Technics SB-311

Commentary

A speaker system with low distortion using the know-how obtained with the SB-1000.

A 25 cm cone type woofer is installed in the low range.
The new TC cone is used for the diaphragm of this unit. The TC cone is made of a material with a high Young's modulus and a material with a high internal loss. It is made into a three layer one plate diaphragm by sandwiching a material with a high internal loss. It has the effect of suppressing divided vibration. The new TC cone uses a new high-crystalline fiber (HXF) for the exterior part of this structure. It is designed to have tensile strength twice as large as carbon fiber, specific gravity 0.75 times as large, and mechanical loss twice as large as carbon fiber.
In addition, magnetic materials that suppress eddy current generation are used for the pole piece and plate of the magnetic circuit near the voice coil to reduce the distortion at the beginning of the energy conversion. This greatly reduces the current distortion flowing in the voice coil and reduces the third harmonic distortion in the frequency range from 100 Hz to 3 kHz by 20 dB compared to the conventional one.
The voice coil adopts a long travel type with a coil winding width of 15.8 mm compared to the plate width of 8 mm. This allows the voice coil to be driven within a constant magnetic flux even at large input and amplitude, minimizing linearity loss due to magnetic leakage. In addition, 50 micron hard aluminum foil is used for the voice coil bobbin to improve input resistance.

The mid-range features a 3.2 cm dome mid-range.
The TC structure is also adopted for the diaphragm of this unit, reducing distortion by suppressing abnormal resonance and split vibration, and improving directional characteristics by narrowing the aperture to 32 mm φ.
It uses a perforated pole piece and a back cavity, and by guiding the air in the rear part of the diaphragm to the back cavity, distortion due to air pressure is eliminated and an optimum acoustic load is applied. This realizes a low-frequency resonance frequency of 650 Hz with a small diaphragm of 32 mm φ. Glass wool with a diameter of 1.25 microns is used for the sound absorbing material of the back cavity.

A 1.3 cm dome type tweeter is installed in the high range.
An aluminum-evaporated polyester film is used for the diaphragm, and stable wide directivity and transient characteristics are obtained from 7 kHz to 20 kHz. In addition, a lightweight CCAW (copper-coated aluminum wire) is used for the voice coil, and by reducing the weight of the vibration system, the high frequency limit is extended.

The enclosure is sealed 18 mm thick and has a walnut oil finish on the exterior.

Level control is mounted on the rear baffle.

Model Rating

Method	3-Way, 3-Speaker, Airtight Type, Bookshelf Type
Units Used	For low band : 25 cm cone type For Middle Area : 3.2 cm Dome Type For high-pass : 1.3 cm dome type
Frequency characteristic	35 Hz to 20 kHz
Impedance	8 Ω
Output sound pressure level	90dB/W/m
Max Input	40W
External dimensions	Width 325x Height 570x Depth 258 mm
Weight	19kg