Altec Domesticates The Horn

Altec Lansing Model 6 loudspeaker, in wood enclosure with wood-veneer finish. Dimensions: 15 by 24 1/2 inches (front) 12.5 inches deep. Price: $350. Warranty: "limited," five years parts and labor. Manufacturer: Altec Lansing International, 1515 S. Manchester Ave., Anaheim, Calif. 92803.

For some forty years, horn-loaded tweeters and ported woofer enclosures have been hallmarks of Altec Lansing's home and professional systems. In the last few years these elements have been refined-especially through the development of the constant-directivity horn and the radial phase plug, nicknamed Mantaray and Tangerine, respectively. First incorporated in large floor-standing speakers (HF test report on the Model 19, February 1978), these and further refinements are now being offered in a line of three less bulky systems with the three-way Model 6 in the middle.

This speaker employs a nicely designed piezoelectric compression driver dubbed an LZT (for its lead zirconate titanate transducer element). The Mantaray horn into which it operates is far smaller than that in previous models and is shaped differently. But like the horns in the Model 19 and Model 14 (both of which are two-way systems, requiring lower tweeter crossovers), that in the Model 6 was designed with the aid of a computer for even sound distribution in a precisely calculated area. In addition, the driver's radial phase plug is said to propagate more high-frequency energy than older circumferential plugs will. The horn assembly can be reoriented by 90 degrees if the speaker is to be used horizontally, thus maintaining the intended directivity, which is broader horizontally than vertically.

The Model 6's remaining drivers are a 5-inch midrange cone and 10-inch woofer in a ported chamber.

A newly developed crossover-referred to as a pass-band stable network-is said to further increase the effective sensitivity of the high-frequency driver while presenting an extremely stable load for the amplifier. To prevent damage to the drivers, an automatic power control circuit lowers the input to the system when safe operating limits are exceeded. Baffle-mounted on the same escutcheon as the mid- and high-frequency controls is a display that lights when the automatic power control circuit activates, and the display is visible through the semitransparent black grille cloth. The baffle board is completely padded with sound-absorbent material to reduce cabinet reflections and diffraction effects that can cause irregularities in frequency response and unstable stereo imaging. Finally, the glossy polish of the cabinet's Endriana wood veneer gives us a refreshing change from the acres of oiled walnut we've viewed over the years.

In the lab tests, the Model 6 emerged with high marks all around. Its sensitivity -90 dB with an input of 2.8 volts (equivalent to 0 dBW or 1 watt into 8 ohms)--is quite high. It accepted a continuous-tone input of 28.3 volts (equivalent to 20 dBW or 100 watts into 8 ohms) without exceeding distortion limits or audibly buzzing. At that drive level, however, the power control circuit activated after about 6 seconds, reducing the speaker's output from 111 to 104 dB SPL. Like a turtle that reacts to danger by withdrawing into its shell, then pokes its head out again to see if the danger has passed, the circuit returned to normal again after an interval of about 8 seconds even though the input had not been reduced. Peak sound pressure levels of 117 dB could be elicited with peak inputs of 56.6 volts (equivalent to 26 dBW or 400 watts into 8 ohms). Yet DSL informs us that the limiting factor in this test was not the speaker, but the amplifier, which simply ran out of steam at that level.

From the woofer resonance at about 62 Hz, the impedance curve falls to a nominal 6.7 ohms at 110 Hz, then rises gradually through the midrange to a maximum of 17 ohms in the upper treble region. Considering both the speaker's high efficiency and relatively smooth and consistent impedance values, the Model 6 should interface nicely with just about any amplifier or receiver. Frequency response is exceptionally flat, with extraordinary output down into the deep bass. Notable, too, is the virtual duplication of both on-axis and off-axis traces in the very high frequency section of the curve. The Mantaray horn obviously does exactly what its designers intended: maintaining consistent high-frequency output over a broad horizontal angle.

The midrange control begins its action at approximately 1 kHz, producing a maximum cut of 15 dB, at 2.5 khz, as the control is rotated from its OPTIMUM setting to the minimum. The control allows some additional rotation beyond OPTIMUM, and up to 2 1/2 dB of boost can be realized at 2.5 kHz. When the high-frequency control is set to its maximum, it delivers about 7 dB of additional output above 8 kHz. Moving the control to its minimum setting results in a gradual rolloff of response starting at 2.5 kHz, with response down by approximately 7 dB or more above 8 kHz. Thus, hefty but not preposterous changes can be introduced at these controls. Harmonic distortion measurements made at loud playing levels (100 dB SPL) are remarkably low. The softer second harmonic predominates in the lower midrange area, though even here it barely exceeds 1%. Third harmonics are even lower, with values averaging less than 1/2% over most of the speaker's range.

At moderate playing levels (90 dB SPL), harmonic distortion is negligible, averaging well below 1/2%. In the listening room, we turned to Altec's particularly comprehensive and well-written owner's manual to help us determine optimum speaker placement. Altec is refreshingly frank about the problems of poor placement; following the manual's admonitions, we placed our pair away from the back wall, approximately three feet from the side walls and about seven feet apart. This gave us broad and detailed stereo imaging that held up well in a broad listening arc. A small cut at the midrange control tamed what we deemed excessive forwardness on voices; one auditioner felt the bass was a hair heavy-handed, but the preamp's bass control solved that, too. The bass is robust, with no hesitancy on even the deepest organ and drum fundamentals. Massed orchestral passages are handled effortlessly, a hallmark of a good speaker.

With the Model 6, Altec has domesticated the horn-loaded loudspeaker. Not only has it tamed the beaminess that has given high-frequency horns a reputation for coloration, but it has reduced the size of the systems from the chunky Model 14 and monumental Model 19. The Model 6 is finished like fine furniture and is small enough to be accommodated even in urban-size rooms. We have no doubt it will take up residence in a great many of them.

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(High Fidelity, USA print magazine)

Also see:

3D Acoustics Model 3D-GTOB three-piece loudspeaker system

The Critics Go Speaker Shopping [June 1981]