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/W) 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 228,000Mx, with flux density of 20,000G, 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.

Specifications

General	TD-4001
Nominal Impedance	16 Ohm
Frequency Range	600-20000 Hz
Rated Input Power	30 Watt
Total Magnetic Flux	228.000 Mx
Voice Coil Diameter	101,0 mm
Phasing Plug	5-slit type
Hole Size for Throat Connection	49,4 mm
Mounting Dimensions	101.6 (4 Holes) mm
Weight	13,5 kg
Dimensions (diameter x depth)	178 x 156 mm
Maximum Input Power	60 Watt
Sound Pressure Level	110 dB/W (1m)
Magnetic Flux Density	20.000 G
Highest Recommended Crossover	600 Hz