Technics SB-7A

Commentary

This 3-way speaker system improves power linearity by adopting a special shape linear damper and a new magnetic fluid in addition to the honeycomb diaphragm.

Each speaker unit uses a honeycomb flat diaphragm that is light and highly rigid.
In order to obtain accurate piston motion while eliminating the air resonance (front chamber effect) that occurs in the cavity in front of the cone of the cone-type speaker, the flat diaphragm uses a honeycomb structure made of aluminum alloys. The rigidity of the flat diaphragm is 1,000 to 1500 times that of a paper cone. There is no distortion due to deformation caused by Dainyu force, or characteristic degradation due to aging or temperature change.
In the case of a flat diaphragm, there is a problem that a part that does not move at all (= node) at a certain frequency occurs when the center is driven. To solve this problem, we have adopted a node drive that drives by connecting a voice coil to the node point. This node drive cancels the resonance mode and expands the piston motion range.
Furthermore, in order to cope with the problem that the appearance of nodes differs depending on the shape and frequency of the diaphragm, we have adopted a unique axially symmetric honeycomb structure in which the density of the honeycomb increases toward the center. This eliminates the difference in strength between the left and right sides and makes the nodes perfectly round, enabling node drive with a single circular voice coil.

A 33 cm honeycomb planar woofer is installed in the low range.
This woofer uses a unique linear damper to improve power linearity in the low frequency range. This damper supports the linear motion of the voice coil more than 10 times the force of the normal damper, minimizing the occurrence of rolling and improving linearity even in the case of Dainyu force. Power linearity is approximately 3 times that of the normal damper.
The magnetic circuit uses a large and strong magnet with a diameter of 145 mm and a weight of 1 kg to realize high efficiency, and the voice coil bobbin uses a laminated film of polyimide resin to provide high input resistance that can withstand high temperatures of 250 ℃.
This unit is capable of piston motion up to 3 kHz, but it is designed with enough space to be used by crossing over at 1 kHz.

Equipped with 8 cm honeycomb planar skoker in the middle area.
By adopting Technics's original nodal drive, wide-band piston motion playback up to 10 kHz is realized. Moreover, by adopting a down roll edge at the edge part, both air compliance between the edge and the edge cover and air mass in the gap between the diaphragm and the edge cover are controlled, and characteristic peaks due to secondary resonance of the diaphragm are eliminated.
In addition, by narrowing the air gap between the voice coil and pole piece to the limit, high efficiency has been achieved. In addition, input resistance has been improved by using a polyimide-based film voice coil bobbin and a highly heat-resistant voice coil.

A 2.8 cm honeycomb planar tweeter is installed in the high range.
The gap between the voice coil, pole piece and yoke of this tweeter is filled with magnetic fluid. Heat generated in the voice coil is released to the pole piece and yoke with a large heat capacity. This greatly improves the heat radiation effect. As a result, high input resistance is obtained, impedance is stabilized, and excellent power linearity is obtained. The magnetic fluid also acts as a damper to suppress unnecessary low frequencies, and the low frequency resonance of the tweeter is suppressed to 1/3 to 1/4 of the conventional one.
The magnetic circuit with high magnetic flux density of 17,500 gauss realizes high efficiency, and the special shape equalizer on the front of the tweeter flattens frequency characteristics.

The network section uses elements that have been carefully examined in terms of performance and reliability. The choke coil uses a ferrite core with low loss and low distortion, and the tweeter circuit uses a metallized polyester film capacitor that prevents degradation of high-frequency characteristics.
In addition, consideration is given to the arrangement of parts to minimize crosstalk between each unit.

The tweeter is equipped with a thermal relay protection circuit with an indicator to prevent unit breakage due to excessive input or abnormal signal.
The indicator lights when the thermal relay is operating, and the reset button on the front panel allows one touch restoration.

Tweeter and Skoker are equipped with independent attenuators.

The enclosure uses a bass reflex system.
The bass reflex port has a special shape. It is integrally molded to prevent standing waves in the enclosure from being exposed. The inner surface is smooth to reduce friction loss during air movement in the port.
High-density particle board is used for the plate material. The baffle plate is 20 mm thick and the other part is 18 mm thick. In addition, three way Z-stop by advanced woodworking technology is used for the wooden frame, making the structure resistant to aging.

There was a speaker stand as an option sold separately.

Model Rating

Method	3-Way, 3-Speaker, Bass reflex system, Bookshelf Type
Unit	For Low Band : 33 cm Flat Type For Middle Area : 8 cm Flat Type For High Frequency : 2.8 cm Flat Type
Frequency characteristic	30 Hz to 35 kHz -16dB 40 hz to 33 khz -10dB
Output sound pressure level	93dB/W/m
Impedance	6 Ω
Allowable input	180W(Music) 90W(Din)
Crossover frequency	1 kHz, 4 kHz
External dimensions	Width 380x Height 670x Depth 325 mm
Weight	21.5kg
Sold Separately	Speaker Stand SH-330 (2 pcs 1 set, ¥ 15,000)