forth – very high efficiency, wide and perfectly flat response from
600Hz to 20kHz, and low distortion.

DIAPHRAGM

The TD-4001 employs a pure beryllium diaphragm 3-15/16 inches
(100mm) across. Beryllium is a light but very rigid material that
features very high-speed sound propagation. The weight of the dome
section has been reduced to a mere 1g contributing to the very high
efficiency, 110dB (1W,1m), of this driver.

VOICE COIL

The TD-4001 employs an aluminum ribbon voice coil, insulated by
alumite film and wound edgewise on the bobbin. The voice coil has a
small mass yet offers a high conversion efficiency. The bobbin is
formed of polyimide film, displaying excellent heat resistance to
temperatures as high as 752ºF (400ºC).

MAGNETIC CIRCUIT

Total magnetic flux is 2.28×10^-3Wb, with flux
density of 2.00T, thanks to the use of a very heavy (6 lbs. 10
oz./3kg) alnico 5DG magnet. An oxygen-free copper shorting ring
prevents impedance rise, resulting in low distortion.

DESIGN

The TD-4001 is of the rear compression design, which eliminates
the resonance and phase distortion produced by a surround. It also
eliminates cavity resonance interference, achieving very flat
frequency response, extremely natural sound and superb definition. A
phasing plug helps smooth the response of extra high frequencies.

CROSSOVER

We recommend the use of a crossover frequency of 600Hz or
higher, and a cutoff slope of 12dB/oct. or sharper.