NEW PRODUCTS: A roundup of the latest in high-fidelity equipment
Kenwood Model Seven Speaker System
The new Model Seven is Kenwood's finest and costliest speaker system. Much of its performance capability is based on the use of special materials said to be uniquely suited to their applications. Three of its four drivers use diaphragms fabricated from different types of wood pulp that, according to the manufacturer's analysis, possess nearly ideal characteristics of density, rigidity, and elasticity. The fourth driver (the super-tweeter) has a 3/4-inch titanium-foil dome. In addition, the woofer has a copper-capped pole piece to combat hysteresis effects and a specially de signed low-deformation surround. The cross over network utilizes silicon steel-core inductors and metal-film capacitors; the enclosure is constructed of solid lumber-core panels overlaid with cross-grained veneers.
The woofer in the Model Seven is a 14-inch air-suspension unit that crosses over at 400 Hz to a 4 1/4-inch dome mid-range. Frequencies from 4,000 to 8,000 Hz are handled by a 1 1/2-inch dome high-frequency driver, while the super-tweeter extends response to 35,000 Hz. The nominal impedance of the system is 8 ohms, with a power-handling capacity of 150 watts program material. Low-frequency response extends down to 20 Hz; distortion is rated at less than 0.5 percent. The Model Seven is finished on all sides, including the speaker-mounting panel behind its removable sculpted grille, which also conceals output-level controls, calibrated in 2-dB steps from-2 to +2 dB, for all drivers but the woofer. Overall size of the enclosure is 37 x 18 1/2 x 15 inches. Price: $1,350.
Electrostatic Research ER-139 Speaker System
The second speaker system from Electro static Research Company is a three-way de sign incorporating a 3 1/2-inch cone mid-range that covers the frequencies from 800 to 3,000 Hz and faces straight up. It is otherwise similar to the previous two-way model also referred to as the ER-139.
The distinguishing feature of the Electro static Research systems is the array of eight electrostatic tweeters mounted around the circumference of a horizontally oriented drum, providing a 360-degree lateral dispersion pattern. Low frequencies are reproduced by a 10-inch woofer facing downward into a sealed enclosure. The back of the cone then becomes the radiating surface, and the drum (positioned just above) acts as a reflector for its output, spreading it out horizontally. The mid-range driver in the three-way model is mounted in the top of the drum and radiates through a small grille. The electrostatic elements in the ER-139 are new designs created by Arthur Janszen, a leading authority on electrostatic transducers.
They are intended to derive their polarizing voltages from the audio signal itself; alternatively, the system can be plugged into a wall outlet with an ordinary extension cord, which will keep the tweeters energized even during listening interruptions. The ER-139 has an impedance of 6 ohms. It is recommended for use with amplifiers having between 15 and 100 watts per channel continuous power-out put capability. Frequency range is 32 to 20,000 Hz. The system occupies a floor area of 16 x 16 inches and stands 28 inches high. Price: $179.90, or $199.90 with the decorative grille top shown. The two-way version costs $139.90.
IMF Model R Speaker System
A new, three-way speaker system from IMF employs a more compact enclosure than this company's "Monitor" systems. It has a 9-inch acoustic-foam-filled duct (called a "resistive line tunnel") of the same cross-sectional area as the woofer diaphragm and ending in a port at the bottom of the cabinet. The main volume of the enclosure's interior is also liberally treated with acoustic foam to absorb internal reflections. The mid-range driver has its own internal sub-enclosure--a long tube filled with acoustic foam of varying density.
The drivers of the Model R, all of which have plastic diaphragms, consist of an 8 x 12-inch flat-oval woofer, a 5-inch cone mid range, and a 3/4-inch dome tweeter. Crossover points are 375 and 3,500 Hz, and the cross over network is phase compensated. The high-frequency energy of the system can be subtly altered (over a 2-dB range in three switch positions) to suit the program material.
Frequency response is said to be essentially flat from 25 to 30,000 Hz. The impedance of the Model R is 8 ohms, and amplifier powers ranging from 35 to 100 watts per channel continuous are recommended. The system is finished in natural walnut with a black grille; dimensions are 28 x 16 x 14 3/4 inches. The Model R is sold in "mirror image" pairs for stereo at a price of $330 each. Optional stands (shown), 8 inches high, cost $50 per pair.
Infinity Monitor II Speaker System
The Monitor II, the latest version of the Infinity speaker system, is now a four-way design with a tall (50 inches) columnar enclosure that provides a damped, ported transmission line for the rear radiation of the 12-inch woofer.
The output of a 11/2-inch dome mid-range driver covers the range between 450 and 5.000 Hz. The system has two tweeters: a 1-inch dome unit for the octave from 5,000 to 10,000 Hz and Infinity's special version of the Walsh transmission-line driver, which is used as a super-tweeter from 10.000 Hz up. (The Walsh driver employs a steep-sided aluminum cone with its widest end terminated only by a damping plug; vibrations of the voice coil are encouraged to travel up the cone in successive waves instead of exciting it as a pure piston radiator.) The crossover network is designed for minimum phase/time error. The overall frequency response of the system is 26 to 28,000 Hz ±4 dB.
The enclosure of the Monitor II has walnut side panels and a front covered almost entirely with black grille cloth. Beneath the cloth, the speaker-mounting panel is clad in black vinyl. The top portion of the enclosure is open on four sides to permit utilization of the Walsh tweeter's fully omnidirectional (in the horizontal plane) radiation pattern. Two top panels come with the system: one of acoustically transparent cloth and a second, solid panel finished in oiled walnut. Like the removable main grille, these snap in and out for easy interchangeability, permitting the user to adapt the system to his own needs.
The Monitor II has a nominal impedance of 8 ohms; an amplifier with an output power of 45 watts per channel minimum continuous is advised for driving the system, while amplifiers capable of 250 watts per channel are the maximum recommended. Controls are pro vided for varying the acoustic outputs of the dome mid-range and tweeter. The Monitor II measures 50 x 17 x 16 inches overall and weighs 94 pounds. Price: $449 (slightly higher in the East).
ADC MK II Phono Cartridges
The Mk II series of phono cartridges from ADC comprises the company's top models: the VLM, XLM, and Super XLM. The MK II designation indicates that the specifications for these cartridges have been more clearly defined and that the useful life of each has been extended by the tightening of mechanical tolerances wherever possible. The VLM and XLM MK II are stereo cartridges equipped with 0.3 x 0.7-mil elliptical styli; the Super XLM MK II is a CD-4 cartridge fitted with a Shibata-type stylus having edge radii of 0.2 mil and bearing radii of 2 mils.
The VLM MK II has a rated tracking force of 1 to 2 grams, a frequency response of 15 to 20,000 Hz-±1.5 dB, and channel separation of 24 dB. The outputs of the two channels are balanced within 2 dB. The XLM MK II tracks at 3/4 to 1 1/2 gram and has the same frequency response, channel separation of 28 dB, and channel balance within 1 dB. Both cart ridges have an output of 0.9 millivolt percent / meter per second of recorded velocity; they are designed to drive an impedance of 47,000 ohms with a maximum shunt capacitance of 275 picofarads.
The Super XLM MK H, with an output of 0.6 millivolt percentimeter per second, has a frequency response of 15 to 50,000 Hz +2,-5 dB. Most other specifications match of the XLM MK II, except that the maximum recommended shunt capacitance is 100 pico farads. The cartridges come in small hinged boxes with stylus brush, screwdriver, and mounting hardware enclosed. Prices: VLM MK II, $75; XLM MK II, $100; Super XLM MK 11, $125.
Teac "White Paper"
The "White Paper" from Teac is a comprehensive discussion of tape-recorder design considerations which can serve as an excellent introduction to tape-recording theory.
The twenty-four-page booklet begins with the nature of the recorded signal on tape, relates this to head-gap configuration and frequency response, and then continues on through recording-level meters, equalization, bias, distortion, and signal-to-noise ratio, concluding with a description of various tape-drive systems. The booklet is liberally illustrated with black-and-white drawings and printed with wide margins suitable for note-taking. High-quality coated stock is used. The Teac "White Paper" is available free of charge by circling the Reader Service number or by writing Teac Corp. of America, Dept. SR, 7733 Telegraph Road, Montebello, Calif. 90640.
PUBLISHER'S NOTICE: Recent fluctuations in the value of the dollar will have an effect on the price of merchandise imported into this country. So, please be aware that the prices quoted in this issue may be subject to change.
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Also see:
AUDIO QUESTIONS and ANSWERS: Advice on readers' technical problems, LARRY KLEIN