Technics SB-X700 Speaker System Review

A good dynamic speaker driver should have a rigid, low-mass diaphragm, or radiating surface, and speaker designers have tried for years to develop driver shapes and materials that approximate a rigid-piston ideal. Rigidity is important because a flexing driver radiating surface produces an uneven frequency response through the effect known as “cone breakup.” A low-mass material is needed for a driver to have reasonably high efficiency; a massive cone may be satisfactory otherwise, but it requires higher amplifier driving power.

Most dynamic drivers use cone-shaped diaphragms (the cone shape imparts considerable rigidity to a driver) molded of paper or low-mass plastic mixtures. A few years ago, Technics developed a “honeycomb” diaphragm structure that the company believes comes closer to the piston-radiator ideal than previous designs, and it has introduced a line of speaker systems whose drivers employ this honeycomb construction.

The “cone” of a Technics honeycomb driver is a flat plate shaped like the classic circular piston. It is made of a very light aluminum honeycomb whose “axial symmetry” gives it equal rigidity (resistance to bending) in all directions. The honeycomb’s cell density increases toward the center of the disc, concentrating the vibration nodes (regions around which the flexing modes pivot) near the center. This enables the voice coil to drive the diaphragm at a vibration node, further minimizing flexing and spurious resonances.

The honeycomb is sandwiched between two layers of thin aluminum-foil “skin,” forming a disc about 1/4 inch thick, with a conventional (though relatively large-diameter) voice coil bonded to its rear surface. In other respects a Technics honeycomb driver is much like a conventional cone speaker, except that its extremely light, rigid diaphragm (about 1,000 times more rigid than paper) is relatively free of the usual cone breakup (resonance) effects. Also, flat-diaphragm drivers mounted in the same plane are necessarily aligned in signal phase; expensive crossover-network designs or unusual cabinet shapes are therefore not needed in order to compensate for the different depths of the drivers in a system.

The SB-X700 is the largest of three honeycomb-driver systems Technics has introduced to the American market. It is a three-way system with a vertically aligned 12-inch woofer, a 3-1/8-inch midrange driver, and a 1-1/8-inch tweeter. The two lower-frequency drivers have honeycomb diaphragms, and the tweeter uses a flat laminated-mica diaphragm radiating through a radially slotted disc so as to improve its dispersion. The crossover frequencies are 1,000 and 4,000 Hz, and the woofer operates in a ported enclosure.

The Technics SB-X700, nominally an 8-ohm system, is rated to deliver a 90-dB sound-pressure level at 1 meter with an input of 1 watt. It is rated to handle a drive power of up to 180 watts of music signal. The frequency response of the SB-X700 is specified as 39 to 30,000 Hz “at 10 dB below average level,” with no explanation of this unconventional rating.

The walnut-grain-veneered cabinet of the SB-X700 is 26-3/8 inches high, 15 inches wide, and 13 inches deep, and the system weighs about 36-1/2 pounds. The black cloth grille unsnaps to reveal the drivers and two knobs for adjusting the levels of the midrange and high-frequency drivers. A thermal circuit breaker with a front-panel reset button protects the speaker against burnout during sustained high-power operation. Price; $250.

Laboratory Measurements

The close-miked woofer response of the Technics SB-X700 showed a smooth rise with decreasing frequency below 1,000 Hz to a maximum of + 5 dB at 75 Hz, falling off at lower frequencies to — 5 dB at 25 Hz. The averaged room response was very smooth, varying only 3 dB overall from about 1,000 to 9,000 Hz. The directivity of the tweeter was apparent (but not excessive) above 10,000 Hz, and splicing the woofer and room-response curves yielded a composite frequency response of +3, —4 dB from 35 to 20,000 Hz. The midrange level adjustment varied the output between 1,000 and 4,000 Hz, reducing it by as much as 10 dB at its minimum setting. The tweeter-level control operated above 3,000 Hz, reducing the output by up to 25 dB above 10,000 Hz. The flattest response (and best sound balance) was obtained with both level controls set at their maximums.

The quasi-anechoic frequency-response measurements made with our IQS 401-L FFT analyzer confirmed the smoothness of the SB-X700’s frequency response as well as extending our measurement range slightly. The axial response at 1 meter varied ± 3 dB from 180 Hz to 23 kHz (the normal range of the analyzer). The phase response was very good, with a group delay falling between 0.1 and 0.4 millisecond from 1,000 to 21,000 Hz.

The system impedance was between 5 and 8 ohms over most of the range from 30 to 15,000 Hz, reaching 30 ohms at the bass resonance of 66 Hz and 20 ohms at 20 Hz. The minimum of 4.3 ohms was measured at about 2,700 Hz. The bass distortion with a 1-watt input was between 1 and 2 per cent from 100 to 50 Hz, rising to 8.5 per cent at 35 Hz. At 10 watts input it was about 5 per cent down to 65 Hz, reaching 15 per cent at 50 Hz. These seemingly high figures must be interpreted in the light of the speaker’s very high sensitivity, which measured 93 dB sound-pressure level at a 1-meter distance with an input of 2.83 volts (1 watt). This is some 6 dB higher than the sensitivity of a typical speaker system of this size; the distortion of such a typical speaker would have to be measured with inputs of 4 and 40 watts to be compared with the performance of the Technics SB-X700 at 1 and 10 watts (and few such speakers would take kindly to this abuse).

Comment

We first heard the Technics honeycomb speakers, then being introduced to the Japanese market, a couple of years ago on a visit to the company’s Osaka headquarters. We were favorably impressed by what we heard and looked forward to hearing and testing them in a familiar environment. (Only too often we find that speakers that sound impressive in the field fail to live up to their promise when they finally come to us for testing.) Although the SB-X700 probably differs slightly from the speakers we heard in Japan, we were not at all disappointed by what we heard and measured in the lab.

To some extent, the sound of the SB-X700 can be predicted from its measured frequency response. Its sound was warm and sometimes bordered on heaviness in our rather absorbent listening/test room. The sound was best with the speakers placed on the floor; positioning them about 28 inches above the floor and against a wall produced excessive bass emphasis in our room (of course, the results in another environment would probably be very different). The middles and highs were smooth and uncolored; the sound stage, at times remarkably lifelike, was located approximately in the plane of the speakers and a couple of feet in front of the wall. These are thoroughly listenable and enjoyable speakers, standing up well in comparisons with a number of far costlier systems.

Frankly, when we heard the Japanese version of the SB-X700, we expected that it would be a rather expensive product when it came to the American market. Instead, the SB-X700 is priced very competitively with many other good speakers in a popular price range, and it should definitely be heard by anyone looking for top-quality sound at reasonable cost.

Read all

Technics reviews

Read all